Reference Guide
ADU Glossary
Your complete guide to ADU, permitting, zoning, financing, and construction terminology — explained in plain English.
300+Terms Defined
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A
California Law
AB 2221
A 2022 California law that further clarified ADU permitting rules, including prohibiting local agencies from requiring applicants to correct existing code violations unrelated to the ADU.
California Law
AB 68
A 2019 California law that streamlined ADU permitting by reducing review timelines to 60 days and eliminating certain local barriers to ADU construction.
California Law
AB 881
A 2019 California law that limited local governments' ability to impose owner-occupancy requirements and parking mandates on ADU projects.
Design
Accessible Design
Design features that accommodate people with disabilities, including wider doorways, grab bars, and barrier-free entries. May be required or voluntary in ADU construction.
Accessory Structure
A building that is subordinate to and located on the same lot as the main building, such as a detached garage, shed, or workshop.
Acrylic Finish
A synthetic exterior coating applied over stucco or foam insulation systems, providing a durable and weather-resistant surface for ADU walls.
ADA (Americans with Disabilities Act)
Federal law requiring accessible design in public accommodations. While residential ADUs are generally exempt, accessibility features can expand usability and market appeal.
Additional Insured
A person or entity added to a contractor's insurance policy for protection during the construction project, often required by homeowners before ADU work begins.
Admixture
A substance added to concrete during mixing to alter its properties, such as accelerating curing time, improving workability, or increasing freeze resistance for ADU foundations.
ADU (Accessory Dwelling Unit)
A secondary housing unit on a single-family residential lot, also known as in-law units, granny flats, or backyard cottages. ADUs provide independent living facilities including a kitchen, bathroom, and sleeping area.
AFCI (Arc Fault Circuit Interrupter)
An electrical safety device that detects dangerous arcing conditions and disconnects power to prevent fires. Required in bedrooms and other living areas by current codes.
Air Barrier
A material or assembly that controls air leakage into and out of the building envelope. Critical for energy efficiency and moisture control in wall and roof assemblies.
Air Handler
The indoor component of an HVAC system that circulates conditioned air through ductwork. Contains the blower, filter, and often the evaporator coil.
Design
Alcove
A recessed area in a wall or room used to create built-in storage, a reading nook, or a bed alcove, maximizing usable space in compact ADU designs.
Finance
Amortization
The gradual repayment of a loan through scheduled payments of principal and interest over time, commonly used when financing ADU construction.
Amperage (Amps)
A unit of electrical current measuring the flow of electrons through a conductor. Residential panels typically range from 100-400 amps.
Anchor Bolt
A bolt embedded in concrete foundations to secure the sill plate and connect the wood framing to the foundation. Required by code at specific intervals.
Finance
Appraisal
A professional assessment of property value, often required for financing. ADUs typically increase property values but appraisal methods vary by market.
Architect
A licensed professional who designs buildings and structures, prepares construction documents, and may oversee construction. In California, architects must be licensed by the California Architects Board.
Architectural Drawings
Technical drawings that illustrate building design, including floor plans, elevations, sections, and details used for construction and permitting.
Architectural Shingle
A premium asphalt roofing shingle with a dimensional, layered appearance that adds visual depth and typically lasts longer than standard three-tab shingles.
Arroyo
A dry creek bed or drainage channel common in Southern California landscapes that may affect ADU site planning and stormwater management.
As-Built Drawings
Drawings that document the actual constructed conditions of a building, reflecting any changes made during construction from the original plans.
Asphalt Shingles
The most common residential roofing material, made of fiberglass mat coated with asphalt and mineral granules. Available in various styles and fire ratings.
Permitting
Assessor
A government official who determines property values for tax purposes. ADU construction may trigger reassessment of the new improvement value.
Attached ADU
An ADU that shares at least one wall with the primary dwelling. Often created through additions or converting existing attached spaces like garages.
Attic
The space between the ceiling of the top floor and the roof. May be unfinished or converted into living space depending on height and access requirements.
Awning
A roof-like cover extending over a window, door, or patio to provide shade and weather protection. Can be fixed or retractable.
B
Backerboard
A cement-based or fiber-reinforced panel installed behind tile in wet areas like showers and kitchen backsplashes to prevent moisture damage in ADU bathrooms.
Backflow Preventer
A plumbing device that prevents contaminated water from flowing backward into the clean water supply. Required at irrigation connections and certain plumbing fixtures.
Backpressure
Pressure in a plumbing system that can push wastewater backward through pipes, requiring backflow prevention devices on ADU water supply connections.
Ballast (Electrical)
A device that regulates the current flowing to fluorescent or HID light fixtures, controlling the starting and operating voltage for proper lamp function.
Balloon Framing
A wood framing method where wall studs run continuously from foundation to roof, common in older construction. Now largely replaced by platform framing.
Baseboard
Molding installed at the base of walls where they meet the floor, covering the joint and protecting walls from damage.
Batt Insulation
Pre-cut sections of fiberglass or mineral wool insulation designed to fit between standard framing spacing. Available in various R-values and thicknesses.
Bay Window
A window assembly that projects outward from the exterior wall, creating additional interior space and allowing light from multiple angles in an ADU.
Beam
A horizontal structural member that carries loads from the floor or roof to vertical supports like columns or walls. Common types include engineered lumber, steel, and glulam.
Bearing Wall (Load-Bearing Wall)
A wall that supports structural loads from above, such as floors, roofs, or other walls. Cannot be removed without providing alternative structural support.
Berm
An earthen mound or embankment used for landscaping, drainage control, or noise reduction. Sometimes used around structures for energy efficiency.
Bid
A formal written proposal from a contractor stating the price and terms for completing ADU construction work, used by homeowners to compare builders.
Bioswale
A vegetated, shallow channel designed to capture and filter stormwater runoff, often required or encouraged in ADU site plans for sustainable drainage.
Birdsmouth Cut
A notch cut into a rafter where it sits on the top plate of a wall, providing a stable bearing surface for the roof framing of an ADU.
Blocking
Short pieces of lumber installed between framing members to provide nailing surfaces, transfer loads, or prevent twisting. Required at specific locations by code.
Blower Door Test
A diagnostic test using a calibrated fan to measure a building's air-tightness, often required to verify energy compliance in new ADU construction.
Blueprints
Traditional term for construction drawings, named for the blue-tinted reproduction process historically used. Now refers to any set of construction documents.
Board Foot
A unit of lumber measurement equal to 144 cubic inches. Used for pricing and estimating lumber quantities.
Bollard
A short, sturdy post installed to protect structures or utilities from vehicle impact, sometimes required near ADU driveways or parking areas.
Bond (Construction)
A financial guarantee ensuring completion of work or payment of obligations. Types include performance bonds, payment bonds, and license bonds.
Branch Circuit
An individual electrical circuit extending from the panel to outlets, switches, or appliances, sized according to the load requirements of the ADU.
Finance
Bridge Loan
Short-term financing used to cover costs between the start of ADU construction and securing permanent funding, bridging the gap until long-term financing is in place.
Builder's Risk Insurance
A specialized insurance policy covering damage to a structure under construction from events like fire, theft, or storms during the ADU building process.
Building Area
The total covered footprint of a building measured at ground level. Used in lot coverage calculations and setback determinations.
Building Code
Regulations governing the design, construction, and occupancy of buildings to ensure safety. California uses the California Building Standards Code (Title 24).
Permitting
Building Department
The local government agency responsible for reviewing building plans, issuing permits, and conducting inspections to ensure code compliance.
Building Envelope
The physical barrier between the conditioned interior and unconditioned exterior, including walls, roof, windows, doors, and foundation. Critical for energy efficiency.
Building Height
The vertical distance from grade to the highest point of the roof. California limits ADU height to 16 feet for detached units, with exceptions for specific configurations.
Permitting
Building Official
The head of a local building department responsible for interpreting and enforcing building codes and overseeing the permit and inspection process for ADU projects.
Permitting
Building Permit
Official approval from the local building department authorizing construction work. Required before starting most construction projects.
Built-Up Roof (BUR)
A flat roofing system consisting of alternating layers of bitumen and reinforcing fabrics, topped with gravel or a cap sheet. Durable but heavy.
Bump-Out
A small addition that extends a room beyond its original footprint, typically 2-4 feet. Often used to add space for bathrooms or kitchens in ADU conversions.
Butt Joint
A connection where two members meet end-to-end without overlapping. Requires additional fastening or support compared to overlapping joints.
Design
Butterfly Roof
A V-shaped roof design where two surfaces slope inward toward the center, creating a modern aesthetic sometimes used on contemporary ADU designs.
California Law
By-Right
Development that is permitted under zoning without requiring discretionary approval such as variances or conditional use permits. California ADU laws establish by-right approval for qualifying ADUs.
C
California Law
CALGreen
California Green Building Standards Code (Part 11 of Title 24), the first state-mandated green building code in the US, establishing requirements for sustainable construction.
Cantilever
A projecting beam or floor structure supported only at one end, commonly used for bay windows, balconies, or extended floor sections.
Finance
Cap Rate (Capitalization Rate)
A real estate metric calculated by dividing net operating income by property value, used to evaluate the potential return on an ADU rental investment.
Carbon Footprint
The total greenhouse gas emissions associated with building and operating an ADU, influenced by material choices, energy systems, and construction methods.
Casement Window
A window hinged on the side that opens outward like a door, typically operated by a crank mechanism. Provides excellent ventilation and egress capability.
Finance
Cash-Out Refinance
Replacing an existing mortgage with a new, larger loan and receiving the difference in cash, often used by homeowners to fund ADU construction.
Catch Basin
A drainage structure that collects surface runoff and channels it into underground storm drains, often required in ADU site grading plans.
Caulking
Flexible sealant material applied to joints and gaps to prevent air and water infiltration. Essential for weatherproofing around windows, doors, and penetrations.
Ceiling Height
The vertical distance from the finished floor to the finished ceiling. Building codes typically require minimum 7-foot ceiling heights for habitable rooms.
Cement Board
A durable, moisture-resistant panel made from cement and fibers used as exterior siding or tile substrate in ADU construction.
Certificate of Insurance (COI)
A document issued by an insurance company verifying that a contractor has active liability and workers' compensation coverage, required before starting ADU work.
Permitting
Certificate of Occupancy (CO)
Document issued by the building department confirming that a building complies with codes and is safe for occupancy. Required before moving into a new ADU.
Cesspool
An older underground pit for sewage disposal that does not treat wastewater, often requiring replacement with a modern septic or sewer connection for ADU permitting.
Change Order
A written amendment to the construction contract documenting changes to the scope, schedule, or cost of work. Should be signed by both owner and contractor.
Chase
A vertical or horizontal enclosure built into walls or ceilings to conceal plumbing pipes, ductwork, or electrical conduit in an ADU.
Circuit Breaker
An automatic electrical safety device that interrupts current flow when it exceeds safe levels, protecting wiring and preventing fires.
Cladding
The exterior finish material applied to walls for weather protection and aesthetics. Includes siding, stucco, brick veneer, and panel systems.
Cleanout
An accessible opening in a drainage system allowing for pipe cleaning and inspection. Required at changes in direction and at regular intervals.
Design
Clerestory
A row of windows set high in a wall above eye level, bringing natural light into an ADU interior without sacrificing wall space or privacy.
California Law
Coastal Zone
An environmentally sensitive area along the California coast where the Coastal Commission may have permit authority, adding an extra layer of review for ADU projects.
Code Compliance
Meeting all applicable building codes, zoning ordinances, and regulations. Essential for obtaining permits and certificates of occupancy.
Coefficient of Performance (COP)
A measure of heat pump efficiency comparing the energy output to energy input, helping homeowners choose the most efficient HVAC system for an ADU.
Column
A vertical structural member that transfers loads from beams or floors to the foundation. Can be wood, steel, or concrete.
Compaction
The process of mechanically densifying soil to increase its load-bearing capacity before pouring an ADU foundation or placing fill material.
Concrete
A composite building material made from cement, aggregate, and water. Used for foundations, slabs, and structural elements with various strength specifications.
Concrete Block (CMU)
Concrete masonry units used for foundation walls, retaining walls, and structural elements. May be reinforced with rebar and grout for added strength.
Condensate Line
A drain pipe that carries moisture removed from the air by an HVAC system's evaporator coil, preventing water damage inside the ADU.
Condensation
The process where water vapor becomes liquid on cold surfaces. Proper insulation and vapor barriers prevent condensation-related damage in wall and roof assemblies.
California Law
Conditional Use Permit (CUP)
A discretionary permit allowing a land use not normally permitted in a zoning district, though California law generally exempts ADUs from this requirement.
Conduit
Protective tubing for electrical wiring, providing physical protection and allowing wire replacement. Types include EMT, rigid metal, and PVC.
Construction Documents
The complete set of drawings and specifications used for construction and permitting, including architectural, structural, mechanical, electrical, and plumbing plans.
Finance
Construction Loan
Short-term financing for building projects, typically disbursed in draws as construction progresses. Often converts to permanent financing upon completion.
Construction Manager
A professional who oversees the planning, coordination, and execution of a construction project on behalf of the homeowner, ensuring the ADU is built on time and on budget.
Contingency
A budgeted reserve, typically 10-20% of total project cost, set aside for unexpected expenses during ADU construction.
Contractor (General Contractor)
A licensed professional who manages construction projects, hires subcontractors, and ensures work is completed according to plans and specifications. In California, must hold a CSLB license.
Conventional Construction
Traditional site-built construction using standard framing methods, as opposed to modular or prefabricated construction.
Conversion ADU
An ADU created by converting existing space within the primary dwelling or an accessory structure, such as a garage, basement, or attic.
Design
Cool Roof
A roofing system designed to reflect more sunlight and absorb less heat, reducing cooling costs and meeting California energy code requirements for ADUs.
Coping
A protective cap or cover placed on top of a wall, parapet, or fence to shed water and prevent moisture damage to the structure below.
Copper Pipe
Metal tubing used for water supply lines, valued for durability and corrosion resistance. Types include M, L, and K with varying wall thicknesses.
Corbel
A structural bracket or projection from a wall used to support beams, shelves, or architectural details in ADU interior and exterior design.
Corner Bead
Metal or plastic trim installed on drywall corners to create straight, durable edges. Covered with joint compound for a finished appearance.
Permitting
Correction Notice
A written notification from a building inspector identifying code violations or plan deviations that must be fixed before the next inspection on an ADU project.
Cost Estimate
A detailed projection of construction costs based on plans and specifications. Typically includes materials, labor, permits, and contingency allowances.
Cost Per Square Foot
A common metric for estimating ADU construction expenses by dividing the total project cost by the total building area in square feet.
Counter Flashing
Metal flashing embedded into walls or chimneys that overlaps base flashing to prevent water infiltration at roof intersections.
Design
Cove Lighting
Indirect lighting installed in a ledge or recess near the ceiling, creating a soft ambient glow that makes compact ADU spaces feel larger.
Crawl Space
A shallow, unfinished space between the first floor and ground, allowing access to utilities. Must be properly ventilated and vapor-protected.
Cripple Stud
Short studs installed above and below wall openings to maintain framing layout and provide nailing surfaces for sheathing and finishes.
Critical Path
The longest sequence of dependent tasks in a construction schedule that determines the minimum project duration for completing an ADU.
Crown Molding
Decorative trim installed at the junction of walls and ceilings. Adds architectural detail and can conceal imperfect corners.
Permitting
CSLB (Contractors State License Board)
The California agency that licenses and regulates the construction industry, protecting consumers and ensuring contractor competence.
Cupola
A small dome or tower-like structure on top of a roof, used for ventilation or as an architectural accent on an ADU.
Curb Appeal
The visual attractiveness of a property from the street. ADU design should complement the main house and maintain neighborhood character.
Curing
The process by which concrete hardens and gains strength. Proper curing requires moisture and temperature control for optimal results.
Curtain Wall
A non-structural exterior wall, typically glass and aluminum framing. Less common in residential but sometimes used in modern ADU designs.
Custom Home
A uniquely designed and built residence. Custom ADUs offer design flexibility but typically cost more than prefabricated or standard plans.
Cut Sheet
A manufacturer's product specification sheet detailing dimensions, performance, and installation requirements. Required for permit review of many products.
Cycle Time
The total duration from permit application to certificate of occupancy. Varies by jurisdiction and project complexity.
D
Dado
A groove cut across the grain of wood to receive another piece, used in cabinetry and shelving construction for ADU built-in furniture.
Damper
A valve or plate controlling airflow in ductwork or chimneys. Manual or automatic dampers balance HVAC distribution and prevent backdrafting.
Design
Daylight Harvesting
Using natural light to reduce artificial lighting needs. Strategic window placement and light shelves maximize daylighting in ADUs.
Design
Daylighting
The practice of using windows, skylights, and reflective surfaces to maximize natural light inside a building, reducing energy use in ADU living spaces.
Dead Bolt
A locking mechanism operated by a key or thumb turn that extends a solid bolt into the door frame, providing enhanced security for ADU entry doors.
Dead Load
The permanent, static weight of building materials and fixed equipment. Includes framing, roofing, flooring, and mechanical systems.
Finance
Debt-to-Income Ratio (DTI)
A financial metric comparing monthly debt payments to gross income, used by lenders to determine eligibility for ADU construction loans or refinancing.
Decibel (dB)
A unit measuring sound intensity. Building codes specify maximum noise levels for HVAC equipment and sound transmission between units.
Deck
An outdoor platform typically made of wood or composite materials, attached to or adjacent to a building. Requires permits when elevated above grade.
Decking (Roof)
The structural sheathing layer, typically plywood or OSB, installed over roof rafters or trusses to create the base for roofing materials on an ADU.
Deed Restriction
A limitation on property use recorded in the deed, which may restrict ADU construction. Some California laws override certain deed restrictions for ADUs.
Deferred Maintenance
Postponed repairs or upkeep on a property that may need to be addressed before or during ADU construction to meet code requirements.
Deflection
The bending of structural members under load. Building codes limit deflection to prevent cracking of finishes and ensure occupant comfort.
Demand Water Heater
A tankless water heating system that heats water on demand as it flows through the unit, saving space and energy in compact ADU installations.
Permitting
Demolition Permit
Authorization required before demolishing or removing structures. May involve asbestos testing and utility disconnection requirements.
Dense Pack Insulation
Cellulose or fiberglass insulation installed at high density to reduce air movement and increase R-value. Common in retrofit wall insulation.
Permitting
Design Review
A local process evaluating the aesthetic and architectural aspects of proposed construction. California limits subjective design review for ADUs.
Design-Build
A project delivery method where a single firm handles both design and construction, streamlining communication and often reducing ADU project timelines.
Detached ADU
A stand-alone ADU that is separate from the primary dwelling, not sharing any walls. California allows detached ADUs up to 1,200 square feet.
Detail Drawing
An enlarged drawing showing specific construction assemblies or connections at a larger scale than plan drawings for clarity.
Permitting
Developer Fee
Charges imposed by local governments to fund infrastructure and public facilities. California limits impact fees for ADUs under 750 square feet.
Dimensional Lumber
Standard-sized lumber used for framing, such as 2x4, 2x6, and 2x12. Actual dimensions are smaller than nominal due to drying and planing.
Dormer
A roofed structure projecting from a sloped roof, containing a window and providing additional headroom and natural light in attic spaces.
Double-Hung Window
A window with two sashes that slide vertically, allowing ventilation from top or bottom. Both sashes may tilt inward for cleaning.
Downspout
A vertical pipe carrying rainwater from gutters to ground level or drainage system. Proper sizing and placement prevents foundation damage.
Drainage
The system for removing water from roofs, foundations, and sites. Proper drainage prevents flooding, foundation damage, and moisture problems.
Finance
Draw Schedule
A payment plan tied to construction milestones that releases funds in stages as ADU work progresses, protecting both the homeowner and contractor.
Drip Edge
Metal flashing installed at roof edges to direct water away from the fascia and into gutters. Required by code on most roof installations.
Drop Ceiling
A secondary ceiling hung below the main structural ceiling, concealing ductwork and wiring while providing access for maintenance in an ADU.
Dry Rot
Wood decay caused by fungi, despite the name requiring moisture. Must be removed and replaced before new construction work.
Drywall (Gypsum Board)
Panel material made of gypsum plaster pressed between paper sheets, used for interior walls and ceilings. Standard thickness is 1/2 inch for walls and 5/8 inch for fire-rated assemblies.
Drywell
An underground structure that collects and disperses stormwater into the ground. May be required for drainage from ADU roofs and paving.
Dual Zone HVAC
A heating and cooling system with separate controls for different areas. Allows independent temperature control for ADU and main house.
Ductwork
The system of channels distributing heated or cooled air from HVAC equipment throughout a building. May be sheet metal, flexible, or fiberglass duct board.
Due Diligence
Thorough investigation before a major decision or purchase. Includes researching zoning, utilities, and feasibility before committing to an ADU project.
Duplex
A building containing two separate dwelling units, either side-by-side or stacked. SB 9 allows lot splits that can create duplex opportunities on single-family lots.
Dwelling Unit
A building or portion of a building designed for residential use, with independent living facilities. Each ADU is a separate dwelling unit.
DWV (Drain-Waste-Vent)
The plumbing system that removes wastewater and sewage while providing ventilation to prevent siphoning of trap seals and sewer gas entry.
E
Earthquake Retrofit
Structural improvements to make an existing building more resistant to seismic activity, sometimes required when converting older structures into ADUs in California.
Easement
A right to use another's property for a specific purpose, such as utilities or access. ADUs typically cannot be built within easements.
Eave
The lower edge of a roof that projects beyond the wall, providing weather protection and architectural detail. Depth affects setback measurements in some jurisdictions.
Efficiency Unit
A small dwelling unit with combined living/sleeping space and kitchen facilities. California allows efficiency ADUs as small as 150 square feet.
Efflorescence
White crystalline deposits that appear on masonry or concrete surfaces caused by water dissolving and carrying salts to the surface as it evaporates.
Egress
A means of exiting a building, particularly in emergencies. Bedrooms require egress windows meeting minimum size and sill height requirements.
Egress Window
A window large enough for emergency escape, required by building codes in ADU bedrooms and sleeping areas to ensure occupant safety.
EIFS (Exterior Insulation and Finish System)
A multi-layered exterior wall system providing insulation and a finished surface, sometimes used on ADUs for its energy efficiency and design flexibility.
Electrical Panel
The main distribution point for electrical circuits in a building, containing circuit breakers or fuses. ADUs may require a subpanel fed from the main panel.
Permitting
Electrical Permit
Authorization for electrical work, typically obtained separately from or as part of the building permit. Required for new circuits, panel upgrades, and significant modifications.
Elevation (Drawing)
An architectural drawing showing the vertical face of a building from the exterior. Elevations document exterior materials, window placement, and height relationships.
Elevation Certificate
A document prepared by a surveyor verifying a building's elevation relative to flood levels, required for ADU construction in or near flood zones.
Embodied Energy
The total energy consumed in producing, transporting, and installing building materials, considered when making sustainable choices for ADU construction.
Eminent Domain
The government's right to acquire private property for public use with compensation, rarely affecting ADU projects but important for homeowners to understand.
Encapsulation
Sealing hazardous materials like asbestos or lead paint in place rather than removing them, sometimes used during garage-to-ADU conversions in older homes.
Encroachment
When a structure extends beyond property lines or into easements, setbacks, or public right-of-way. May require encroachment permits or removal.
End Lap
The overlapping joint between two pieces of roofing, siding, or flashing material, ensuring water tightness at transitions on ADU exterior surfaces.
Energy Code (Title 24 Part 6)
California's building energy efficiency standards, among the most stringent in the nation. Affects insulation, windows, HVAC, lighting, and solar requirements.
ENERGY STAR
A US EPA program certifying energy-efficient products and buildings. ENERGY STAR appliances and windows help meet California's energy code requirements.
Engineer
A licensed professional who designs structural, mechanical, electrical, or civil systems. Structural engineers are often required for ADU foundation and framing design.
Engineered Lumber
Manufactured wood products designed to be stronger and more stable than solid lumber, including LVL, I-joists, glulam beams, and LSL.
California Law
Environmental Review
Analysis of a project's environmental impacts under CEQA. Most ADUs are exempt from environmental review.
Finance
Equity (Home Equity)
The difference between a property's market value and outstanding mortgage balance. Often used to finance ADU construction through HELOCs or cash-out refinancing.
Erosion Control
Measures to prevent soil loss during and after construction, including silt fences, straw wattles, and vegetation. Required in many jurisdictions.
ERV (Energy Recovery Ventilator)
A ventilation device that exchanges stale indoor air with fresh outdoor air while recovering both heat and moisture energy, improving ADU air quality efficiently.
Finance
Escrow
A neutral third party that holds funds and documents during real estate transactions. Construction escrow accounts may be used for progress payments.
Evaporative Cooler (Swamp Cooler)
A cooling system that uses water evaporation to lower air temperature. Effective in dry climates and more energy-efficient than refrigerant-based air conditioning.
Excavation
The process of digging and removing earth for foundations, utilities, or grading. Requires proper shoring, drainage, and soil disposal.
Exhaust Fan
A ventilation device that removes indoor air to the outside, required in bathrooms and kitchens for moisture and odor control.
Expansion Joint
A gap between building elements allowing movement from thermal expansion, settling, or seismic activity without causing damage.
Exterior Finish
The visible outer surface materials of a building, including siding, stucco, paint, and trim. Must be compatible with local fire hazard severity zones.
F
Fair Housing Act
A federal law prohibiting discrimination in housing based on race, color, religion, sex, disability, familial status, or national origin, applicable to ADU rentals.
Fall Protection
Safety measures such as guardrails, nets, or harnesses required during ADU construction when workers operate at heights above six feet.
Fascia
The vertical board at the edge of a roof, covering rafter ends and providing a surface for gutter attachment. Material and size affect aesthetics and durability.
Fascia Board
A horizontal board mounted at the point where the roof meets the outer walls of a building, supporting the bottom row of roof tiles and the gutter system on an ADU.
Feasibility Study
A preliminary analysis determining whether an ADU project is possible on a specific property, considering zoning, setbacks, lot coverage, and utility capacity.
Fee Simple
Complete ownership of real property, including the right to build, modify, or transfer. The most common form of property ownership for ADU projects.
Fenestration
The arrangement and design of windows, doors, and other openings in a building. Critical for natural lighting, ventilation, and energy performance.
Fiber Cement Siding
Exterior cladding made from cement, sand, and cellulose fibers. Durable, fire-resistant, and available in various profiles mimicking wood or masonry.
Field Change
A modification to construction plans made during building. May require plan revision approval from the building department.
Final Inspection
The last building department inspection verifying all work is complete and compliant with approved plans and codes. Required before certificate of occupancy.
Finish Schedule
A document specifying materials and colors for surfaces including flooring, paint, tile, and fixtures in each room of a building.
Fire Blocking
Materials installed to prevent the spread of fire within concealed spaces such as wall cavities and soffits. Required at specified locations by building codes.
Fire Hazard Severity Zone
State-designated areas of high wildfire risk requiring specific construction materials and vegetation management. Affects ADU requirements near wildland areas.
Fire Rating
The duration that building elements can resist fire, expressed in hours. Affects wall, floor, and roof assembly requirements, especially near property lines.
Fire Sprinklers
Automatic fire suppression system that releases water when activated by heat. California requires sprinklers in new ADUs when the primary dwelling has them.
Fire-Resistant Landscaping
Vegetation and landscape design that reduces wildfire risk around structures, required in designated fire hazard zones when building an ADU in California.
Fireplace
A structure for containing fire, typically with a chimney or direct vent. Gas fireplaces are common in ADUs due to efficiency and air quality regulations.
Firestop
A fire-resistant material installed in concealed spaces like wall cavities and floor penetrations to slow the spread of fire and smoke in an ADU.
Fixed Window
A window that does not open, used primarily for light and views. Cannot serve as emergency egress but offers better energy efficiency and lower cost.
Finance
Fixed-Rate Mortgage
A home loan with an interest rate that remains constant throughout the loan term, providing predictable payments when financing an ADU through refinancing.
Flashing
Sheet metal or membrane material installed at roof intersections, penetrations, and wall connections to prevent water intrusion. Critical for weatherproofing.
Flat Roof
A roof with minimal slope, typically less than 2:12 pitch. Requires specialized waterproof membrane roofing systems and proper drainage.
Flitch Beam
A composite beam made by sandwiching a steel plate between wood members, providing high strength in a compact profile for ADU structural support.
Floor Area Ratio (FAR)
The ratio of total building floor area to lot area, used to regulate building density. Many California cities exempt ADUs from FAR calculations.
Floor Drain
A plumbing fixture in floors allowing water drainage. Required in laundry rooms, mechanical spaces, and shower areas without curbs.
Floor Joist
Horizontal framing member that supports floor loads, spanning between foundation walls, beams, or bearing walls. Sizing depends on span and load requirements.
Floor Leveler
Self-leveling compound used to create flat surfaces over uneven subfloors. Essential when installing tile or hardwood over concrete.
Floor Plan
A drawing showing the horizontal arrangement of rooms, doors, windows, and fixtures as viewed from above. Essential for permit applications and construction.
Floor Truss
A prefabricated structural frame used in place of traditional floor joists, allowing longer spans and easier routing of mechanical systems in ADU floor assemblies.
Flue
A pipe or channel carrying combustion products from appliances to the exterior. Proper sizing and installation are critical for safety.
Fluorescent Lighting
Lighting technology using gas-discharge tubes. Being replaced by LED for energy efficiency but still found in older buildings.
Flush Mount
A light fixture mounted directly against the ceiling with no gap. Appropriate for low ceiling heights common in some ADUs.
Fly Rafter
A rafter that extends beyond the gable end wall to form a roof overhang, providing weather protection and architectural detail on an ADU.
Foam Insulation
Spray-applied or board insulation made of polyurethane or polystyrene. Provides high R-value and air sealing in a single application.
Footing
The widened base of a foundation that distributes building loads to the soil. Size and reinforcement depend on soil conditions and structural loads.
Forced Air
A heating and cooling system using ductwork to distribute conditioned air. Common but requires space for ducts that may not fit in compact ADUs.
Formwork
Temporary molds that shape poured concrete until it cures. Forms may be wood, metal, or plastic; some are reusable.
Foundation
The structural system transferring building loads to the earth. Common types for ADUs include slab-on-grade, raised floor, and pier or post foundations.
Frame Wall
A wall constructed of dimensional lumber studs. Standard residential construction allowing for insulation within the wall cavity.
Framing
The structural skeleton of a building, typically wood or steel studs, joists, and rafters. Platform framing is standard for residential construction.
Freestanding (ADU)
A detached ADU separate from the primary dwelling. May have different height allowances and setback requirements than attached units.
French Door
A pair of glass-paned doors hinged on opposite sides. Popular for ADU entries and patio access, providing light and visual connection.
French Drain
A gravel-filled trench with a perforated pipe that redirects groundwater away from an ADU foundation, preventing water intrusion and structural damage.
Frost Depth
The depth at which ground freezes in winter, affecting foundation depth requirements. California's mild climate allows shallower foundations.
Frost Line
The maximum depth at which soil freezes in a given climate, determining the minimum depth for footings and foundations, though rarely a concern in most of California.
Full Bath
A bathroom with toilet, sink, and bathtub or shower. Required for ADUs; the shower may substitute for a bathtub in accessible design.
Furnace
A heating appliance that warms air for distribution through ducts. Gas furnaces are being phased out in favor of heat pumps in new California construction.
Furring
Thin strips of wood or metal attached to walls or ceilings to create an air space, level surfaces, or provide attachment for finish materials.
Furring Strip
A thin strip of wood or metal attached to a wall, ceiling, or floor to create a level surface for attaching finish materials in an ADU.
G
Gable
The triangular portion of a wall between the edges of intersecting roof slopes. Gable roofs are common for ADUs due to simplicity and attic space.
Galvanized Steel
Steel coated with zinc for corrosion resistance. Used for framing, connectors, and exterior applications. Avoid contact with copper to prevent electrolysis.
Design
Gambrel Roof
A symmetrical two-sided roof with two slopes on each side, the lower slope steeper than the upper, sometimes used on barn-style ADU designs.
Garage Conversion
Converting an existing garage into living space, often an ADU. California law prohibits requiring replacement parking when converting garages to ADUs.
Gas Line
Piping that supplies natural gas or propane to appliances. Installation requires permits and inspection due to safety concerns.
Gasket
A sealing material between surfaces to prevent air or water leakage. Used around doors, windows, and mechanical connections.
Gauge
A measurement of thickness for metal and wire. Lower gauge numbers indicate thicker material. Critical for structural components and wiring.
Gazebo
A freestanding, open-sided outdoor structure. Unlike ADUs, gazebos are not habitable and have different permit requirements.
General Contractor (GC)
A licensed contractor who oversees construction projects, coordinates subcontractors, and is responsible for completing work according to contract specifications.
Generator Panel
An electrical panel with transfer switch capability for connecting a backup generator. Useful for ADUs in areas prone to power outages.
Geotechnical Report
A soils engineering study analyzing ground conditions to determine appropriate foundation design. May be required on hillsides or in areas with poor soils.
GFCI (Ground Fault Circuit Interrupter)
An electrical safety device that shuts off power when it detects current leakage, preventing electrocution. Required in kitchens, bathrooms, and outdoor locations.
GFI (Ground Fault Interrupter)
Another term for GFCI, a safety device that quickly shuts off electrical power when it detects current flowing through an unintended path, such as water.
Girder
A large beam that supports other beams or floor joists, typically running perpendicular to joists. Common in raised floor foundations.
Glass Block
Translucent masonry units used for walls allowing light while maintaining privacy. Common for bathroom windows and accent walls.
Glazing
Glass installed in windows and doors. Types include single, double, and triple pane with various coatings for energy efficiency and safety.
Glue Laminated Beam
An engineered beam created by laminating dimensional lumber with structural adhesive. Strong, stable, and can span long distances.
Glulam (Glued Laminated Timber)
Engineered wood made by bonding layers of lumber with adhesive, creating large, strong beams suitable for long spans and architectural exposure.
Gooseneck
A curved pipe fitting or fixture neck. Common in plumbing fixtures and electrical conduit transitions.
Grab Bar
A safety bar for support in bathrooms, required for accessible design. Blocking must be installed in walls during framing for secure mounting.
Grade
The ground level around a building, or the slope of land for drainage. Finish grade should slope away from foundations to prevent water infiltration.
Permitting
Grading Permit
Authorization for significant earthwork including excavation, fill, and drainage modifications. Required for projects exceeding specified volume or depth thresholds.
Grading Plan
A detailed drawing showing existing and proposed ground elevations on a building site, ensuring proper drainage away from ADU foundations.
Granite
Natural stone used for countertops, flooring, and exterior applications. Durable but requires sealing and is heavier than engineered alternatives.
Granny Flat
A colloquial term for an ADU, originally referring to small homes built for aging parents. Now used interchangeably with ADU, in-law unit, and guest house.
Gravel
Crushed stone used under foundations, around drainage systems, and as a landscaping material. Various sizes for different applications.
Gray Market ADU
An unpermitted dwelling unit that exists without official approval, which homeowners may seek to legalize under California's ADU amnesty or permit correction programs.
Design
Green Building
Construction practices that reduce environmental impact through energy efficiency, sustainable materials, water conservation, and healthy indoor environments.
Design
Green Roof
A roof system partially or completely covered with vegetation planted over a waterproof membrane, providing insulation and stormwater management for an ADU.
Greenboard
Moisture-resistant drywall formerly used in wet areas. Now largely replaced by cement board and fiberglass-faced products for tile substrates.
Greenhouse
A glass or plastic-enclosed structure for growing plants. Not habitable space; has different permit requirements than ADUs.
Greywater
Wastewater from showers, sinks, and laundry (not toilets) that can be recycled for landscape irrigation. California allows greywater systems with proper permits.
Grid-Tied Solar
A photovoltaic system connected to the utility power grid, allowing ADU owners to export excess energy and receive credits through net energy metering.
Gross Floor Area
The total floor area within the outside perimeter of a building, including all stories. Different from net or livable floor area which excludes walls and utility spaces.
Ground Cover
Low-growing plants used for landscaping. May be required in landscape plans as part of ADU permit conditions.
Ground Fault
An unintended electrical path between a current-carrying conductor and ground. GFCI devices detect ground faults and interrupt power to prevent shock.
Ground Rod
A copper-clad steel rod driven into the earth for electrical system grounding. Required depth and number depend on soil conditions.
Ground Wire
The bare or green-insulated conductor providing a safe path for fault currents. Required in all modern electrical installations.
Grounding
Connecting electrical systems to earth for safety, directing fault currents away from people and equipment. Required by electrical codes.
Grout
Cement-based material filling joints between tiles. Available in sanded and unsanded varieties; sealing prevents staining and water penetration.
Guardrail
A protective railing installed along elevated edges such as decks, stairs, and loft areas in an ADU to prevent falls, typically required at heights of 30 inches or more.
Guest House
A secondary dwelling traditionally without a full kitchen, used for guests. Many former guest houses now qualify as ADUs under California law.
Gutter
A channel at the roof edge that collects and directs rainwater to downspouts. Proper sizing and maintenance prevents water damage and foundation issues.
H
Habitable Space
Space used for living, sleeping, eating, or cooking. Has specific requirements for ceiling height, light, ventilation, and egress distinct from storage or utility areas.
Half Bath
A bathroom with only a toilet and sink, no shower or bathtub. Also called a powder room. May be adequate for studio or one-bedroom ADUs.
Handrail
A graspable rail along stairs or ramps for support. Building codes specify height, size, and return requirements for safety.
Hanger (Joist Hanger)
Metal bracket that supports the end of a joist or beam where it connects to another member. Required for code-compliant framing connections.
Hardboard
A dense, engineered wood panel product used for siding, underlayment, or cabinetry backing in ADU construction, made from compressed wood fibers.
Hardscape
Non-plant landscaping elements including patios, walkways, driveways, and retaining walls. Affects drainage, lot coverage calculations, and permeable surface requirements.
Hardwood Flooring
Solid or engineered wood flooring prized for durability and appearance. Engineered hardwood is often preferred for ADUs due to stability over concrete.
Hazard Insurance
Property insurance covering damage from specific perils like fire, windstorm, or hail, required by lenders and essential for protecting your ADU investment.
Hazardous Materials
Substances that pose health or environmental risks, including asbestos, lead paint, and some chemicals. Testing may be required before renovation work.
Header
A horizontal structural member spanning door and window openings, transferring loads around the opening to adjacent studs or posts.
Hearth
The floor area in front of and beneath a fireplace, made of noncombustible material. Size requirements vary by fireplace type and local codes.
Heat Island Effect
The phenomenon where urban areas experience higher temperatures than surrounding rural areas, addressed in ADU design through cool roofs and shade landscaping.
Heat Pump
An HVAC system that moves heat between indoor and outdoor environments for both heating and cooling. Highly efficient and increasingly required in California new construction.
Heating Degree Day
A measure of how cold a location is, used for energy calculations. Higher values indicate greater heating needs.
Heel Height (Truss)
The vertical distance from the top plate to the top of a truss at the eave. Greater heel height allows more insulation at roof edges.
Finance
HELOC (Home Equity Line of Credit)
A revolving credit line secured by home equity, commonly used to finance ADU construction. Offers flexibility with variable interest rates.
Heritage Tree
A protected tree due to age, size, or species. May limit ADU placement and require special permits or mitigation for removal.
HERS Rating
Home Energy Rating System index measuring building energy efficiency. California requires HERS testing and verification for new construction compliance.
HET (High Efficiency Toilet)
A toilet using 1.28 gallons per flush or less, compared to the 1.6 gallon federal standard. Required by CALGreen for new construction.
Hidden Fastener
Mounting hardware that is not visible in the finished installation. Used for decking, siding, and trim for cleaner appearance.
Hillside Lot
Property on sloped terrain requiring special engineering for foundations, drainage, and structural support. May have additional permit requirements.
Design
Hip Roof
A roof where all sides slope downward to the walls, with no vertical ends. More stable in high winds than gable roofs but with less attic space.
Historic District
A designated area with special protections for historic character. ADUs in historic districts may face additional design review requirements.
HOA (Homeowners Association)
A private organization that governs a residential community. California law limits HOA ability to prohibit ADUs but allows reasonable architectural standards.
Hold Harmless Agreement
A contract provision protecting one party from liability for another's actions. Sometimes required by cities for non-conforming ADU conditions.
Holddown
Metal hardware anchoring shear walls to foundations, resisting uplift from lateral forces. Size and spacing specified by structural engineer.
Hollow Core Door
A lightweight interior door with a hollow center. Not suitable for fire-rated or exterior applications; solid core doors required where fire rating is needed.
Finance
Home Equity Loan
A fixed-rate loan that uses your home's equity as collateral, providing a lump sum often used to finance ADU construction costs.
Homeowner's Exemption
A California property tax reduction available to owner-occupied primary residences, which is not affected by adding an ADU to your property.
Hood (Range Hood)
A ventilation device over cooking surfaces to remove smoke, heat, and odors. Must exhaust to the exterior per code.
Horizontal Bracing
Structural elements resisting lateral forces in the horizontal plane, including floor diaphragms and roof diaphragms that transfer loads to vertical resisting elements.
Hose Bibb
An outdoor faucet for connecting garden hoses. Frost-proof models are recommended; location affects landscape irrigation access.
Hot Mop
A waterproofing method using hot asphalt applied to shower pans and built-up roofing. Traditional but still effective technique.
House Wrap
A synthetic material applied to exterior walls behind siding, providing weather resistance while allowing moisture vapor to escape. Common brands include Tyvek.
California Law
Housing Element
A required component of California city and county general plans addressing housing needs. ADU-friendly policies help meet housing element goals.
HRV (Heat Recovery Ventilator)
A ventilation device that transfers heat from exhaust air to incoming fresh air, improving energy efficiency while maintaining indoor air quality.
Hurricane Clip (Tie)
Metal connector securing roof framing to wall framing, preventing uplift from wind forces. Required in many jurisdictions and by insurance.
HVAC (Heating, Ventilation, Air Conditioning)
The building systems that provide thermal comfort and indoor air quality. ADUs may use mini-splits, through-wall units, or central systems.
HVAC Load Calculation
An engineering analysis determining the heating and cooling capacity required for an ADU based on its size, insulation, orientation, and climate zone.
I
I-Joist
Engineered wood framing member with top and bottom flanges connected by a vertical web, resembling the letter I. Used for floors and roofs.
Ice Dam
Ice buildup at roof edges preventing drainage, causing water backup. Prevention requires proper attic insulation and ventilation.
Impact Driver
A power tool that delivers high rotational torque in quick bursts, commonly used for driving screws and lag bolts during ADU framing and deck construction.
Permitting
Impact Fees
Charges imposed on new development to fund public infrastructure. California exempts ADUs under 750 sq ft from impact fees and limits fees for larger ADUs.
Impervious Surface
Any surface that prevents water from soaking into the ground, such as rooftops, concrete, and asphalt, factored into stormwater calculations for ADU projects.
In-Fill
Construction on vacant or underutilized lots in developed areas. ADUs represent a form of in-fill development within existing neighborhoods.
In-Law Unit
A common term for an ADU, originally referring to housing for extended family members. Now used interchangeably with ADU, granny flat, and accessory apartment.
Indemnification
A contractual clause where one party agrees to compensate the other for specified losses, commonly found in ADU construction contracts between homeowners and contractors.
Infill Development
Building on vacant or underused parcels within existing developed areas, which ADU construction exemplifies by adding housing to established neighborhoods.
Infiltration (Air)
Uncontrolled air leakage into a building through cracks and openings. Reduces energy efficiency and can cause moisture problems.
Inlet (Plumbing)
A point where water enters a fixture or system. Inlet valves control water flow to toilets, water heaters, and other fixtures.
Permitting
Inspection
Official examination of construction work by building department staff to verify code compliance. Required at specific stages including foundation, framing, and final.
Permitting
Inspection Card
A document posted on the job site recording required inspections and their results. Must be visible and accessible to inspectors.
Insulation
Material that reduces heat transfer through the building envelope. Types include fiberglass, cellulose, spray foam, and rigid board, with R-value indicating thermal resistance.
Insurance (Construction)
Coverage protecting against construction risks including liability, property damage, and workers' compensation. Contractors must carry appropriate insurance.
Interior ADU
An ADU created within the existing space of a primary dwelling, such as converting a basement, attic, or portion of the house.
Interior Designer
A professional who plans interior spaces for function and aesthetics. May help with ADU finish selections, furniture layout, and color schemes.
Interior Partition
A non-load-bearing wall that divides interior spaces. Can be added, moved, or removed without structural modifications.
Interlock
A safety device preventing improper operation. Includes electrical interlocks for generator panels and mechanical interlocks for HVAC systems.
Irrigation System
A system for watering landscaping, including sprinklers, drip systems, and controllers. May require separate permits and backflow prevention.
Island (Kitchen)
A freestanding counter unit in a kitchen. May include seating, storage, and appliances. Requires careful planning in compact ADU kitchens.
Isometric Drawing
A three-dimensional representation showing plumbing or electrical systems without perspective distortion. Used to clarify complex assemblies.
J
J-Channel
A trim piece shaped like the letter J used around windows, doors, and other openings to receive the edges of vinyl or aluminum siding on an ADU.
Jack Rafter
A short rafter that runs from a hip or valley rafter to the ridge or wall plate, not spanning the full roof.
Jack Stud (Trimmer)
A shortened stud that supports the ends of headers over door and window openings. Works with king studs to transfer loads.
California Law
JADU (Junior ADU)
A small ADU of 500 sq ft or less created within the walls of an existing single-family home. Must have separate entrance and efficiency kitchen; bathroom may be shared.
Jamb
The vertical side pieces of a door or window frame. Door jambs include hardware locations for hinges, strike plates, and weatherstripping.
Joint Compound
Material used to fill seams between drywall panels and cover fastener holes. Applied in multiple coats and sanded for a smooth finish.
Joint Tape
Paper or fiberglass mesh tape embedded in joint compound to reinforce drywall seams and prevent cracking.
Joist
A horizontal structural member supporting floors or ceilings, spanning between beams or bearing walls. Spacing is typically 12, 16, or 24 inches on center.
Journeyman
A skilled tradesperson who has completed an apprenticeship in a specific trade such as plumbing, electrical, or carpentry and is qualified to work on ADU projects.
Junction Box
An electrical enclosure where wires are connected and spliced. Must remain accessible and covered with appropriate rated covers.
K
Kerf
The width of a cut made by a saw blade, important for precise measurements when cutting framing lumber and finish materials for ADU construction.
Key (Lock)
ADU entrances require independent locking systems. Consider whether to share master key systems with the primary dwelling.
Kick Plate
A protective metal plate at the bottom of a door to prevent damage from foot traffic. Common on commercial doors and accessible entries.
Kickback (Plumbing)
A short section of pipe that changes direction at a slight angle, used to route plumbing lines around obstacles in tight ADU floor and wall cavities.
Kilowatt (kW)
A unit of electrical power equal to 1,000 watts. Solar panel systems are rated in kilowatts, and electrical service capacity is often expressed in kW.
King Stud
Full-length studs on either side of an opening that run from the bottom plate to the top plate, supporting header loads.
Kitchen
A room or area for food preparation with cooking appliances, sink, and storage. Full ADUs require complete kitchens; JADUs may have efficiency kitchens without full-size ranges.
Knee Wall
A short wall, typically under 4 feet, often found in attic conversions where the roof slope meets the floor. Creates usable space under low ceilings.
Knob and Tube Wiring
An obsolete electrical wiring method using ceramic insulators. Must be replaced during renovations and not covered with insulation.
L
Lag Bolt
A heavy-duty wood screw with a hex head, used to make strong structural connections such as attaching a ledger board to a house for an ADU deck.
Laminate Flooring
A multi-layer flooring product with a photographic image layer that simulates wood or stone, offering a durable and affordable finish option for ADUs.
Landscape Plan
A drawing showing proposed vegetation, hardscape, and irrigation. May be required for ADU projects in some jurisdictions, especially in drought-prone areas.
Lap Siding
Horizontal siding where each board overlaps the one below. Available in wood, fiber cement, and vinyl. Classic appearance suitable for many ADU styles.
Lateral Load
Horizontal forces acting on a structure, primarily from wind and earthquakes. Resisted by shear walls, diagonal bracing, or moment frames.
Lath
The base material for stucco or plaster, traditionally wood strips but now typically metal mesh or self-furring wire.
Lead Paint
Paint containing lead, found in homes built before 1978 and requiring special testing and abatement procedures when renovating or converting older structures into ADUs.
Lean-To
A simple structure with a single-slope roof leaning against an existing wall, sometimes used as a basic form for attached ADU additions or covered patios.
Ledger Board
A horizontal framing member attached to an existing structure to support floor or deck joists. Must be properly flashed and fastened per code.
Design
LEED (Leadership in Energy and Environmental Design)
A green building certification program rating projects on sustainability criteria including energy, water, materials, and indoor environmental quality.
Legal Nonconforming
A use or structure that was lawful when established but no longer complies with current regulations. May be allowed to continue with restrictions on expansion.
Licensed Contractor
A construction professional holding a valid state license. California requires CSLB licensing for contractors on projects over $500.
Finance
Lien
A legal claim against property as security for payment. Contractors and suppliers can file mechanics' liens for unpaid work or materials.
Finance
Lien Waiver
A document from a contractor or supplier relinquishing the right to file a mechanic's lien against the property, important for homeowners to collect during ADU construction payments.
Life Safety
Building code provisions focused on protecting occupants from hazards including fire, structural failure, and toxic exposure, applied to all ADU construction.
Light Fixture
An electrical device for mounting and powering light sources. Selection affects energy efficiency, lighting quality, and code compliance.
Lintel
A horizontal member spanning an opening in masonry construction, similar to a header in wood framing. May be steel, precast concrete, or reinforced masonry.
Live Load
Variable weight from occupants, furniture, and movable objects. Building codes specify minimum live load requirements for structural design.
Load Path
The continuous route through which structural forces travel from the roof to the foundation, which must be properly designed in ADU framing to resist gravity and lateral loads.
Load-Bearing
A structural element that supports weight from above, including walls, beams, and columns. Removal or modification requires structural engineering.
Design
Loft
A raised platform or partial floor within a room, often used for sleeping in compact ADUs. Height and access requirements vary by code.
Lot Coverage
The percentage of a lot covered by buildings and impermeable surfaces. Zoning codes set maximum lot coverage, though ADUs often receive exemptions or allowances.
Lot Line
The legal boundary of a property parcel. Setbacks are measured from lot lines, and construction typically cannot cross them without easements.
Low-E Glass
Window glass with a microscopically thin metallic coating that reflects radiant heat, improving energy efficiency. Required by California energy code for most applications.
Low-Flow Fixture
A plumbing fixture designed to use less water than standard models while maintaining performance, often required by CALGreen standards in new ADU construction.
LVL (Laminated Veneer Lumber)
Engineered lumber made from thin wood veneers bonded together, used for headers, beams, and rim boards. Stronger and more stable than solid lumber.
M
Main Panel
The primary electrical distribution panel in a building, receiving power from the utility and distributing it to branch circuits. May need upgrading for ADU electrical loads.
Manhole
An access point in underground utility systems. May be required for sewer connections depending on depth and local requirements.
Design
Mansard Roof
A roof with two slopes on each side, the lower slope being steeper. Creates usable attic space and distinctive architectural character.
Manufactured Housing
Factory-built homes constructed to federal HUD standards, distinct from modular homes built to local codes. Not typically permitted as ADUs in most jurisdictions.
Masonry
Construction using brick, stone, concrete block, or similar units. Used for foundations, walls, chimneys, and decorative elements.
Design
Massing
The overall shape, size, and volume of a building as perceived from the exterior, considered in ADU design to ensure compatibility with the primary residence.
Material Safety Data Sheet (MSDS)
A document detailing the properties, hazards, and safe handling of chemical products used on construction sites, required to be available during ADU building.
Permitting
Mechanical Permit
Authorization for HVAC system installation and modification. May be separate from or included in the building permit depending on jurisdiction.
Mechanical Plan
A construction drawing showing the layout of HVAC ductwork, equipment, and ventilation for an ADU, required for permit submittal.
MEP (Mechanical, Electrical, Plumbing)
The building systems that provide comfort, power, and water. MEP design is critical for ADU functionality and code compliance.
Metal Stud
A lightweight steel framing member used as an alternative to wood studs, offering fire resistance and dimensional stability for ADU wall framing.
Meter
A device measuring utility consumption. ADUs may share meters with the primary dwelling or have separate meters, affecting billing and utility connections.
Meter Base
The mounting equipment for an electric meter. ADUs may require a separate meter base or connection through a subpanel.
Milestone
A significant point in the ADU construction timeline, such as foundation completion, framing inspection, or final walkthrough, used to track project progress.
Mini-Split
A ductless HVAC system with an outdoor compressor and one or more indoor air handlers. Popular for ADUs due to efficiency, compact size, and easy installation.
Minimum Lot Size
The smallest parcel area allowed for building in a given zone, though California law generally prohibits minimum lot size requirements for ADU approval.
California Law
Ministerial Approval
Permit approval based on objective standards without discretionary judgment. California requires ministerial ADU approval within 60 days for compliant applications.
Miter Joint
A joint formed by cutting two pieces at matching angles, typically 45 degrees, to form a corner. Common in trim and molding work.
Modular Construction
Building method where sections are manufactured off-site and assembled on the property. Must meet the same codes as site-built structures and is increasingly popular for ADUs.
Moisture Barrier
Material that prevents water vapor transmission, installed in crawl spaces, under slabs, and within wall assemblies to prevent condensation and moisture damage.
Mold
Fungal growth resulting from moisture problems, causing health issues and structural damage. Prevention requires proper ventilation, drainage, and moisture control.
Moment Frame
A structural system using rigid beam-column connections to resist lateral forces. Allows open floor plans without diagonal bracing.
Monolithic Slab
A concrete foundation where the footing and floor slab are poured as a single unit, commonly used for detached ADUs on level sites.
Mortar
A mixture of cement, sand, and water used to bind masonry units. Different types are specified for various applications and exposures.
Mullion
A vertical or horizontal member dividing a window or door into sections. May be structural or purely decorative.
Multifamily
A building containing multiple dwelling units, such as apartments, condos, or townhouses. California ADU laws also apply to multifamily properties with specific provisions.
N
Nail Gun (Pneumatic Nailer)
A power tool that drives nails using compressed air. Essential for efficient framing and finish work. Different types for different nail sizes.
Nail Plate
A metal plate installed over studs to protect wires and pipes from nail or screw penetration. Required by code where utilities run near the face of framing.
Natural Gas
A fossil fuel delivered by pipeline for heating, cooking, and hot water. New California construction increasingly requires all-electric design.
Natural Light
Daylight entering through windows and skylights. Building codes require minimum glazing area (typically 8% of floor area) for habitable rooms.
NEC (National Electrical Code)
The standard for safe electrical installation in the United States, adopted with modifications by most jurisdictions. Updated on a three-year cycle.
Negative Drainage
A site condition where water flows toward a building foundation rather than away from it, requiring correction before or during ADU construction.
Finance
Net Energy Metering (NEM)
A billing arrangement that credits solar energy system owners for electricity they add to the grid, applicable to ADUs with photovoltaic panels in California.
Design
Net Zero
A building that produces as much energy as it consumes annually, typically through solar generation and high efficiency. A goal for sustainable ADU design.
Neutral Wire
The grounded conductor in an electrical circuit that carries current back to the panel, required in modern wiring to support smart switches and dimmers in ADUs.
New Construction
Building a structure from the ground up, as opposed to renovation or conversion. New construction ADUs must meet current code requirements.
Noise Ordinance
Local regulations limiting noise levels and construction hours. ADU construction must comply with restrictions on work hours and noise levels.
Nominal Size
The named dimension of lumber before drying and planing, such as a 2x4 which actually measures 1.5 by 3.5 inches, important for accurate ADU framing calculations.
Noncombustible
Materials that will not ignite, burn, or release flammable vapors. Required for certain applications, especially near property lines or in fire-prone areas.
Nonconforming
A structure or use that was legal when built but doesn't meet current zoning requirements. Existing nonconforming setbacks may be allowed for ADU conversions.
Permitting
Notarized Affidavit
A sworn written statement verified by a notary public, sometimes required during ADU permitting to confirm property ownership or other legal facts.
O
Occupancy
The classification of building use and the number of people permitted. Residential occupancy codes apply to ADUs.
Permitting
Occupancy Classification
A building code category based on the intended use of a structure, with residential ADUs classified as R-3 occupancy under California building codes.
Occupant Load
The calculated number of people a space can accommodate, used for determining egress, plumbing fixtures, and ventilation requirements.
Offset
A horizontal change in direction of a plumbing drain line. Requires proper fittings and may need additional cleanouts for maintenance access.
On Center (OC)
Measurement from the center of one framing member to the center of the next. Standard stud spacing is 16 inches OC, though 24 inch OC is common in some applications.
Permitting
On-Site Wastewater
A private sewage treatment system such as a septic tank and leach field, required when an ADU cannot connect to a public sewer system.
One-Hour Rated
A wall or floor assembly that can resist fire for one hour. May be required for ADUs within certain distances of property lines.
Design
Open Floor Plan
A layout with minimal walls between living areas, popular in ADUs to maximize perceived space. Requires careful attention to structural support and mechanical systems.
Operable Window
A window that can be opened for ventilation. Building codes require operable windows in bedrooms for emergency egress and in living spaces for natural ventilation.
Oriented Strand Board (OSB) Sheathing
Engineered wood panels made from compressed wood strands, commonly used for wall and roof sheathing in ADU framing due to its strength and cost-effectiveness.
OSB (Oriented Strand Board)
Engineered wood panel made from compressed wood strands, used for sheathing and subflooring. Performance is similar to plywood at lower cost.
Outfall
The point where a drainage system discharges water, which must be directed away from the ADU and neighboring properties to prevent erosion and flooding.
Outlet
A point in the electrical system where current is taken to supply equipment. Receptacle outlets must be installed per NEC spacing requirements.
Permitting
Over-the-Counter Permit
A building permit approved at the counter during a single visit to the building department, available in some jurisdictions for simple ADU projects with pre-approved plans.
Overhang
Roof extension beyond the exterior wall, providing shade and weather protection. Depth affects solar heat gain and rain protection at windows and doors.
California Law
Overlay (Zoning)
Additional zoning regulations applied to specific areas such as historic districts, hillsides, or transit corridors. May affect ADU requirements.
Owner-Builder
A property owner who acts as their own general contractor. Requires signing a disclosure acknowledging responsibilities and may affect insurance and financing.
P
Panelized Construction
A building method using pre-assembled wall, floor, and roof panels manufactured off-site. Faster than stick-built and more customizable than modular.
Parapet
A low wall extending above the roof line. Common on flat-roofed buildings, providing edge protection and concealing rooftop equipment.
Parcel
A legally defined piece of real property. ADUs must be located on the same parcel as the primary dwelling unless the parcel is subdivided under SB 9.
Parge Coat
A thin cement plaster applied to masonry or concrete surfaces for smoothing, waterproofing, or decoration.
Parging
A thin coat of cement or mortar applied to foundation walls to smooth the surface and provide basic moisture resistance for ADU below-grade construction.
Parking
Off-street vehicle storage. California prohibits parking requirements for ADUs near transit, in historic districts, or when converting existing structures.
Partition Wall
A non-load-bearing wall dividing interior spaces. Can be easily modified or removed without affecting structural integrity.
Design
Passive House
An energy-efficiency building standard emphasizing airtight construction, continuous insulation, and heat recovery ventilation. Achievable for high-performance ADUs.
Design
Passive Solar
Design strategies that use building orientation, windows, and thermal mass to collect and store solar energy without mechanical systems.
Patio
An outdoor living area typically at ground level, made of concrete, pavers, or other paving materials. Generally does not require a building permit unless covered.
Paver
Interlocking concrete, brick, or stone units for paving driveways, patios, and walkways. Permeable pavers can help with stormwater management.
Peck Test
Exploratory excavation to determine soil conditions before foundation design. May reveal underground obstacles or inform engineering decisions.
Pedestal
A support post for raised flooring or deck systems. Adjustable pedestals simplify leveling over uneven surfaces.
Pedestal Foundation
A foundation system using isolated concrete piers to support the structure, often used for additions and ADUs to minimize site disturbance.
Penny (Nail Size)
A traditional unit for classifying nail length, where common sizes like 16d nails are used for structural framing in ADU wall and roof assemblies.
Percolation Test (Perc Test)
A soil test measuring how quickly water drains through the ground, used to determine if a site can support a septic system for an ADU.
Pergola
An outdoor structure with open-beam roof, providing partial shade. Often included in ADU landscape design for outdoor living space.
Pergola Kit
A prefabricated outdoor shade structure assembled from pre-cut components, sometimes installed adjacent to ADUs to extend usable outdoor living space.
Perlite
Volcanic glass expanded by heat, used as lightweight insulation fill or aggregate in concrete. Provides thermal and acoustic benefits.
Permeable Paving
Paving materials that allow rainwater to filter through to the ground below, helping meet stormwater requirements for driveways and walkways around ADUs.
Permitting
Permit
Official authorization from government agencies to perform construction work. ADU projects typically require building, electrical, plumbing, and mechanical permits.
Permitting
Permit-Ready Plans
Pre-designed ADU plans that meet common code requirements and can be submitted for permit with site-specific modifications. Reduces design time and costs.
PEX Piping
Flexible cross-linked polyethylene tubing used for water supply lines, popular in ADU plumbing for its ease of installation, durability, and freeze resistance.
Phase (Electrical)
The type of electrical power service. Residential is typically single-phase; some large properties have three-phase service.
Photovoltaic Panel
A solar panel that converts sunlight directly into electricity, often required on new ADU construction in California to comply with energy code mandates.
Pier
A vertical foundation element that transfers loads deep into the soil, used when surface soils are inadequate. May be drilled concrete, driven piles, or helical piers.
Pilot Hole
A small-diameter hole drilled before inserting a screw, preventing wood splitting. Essential for hardwoods and near board edges.
Pitch Pocket
A metal flashing container filled with sealant around roof penetrations. Common detail for pipes, conduits, and supports on flat roofs.
Permitting
Plan Check
Review of construction documents by the building department for code compliance. California limits ADU plan check time to 60 days.
Permitting
Plan Examiner
A building department official who reviews construction documents for code compliance before issuing a building permit for an ADU.
Plat Map
A legal document showing the boundaries, dimensions, and easements of a property, referenced during ADU planning to confirm buildable area and setbacks.
Plate Height
The distance from the floor to the top plate of a wall, determining rough ceiling height. Standard is 8 feet; higher plates create roomier spaces.
Platform Framing
Standard wood framing method where each floor is built as a separate platform, with wall studs extending only one story. The most common residential framing system.
Plenum
An air-handling space in HVAC systems, such as the chamber in furnaces or the space above dropped ceilings used for air distribution.
Plug Load
The electrical power consumed by devices plugged into outlets. Energy modeling considers plug loads in addition to fixed equipment.
Permitting
Plumbing Permit
Authorization for plumbing work including water supply, drainage, and fixtures. May be obtained separately or as part of the building permit.
Plywood
Engineered wood panel made from thin veneer layers bonded with alternating grain directions. Used for sheathing, subflooring, and structural applications.
Pocket Door
A door that slides into a wall cavity rather than swinging open. Saves floor space in compact ADU layouts.
Point of Connection
The location where a new utility service connects to existing infrastructure. ADU utility connections may tap existing house services or require new connections.
Post and Beam
A structural system using vertical posts and horizontal beams to create open floor plans without load-bearing walls. Popular for modern architectural designs.
Finance
Pre-Approval (Financing)
A lender's conditional commitment to provide financing up to a specified amount, giving homeowners confidence to begin ADU design and contractor selection.
Prefabricated (Prefab)
Building components manufactured off-site and assembled on location. Includes modular units, panelized systems, and pre-built components. Growing segment of ADU market.
Pressure-Treated Lumber
Wood infused with chemical preservatives to resist rot, decay, and insects, required for ADU framing members in contact with or near the ground.
Prevailing Wage
The hourly wage and benefits required by law for workers on publicly funded projects, generally not applicable to private residential ADU construction.
Primary Dwelling
The main residential structure on a property, to which an ADU is accessory. California ADU laws require a primary dwelling to exist or be proposed concurrently.
Program (Architectural)
A description of the spaces, functions, and requirements for a building project, developed during early ADU planning to define rooms, sizes, and layout goals.
Property Line
The legal boundary of a parcel. Setbacks are measured from property lines, and structures typically cannot encroach without easements or variances.
Punchlist
A detailed list of minor defects, incomplete items, and touch-ups that must be corrected by the contractor before final payment and project closeout on an ADU.
PV System (Photovoltaic)
Solar panels that convert sunlight to electricity. California requires solar on most new construction, including some ADUs, depending on size and energy use.
Q
Quality Control
Systematic processes ensuring construction meets plans and specifications. Includes inspections, testing, and documentation throughout the project.
Quarter Round
Molding with a quarter-circle profile, often used at the base of baseboards to cover gaps between the baseboard and floor.
Quick Connect
A plumbing or gas fitting designed for fast, tool-free connections, used on ADU appliances like dishwashers, gas ranges, and water heaters for easy installation.
Quoin
Decorative stone or brick blocks at building corners, providing visual accent. May be genuine masonry or simulated with stucco or foam.
R
R-Value
A measure of thermal resistance in insulation materials. Higher R-values indicate better insulating performance. California energy code specifies minimum R-values by climate zone.
Rabbet Joint
A step-shaped recess cut along the edge of a board to receive another piece, commonly used in ADU cabinetry and window frame construction.
Radiant Heating
A heating system using panels or tubing in floors, walls, or ceilings to radiate heat. Provides comfortable, even heat distribution without ducts.
Radon
A naturally occurring radioactive gas that can seep into buildings through cracks in foundations, with mitigation measures sometimes recommended for ADU slab construction.
Rafter
A sloped framing member extending from the ridge or hip to the wall plate, supporting roof sheathing and loads. Sized based on span, spacing, and load requirements.
Rain Screen
A wall system with an air gap between siding and sheathing, allowing drainage and drying of moisture that penetrates the cladding.
Rainwater Harvesting
The collection and storage of rainwater from roofs for landscape irrigation or other non-potable uses, an eco-friendly addition to ADU site design.
Raised Floor
A floor elevated above grade on piers or a short foundation wall, creating a crawl space beneath. Provides utility access and flood protection.
Rake
The sloped edge of a gable roof, running from eave to ridge. Rake trim protects the exposed roof edge and provides architectural detail.
Range Hood
A ventilation device over a cooking surface that removes smoke, grease, and odors. Required in ADU kitchens and must vent to the exterior.
Real Property
Land and any permanent structures attached to it, including an ADU, which becomes part of the real property and is included in property assessments.
Rear Setback
The required distance between a structure and the rear property line. California allows ADUs within 4 feet of rear property lines when meeting height limits.
Rebar (Reinforcing Steel)
Steel bars embedded in concrete to increase tensile strength. Size, spacing, and placement are specified by structural engineers based on loads and codes.
Receptacle
An electrical outlet for plug-in devices. NEC requires receptacles at specific intervals, near counters, and in bathrooms, garages, and outdoor locations.
Recessed Lighting
Light fixtures installed into the ceiling so the housing sits above the ceiling surface, providing clean, modern illumination in compact ADU rooms.
Recording (Property)
The official filing of documents such as deeds and deed restrictions with the county recorder, sometimes required for ADU-related covenants or lot splits.
Reflective Insulation
An insulation material with a reflective surface that reduces radiant heat transfer, useful in ADU attic spaces and walls to improve energy efficiency.
Finance
Rental Income
Revenue from renting an ADU, which can help offset construction costs and mortgage payments. Lenders may consider projected rental income for ADU financing.
Retaining Wall
A structure that holds back soil at different elevations. Required on sloped sites and may need engineering and permits depending on height and location.
Retention Basin
A constructed area designed to hold stormwater temporarily and release it slowly, sometimes required as part of ADU site drainage plans.
Finance
Return on Investment (ROI)
The financial gain relative to investment cost. ADUs typically provide strong ROI through rental income and property value increases.
Permitting
Revision (Plan)
Changes to approved plans requiring review and approval by the building department. Major revisions may incur additional fees and review time.
Ridge
The highest point of a roof where two slopes meet. Ridge height often determines overall building height for setback and zoning calculations.
Ridge Vent
A continuous ventilation opening along the peak of a roof that allows hot air to escape from the attic space, improving air circulation in an ADU.
Right of Way
Land reserved for public use such as streets, sidewalks, and utilities. Structures cannot typically be built in the public right of way.
Rim Joist
The perimeter joist at the edge of a floor system, enclosing the ends of floor joists. Important for insulation and air sealing at the floor-wall junction.
Riser
The vertical portion of a stair step. Building codes specify maximum riser height and require uniform risers in a flight of stairs.
Romex (NM Cable)
Non-metallic sheathed cable used for interior residential wiring. Contains insulated conductors and ground wire within a plastic jacket.
Roof Drain
A drain installed in a flat roof to remove water, connected to an internal drainage system or scupper. Requires regular maintenance.
Roof Pitch
The slope of a roof expressed as rise over run. Affects drainage, attic space, and aesthetics.
Rough-In
Installation of mechanical, electrical, and plumbing systems within walls and floors before covering with finish materials. Requires inspection before closing up.
S
California Law
SB 1211
A 2024 California law that further streamlined ADU regulations, allowing ADUs to be sold separately from the primary dwelling under specific conditions.
California Law
SB 13 (California Senate Bill 13)
2019 California law that reduced ADU development barriers, including eliminating owner-occupancy requirements and limiting impact fees for smaller ADUs.
California Law
SB 897
A 2022 California law that increased allowable ADU height limits, permitted ADUs on multifamily properties, and expanded construction options for homeowners.
California Law
SB 9 (California Senate Bill 9)
California law (2022) allowing lot splits and duplexes on single-family lots in urban areas, potentially enabling up to four units per parcel when combined with ADUs.
Schematic Design
The initial design phase establishing overall project scope, size, and character through basic drawings and diagrams before detailed design development.
Scope of Work
A detailed description of work to be performed under a contract, including materials, methods, and outcomes. Essential for accurate bids and avoiding disputes.
Scupper
An opening in a parapet wall or roof edge that allows water to drain off a flat roof, directing runoff into downspouts or away from ADU walls.
Scuttle
An access opening to an attic or roof, typically covered by a removable panel or hatch. Required for access to attic spaces and equipment.
Seismic Zone
A geographic area classified by earthquake risk levels, which determines the structural design requirements for ADU foundations and framing in California.
Permitting
Self-Certification
A process where a licensed architect or engineer certifies that plans meet code requirements, potentially bypassing standard plan check review for ADU permits.
Septic System
An on-site sewage treatment system using a tank and leach field. ADUs on septic properties may require system evaluation and potential upgrades.
Service Panel
The main electrical distribution panel containing the main breaker and branch circuit breakers. Location and capacity are key factors in ADU electrical design.
Setback
The required distance between a structure and property lines. California limits ADU setbacks to 4 feet from side and rear property lines for compliant projects.
Sewer Lateral
The underground pipe connecting a building's drainage system to the public sewer main. ADUs may connect to existing laterals or require new connections.
Shared Wall
A wall common to two adjacent units or structures, requiring specific fire-rating and sound-insulation standards when building an attached ADU.
Shear Wall
A wall designed to resist lateral forces from wind and earthquakes through rigid sheathing and proper fastening. Essential for structural stability.
Sheathing
Structural panels attached to framing to provide rigidity and a surface for exterior finishes. Also provides lateral bracing for walls.
Design
Shed Roof
A single-slope roof, simple to construct and popular for modern ADU designs. Allows for clerestory windows and easy drainage.
Shim
A thin wedge used to fill gaps and level or plumb components during installation. Made of wood, plastic, or metal depending on application.
Shoe Molding
A small molding at the junction of the baseboard and floor, covering expansion gaps and providing a finished appearance.
Shop Drawings
Detailed fabrication drawings produced by manufacturers or subcontractors showing how specific components like trusses or cabinets will be built for an ADU.
Short-Term Rental
Renting property for less than 30 days, typically through platforms like Airbnb. Many California cities restrict or prohibit short-term ADU rentals.
Shutoff Valve
A valve that stops water or gas flow to fixtures or appliances. Individual shutoffs are required at each fixture for isolation during repairs.
Siding
Exterior wall cladding providing weather protection and aesthetics. Types include wood, fiber cement, vinyl, and metal. Some require fire-resistant materials near property lines.
Sill Plate
The lowest horizontal member of a wall frame, anchored to the foundation. Must be pressure-treated or naturally decay-resistant when in contact with concrete.
Simpson Tie
A brand of engineered metal connector widely used in residential construction to join wood framing members at critical structural points in ADU framing.
Single-Family
A zoning classification for properties with one primary dwelling unit. California ADU laws primarily apply to single-family zoned properties.
SIP (Structural Insulated Panel)
A prefabricated building panel consisting of rigid foam insulation sandwiched between two structural facings, offering fast and energy-efficient wall and roof construction for ADUs.
Sister (Framing)
To attach a new framing member alongside an existing one for reinforcement. Common repair technique for damaged joists or studs.
Site Plan
A drawing showing the property boundaries, existing and proposed structures, setbacks, utilities, and other site features. Required for ADU permit applications.
Skylight
A window in the roof providing natural light and, in some designs, ventilation. Requires proper flashing and may contribute to required light and ventilation.
Slab-on-Grade
A concrete foundation poured directly on prepared ground, serving as both foundation and floor. Common for ADUs due to cost-effectiveness and accessibility.
Sleeper
Wood strips laid over concrete to create a nailing surface for finish flooring. Provides a level surface and allows for insulation beneath.
Sliding Door
A door that opens horizontally by sliding along a track, popular in ADU designs for saving floor space and providing wide openings to outdoor areas.
Slope
The incline of land, expressed as ratio or percentage. Steep slopes affect ADU feasibility, foundation design, drainage, and access requirements.
Design
Smart Home
Technology integration for automated control of lighting, HVAC, security, and appliances. Increasingly popular in modern ADU design.
Smoke Detector
A device that detects smoke and sounds an alarm. Required in each bedroom, outside sleeping areas, and on every level of an ADU. May need to be interconnected.
Snap-In (Plumbing)
A pipe support or clamp that clips onto framing members without tools. Simplifies installation of plumbing supply and drain lines.
Soaker (Flashing)
Metal flashing pieces interwoven with roofing material at wall-to-roof junctions. Prevents water infiltration at critical transitions.
Soaker Hose
A porous garden hose that slowly seeps water along its length, used for efficient landscape irrigation around ADU plantings.
Soffit
The underside of an overhanging element such as a roof eave. Provides ventilation for attic spaces and protects rafter ends from weather.
Soil Stack
The main vertical drain pipe in a plumbing system that carries waste from upper floors to the building sewer, sized according to the number of fixtures in an ADU.
Soils Report
A geotechnical study analyzing soil conditions to determine appropriate foundation design. May be required for hillside sites or areas with problematic soils.
Solar Pathfinder
A tool used to assess a site's solar exposure by mapping shading patterns throughout the year, helping optimize solar panel placement on an ADU roof.
Solar Ready
Design features facilitating future solar panel installation, including conduit pathways, electrical panel capacity, and unobstructed roof area.
Sole Plate
The bottom horizontal member of a wall frame, resting on the subfloor or sill plate. Also called the bottom plate.
Sound Transmission Class (STC)
A rating measuring how well a wall or floor assembly blocks airborne sound, important for privacy between an ADU and the primary dwelling.
Design
Space Planning
The organization of interior spaces for optimal function and flow. Critical for efficient ADU layouts that maximize limited square footage.
Span
The horizontal distance between supports for a structural member. Span tables in building codes specify allowable spans based on member size, spacing, and loads.
Spandrel
The triangular space between the curve of an arch and the surrounding structure. Also refers to panels between floor levels on multi-story buildings.
Spec Home
A house built on speculation without a specific buyer. Prefab ADU manufacturers often display spec units to showcase their designs.
Spec Sheet
A detailed document listing the materials, finishes, fixtures, and appliances specified for an ADU project, ensuring all parties agree on the scope and quality of work.
Specifications
Written descriptions of materials, products, and workmanship standards supplementing construction drawings. Part of the complete construction documents.
Splice
A connection joining two structural members or wires end-to-end. Requires proper technique and, for electrical, appropriate junction boxes.
Split System
An HVAC system with separate indoor and outdoor components connected by refrigerant lines. Includes mini-splits popular for ADUs.
Sprinkler System (Fire)
An automatic fire suppression system. May be required for ADUs in certain conditions, such as those attached to the primary dwelling.
Square Footage
The area of a space measured in square feet. ADU size limits vary by jurisdiction, with California setting a state minimum of 850-1,200 sq ft depending on bedroom count.
Stack Effect
Air movement in buildings due to temperature differences between inside and outside. Warm air rises, creating pressure differences that affect ventilation.
Staging Area
A designated space on site for storing materials and equipment during construction. Planning staging is important for ADU projects with limited space.
Step Flashing
L-shaped metal pieces woven into roof shingles where the roof meets a vertical wall, providing waterproof protection at ADU roof-to-wall intersections.
Stormwater
Rainwater runoff from roofs and paved surfaces. New impervious area may trigger stormwater management requirements including retention or treatment.
Story Pole
A measuring stick marked with key height dimensions used during framing to ensure consistent wall heights and opening placements throughout an ADU.
Structural Engineer
A licensed professional who designs structural systems for buildings, ensuring they safely resist loads. Required for most ADU projects in California.
Structural Pest Report
An inspection report identifying wood-destroying organisms and conditions such as termites and fungus, often required before financing or permitting an ADU conversion.
Stub-Out
A capped pipe extending from a wall or floor to mark the future connection point for plumbing fixtures during ADU rough-in construction.
Stucco
A cement-based exterior plaster applied over lath, popular in California for durability and fire resistance. Requires proper flashing and weep screeds.
Stud
Vertical framing member in walls, typically 2x4 or 2x6 lumber or steel. Standard spacing is 16 or 24 inches on center depending on structural and insulation requirements.
Subcontractor
A specialty contractor hired by the general contractor for specific work such as electrical, plumbing, HVAC, or roofing. Must be properly licensed.
Subfloor
The structural floor sheathing installed over floor joists, providing a base for finished flooring. Typically plywood or OSB panels.
Subpanel
A secondary electrical panel fed from the main panel, distributing power to circuits in a portion of the building. Common for ADU electrical service.
Sump Pump
A pump that removes water collected in a sump basin, typically in basements or crawl spaces prone to flooding. Helps keep foundations dry.
Supplemental Property Tax
An additional property tax bill issued by the county assessor when an ADU or other improvement increases the assessed value of a property.
Survey
A professional measurement and mapping of property boundaries and features. May be required to verify setbacks and property line locations for ADU permits.
Swale
A shallow, vegetated depression in the landscape designed to channel and slow stormwater runoff, often incorporated into ADU site grading plans.
T
T&G (Tongue and Groove) Plywood
Plywood panels with interlocking edges that create a tight, smooth subfloor surface, commonly used in ADU floor framing for structural rigidity.
T-Bar Ceiling
A suspended ceiling system using T-shaped metal tracks to support acoustic tiles. Provides easy access to utilities above but reduces ceiling height.
Takeoff (Quantity)
The process of measuring quantities of materials needed from construction drawings. Used for cost estimating and ordering materials.
Tankless Water Heater
An on-demand water heating system that heats water only when needed, saving space and energy. Popular choice for ADUs due to compact size.
Tempered Glass
Heat-treated glass that breaks into small, safer fragments. Required in locations prone to impact, including doors, near bathtubs, and low windows.
Temporary Power
Electrical service established for construction purposes before permanent service is installed. Provides power for tools and equipment during building.
Thermostat
A device controlling HVAC systems to maintain desired temperature. Programmable and smart thermostats help meet California energy code requirements.
Threshold
The strip at the bottom of an exterior door providing a seal against weather. Accessible designs require low thresholds.
Tie-Down
Metal hardware connecting walls to foundations to resist uplift forces. Required by building codes, especially in high-wind and seismic zones.
Tile
Ceramic, porcelain, or stone units for floors, walls, and countertops. Requires proper substrate preparation and waterproofing in wet areas.
Tilt-Up Construction
A method where concrete wall panels are cast on-site and tilted into position, occasionally used for commercial-style ADU builds or retaining walls.
Finance
Time and Materials Contract
A construction agreement where the homeowner pays for actual labor hours and materials used, offering flexibility but less cost certainty than a fixed-price ADU contract.
Title 24
California Building Standards Code, including energy efficiency, CALGreen, and accessibility requirements. ADUs must comply with applicable sections.
Finance
Title Insurance
Insurance protecting property owners and lenders against claims arising from defects in the property title, recommended when purchasing a lot for ADU development.
Title Search
An examination of public records to verify legal ownership and identify liens or encumbrances on a property before ADU construction or sale.
Tongue and Groove
An interlocking joint system where one board's projecting edge fits into an adjacent board's groove. Used for flooring, paneling, and decking.
Top Plate
Horizontal framing member at the top of wall studs. Double top plates are typical in load-bearing walls; single plates may be used in non-bearing walls.
Topography
The shape and features of land surfaces, including elevation changes. Affects ADU placement, foundation design, drainage, and construction costs.
TPO Roofing
Thermoplastic polyolefin membrane roofing for flat roofs. Energy-efficient white surface and heat-welded seams make it popular for modern ADUs.
Tract Map
A recorded document showing the division of land into lots. May contain conditions or restrictions affecting ADU construction.
Finance
Transfer Tax
A tax imposed by state or local government on the transfer of real property ownership, applicable when selling a home with an ADU.
Design
Tray Ceiling
A recessed ceiling design where the center section is higher than the surrounding perimeter, adding visual interest and a sense of height in ADU living spaces.
Tread
The horizontal portion of a stair step. Building codes specify minimum tread depth and require uniform treads in a flight of stairs.
Trim
Finish moldings applied to interior and exterior surfaces, including baseboards, door and window casings, crown molding, and corner boards.
Truss
A prefabricated structural frame typically used for roofs and floors, composed of wood or steel members in a triangulated configuration. Faster to install than stick-built framing.
Turnkey
A construction approach where the contractor delivers the ADU fully complete and ready for occupancy, requiring no additional work by the homeowner.
U
U-Factor
A measure of heat flow through building materials, the inverse of R-value. Lower U-factors indicate better insulating performance. Used for window ratings.
Ufer Ground
An electrical grounding system using rebar in concrete foundations. Provides excellent grounding and is required in new California construction.
UL Listed
A product certification indicating that it has been tested and meets safety standards, required for many electrical and building products used in ADUs.
Underfloor
The space beneath a raised floor, providing access for utilities and requiring proper ventilation and vapor barriers in crawl space configurations.
Underlayment
A layer between the structural substrate and finish material, such as roof felt under shingles or plywood under finished flooring.
Underpinning
A method of strengthening existing foundations by extending them deeper or wider, sometimes necessary when building an ADU close to an existing structure.
Unfinished Space
Areas without interior finishes such as attics, crawl spaces, and garages. Conversion to habitable space requires finishing and may create ADU opportunities.
Unit Mix
The combination of different dwelling unit sizes and types on a property, relevant when planning multiple ADUs or considering ADU and JADU combinations.
Design
Universal Design
Design principles creating spaces usable by all people regardless of age or ability. Includes wider doors, lever handles, and accessible bathrooms.
Unpermitted Construction
Work done without required permits, creating liability and complications for future sales or modifications. May need to be legalized before adding an ADU.
California Law
Upzoning
Changing zoning to allow more intensive use or higher density. California's ADU laws effectively upzone single-family properties for accessory units.
California Law
Urban Lot Split
A subdivision process created by SB 9 allowing qualifying single-family parcels in urban areas to be divided into two lots, each potentially hosting additional units.
California Law
Use Permit
A permit authorizing a specific use of property that may not be allowed by-right under zoning, though California ADU law generally grants by-right approval for qualifying ADUs.
Utility Connection
The point where building systems connect to public utilities. ADU connections may be new or tap existing service.
V
Valley
The internal angle where two roof slopes meet, channeling water to gutters or downspouts. Requires careful flashing to prevent leaks.
Value Engineering
The process of analyzing a design to reduce costs while maintaining quality and function. Common in ADU projects to meet budget constraints.
Vanity
A bathroom cabinet with a sink, providing storage and counter space. Compact vanities are essential for efficient ADU bathroom design.
Vapor Barrier
Material that resists moisture vapor diffusion through walls, floors, and ceilings. Placement depends on climate; in California typically on the warm side of insulation.
Finance
Variable-Rate Mortgage
A home loan with an interest rate that adjusts periodically based on market conditions, sometimes used to finance ADU construction with lower initial payments.
Variance
An exception to zoning regulations granted when strict compliance creates undue hardship. California's ADU laws reduce the need for variances by establishing statewide standards.
Veneer
A thin decorative layer of material applied to a surface, such as stone veneer on exterior walls or wood veneer on cabinetry, used to enhance ADU finishes.
Vent
An opening or pipe allowing air movement. Includes plumbing vents, attic vents, and exhaust vents, each with specific code requirements.
Vent Stack
A vertical pipe in the plumbing system that extends through the roof, allowing air into the drainage system and releasing sewer gases safely.
Ventilation
The exchange of indoor and outdoor air to maintain air quality. Required in habitable rooms, bathrooms, and kitchens through operable windows or mechanical systems.
Vermiculite
A lightweight mineral used as loose-fill insulation in older homes, which may contain asbestos and require testing and abatement during ADU conversion projects.
VHFHSZ (Very High Fire Hazard Severity Zone)
Areas designated as having extreme fire risk, requiring enhanced fire-resistant construction. May affect ADU materials, roof covering, and exterior finish choices.
Vinyl Flooring
Synthetic flooring material available in sheets, tiles, or planks. Water-resistant, durable, and affordable, making it popular for ADUs.
VOC (Volatile Organic Compound)
Chemicals released as gases from paints, adhesives, and finishes that can affect indoor air quality, with low-VOC products recommended for healthy ADU interiors.
Volt
A unit of electrical pressure. Residential circuits are typically 120 volts; heavy appliances like dryers and ranges use 240-volt circuits.
W
Wainscoting
Wood paneling or other material covering the lower portion of walls. Provides protection and decorative detail in traditional or transitional designs.
Permitting
Waiver (Permit)
An official exemption from a specific code requirement or fee, sometimes granted for ADU projects under California's streamlined permitting laws.
Walk-Through
A thorough inspection of the ADU by the homeowner and contractor near project completion to identify any remaining defects or unfinished items for the punchlist.
Warranty
A guarantee of work quality and materials. Contractors provide workmanship warranties; manufacturers warranty products. Document and understand coverage.
Waste Factor
The percentage of extra material ordered to account for cutting waste, damage, and errors during ADU construction, typically 5-15% depending on the material.
Water Heater
An appliance for heating domestic water. ADUs may have dedicated water heaters or share systems with the primary dwelling.
Water Meter
A device measuring water consumption. California prohibits requiring separate water meters for ADUs, allowing shared service with the primary dwelling.
Water Pressure
The force of water in supply lines, measured in PSI. Adequate pressure ensures proper fixture operation; pressure regulators may be needed.
Water Service
The pipe connecting a property to the public water main. ADUs typically tap into existing service; new connections may require upsizing.
Waterproofing
Treatments and materials preventing water penetration into building assemblies. Critical for foundations, below-grade walls, and wet areas like bathrooms.
Watt
A unit of electrical power measuring the rate of energy consumption, used to size electrical circuits and calculate energy costs for ADU appliances and systems.
Weatherstripping
Sealing material applied around doors and windows to prevent air and water infiltration. Essential for energy efficiency and comfort.
Weep Screed
A metal flashing at the bottom of stucco walls that allows moisture to drain while providing a clean termination point above grade.
Wet Wall
A wall containing water supply and drain lines, typically serving bathrooms and kitchens. Back-to-back wet walls reduce plumbing costs.
Window Schedule
A document listing all windows with sizes, types, locations, and specifications. Required for energy code compliance and permit applications.
Wire Gauge
The size of electrical wire, with lower numbers indicating larger wire. Common residential gauges support 15, 20, and 30-amp circuits.
Wire Mesh
A grid of welded steel wires placed in concrete slabs to control cracking and improve structural integrity in ADU foundation and floor construction.
Wiring
Electrical cables and conductors in a building. Most residential wiring is nonmetallic sheathed cable in protected locations or conduit where exposed.
Wood Frame Construction
Building using dimensional lumber for structural framing. The dominant construction method for residential buildings including ADUs in California.
Design
Work Triangle
A kitchen design concept measuring the distance between refrigerator, sink, and range. Optimal layout keeps the total distance between 13 and 26 feet.
WUI (Wildland-Urban Interface)
Areas where development borders wildland vegetation, subjecting ADU construction to enhanced fire-resistant building requirements in many California communities.
X
X-Bracing
Diagonal cross-bracing that provides lateral stability to structural frames. Common in steel construction and under raised floors.
X-Ray (Concrete Scanning)
A non-destructive testing method using X-ray or ground-penetrating radar to locate rebar, conduit, and voids in existing concrete before cutting or drilling during ADU construction.
Xeriscaping
Landscaping designed to minimize water use through drought-tolerant plants and efficient irrigation. Encouraged or required in many California jurisdictions.
Y
Yard
In zoning terms, the open space between a building and property lines. Front, side, and rear yards are defined by setback requirements.
Yield Point
The stress level at which a structural material permanently deforms, considered in engineering calculations for steel beams and connections used in ADU framing.
Yoke (Electrical)
The metal frame holding electrical switches and receptacles in an outlet box. Also called a strap or mounting bracket.
Yurt
A portable, round tent-like structure that some homeowners consider as alternative living space, though it typically does not qualify as a permitted ADU in California.
Z
Z-Flashing
Metal flashing with a Z-shaped profile used at horizontal joints in siding to direct water away from wall assemblies.
Zero Lot Line
Construction that extends to the property line with no side setback. Typically requires fire-rated wall construction and may be allowed for certain ADU configurations.
Zone (HVAC)
A section of a building with independent temperature control. ADUs typically constitute a single zone with dedicated HVAC equipment.
Zoning
Local regulations dividing land into districts with specific permitted uses and development standards. California ADU laws override some local zoning restrictions.
Permitting
Zoning Clearance
Verification that a proposed project complies with zoning regulations. Often required before or concurrent with building permit approval.
Zoning Map
An official map showing the designated land use zones within a jurisdiction, used to determine what types and sizes of ADUs are allowed on a specific property.
Zoning Variance
A formal exception to zoning regulations granted by a local board or commission, sometimes needed for ADU projects that do not meet standard zoning requirements.
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