Nothing tests a homeowner’s patience mid-build quite like a contractor showing up and saying, “We found something; this is going to cost a bit more.” Whether that sentence is fair or a red flag depends entirely on what happens next. If it’s followed by a written document with a scope description, a price breakdown, and your signature line, you’re looking at a normal part of construction. If it’s just a verbal number and a request to keep moving, that’s where budgets quietly spiral.
ADU change orders are one of the most common sources of anxiety in a backyard-unit build, and also one of the most misunderstood. Some are completely legitimate: a sewer line that wasn’t where the plans said it would be, a soil condition nobody could have seen before excavation. Others are the result of an incomplete bid or a contractor padding scope after the contract is signed. This guide breaks down exactly how to tell the difference, what a fair change order should contain, and how to keep one surprise invoice from becoming five.
What an ADU Change Order Actually Is
An ADU change order is a written amendment to your construction contract. It changes the scope of work, the price, the schedule, or some combination of the three, and it needs signatures from both you and your contractor before it takes effect. That’s the whole definition, and it’s worth repeating because so much budget damage happens when homeowners skip the “written” part.
A verbal “it’ll cost a little more” is not an ADU change order. It’s an informal heads-up that should be followed, within a day or two, by an actual document you can read, question, and sign. If your contractor is reluctant to put a change in writing before starting the extra work, that reluctance is itself useful information.
Why ADU Projects Generate So Many ADU Change Orders
ADU builds run into more of these than a typical remodel for a few structural reasons, not because ADU contractors are worse at their jobs.
Backyards hide things. Old sewer laterals, abandoned irrigation lines, and buried debris from a previous structure show up constantly once excavation starts, and none of it appears on a standard site survey. Soil conditions are another frequent trigger; a foundation designed around assumed soil bearing capacity sometimes needs revision once a geotechnical report or the excavation itself reveals something different.
Permit and inspection requirements add a second layer. A plan reviewer’s correction, an inspector flagging something mid-build, or a jurisdiction’s specific utility connection requirement can all force scope changes that neither you nor your contractor controlled. Add owner-driven upgrades, a bigger window, upgraded flooring, a moved outlet, and you can see why change orders on an ADU are the rule rather than the exception.
Five Types of ADU Change Orders
Sorting a request into one of these categories is usually the fastest way to judge whether it’s fair.
Owner-requested changes cover anything you decide to add or modify after the contract is signed: a design tweak, an upgraded fixture, a layout adjustment once you see the framed space in person. These are the most straightforward, since you initiated them and the cost conversation is expected.
Concealed or differing site conditions are physical realities that weren’t visible or knowable at bid time: buried utility lines, unsuitable soil, a septic issue discovered during grading. Most construction contracts include a concealed-conditions clause specifically addressing how these get priced and approved, and courts have generally sided with owners when a contractor should reasonably have caught something during a proper site inspection but didn’t disclose it.
Permit or inspection-driven changes come directly from the building department or an inspector requiring something the original plans didn’t show, whether that’s a structural detail, a fire separation requirement, or an energy compliance fix.
Design conflicts surface when two parts of the plan don’t actually work together once construction starts: a duct run that collides with a beam, a door swing that hits a fixture nobody caught on paper.
Contractor error is the category worth watching most closely. This covers something the contractor missed on already-approved plans, underbid, or failed to account for during a proper site walk. A legitimate hidden-conditionADU change order and a contractor error can look identical on the invoice, which is exactly why the next section matters.
What Every Written ADU Change Order Should Include
A defensible ADU change order isn’t just a number. It should show:
- A clear description of the scope change, in plain language you can actually picture
- A reference to the specific drawing, spec sheet, or plan detail affected
- An itemized price breakdown covering labor, materials, and any subcontractor quote involved
- The contractor’s markup, shown separately rather than folded into a single lump figure
- Any credit for work being removed from the original scope
- The schedule impact in actual days, not a vague “this might take longer”
- The revised total contract amount after the change
- Signature lines and a date for both parties
If a request arrives without most of these elements, that’s not automatically a scam, but it is a sign the paperwork isn’t ready for your signature yet.
When to Approve and When to Push Back
Two examples with the same dollar amount can call for completely different responses.
A hidden sewer line conflict discovered during excavation, something no reasonable site inspection would have caught before digging, is a legitimate ADU change order. The cost belongs to the project regardless of who signed the contract, because neither party could have priced around information that wasn’t available.
An item clearly shown on the approved plans that the contractor now says was “missed in the original bid” is a different story. If your stamped, approved drawings already called for a feature and the estimate somehow left it out, that’s closer to a bidding error than a legitimate scope change, and it’s reasonable to ask why the cost should fall on you rather than be absorbed as part of the original contract price.
The test that separates the two: could this have reasonably been known or estimated before signing the contract? If yes, push back and ask for documentation showing why it wasn’t caught. If no, it’s likely a fair ADU change order and the conversation should shift to whether the price itself is reasonable.
How to Evaluate the Price on a Change Order
Once you’ve decided a change is legitimate, the next question is whether the number is fair. Ask your contractor to break the change order into:
Labor, listed by hours or a flat labor charge tied to the specific task, not a round number with no basis shown.
Materials, with actual costs or a supplier quote attached rather than an estimate pulled from memory.
Subcontractor pricing, if the change involves a trade your general contractor doesn’t perform directly, plumbing, electrical, structural work.
Markup, which typically runs somewhere in the range of 15 to 25 percent combined for overhead and profit on most residential contracts, though the exact figure should already be defined in your original agreement rather than negotiated fresh each time. If your contract is silent on markup percentage, that’s worth clarifying before your first change order rather than your fifth.
Permit and tax impact, since a scope change can sometimes trigger a permit revision fee on top of the construction cost itself.
Schedule effect, stated in calendar days added to the project, which matters just as much as the dollar figure if you have a move-in date or a tenant lined up.
Getting a second opinion on a large change order is reasonable, particularly for anything involving structural work or a five-figure price tag. Comparing pricing against a general market range through our ADU cost calculator can help you sanity-check whether a change order estimate is in a normal ballpark before you sign off.
Preventing Change-Order Overload Before You Break Ground
The single best way to control ADU change orders is spending more time in preconstruction than feels necessary at the time.
Finalize your selections- flooring, fixtures, appliances, paint- before construction starts rather than during it. Every decision made mid-build tends to cost more than the same decision made on paper, because it usually means undoing something already installed.
Push for a real site investigation before signing, including a soil report if your contractor hasn’t already recommended one. This is exactly the kind of cost that’s cheap to identify upfront and expensive to discover mid-excavation.
Ask specifically about utility locations. A locate request before design finalization can catch a buried line that would otherwise turn into a change order once digging starts.
Keep allowances realistic. If your contract includes an allowance for something like flooring or fixtures, make sure the number reflects what you actually intend to spend, not a placeholder figure that guarantees a change order the moment you pick real materials.
Build a contingency into your budget from day one. Most experienced builders recommend somewhere between 8 and 15 percent of your total construction cost specifically for change orders and unknowns, with the higher end reserved for older properties, tight or irregular lots, or sites with known drainage or soil concerns. Running this against your actual numbers in our ADU loan calculator helps you see whether your financing already accounts for that buffer or whether you’re building without one.
Complete, coordinated drawings before permitting reduce design-conflict change orders significantly, since most of those conflicts get caught on paper instead of on site. If your project is still in the design phase, our AI ADU design advisor can help flag common coordination issues before they reach a contractor’s desk.
Your Response Script for a Surprise Change Order Request
When a contractor tells you something is going to cost more, you don’t need to agree or argue on the spot. A simple response works:
“Please send me the written change order with the scope description, an itemized price breakdown, the schedule impact, and the plan or contract reference this relates to. I’ll review and sign once I have that.”
This isn’t confrontational, and any legitimate contractor will already expect this request. It buys you time to evaluate the change calmly instead of approving something under pressure while a crew is standing around waiting.
A Simple Change-Order Tracker
Keeping a running log prevents the most common budget failure on ADU projects: losing track of how many small approvals have added up. A basic tracker needs just a few columns.
Request number, cause (owner request, concealed condition, permit-driven, design conflict, or error), a short description, the approved dollar amount, your remaining contingency after that approval, and the schedule impact in days. Updating it after every signed change order, rather than trying to reconstruct the total at the end of the project, is what actually keeps a budget from quietly drifting.
Frequently Asked Questions
Can a contractor start extra work before I sign a change order? For genuine emergencies, a burst pipe, a structural safety issue, most contracts allow work to proceed with verbal authorization, followed by written documentation within a short window. For anything non-emergency, work shouldn’t start until you’ve signed, since verbal agreements are exactly what creates disputes over price later.
Is a contractor allowed to charge markup on a change order? Yes, and it’s standard practice. Markup covering overhead and profit is typically built into your original contract terms, so the relevant question isn’t whether markup applies but whether the percentage matches what you already agreed to.
What if I think a change order is actually a contractor’s bidding mistake? Ask for documentation showing when the item was identified and why it wasn’t included in the original scope. If it was clearly shown on approved plans, it’s reasonable to request that the cost be absorbed into the original contract rather than billed as new work.
How much contingency should I budget for an ADU build? Most experienced builders suggest 8 to 15 percent of total construction cost, with older homes, difficult sites, or extensive design customization sitting at the higher end of that range.
Getting a Second Opinion Before You Sign
A change order isn’t automatically bad news, but signing one without understanding what’s driving it usually is. If you’re staring at a request that feels too large, too vague, or oddly timed, getting a second set of eyes on the scope and pricing before you approve it is worth the delay. Our contractor license lookup tool is a useful first step if you’re considering bringing in an independent contractor or consultant to review a disputed change order before you commit to signing it.
