What a change order actually is
A change order is a written, signed amendment to your construction contract. It should state exactly what's changing, the price impact (add or credit), and any effect on the schedule — before the work is done. If a contractor does extra work first and hands you the bill later, that's not a proper change order; it's a dispute waiting to happen. The rule to hold: no work outside the contract proceeds until the change order is written, priced, and signed by both of you.
Why ADU projects generate change orders
| Trigger | Fair or avoidable? |
|---|---|
| Hidden site conditions — surprise soil, buried utilities, undersized electrical panel, foundation surprises on a garage retrofit | Often genuinely unforeseeable; fair — but a thorough site assessment shrinks the surprise list. |
| You changed your mind — upgraded finishes, moved a wall, added a fixture | Fair. This is a real add; just get it priced before it's built. |
| Plan-check or inspector requirements — the city requires something the plans didn't show | Usually fair, though a complete permit set (see readiness checklist) prevents many. |
| Under-scoped bid — the original price left out work everyone knew was needed | Avoidable. This is the change order you prevent at the bidding stage, not the build stage. |
| Vague allowances — a placeholder dollar amount for finishes that was set unrealistically low | Avoidable. Low allowances make a bid look cheap and guarantee change orders later. |
The last two are the ones that hurt, and they trace back to how you compared bids. Our bid-comparison guide and why budgets increase guide cover how an under-scoped bid becomes a change-order machine.
The contract terms that keep change orders honest
Look for these before you sign
- A written change-order process — states that no extra work proceeds without a signed, priced change order. This single clause prevents most disputes.
- Markup disclosed up front — the contract should say what markup applies to change-order work (a percentage over cost), so you're not negotiating it under pressure mid-build.
- Realistic allowances, itemized — for finishes not yet selected, the allowance amounts should be reasonable, not lowball placeholders. Ask what each allowance assumes.
- A contingency line — a stated contingency (often for the unforeseeable site conditions above) tells you the contractor is being honest that surprises happen.
- Schedule impact stated — each change order should note whether it moves the completion date, so "just a small add" doesn't quietly become a month.
How the base contract is structured shapes all of this — a fixed-price and a cost-plus contract handle changes very differently. Our fixed-price vs. cost-plus guide explains which puts the risk on whom.
When a change order lands: five moves
- Get it in writing before agreeing. A verbal "it'll be a little more" is not a change order. Ask for the written version with a specific number.
- Ask "fair or avoidable?" A genuine hidden condition is different from work that should have been in the original scope. It's reasonable to push back on the second.
- Check the price against the markup you agreed to. If your contract disclosed change-order markup, hold the number to it.
- Ask about schedule. Confirm whether it moves your completion date.
- Sign before work proceeds — but only then. Keep every signed change order with the contract; they're now part of your agreement.
None of this makes change orders disappear — they're a normal part of building. It makes them predictable, which is the whole game. A homeowner who set realistic allowances, compared bids on equal scope, and signed a contract with a clear change-order clause treats each one as a decision. A homeowner who took the lowest bid with vague allowances treats each one as a shock. Which one you are is mostly decided before the first shovel.
Frequently asked questions
A few change orders are normal on almost any ADU — genuinely hidden site conditions and your own upgrade decisions produce them. The red flag is a pattern of change orders for work that clearly should have been in the original scope, or a contractor who starts extra work before pricing it. The way to tell the difference is whether you compared bids on equal scope and set realistic allowances up front; our bid-comparison guide covers that.
You should never authorize a change order after the fact. A proper change order is written, priced, and signed by both parties before the extra work is done — that's the standard to hold in your contract. If a contractor performs out-of-scope work and bills you later without a signed change order, that's a dispute, not a legitimate charge. Insist on a written change-order process clause before you sign.
Prevent the avoidable ones at the bidding stage: compare bids on identical scope so no one wins by leaving work out, and insist on realistic, itemized allowances instead of lowball placeholders. Then structure the contract with a written change-order process, disclosed markup, and a stated contingency. That turns change orders from surprises into priced decisions. Our why ADU budgets increase guide breaks down where the overruns actually come from.