Change Order Clause: How It Reopens a Fixed Price

A fixed price stops being fixed in one sentence, and it is never the sentence in the bold box. Here is a change-order clause, copied off an estimate word for word: "Any additional work required due to conditions not visible at the time of the estimate will be performed at prevailing rates."

Twenty-one words. They sit under the total, in the same type size as the disposal fee, and they undo it. Not partly. Entirely — because nothing in that sentence says who decides a condition was not visible, what number "prevailing rates" resolves to, or whether you learn that number before the work happens or on the final invoice.

"Prevailing rates" is the phrase carrying the most weight, and it is borrowed from a place where it means something. On federally funded construction the Department of Labor determines the locally prevailing wage and fringe rate for each classification of worker in each area, and contractors must pay no less than that figure — the schedule is published before anyone picks up a tool (Davis-Bacon and Related Acts). Your estimate keeps the word and drops the schedule. What is left is a rate nobody has published, chosen by the party writing the invoice, at a moment you will not be in the room for.

One thing to be clear about before this goes any further. I read paper; I do not visit houses, hold a licence in any trade, or know what is behind your ceiling. So this is not a ruling on whether your contractor is entitled to the money — it is a guide to what the document in your hand actually commits you to, and where the wording came from. Statutes are amended, so every source below carries the date I opened it: 18 August 2026. A statute quoted on a website is also not a lawyer reading your contract, and on anything with money already in dispute that distinction stops being academic.

The three questions a change-order clause has to answer

Take your clause and put these to it, in order.

Who declares the change necessary, and how do you see the evidence? In commercial contracts this is a formal event with a name and a procedure. Section 3.7.4 of the AIA A201-2017 general conditions covers differing site conditions; AIA's own explanation of the clause quotes it as "subsurface or otherwise concealed physical conditions that differ materially from those indicated in the Contract Documents," or "unknown physical conditions of an unusual nature," and has the contractor give notice to the owner and the architect before conditions are disturbed. Two features of that survive into almost no residential estimate: notice comes first, and a third party who is not the contractor evaluates the claim. What your bid probably has instead is the contractor deciding, the contractor pricing, and you finding out. If the clause names no moment at which you see the condition, that is the gap.

What is the price, in a unit you can count? "Prevailing rates," "our standard rates," and bare "time and materials" are the same answer, which is no answer. The fix is a unit price agreed before signing — a figure per sheet of decking, per linear foot of line set, per hour of a two-person crew with the overtime rule spelled out.

When do you find out? Before the work or after it. This is the only one of the three with real money in it, and it turns on a single distinction: whether the contractor must obtain your written approval prior to performing the extra work, or merely has to tell you about it.

Where the law makes writing mandatory, and where it does not

Two things fall out of that table.

"It has to be in writing, that's the law" is only true in some places, and the person saying it to you may not know which place you are standing in. That is the first.

The second is quieter. Where the statute is silent about changes, the merger language does the work instead. A contract that "contains the entire agreement" also means the crew leader's verbal promise about the chimney flashing is not part of anything. Silence about changes is not neutral — it defaults to the paper.

Look your own state up before relying on any row above. The licensing agency's consumer pages are the fastest route, and the same visit tells you whether the licence number printed on the bid belongs to the entity that will actually be doing the work.

The four blanks to fill in before you sign

These belong in the original contract, not in the change order. By the time a change order exists, your leverage is a crew standing in the driveway with the roof open.

1. A unit-price schedule for the three or four things most likely to be found. Re-roof: decking replacement per sheet and per square, fascia per linear foot, chimney flashing as a lump sum. HVAC changeout: line set per foot, new disconnect, gas line resize, plenum fabrication. Water heater: expansion tank, pan and drain line, T&P discharge piping, and whatever code upgrade the inspector calls. Ask both bidders for these numbers and compare them against each other — priced for your house, in your market, this month, which is more than any national average can say. The bid comparison calculator is built for exactly that: adding back what each sheet leaves out before you call one of them cheaper.
2. A stop-and-notify duty. "Contractor shall stop the affected work, photograph the condition, and obtain the owner's written approval of scope and price before proceeding." One sentence. It is the one that converts a surprise into a decision.
3. Put a not-to-exceed figure on anything billed as time and materials, and a duty to telephone you when the running total reaches it. A cap with no notification clause is discovered, not enforced.
4. Say what happens when an allowance lands under the estimate, not just over. If the item you pick costs less than the allowance, the difference comes back to you — write that down, because the pre-printed form almost never does.

None of the four is an exotic request. Federal procurement will not buy work on an open time-and-materials basis without the same protections: FAR 16.601(d) permits that contract type only where the contracting officer has signed a determination that no other type is suitable and "the contract or order includes a ceiling price that the contractor exceeds at its own risk," and subsection (e) obliges the contracting officer to analyse and document any later increase in that ceiling. Asking for a cap, a unit price and a written approval step is asking for less than a federal buyer is given by rule.

Signing anything with an empty dollar box

Massachusetts wrote "Do not sign this contract if there are any blank spaces" into the statute, in ten-point bold, directly above the signature line. Legislatures do not spend words on hypotheticals. That sentence exists because of a specific move: a form signed with the price field empty and filled in afterwards.

The change-order version of the move is softer. A pre-printed pad. The description written in by hand. The amount left as "TBD pending final measure." A signature taken while the crew waits and the attic is open. Everything about the moment pushes toward signing — the noise, the weather, the fact that you want this finished.

But a signed change order with an open price is a worse document than no document at all, because the scope is now agreed and only the number is left to argue about, and you have already conceded the half that was arguable.

The counter is boring. Initial the description. Write "price to be agreed in writing before this work proceeds" across the amount field. Photograph the sheet with your phone before you hand it back. If the answer is that the crew cannot wait, you have learned something about the schedule, not about the price.

California reached the same suspicion of blanks from a different direction. B&P §7159(d)(4) puts one sentence on every home improvement contract in 12-point boldface: "You are entitled to a completely filled in copy of this agreement, signed by both you and the contractor, before any work may be started." Completely filled in, and before work starts — a pad sheet reading "TBD pending final measure" fails both conditions at once. That statute governs California contracts; the test it sets out travels anywhere.

Reading the finished change order against the original bid

A change order doing its job carries eight things: the date; the contract it amends; the added or deleted work described in physical terms; the quantity; the unit price or lump sum; the resulting new contract total; the effect on the payment schedule; and the effect on the completion date.

California's statute makes that seventh item explicit, and it is the one people skim. A change order that adds work and silently pulls money forward in the payment schedule has changed two things while appearing to change one. The total on the last page is not the only number that moved.

Then go looking for the deletions. California's wording is "the cost to be added or subtracted from the contract" — the form contemplates both directions, and a subtraction is the half nobody chases. If something in the original scope was dropped when the extra went in, line the change orders up against the original itemisation and confirm it came off the total. If your original bid was never itemised finely enough to do that comparison, the problem started one document earlier; the 14 lines a complete HVAC replacement bid must contain is the checklist for that stage.

One last separation to keep straight in your head. Cancelling the original contract and cancelling a change order are different questions under different rules. Maryland's guidance is the clearest published example of a change order carrying its own waiver requirement, and the federal definitions in 16 CFR 429.0 turn on who initiated the visit and what was sold once the visit was underway — including the point that extra goods or services sold during a repair call are not covered by the repair-call exclusion. Whether any deadline runs from your original signature or from the change order is a question for your state's consumer protection office. Ask it on the day. It is a much less pleasant question a week later.