How are builder allowance overages billed on a cost-plus vs fixed-price contract?

How an allowance overage gets billed depends on your contract type. On a fixed-price contract, the overage is billed as a written change order that raises your otherwise locked price. On a cost-plus contract, there is no locked price to break, so your actual selection cost flows straight onto the open-book invoice, usually with the builder's fee applied to the higher amount. An allowance is a budget placeholder for an item you have not chosen yet, like flooring or cabinets, and an overage is the amount your real choice runs over that placeholder. The difference between the two contracts is mechanical. Fixed-price treats the overage as a formal change to a fixed number, documented and signed. Cost-plus treats the allowance as an estimate that the real cost simply replaces on the invoice. Either way you pay the difference, but how it shows up, and whether a fee rides on top of it, is not the same.

This page explains how each contract bills an overage, where the builder's fee fits, why the paperwork differs, and how to protect yourself under both. For what an allowance is in the first place, see what a builder allowance is and what happens if you go over.

How a fixed-price contract bills an overage

On a fixed-price contract, an allowance overage is billed as a written change order that adds to your locked contract price. A fixed-price contract, also called a lump-sum contract, gives you one number for the finished home. The NAHB describes it as a bid that "tells you exactly how much you will pay to have a finished home by such and such date." When your real selection costs more than the allowance built into that number, the only clean way to adjust the price is a change order.

Here is the mechanic. Say your contract carries a $20,000 cabinet allowance and you choose cabinets that come to $26,000 installed. You are $6,000 over. That $6,000 is written up as a change order, you sign it, and the contract price rises by $6,000. The locked number is still locked. It just moved by the documented amount you approved. A change order is the formal document that adjusts the price and scope of your contract. You can read more on the change order glossary page.

The reverse can also happen on a fixed-price deal. If your cabinets come in under the allowance, you may get a credit, but only if the contract says you do. Some fixed-price agreements credit underages back to you. Others keep them. Read that clause before you sign. On a fixed-price contract, every move off the original number, up or down, should run through a signed change order so the price stays clear.

How a cost-plus contract bills an overage

On a cost-plus contract, the allowance is only an estimate, so your actual cost replaces it on the invoice, plus the builder's fee on the higher amount. A cost-plus contract charges you the real cost of the work plus a builder fee. The NAHB describes it as basing the estimate "on the amount of time and labor it will take to construct your home, plus a percentage markup on all material." There is no fixed price to protect, so an overage is not really a "change" to a locked number. It is just the true cost flowing through.

That changes how the overage appears. On cost-plus, the allowance was a planning figure in your budget. When you pick the $26,000 cabinets against a $20,000 allowance, the invoice simply shows the real $26,000, not the $20,000 estimate. You pay the actual cost. If the builder's fee is a percentage, that fee usually applies to the real cost, so a higher selection also raises the fee on that line. The fee follows the actual dollars, not the original allowance.

This is the part owners miss. Under cost-plus, a high-end selection costs you the overage and a bit more fee on top, because the markup rides on the real number. Under a fixed-price change order, the overage is typically a fixed add with the builder's profit already baked into the change-order price. So the same cabinet upgrade can carry its fee differently depending on the contract. For the full comparison of the two contract types, see cost-plus vs fixed-price custom home contract: which is better.

Why the paperwork differs, and what Arizona law requires

The paperwork differs because a fixed-price contract has a locked number that a change order has to formally amend, while cost-plus is open-book by design. On a fixed-price job, the contract price is a promise, so any change to it needs a documented, signed change order to keep that promise clear. On a cost-plus job, you are already seeing real costs on every invoice, so an over-allowance selection is just another real cost in the open book. The transparency is built in.

Arizona law sets the floor for what has to be in writing, and it is worth knowing what it does and does not require. Under A.R.S. 32-1158, a written home construction contract over a set amount must state "the total dollar amount to be paid to the contractor by the owner for all work to be performed," along with the deposit and the progress-payment schedule tied to construction stages. That total-price requirement is the anchor your allowances and overages attach to on a fixed-price deal.

What the statute does not do is require a written change order for every overage. The required contract terms in A.R.S. 32-1158 do not spell out change-order or allowance procedures. So the written change-order discipline on a fixed-price job comes from a well-written contract, not the statute alone. That is exactly why your contract language matters. The Arizona Registrar of Contractors (ROC) licenses residential builders and handles complaints, so a builder is expected to honor the written contract, but the protection you actually get on overages is the protection you negotiate into the agreement.

How to protect yourself under either contract

Protect yourself by getting the overage rules in writing for your specific contract type before you sign, then tracking selections as you go. The risk is different for each, so the defense is too. On fixed-price, the risk is a stack of change orders. On cost-plus, the risk is a budget that quietly drifts past the allowances. Both are manageable if you watch the numbers.

A practical checklist:

• On fixed-price, require a signed change order for every overage. No verbal adds. The signed change order is your record of why the locked price moved.
• On cost-plus, confirm whether the fee applies to overages. Ask if the percentage fee rides on the real selection cost, so a high-end pick does not surprise you on the markup.
• Pin down underage credits. On either contract, confirm in writing whether coming in under an allowance credits back to you.
• Set realistic allowances up front. Low allowances make any bid look cheap, then every selection runs over. Push to set them where your real choices will land.
• Track a running total. Keep a simple list of each allowance, your actual selection, and the running overage, so the number stays in front of you.

A run of overages is the most common reason a build drifts past its budget. For why that happens and how to catch it early, see why your custom home is coming in over budget in Arizona. The same contract-type logic decides who pays other pass-through costs too, like a failed inspection, covered in who pays the re-inspection fee, the builder or the owner, in Arizona.

Contract terms, fee structures, and how a given builder bills overages vary widely, and they are set by your agreement, not by statute. So confirm your specific contract's allowance and overage rules in writing before you sign. A builder who bills transparently, like Jematell Homes, spells out how allowances, overages, and any fee on them work for your contract type up front, so the way an overage gets billed is never a surprise on an invoice.

How Jematell Homes helps

We build the budget line by line so the number you sign is the number you build to. We would rather answer your questions before you build than after, so get in touch any time.

Sources

• A.R.S. 32-1158 (Home construction contract requirements; total dollar amount and progress payments in writing)
• NAHB: How Do Builders Charge for Their Services? (fixed bid vs cost-plus)
• Arizona Registrar of Contractors (residential contracts and license classifications)