Fixed price and time and materials are two ways of deciding who carries the risk of a renovation costing more than expected. Under a fixed price the contractor carries it, and prices it in. Under time and materials the homeowner carries it, and pays only for what is actually used. Neither model is safer in the abstract. The right one depends on how well defined the work is.
What is a fixed-price contract?
A fixed-price contract — sometimes called lump sum or stipulated sum — commits the contractor to complete a defined scope for a stated amount. If the work takes longer than planned or a material costs more than budgeted, the contractor absorbs it. If it goes faster, the contractor keeps the difference.
That certainty is the product, and it is not free. A contractor pricing a fixed sum has to include contingency for everything that might go wrong, which means you pay for risks that may never materialise. The better defined the scope, the smaller that contingency needs to be — which is why a fixed price quoted from a vague description tends to be either expensive or fragile.
The important limit: a fixed price is fixed against a defined scope, not against the project. Anything outside the written scope is a change order at a new price, negotiated when you have no competing bidders. This is why the scope, allowances, and exclusions sections of the document matter more under a fixed price than under any other model — see what should be in a contractor's quote.
What is a time-and-materials contract?
A time-and-materials contract bills the actual hours worked at agreed rates, plus the actual cost of materials, usually with a markup for overhead and profit. The contractor is not guessing at a total, so there is no risk premium built into the number. You see what the job really costs as it happens.
The trade is that the total is unknown until the work is done. Time and materials rewards efficiency on your side — decisive answers, fewer changes of mind, materials chosen in advance — and punishes hesitation, because indecision is billed by the hour along with everything else.
What makes this model workable is visibility. A well-run time-and-materials job comes with agreed hourly rates by trade, a stated markup on materials, itemized invoices showing hours and receipts, and a running total you can check against your budget. Without those, "time and materials" is just an open tab. Ask for the invoicing format before the work starts, not after the first bill arrives.
Which projects fit each model?
Match the model to how much is unknown. Well-defined, visible, repeatable work suits a fixed price. Work involving discovery, old buildings, or decisions you have not made yet suits time and materials — or it suits waiting until you can define it.
Fixed price tends to fit:
- Scope that can be fully described before work starts, such as a like-for-like bathroom replacement or a straightforward run of new cabinetry.
- Projects where every material has already been chosen.
- Homeowners who need a firm number for planning or financing reasons.
- Work in a building whose condition is already well understood.
Time and materials tends to fit:
- Repairs where nobody knows what is behind the wall until it opens.
- Older homes with unknown wiring, plumbing, or structural history.
- Small jobs where writing a detailed fixed scope costs more than the work.
- Projects that will evolve as they go, by design, with an engaged homeowner on site.
A useful rule of thumb: if you cannot write the scope down clearly, a fixed price will not protect you, because everything you failed to specify becomes a change order anyway. Writing a proper renovation brief first is often what makes a fixed price available to you at a fair number. TrueBuild is built for that step: you describe the project in plain English and TrueBuild drafts a written summary you can edit before anything is sent. See how TrueBuild works.
Can a project use both models at once?
Yes, and many well-run renovations do. The common hybrid is a fixed price for the defined majority of the work with a separate time-and-materials line for the genuinely unknown part — the condition of the subfloor, the state of the drain, whatever cannot be seen yet. That way you are not paying a risk premium on the whole job to cover one uncertainty.
The other useful hybrid is time and materials with a not-to-exceed cap: you pay actual costs, but the contractor commits to a ceiling. It gives you the transparency of hourly billing and a bound on the downside. Expect the ceiling to sit above what the contractor genuinely expects, because it functions as a fixed price for the worst case, and expect it to be tied to a specific scope.
Both hybrids depend on one thing: everyone agreeing in writing which parts of the job are in which bucket, before the work starts.
How does the contract type change your paperwork?
Under a fixed price, the scope document does the heavy lifting. Every hour you spend tightening the scope, closing allowances, and reading the exclusions is an hour spent protecting the number you agreed. Your ongoing job during the project is comparatively light: track change orders and confirm each stage before releasing payment.
Under time and materials, the rate sheet and the invoices do the heavy lifting. You need agreed labor rates by trade, the materials markup in writing, an invoicing rhythm frequent enough that surprises stay small, and receipts or supplier documentation available on request. Your ongoing job is heavier: read every invoice when it arrives and query anything you do not recognize while people still remember the week in question.
The budgeting approach differs too. A fixed price lets you plan against a number and hold a reserve for change orders; time and materials means planning a budget around a range and a stopping rule you decide in advance.