The contract type decides who carries the risk when costs move. Understanding both common structures lets you choose the one that matches your plans and your tolerance for uncertainty.
In a fixed-price contract, sometimes called a lump-sum or stipulated-sum contract, the builder agrees to complete a defined scope of work for an agreed price. In a cost-plus contract, you pay the actual cost of labor, materials and subcontractors, plus an agreed fee or markup for the builder's overhead and profit, which may be a percentage or a fixed amount.
Neither is inherently better. Each assigns risk differently, and each works well when the project and the people suit it. Contract practices also vary by region, so ask local professionals how agreements are commonly structured where you build.
Some builders offer both and let the owner choose, while others use only one. Asking why a builder prefers a particular structure tells you something about how they manage risk and how they expect to work with you.
A fixed price gives you a number to plan around, which many owners and lenders prefer. The builder takes on the risk of cost increases within the defined scope, so the quality of the scope definition matters enormously. The price is only as firm as the documents behind it.
A fixed price also depends on the stage of the design. A price based on partial drawings is closer to an estimate, and the contract should say how the remaining items will be priced once they are defined.
Cost-plus offers transparency, since you see the actual costs and pay for what the project truly requires. It can suit projects where the design is still evolving, where scope is hard to define in advance or where you want to see exactly where money goes. The owner, however, carries more of the cost risk, because if materials or labor cost more than expected, the total rises.
Look closely at how the agreement handles the fee, whether a percentage or a fixed amount, which costs are reimbursable, how receipts and records are shared and whether there is an estimated total or a cap. Ask how the builder's own staff time is charged and whether discounts or rebates are passed along.
Many projects use a blend. A common variation is cost-plus with a guaranteed maximum price, where costs are tracked openly but the total cannot exceed an agreed ceiling, subject to the terms of the contract. Others fix the price for certain phases, such as the structure, while handling finishes through allowances or cost-plus.
If you choose a hybrid, read how savings and overruns are shared, what counts as an approved change and how the ceiling is adjusted. These details decide whether the structure protects you in practice.
Whichever structure you use, the protections come from clear documentation. Ask the builder to explain, in writing, the points below, and have an attorney review the agreement if you have any doubt. Our guide to choosing a home builder lists further questions to raise.
If your lender is involved, ask whether it has requirements about contract type or about how costs are documented. Some lenders prefer fixed-price or guaranteed maximum arrangements because they make the budget easier to verify.
In both structures, three provisions do most of the work of protecting the owner. Allowances set placeholder amounts for items not yet selected, and they should reflect realistic costs for the level of finish you want. Change orders document any change to the agreed scope, including its price and schedule effect, and should be written and signed before the work proceeds.
Unforeseen conditions clauses explain who pays when the ground, the structure or existing utilities turn out different from what was assumed. These clauses are often overlooked and frequently the source of disputes. Read them with particular care on sloped, wooded or previously developed sites.
Payments should be tied to completed stages of work, not simply to dates. Ask how each payment is calculated and what documentation supports it. Laws about liens, which allow unpaid subcontractors and suppliers to claim against a property, differ by state, so ask a local attorney or your lender how to protect yourself, for instance by obtaining lien waivers as payments are made.
Make sure the contract describes what happens if either party wants to end the agreement, including how work completed to date is valued. Clear exit terms are uncomfortable to discuss at the start, but they are far easier to settle then than in the middle of a disagreement.
If your plans are complete and you value price certainty, fixed-price may fit. If the design is still developing or you want transparency, cost-plus, ideally with a cap, may fit better. Whichever you choose, solid pre-construction planning makes any contract more reliable, because the clearer the scope, the fewer disputes later.
The price is fixed for the scope described. Changes to that scope, allowance overages and certain unforeseen conditions can still change the final cost, depending on how the contract is written.
You pay the actual cost of the work plus an agreed fee or markup for the builder. The contract should define which costs are reimbursable and how the fee is calculated.
It is a ceiling on the total cost in a cost-plus arrangement. The contract should explain how the ceiling can be adjusted and how any savings are shared.
Many first-time builders value the predictability of a well-defined fixed price, but only if scope and allowances are clear. A capped cost-plus arrangement can also work. Choose based on your plans and comfort with risk.
It is a worthwhile safeguard for a transaction of this size, particularly for payment, lien, change-order and termination provisions.
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