Fixed Price Contract vs. Cost Plus Contracts

A fixed price contract sets the total cost of your project before construction begins, with allowances, exclusions and adjustments governed by the contract. A cost plus contract bills you for actual labour, materials and subcontractors, plus a fee of usually 15 to 25 per cent. The difference decides who carries the risk of a price rise: the builder, or you.

Alongside builder experience, portfolios, and references, review how the proposed contract structures costs and decisions.

The contract sets out how costs, scope changes, approvals, and responsibilities will be managed throughout your project.

Here’s how each model works and what to review with your builder before signing.

What a fixed price contract actually means

A fixed price contract sets the total cost of your project before construction begins. Drawings, finishes, specifications, scope; all agreed upfront. The builder commits to delivering everything for one number.

And that number doesn’t move unless you change the scope.

A fixed price contract allocates cost responsibilities in advance. Review the scope, allowances, exclusions, and adjustment clauses to understand which costs the builder carries.

A clear fixed price proposal starts with detailed drawings, confirmed finishes, engineering specifications, trade pricing, and a construction schedule.

What a cost plus contract actually means

Cost plus works the opposite way. The builder bills you for the actual costs, labour, materials, subs, plus a fee. That fee is usually a percentage (often 15 to 25%) or a flat management charge.

There’s no committed total. You pay what the project ends up costing, whatever that turns out to be.

Cost plus has its place. It can make sense for projects where the scope genuinely can’t be defined upfront, heritage restoration with unknown structural conditions, or experimental architectural work where the design evolves on site.

For projects with a well defined scope, compare a fixed price proposal with the reporting, allowances, and cost controls offered under cost plus.

When the builder’s fee is a percentage of total spend, the fee changes with eligible project costs. Confirm the percentage, which costs it applies to, and how spending is approved.

Side by side: how they compare

Here’s how the two contracts actually behave once you’re underway:

Contract feature	Fixed Price	Cost Plus
Final cost	Agreed for the defined scope, subject to contract terms	Based on actual costs and the agreed fee
Cost responsibilities	Allocated in the contract	Allocated in the contract, with actual costs billed
Changes mid project	Quoted and approved before any work happens	Often added to the running total
Builder’s fee	Included in the agreed price	Percentage or management fee, as agreed
Best for	Projects with a properly planned scope	Truly unpredictable work
Financing	Lender reviews the agreed price and terms	Lender reviews the estimate, reporting, and any cost cap

Cost Controls to Review in a Cost Plus Contract

A cost plus contract should explain how costs are recorded, reviewed, and approved. Discuss these points before signing:

Budget tracking: Agree on an estimate, regular cost reports, and a contingency. Confirm how changes will be priced and approved, and whether the contract includes a maximum price.
Markup scope: Confirm whether the fee applies to labour, materials, permits, dumpsters, supervision, and trades.
Spending approvals: Agree on approval limits and review how a percentage fee changes with total eligible costs.
Financing requirements: Ask your lender how estimates, cost changes, and reporting affect construction draws and refinancing.
Written records: Keep approvals and cost reports together so the final invoice can be checked against the agreed work.

Choose the contract structure that fits your scope, financing, and preferred level of cost oversight.

When cost plus actually makes sense

To be fair to the model, there are projects where cost plus is the right call:

Heritage and century home restoration where structural conditions are truly unknown until walls come open.
Highly experimental architecture where the design is being developed during construction, not before it.
Insurance restoration where scope evolves as remediation progresses.

For a planned addition, custom home, kitchen renovation, or basement finish, developing the scope early helps you compare pricing models on the same basis.

Why fixed price takes more work upfront

A fixed price contract is harder to put together. The builder has to invest in drawings, engineering, finish selections, and trade pricing before any contract is signed. That takes time. It also takes a willingness to walk away from projects where the homeowner wants to break ground before the planning is finished.

Fixed price puts more decisions into the planning phase. Cost plus allows costs to be confirmed as work progresses, with reporting and approval procedures agreed upfront.

With either model, agree when selections are due, how progress will be reported, and how changes will be priced and approved.

How to read the contract before you sign

Whichever model you’re looking at, the contract itself tells you most of what you need to know. Here’s what to actually look for:

In a fixed price contract

A complete scope of work, not a one page summary, but a detailed schedule of finishes, fixtures, and inclusions.
A clearly defined change order process. Any change should require written approval and a quoted cost before work proceeds.
A payment schedule tied to construction milestones, not arbitrary calendar dates.
Allowances clearly identified in writing, with amounts and adjustment rules explained.

In a cost plus contract

A clear definition of what “cost” includes, labor rates, material handling, subcontractor markups, supervision time.
A cap or guaranteed maximum price (GMP), if one is being offered. Without it, the builder has no ceiling.
Detailed reporting. You should get itemized statements with receipts, not a one line summary invoice.
An exit clause. If costs run far over the estimate, what are your options?

Why this matters more in Toronto right now

Toronto project budgets should account for material pricing, trade availability, and permit timelines. Review how your proposed contract allocates these costs and scheduling responsibilities.

A detailed fixed price proposal shows the scope, pricing assumptions, and responsibilities agreed before work begins.

Licensing requirements and the pricing model are separate questions. The HCRA regulates new home builders and sellers; renovations to an existing home do not usually require an HCRA licence. Confirm the requirements for your project and review the contract terms separately.

How we approach it at Grand Design Build

Every Grand Design Build project is delivered on a fixed price contract. Before any number is committed, the design is fully developed, finishes are selected, engineering is complete, and trades are quoted. The contract documents the agreed work.

Review the scope, relevant licensing, insurance and contract terms before work begins. Good planning makes the responsibilities and next steps clearer for everyone.

When comparing builders, review the scope, allowances, reporting, and change approval process alongside the contract price.

Planning a renovation or custom build in Toronto?

Grand Design Build delivers premium custom homes, additions, and renovations across Toronto, North York, Forest Hill, Rosedale, Yorkville and Etobicoke. Review the scope, inclusions, exclusions and contract options with our team.

Learn more about our custom build process.

Planning work on your property? Contact us for a feasibility study.

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