Quick Answer
- Fixed-price: one agreed number for a defined scope. The builder absorbs cost increases, estimating errors, and market swings. Your price only changes if you change the scope.
- Cost-plus: you pay actual costs (labour, materials, trades) plus the builder's fee. No guaranteed final price — you carry the risk of overruns.
- Who owns the risk: fixed-price puts it on the builder; cost-plus puts it on you.
- The catch: a fixed price is only as real as the pre-construction work behind it. A low quote off incomplete drawings just defers the cost to change orders.
- Best rule of thumb: if one quote is dramatically lower, ask what's excluded, how complete the drawings are, and whether it's a true fixed price or an open estimate.
Two contracts can describe the exact same renovation and leave you in completely different financial positions. The difference isn't the work — it's who absorbs the cost when reality doesn't match the estimate. That question decides more about how your project feels than the finishes, the timeline, or the crew ever will.
How each contract actually works
Fixed-price (lump-sum or stipulated-price)
You and the builder agree on one price for a clearly defined scope, in writing, before construction begins. If lumber spikes or a trade's rate rises mid-project, that's the builder's problem, not yours. Changes you request are handled through written change orders, priced and approved before the work proceeds. The core number doesn't move.
The trade-off: to take on that risk, the builder prices in a contingency. If the feared problems never materialise, you paid for protection you didn't end up needing — that's the premium for certainty. Fixed-price also demands discipline upfront: every meaningful selection has to be pinned down before a number can be honest.
Cost-plus
You pay the project's actual costs as they're incurred — labour, materials, subcontractors, site expenses — plus the builder's fee, usually a percentage or fixed management fee. The appeal is transparency and flexibility: costs are visible as they happen, and the design can keep evolving without repricing the whole contract. On a genuinely fluid, high-customisation build, that flexibility is a real advantage.
The risk: "actual costs" is an open number. On an under-specified project there's no ceiling and limited pressure to control spending, because every dollar flows through to you plus markup. Cost-plus can be transparent and well-managed — but it isn't automatically controlled.
Who owns the risk: a side-by-side
| Fixed-Price | Cost-Plus | |
|---|---|---|
| Material price increases | Builder absorbs | You pay |
| Estimating errors | Builder absorbs | You pay |
| Trade / labour rate rises | Builder absorbs | You pay |
| Cost certainty at signing | High (if scope is complete) | Low by design |
| Flexibility mid-build | Lower — via change orders | Higher |
| Homeowner involvement | Front-loaded, in design | Ongoing, throughout |
| Best when | Scope can be defined | Scope genuinely can't be |
The catch nobody mentions: a fixed price is only as real as the scope behind it
This cuts against a lazy "fixed-price good, cost-plus bad" story. A fixed price is only as strong as the pre-construction work behind it. If a builder quotes a low lump sum off incomplete drawings, the missing items don't vanish — they resurface as change orders and allowance overruns once the wall is open and you can't say no.
That's why a suspiciously low fixed quote can cause more trouble than an honest one. The savings were never real; they were deferred.
How to read a low quote
If one builder's opening number is dramatically lower than another's, ask why — and look for these specific answers:
- What's excluded? Low bids often leave out items you'll certainly need, so the "savings" return later as change orders with markup.
- What's buried in allowances? An allowance is a placeholder. Set it unrealistically low and your real selections blow past it.
- How complete are the drawings? A price built on finished, detailed drawings is a real number. A price built on a sketch is a hope.
- Is it fixed-price, or cost-plus dressed up as an "estimate"? Price-per-square-foot figures ignore site prep, servicing, and finish quality. Only a total contract price with clear inclusions means anything.
What legitimately changes a fixed price
"Fixed" doesn't mean the number can never move — it means it can only move for narrow, legitimate reasons, all controlled through written change orders:
- You change the scope. Add a bathroom or upgrade the flooring mid-project, and that's a change order — priced and approved before work proceeds.
- A genuinely unforeseen condition that even good pre-construction couldn't catch. The classic example: a failing structural beam hidden behind century-home plaster. No one can price the exact fix until the wall is opened. An honest builder flags this before you sign, and prices it at worst-case rather than guessing.
A well-run fixed-price project doesn't have many change orders, because the work that prevents them happened before construction started. Finding a problem during pre-construction is a planning exercise. Finding it in week three is a crisis.
How we do it
We quote fixed prices. Not because cost-plus is illegitimate — it suits certain highly custom or multi-unit builds where scope truly can't be locked in — but because for the overwhelming majority of renovations, additions, ADUs, and custom homes, cost certainty is what lets a family actually plan. We do the procurement, the specifications, and the subcontractor pricing before a number goes on paper, so that when it does, it's a real number. And when something genuinely can't be seen until we open a wall, we tell you upfront and price it worst-case.
That's the thinking behind our fixed-price guarantee: the number on your contract is the number on your final invoice, and it only changes when you change the scope. If you want to see how we get to that number before you commit, that's what a Blueprint Session is for.
Frequently asked questions
Is fixed-price or cost-plus better for a renovation?
For most homeowners, fixed-price is better because it provides cost certainty and puts the risk of price increases on the builder. Cost-plus can suit highly customised builds where the scope genuinely can't be defined upfront, but it leaves the homeowner paying for every cost increase, delay, and inefficiency.
Who pays if costs go up in a fixed-price contract?
The builder. In a fixed-price contract, the builder absorbs material price increases, trade rate rises, and estimating errors after signing. The homeowner's price only changes if the homeowner changes the scope, through a written change order.
Why is one renovation quote so much lower than another?
A dramatically lower quote often reflects incomplete scope rather than genuine savings. Missing items typically resurface as change orders with markup, and unrealistically low allowances get exceeded once real selections are made. Ask what's excluded, how complete the drawings are, and whether the number is a true fixed price or an open estimate.
What is a change order?
A change order is a written, priced, and approved modification to a fixed-price contract. On a well-run fixed-price project, legitimate change orders are limited to homeowner-requested changes and genuinely unforeseen conditions that thorough pre-construction couldn't have caught, such as hidden structural damage.
What does cost-plus mean in construction?
Cost-plus means the homeowner pays the actual costs of labour, materials, and subcontractors, plus the builder's fee (a percentage or fixed management fee). It offers transparency and flexibility but no guaranteed final price, so the homeowner carries the risk of cost overruns.
Comparing quotes that don't line up? A Blueprint Session gives you a real read on your project — scope, feasibility, and an honest price range — before you commit to anyone.