One of the most consequential decisions you will make before breaking ground is choosing the right contract structure for your project. The difference between a lump sum and a cost-plus agreement determines how risk is shared, how costs are tracked, and how much control you retain over the budget as the project evolves. Getting this decision right at the outset protects you from surprises and keeps the financial relationship between you and your builder working the way it should.
What Is a Lump Sum Construction Contract?
A lump sum contract — also called a stipulated price or fixed price contract — is an agreement where the contractor commits to completing a defined scope of work for a single, agreed-upon price. The contractor assumes the risk of any cost overruns: if labour costs rise or materials come in higher than expected, that is their problem to manage. For owners, the appeal is straightforward — you know the total before construction begins, and the number does not change unless you change the scope.
Lump sum contracts perform best when the project scope is fully defined before tendering. If drawings are detailed, specifications are complete, and site conditions are well understood, contractors can price the work accurately and the fixed price holds up. On projects where the design is still evolving or the scope has meaningful unknowns, the fixed price often comes with significant contingency built in by the contractor — or a low tender followed by change orders that inflate the final cost well beyond what a cost-plus arrangement would have produced.
What Is a Cost-Plus Construction Contract?
A cost-plus contract is an arrangement where the owner pays the contractor’s actual costs — labour, materials, subcontractors, equipment — plus an agreed fee, either a fixed amount or a percentage of total costs. The owner takes on more of the cost risk, but gains transparency: every invoice and trade quote is visible, and there is no mark-up hidden inside a padded lump sum.
The fee structure matters significantly. A fixed fee gives the contractor no incentive to increase costs, since their margin stays flat regardless of what gets spent. A percentage fee, by contrast, can create a perverse incentive — the more the project costs, the more the contractor earns. Most experienced owners working on a cost-plus basis prefer fixed-fee or guaranteed maximum price arrangements because they align incentives properly and limit exposure. For a closer look at how these fees are typically calculated and what they include, see our overview of what a construction management fee covers.
Construction Management as a Delivery Model
Construction management is a distinct contract delivery approach that uses cost-plus principles but separates the management function from the trade work entirely. Under this model, the owner retains a professional construction manager to oversee procurement, budgeting, scheduling, and quality assurance on their behalf. The construction manager is accountable to the owner’s interests, not to maximizing margin on subcontracted work.
This structure is particularly well-suited to complex or phased projects where early coordination between design and construction has a meaningful impact on cost and schedule. Rather than waiting for fully complete drawings before tendering trades, construction management allows procurement to begin as design advances — compressing timelines and reducing the risk of costly late-stage changes. For multi-family and commercial developments in Kelowna and the Okanagan, where scope, phasing, and site conditions regularly introduce uncertainty, it is often the delivery model that produces the most predictable outcomes.
When a Lump Sum Contract Makes Sense
Lump sum contracts are most effective when design is essentially complete, scope is clearly defined, and site conditions are well understood before tendering. Competitive tendering on a complete document set also works well when the market supports multiple qualified bidders, since competition drives pricing toward fair value. The critical requirement is document quality: vague specifications or incomplete drawings in a lump sum contract invite change orders and disputes that eliminate the cost certainty the owner was counting on. Whatever contract structure you choose, it is worth mapping out all project costs from the outset — including soft costs such as design fees, permits, and financing charges that sit outside the construction contract entirely.
When Cost-Plus or Construction Management Is the Better Fit
Cost-plus and construction management arrangements are the right choice when complexity, design evolution, or compressed schedules make a fully defined scope impractical before construction begins. Large multi-family developments, mixed-use commercial buildings, institutional projects, and phased ground-up construction frequently fall into this category. When you are working with a trusted construction manager on an open-book basis with a fixed fee, the cost-plus structure gives you more transparency and flexibility than a lump sum tender can deliver. If you are weighing delivery models for an upcoming project in Kelowna, our post on how to select a construction manager in Kelowna covers the key criteria for evaluating any potential partner before committing to a contract structure.
How Team Construction Approaches Contract Structure
We work across lump sum, cost-plus, and construction management delivery methods and help clients choose the structure that fits their project complexity, design maturity, and risk profile — not the one that is most convenient for us. If you are planning a development in Kelowna or the broader Okanagan and want a straight assessment of which contract model fits your situation, contact Team Construction to set up a consultation.