A charge-up building contract charges the actual cost of labour, materials, plant, and subcontractors, plus a builder's margin that is agreed upfront. There is no fixed contract sum. The client sees all costs as they are incurred. For architectural homes where drawings are still being refined and the specification evolves through the design and build process, charge-up is generally the more transparent and commercially rational approach. W O Flatz Construction works on a charge-up basis for all our architectural residential projects.

Why does a fixed price contract fail when drawings are still evolving?

A fixed price contract requires a complete, fully coordinated set of construction drawings before a builder can price it accurately. When a client signs a fixed price contract on drawings that are 70 percent resolved, the builder has two choices: price the unknown 30 percent conservatively, loading the contract price with contingency that the client pays regardless of actual outcome, or price it tightly, win the job, and recover the difference through variation claims as the design resolves. Neither outcome serves you well.

Architectural homes rarely have fully resolved drawings at the point when a client wants to commit to a builder. Interior fit-out, joinery specifications, cladding details, and finish schedules are often still in development. Charge-up removes that tension. The builder has no incentive to load the price or pursue aggressive variations, because all costs are passed through at actual rates and the margin is transparent.

How is cost tracked and reported on a charge-up project?

On a well-run charge-up project, the builder provides regular cost reporting against an agreed budget estimate. At W O Flatz Construction, we hold Tuesday morning site meetings and send a written summary after each one. Cost reporting is part of that process. Clients see labour hours, materials invoiced, and subcontractor costs as they come through. There are no surprises saved for the final account.

A budget estimate is prepared before work starts based on the best available information from the drawings and specification at that time. That estimate is not a fixed price, but it is the benchmark against which actual spend is tracked. As design decisions are made and the specification firms up, the estimate is updated. Every subcontractor invoice and materials docket is available for the client to review.

What is the builder margin on a charge-up contract?

The margin is agreed before work starts and expressed as a percentage of net costs. On residential architectural projects in Auckland, builder margins on charge-up contracts typically run between 15 and 22 percent, depending on project complexity, programme, and the level of site management required. The margin covers the builder's overhead, project management, site supervision, and profit. Ask for it in writing before you sign. A builder who is vague about their margin on a charge-up project is not running an open-book process.

When does the client get budget certainty on a charge-up project?

Budget certainty builds as the design resolves. At concept stage, a cost estimate has a wide range, perhaps plus or minus 25 percent. By the time consent is granted and construction drawings are complete, that range narrows to plus or minus ten percent on well-documented projects. Once all subcontractors are priced and long-lead materials are ordered, the remaining uncertainty sits mostly in labour productivity and any design changes the client makes during construction.

Clients who want more certainty earlier can achieve it by resolving the specification before construction starts rather than during it. Every decision made before work begins is a decision that does not generate a variation on site.

What does a charge-up contract look like in practice?

The contract sets out the scope of work as understood at signing, the agreed margin percentage, the reporting frequency, the variation process, and the payment schedule. Payment is typically made fortnightly or monthly against invoices for actual costs incurred plus margin. Under NZS 3910 and related New Zealand Standards, both fixed price and cost-reimbursable contracts have standard forms. For residential work, the NZ Residential Building Contract or a bespoke contract tailored to the project is more common. Whatever form is used, scrutinise the margin rate, the reporting obligations, and the variation process.

If you are planning an architectural home or a significant renovation and want to understand how charge-up pricing would work on your project, contact W O Flatz Construction. We will explain the model, show you what reporting looks like, and give you an honest view of where cost certainty is achievable and where it is not.