The design of a building within the client’s specified project brief and project budget is a core skill/service of an architect. Clients need to be made aware of the consequences of not following professional advice.Designs that exceed budgets are a frequent cause of PI claims. Sometimes it can be argued that “mission creep” initiated by the client was the underlying problem, but clients routinely respond that they did not realise that their minor input would lead to major overspend. Often, earnest efforts spent in design cannot overcome an initial insufficiency in funding. Sometimes, unnecessarily complex design is at odds with reality. Regrettably, other projects do not face up to cost management until it is too late.In smaller projects the relative impact of unexpected costs can be very significant: in larger projects the same costs may be merely incidental. Those smaller projects are also the ones where a client - perhaps with a view about the inevitable variance in estimating – can be very resistant to incurring fees for a quantity surveyor.Architects who do not possess cost-estimating skills should pass this task to a QS. But the question is “When?”. To some extent this will depend on the risk appetite of client and architect, but if cost is a priority, then it should be established and monitored as soon as the design information allows. It makes little difference if the QS is contracted to the architect as a sub-consultant, or directly to the client: if there is an cost-estimation error, the legal responsibility will ultimately rest with the QS. But if the design is out of step with the budget, there could be significant commercial problems for the architect.Of course, there is no reason why an architect could not engage a QS for direct input, and include the costs within the architect’s fees as a necessary component of the design process; such an arrangement does not necessarily imply that QS input or access to it is made available to the client.Regrettably, if project costs become an issue, clients tend to use the first estimates as the benchmark. If the initial budget is recorded in the agreement for services, then the client’s lawyer will be using that as a benchmark. So that makes it important to establish and record who is responsible for cost control, who has the authority to vary the budget, what the cost consequences of design decisions or scope changes are, and what happens to your fees when there is a change which affects the budget.If clients insist on assuming responsibility for cost control, they may rely on a builder’s estimate, or appoint a QS. NZACS Members have faced claims where the builder’s estimate on preliminary information has been well short of the final costs on the final documentation; it is not unknown for a QS estimate to be off the mark. Builder’s estimates can also be very dependent on circumstances (including the availability of that builder) which no longer apply when the final costs are tallied. But despite the architect proceeding in good faith, it is on the “real” costs that the design will be judged. Arguing the toss over mission creep or unexpected design problems is time-consuming and stressful for all. Re-design by the architect - perhaps within the original agreed fee - is commercial folly. The costs of resolving a cost blowout may significantly exceed the fees involved in obtaining competent and professional QS input.Whether or not the cost-estimating responsibility passes to the client, the timing and the need for estimating input should be clearly understood at the outset and recorded in writing. The development of the design from stage to stage should not proceed until an adequate assurance as to costs is available. Moreover, it would be prudent for the architect to clearly express, in writing, the consequences of not having a reliable project cost-estimate before proceeding with detailed design and/or construction documentation.Management (or at least monitoring) of the cost control process, and the recording of that process, is a responsibility for the architect. It should be clear from the initial agreement for services, or from following correspondence. It is not a matter that should be left to the notionally uninformed client.