Edited Feb 2017Inevitably you have to make assumptions about hidden construction or services. Your client should be aware of your assumptions as soon as you can explain them. Your knowledge of the existing building will evolve as the design evolves, but the existing level of compliance is best sorted before the scope of work is nailed down. If your reasonable assumptions are wrong, there is the prospect of a claim for the unexpected costs.Even minor projects – at minor fees - can throw up unforeseen problems with cladding, drains, insulation, ground clearances, bracing etc. For such projects, the architect is less likely to be fairly paid, and more likely to be blamed for the escalating costs.Such problems are compounded in the event that your engagement does not include the opportunity to review the construction process as it proceeds: See articles on Limited (or partial) Services.