A provisional sum is an allowance, not a magical force field around the budget. The useful review is whether the quantity, scope and rate assumptions are reasonable before the contract position is locked.
Identify exactly what work the provisional sum is intended to cover. A single label such as landscaping or excavation can hide several different scopes, interfaces and exclusions.
Where drawings allow measurement, compare the allowance with the likely quantity. A rate can look perfectly reasonable while the assumed quantity is wildly optimistic. This is where a take-off provides useful commercial evidence.
Ask whether the allowance reflects current supplier or subcontractor pricing, whether labour and materials are both included, and whether access, waste, delivery or other project-specific factors have been considered.
The contract treatment matters. Review how actual cost, builder margin, administration and client adjustments will be calculated if the final amount differs from the provisional sum. The commercial risk is not only that the allowance is low, but that nobody has modelled the effect of being low.
One provisional sum may be manageable. Ten underdeveloped allowances across the same project can produce substantial contract and margin volatility. Review the aggregate exposure rather than each allowance in isolation.