This page provides general practical guidance and does not replace project-specific legal, engineering, planning, ecological, asbestos or waste advice.
The short answer
When demolition or strip-out reveals construction that differs materially from the information and assumptions on which the scope was priced — hidden steelwork, additional wall layers, unexpected reinforced concrete, larger or thicker slabs, unknown foundations, buried structures, hidden services, asbestos-containing material, concealed structural supports, or materially greater quantities — the correct response is to expose and identify the actual condition, pause the affected operation where required, assess the implication, obtain engineer or specialist input where necessary, establish any changed method, temporary works, cost or programme, communicate and agree the variation, and then proceed with the revised scope.
Why it matters
Not every unexpected condition creates additional cost. Some findings are within the scope of the original assumptions; others represent a genuine change. The distinction matters. A variation should reflect what has actually changed from the priced scope — not simply the fact that something was found. Clear communication between contractor and client at the point of discovery, before the scope is extended, is the basis for a fair outcome.
Information that may be needed
The original scope, drawings, survey information, asbestos information and any structural information provided at the time of quotation are the reference point for assessing whether a condition is genuinely unexpected. Photographs and written records of the actual condition found should be prepared at the point of discovery.
What can affect the scope
Whether the condition was reasonably foreseeable from the information available at the time of quotation, the extent to which it changes the method, programme or waste arrangement, whether specialist input is required before the affected operation can continue, and the agreed variation process set out in the contract can all affect how an unexpected condition is handled.
When specialist input may be needed
A structural engineer, asbestos professional, utility specialist or other adviser may be required depending on the nature of the unexpected condition. Where asbestos-containing material is found, work in the affected area must stop until a competent asbestos professional has assessed the material.