Temporary works: the hidden design and construction package bidders routinely underprice

Temporary works are frequently absent from the permanent design drawings and therefore invisible in early estimates. Yet they can control the construction method and critical path. Bridge falsework, deep-excavation support, cofferdams, marine access, haul roads, crane pads, temporary drainage, railway possessions and traffic diversions can each become substantial engineered works in their own right.

The red flag is a clause making the contractor fully responsible for design, approval, maintenance and removal of all temporary works while the BOQ provides little or no dedicated payment. In that case the bidder must price design engineers, calculations, independent checks if required, materials, installation, monitoring, inspections, redesign after changes and removal/reinstatement.

Temporary works also create interface risk. A traffic diversion may require police or road-authority approval; a cofferdam may need environmental constraints and flood assumptions; a crane pad may depend on third-party land; temporary power may require utility approvals. These dependencies belong in the programme and Employer-dependency register, not only in the method statement.

A strong bid separates temporary works into engineered packages with quantity, design responsibility, approval route, duration and recovery basis. If the item is not separately measurable, its cost still needs a defined recovery route across the permanent-work rates or preliminaries.

This article is engineering and tender-risk guidance. The signed bidding documents, conditions of contract, technical specifications, drawings, bill of quantities, method of measurement and applicable law govern each project. Contractual and legal interpretations should be confirmed by qualified advisers where material.