Contractors Face Variation Claims Over Changed Window Specifications

Navigating Specification Changes on Live Construction Projects

When a client requests a modification to specified materials—such as altering the window package on an active housing site—contractors must establish whether the instruction constitutes a formal variation under the contract terms. Legal expert Leon Harris from Construction Management has outlined the steps required to determine if additional costs and extended timelines can be formally claimed.

A formal variation typically arises when the client alters the scope of works, the quality or quantity of materials, or the sequence of construction initially agreed upon. If the window specification is changed to satisfy updated statutory compliance or simple design preference, the contractor must review the precise wording of their contract, specifically looking at how instructions are issued and how notice periods are managed.

Implications for Material Sourcing and Project Timelines

Changing window specifications mid-project directly impacts sub-contractor scheduling, lead times, and structural opening dimensions. Unilateral changes by the client can trigger financial losses if materials have already been ordered or custom-fabricated based on the original bill of quantities.

Contractual Notice Requirements

• Written Instructions: Ensure any request to alter specifications is provided in writing by the contract administrator or client.
• Cost Impact Assessment: Provide timely notification of price differences, including changes in unit costs and delivery surcharges from window suppliers.
• Time Extensions: Submit formal requests for additional time if longer manufacturer lead times affect the overall handover date.

What This Means for Buyers and Sub-Contractors

What does this mean for a UK tradesperson or DIYer actually buying this kit — does it change what they should pay, buy, or watch out for?

For sole traders, joiners, and small sub-contractors purchasing glazing units and fixings, this highlights the necessity of securing firm quotes before accepting client revisions. When a client alters a window spec, never purchase updated stock from trade merchants like Wickes or Travis Perkins without a written variation order that explicitly covers price increases and potential restocking fees for returned units. Unwritten verbal changes leave installers liable for material price gaps and wasted labor.

Reported by Construction Management — original article