Preparing for Approved Document L 2026

A guide to opening-specific U-value calculations for window and door manufacturers, fabricators and system providers.

Introduced and approved Document L 2026 changes

Understand how actual-size U-value calculations will impact compliance, software systems and data requirements across the fenestration supply chain.

Ensure every window and doorset is assessed using its exact size and configuration.
Meet new calculation requirements by accounting for all relevant product components.
Future-proof your business with scalable software, integrated data and automated workflows.
Provide thermal data that better reflects real-world installed performance.

We provide independent third-party testing and certification for fenestration products including PVC-U windows doors and profiles, as well as aluminium, steel, composite, timber doors and windows and hardware.

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