The Future Homes Standard, published on 24 March 2026, changes how window performance is evidenced in new build homes in England. The notional U-value stays at 1.2 W/m²K for new build windows, as set out in Approved Document L 2026. The calculation method behind it has changed.

Every window supplied into new build now has to be evidenced at its actual size and configuration. For years the industry modelled against a standard 1230 x 1480 open or fixed window, as set out by the GGF. That baseline no longer holds for new build.

For fabricators, that makes this an evidence and traceability question. This session sets out what the method change means, where the calculation data sits, and how the industry is working through it.

What the session covers:

Why the requirement has changed even though the notional U-value has not. Notional and limiting U-values for fenestration elements are unchanged from the 2021 versions, according to the Council for Aluminium in Building. The method used to demonstrate them has changed.

What evidencing each window at its actual size and configuration means for your order book, and why transoms, mullions, bars and add-on components make the calculation harder than the standard window assumed.

​ Which data you need and where it comes from. The calculation data sits with your systems house. Your accountability for what you manufacture does not move.

Where the discussion about triple-glazed specifications currently sits. The GGF describes it as a view being discussed in the industry, with no settled outcome yet.