A builder in Parkstone has just quoted for a rear extension and, buried in the spec, there’s a line about window U-values. Fair enough. But it’s worth a quick look at what’s changing, because the rules for windows are moving, and it affects anyone replacing frames in Poole or Bournemouth over the next year or two.
Industry press has been covering the updated Approved Document L and the Future Homes Standard, with England’s timetable pointing to 24 March 2027 for standard building work. For replacement windows in an existing house, the benchmark is a U-value of 1.4 W/m²K or a Window Energy Rating of Band B. Glazed doors with more than 60% glass should hit 1.4 or Doorset Energy Rating Band C. New builds have a limiting value of 1.6 in England, though the notional target is a tougher 1.2.
The part that catches fitters out is how the figure’s worked out. Calculations now need to reflect the actual size and configuration of each unit, so cills, couplers, transoms and decorative bars all count, rather than leaning on a standard reference window. Installers also need to seal the frame to the air barrier all the way round, and keep photos and paperwork on file. A 1,200 by 1,200mm casement with a thick mullion won’t perform like a clean fixed pane, and the certificate should say so.
For you, the homeowner, that means a few simple questions. What’s the U-value or WER band on this specific window? Is the glazing a 24mm or 28mm sealed unit with warm-edge spacers and argon? Will the FENSA or CERTASS certificate come through afterwards? Any decent supplier should answer all three without blinking.
DTU Trade Windows supply windows, doors, sliding doors and roof lanterns to fitters and homeowners across Poole and Bournemouth. If you’re planning a replacement and want the spec checked against what’s coming, take a look at https://www.dtutradewindows.com/ and get a quote.
