What U-value do replacement windows need to meet?
In England, replacement windows must achieve a maximum U-value of 1.4 W/m²K, or a Window Energy Rating of Band B or better. These limits apply under Approved Document L from 15 June 2022. The U-value must be for the whole window, not just the glass.
What does 1.4 W/m²K mean?
A lower U-value means less heat loss. The limit applies to the whole window (frame plus glass), which is why a BFRC certificate is the easiest proof.
Which specification usually meets it?
- Double glazing with a low-E coating
- Argon gas fill
- Warm-edge spacer bar
- Multi-chamber uPVC profile
Are there exceptions?
Listed buildings and some conservation or heritage situations are treated differently, and new extensions and new dwellings have their own limits. Scotland and Wales also follow different regulations. Check the job with building control. Our supply-only windows are listed with their rated performance. Always request the BFRC certificate, which records the whole-window figure for your exact specification. Glass-only centre-pane figures look better than the whole-window result, so do not quote them as the window U-value on paperwork.
Need a trade price? Call the trade counter on 01903 262 636 or visit us at Unit 1, Friar Walk, Worthing. We offer free delivery within 30 miles.
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