What U-value does a rooflight need for Building Regs?
A new or replacement rooflight in England needs a U-value of 2.2 W/m²K or better, and that figure covers the rooflight and its kerb together. A roof window in the plane of a pitched roof of 15 degrees or more has a tighter limit of 1.6 W/m²K.
What if only the glass is replaced?
If only the glazing is replaced as a repair, it does not have to meet the full energy requirement, but it must not perform worse than the glazing it replaces.
Which U-value should you use?
- Use the figure for the installed angle: a lantern or flat rooflight is not a vertical window
- Check the supplier’s figure is adjusted for rooflight use, not quoted for a vertical window
- Include the kerb, since the kerb is part of the assembly
- Site-built upstands should reach about 0.35 W/m²K
Are there glazing area limits too?
Yes. In a dwelling extension, total glazing is limited to 25 percent of the floor area. The U-value and area limits work together.
Order from the trade counter at Unit 1, Friar Walk, Worthing, with free delivery within 30 miles. See the rooflights range for specs.
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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