How high does a roof lantern upstand need to be?
Plan for an upstand at least 150 mm above the finished roof surface. That is the usual minimum quoted for lanterns and rooflights on flat roofs, and 150 to 200 mm is typical. Pitched roofs may need more. Some systems state a lower minimum, so follow the maker’s installation instructions.
Why does the height matter?
- It keeps water out by clearing ponding and drainage
- The waterproof membrane must run up the sides and be sealed at the top
- It gives the lantern a stable base that spreads the load
- The insulation must stay continuous with the roof insulation
Is 150 mm a legal requirement?
Not a single fixed regulation. It is the common guidance figure, and the right height depends on the roof type and lantern system. Check the maker’s data sheet and the roof waterproofing manufacturer’s detail.
What U-value does the upstand need?
A site-built upstand should reach about 0.35 W/m²K or better. A new rooflight and kerb assembly together need 2.2 W/m²K or better under Approved Document L.
Order from the trade counter at Unit 1, Friar Walk, Worthing, with free delivery within 30 miles. See the roof lanterns 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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