For builders and roofers
Rooflight Upstand Sizes
The dimensions
Short answer
Build the upstand 75mm wide and 150mm high from its lowest point. Then add 50mm of extra height per 1m of width. These figures are for flat rooflights, not lanterns or pyramids.
Why the height changes with the width
A flat rooflight is not flat. It is laid to a fall so water leaves it, and the wider the opening the further that water has to travel before it reaches an edge. The minimum 150mm is measured from the lowest point of the upstand, and every additional metre of width needs 50mm of extra height per 1m of width to keep the fall working across the span.
A 1m unit sits on 150mm. A 3m unit needs 250mm at the low point. Build every upstand to the same 150mm and the widest one on the job is the one that ponds.
What these figures are not for
Flat rooflights only. Lanterns and pyramids are a different build-up entirely and their upstands are not covered by the numbers above. If the drawing says lantern, ask us for the detail rather than scaling from this page.
Before you build it
Send the opening size and we will confirm the upstand against the actual unit rather than the general rule, because the general rule is a minimum and a specific unit occasionally wants more. Openings are surveyed by our Project Manager and Designer, and we ask for 1 to 2 weeks before the openings are ready.
As with any opening, the upstand needs to be finished 2 weeks before installation and confirmed by photographs.
Common questions
What size upstand does a flat rooflight need?
75mm wide and 150mm high from the smallest point, plus 50mm of extra height per 1m of width.
Does a 3 metre rooflight need a taller upstand?
Yes. At three metres wide the low point needs 250mm rather than 150mm.
Do these dimensions apply to a lantern?
No. These are for flat rooflights only. Lanterns and pyramids use a different build-up.
When does the upstand need to be finished?
2 weeks before installation, confirmed by photographs.