An upstand lifts the rooflight above the roof surface so water cannot flow over the frame, gives the roof membrane something to turn up against, and carries insulation around the opening. Manufacturers set a minimum height above the finished roof — commonly 150 mm — and the unit must sit square and level on it.
How high should an upstand be?
High enough to meet the rooflight maker's minimum above the finished roof surface, which is commonly 150 mm. Green roofs, ballast and paving raise the finished level, so the upstand has to rise with them.
What is an upstand made of?
Site-built upstands are usually timber with insulation fixed inside or out. Proprietary insulated kerbs are also available. Approved Document L gives a limiting U-value of 0.35 W/m²K for a site-built rooflight upstand in an existing English dwelling.
How is the membrane finished?
The roof covering is dressed up the outside face and over the top of the upstand, sealed at the corners, before the rooflight frame goes on. The rooflight then overlaps the membrane so water runs off rather than behind it.
Why do most leaks start at the upstand?
Low upstands, membranes cut short of the top, failed corner details and blocked roof outlets are the usual causes. Glass units themselves rarely leak. That is why a repair visit checks the upstand and roof before blaming the rooflight.
Does the rooflight need a fall?
Flat rooflights are designed so the glass sheds water — often with a few degrees built into the frame or the upstand. Follow the manufacturer's detail; do not rely on a dead-flat installation.
This guide gives general information, not legal or structural advice. Rules change and every property is different — check with your council or building control for your address. We review our guides regularly; the date above shows the last review.
Sources
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