- An uninsulated upstand with condensation on the inside
- Roofing that does not run high enough up the upstand
- Water standing against the upstand due to the wrong fall
- Overheating in summer from a lot of south-facing glass
Building detail · Roof
Roof light in a flat roof: upstand and connection
A roof light brings plenty of daylight into an extension. The detail around the opening decides whether it also stays dry and free of condensation: an insulated upstand, continuous roofing and trimming in the roof structure.
- An insulated upstand around the opening
- Roofing carried up the upstand
- Trimming in the roof joists
Principle sketch
Build-up of the detail
Vertical section through a roof light in a flat roof. The numbers in the sketch refer to these parts:
- Roof build-up with insulation and roofing
- Insulated upstand around the opening
- Roofing carried up the upstand
- Roof light with insulating glass
- Trimmer beams around the roof opening
- Finish of the reveal inside
- Roof fall, away from the upstand
Common mistakes
Where it often goes wrong
Leaks, condensation and cracks usually start at the junctions, not in the middle of a wall or roof.
In the drawing
What we look out for
We work out the detail for your home, based on a site survey and the chosen materials.
- The size and position of the opening in the roof joists
- Insulation and height of the upstand
- Fall and drainage around the roof light
- The type of glass and the sun shading
- The connection of the reveal to the ceiling inside
A roof light is often designed together with an extension. Renovating and extending a terraced house
Detail FAQ
Frequently asked questions about this detail
What is the difference between a roof light and a rooflight dome?
A roof light (lichtstraat) is an elongated glass ridge, often in an extension. A rooflight dome is usually smaller and has a plastic or glass dome.
Why does condensation form at a roof light?
Usually because of a cold upstand or cold profiles. An insulated upstand and a good glass and profile system limit this.
Does the roof structure need to be adapted?
Yes, for the opening, roof joists are interrupted and picked up by trimmer beams. That is part of the structural design.
Can I use this principle sketch for my own home?
The principle sketch shows the build-up, but it is not a working drawing. Dimensions, materials and fixings depend on your home. We work out the detail for your situation.
Detail library