- Roofing that stops short of the upstand, letting water get behind the trim
- A cold edge because roof and wall insulation do not connect
- An upstand that is too low, so water flows over the edge in heavy rain
- A roof trim without room for expansion, with leaking joints
Building detail · Roof
Flat roof edge: upstand and roof trim
The roof edge is where roofing, insulation and facade meet. A good upstand and roof trim keep water on the roof and away from the facade, and the insulation continues without a cold edge.
- Roofing that continues over the upstand
- A roof trim that caps the edge
- Roof insulation that meets the cavity insulation
Principle sketch
Build-up of the detail
Vertical section through the edge of a flat roof above a cavity wall. The numbers in the sketch refer to these parts:
- Outer leaf
- Cavity insulation
- Inner leaf
- Timber roof joist
- Roof deck with vapour control layer
- Roof insulation (warm roof)
- Roofing, carried over the upstand
- Timber upstand at the roof edge
- Roof trim over the edge
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 height and insulation of the upstand
- The continuous roofing and the fixing of the trim
- The connection of the roof insulation to the cavity insulation
- Drainage to the outlets, not over the edge
- The finish of the facade below the trim
For an extension or roof extension, we draw the roof edge as part of the complete facade and roof detail.
Detail FAQ
Frequently asked questions about this detail
What is a roof trim?
A metal capping profile over the roof edge that protects the top of the upstand and the roofing.
Should the roof insulation meet the cavity insulation?
Yes, otherwise a cold edge forms where condensation and mould can develop.
How high should an upstand be?
That depends on the roof, the drainage and the supplier's requirements. We include the height in the detail for your situation.
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