- A lintel that is too light and sags, cracking the brickwork
- A missing cavity tray, so water from the cavity gets inside
- Filled-in perpends that stop water from draining
- Rust on an unprotected steel lintel
Building detail · Window frame
Lintel above a window frame: support and cavity tray
Above every window frame in a cavity wall, a lintel carries the brickwork. On the outside this is often a steel lintel, on the inside a lintel in the inner leaf. A cavity tray above the lintel drains water from the cavity to the outside.
- A lintel that suits the width of the opening and the load
- A cavity tray with open perpends above it
- Attention to thermal bridges and corrosion
Principle sketch
Build-up of the detail
Vertical section above a window frame in a cavity wall. The numbers in the sketch refer to these parts:
- Outer leaf
- Steel lintel (facade support) under the outer leaf
- Open perpends for drainage and ventilation
- Cavity tray above the lintel, rising towards the inside
- Cavity insulation
- Inner leaf
- Concrete lintel in the inner leaf
- Head of the window frame
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 span and the bearing on both sides of the opening
- The load of the brickwork and any floors above
- A cavity tray that runs past the ends of the lintel
- Corrosion protection for the steel
- The connection to the frame head and the cavity insulation
Enlarging a facade opening often calls for a heavier lintel or a steel beam. That comes with a structural calculation. Structural calculations
Detail FAQ
Frequently asked questions about this detail
When is a steel lintel needed?
Over openings in a cavity wall, a lintel carries the outer leaf. Whether that is a steel lintel or another solution depends on the width of the opening and the load above it.
Why are there open perpends above the lintel?
The open perpends let water that lands on the cavity tray drain to the outside, and let the cavity ventilate.
Do I need a calculation if I make a window larger?
Often yes, because the load on the new lintel or beam has to be demonstrated. That depends on the width of the opening and what rests above it.
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