What is a cavity cleat?
A cavity cleat is a batten that sits in the cavity alongside a window or door opening and to which the frame is fixed, via a sub-frame. The Dutch call it a spouwlat. It connects the sub-frame to both the inner and the outer leaf of a cavity wall, so the frame is effectively “locked” into the opening. The detail is typical of Dutch construction, where cavity walls with a timber sub-frame (stelkozijn) are standard practice.
How it works
- Linking two leaves. A cavity wall consists of two separate walls with a cavity in between. The cleat bridges that cavity at the opening.
- Position. The cleat sits between the sub-frame and the masonry, at the sides and head of the opening. The actual frame is then fitted into or against the sub-frame.
- Closing the cavity. Along the opening, the cleat closes off the cavity and gives a flat stop for the frame and the reveal finish.
Application
- Set out first. Fix the overall frame size, rebate size and clear opening before the sub-frame and cleats go in. A misplaced cleat shifts the whole frame.
- Use durable or treated timber. The cleat sits in a damp zone and cannot be reached later.
- Watch the thermal bridge. Solid timber insulates less well than cavity insulation. Butt the insulation tightly against the cleat, or choose an insulated frame connection.
- Do not forget the cavity tray. Above the frame you need a damp-proof tray that leads water out of the cavity. The cleat does not replace it.
- Seal airtight. Seal the joint between frame and inner leaf to prevent draughts and condensation.
Common mistake: leaving the old cleat in place when replacing a window without checking it for rot. A rotten cleat gives the new frame no grip.
Related terms
- Window frame
- Frame anchor
- Cavity wall
- Inner cavity leaf
- Outer cavity leaf
- Reveal
- Cavity wall insulation
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