Cavity Closure

A cavity closer is the component that closes off the open cavity between the inner and outer leaves of masonry in an external wall, which would otherwise be left open.

Left open, the cavity at a reveal would expose the insulation within it, let water track in around the frame, and create an easy path for heat to escape at the edge of the opening: one of the most common places for a cold bridge in a masonry wall. The closer seals that edge, usually incorporating both a vertical DPC strip (to stop water tracking in) and an insulated core (to maintain the wall's thermal line right up to the frame).

At the vertical reveals of every door and window opening in a cavity wall: both jambs, running the full height of the opening.

It's also used at the head of the opening where each leaf has its own separate lintel, rather than one lintel spanning the full wall thickness.

Cavity closers are most commonly a proprietary insulated PVC or composite profile, built into the wall as it's constructed, combining the vertical DPC and insulation in one fitted component rather than assembling both separately on site.

The closer is chosen to match the cavity width it's closing and the insulation thickness used elsewhere in the wall, so the thermal line is continuous rather than stepping down at the opening. It's specified alongside the window or door manufacturer's fixing details, since the frame fixes back into or against it.

A reveal is one of the most common places for a cold bridge and for water ingress in a cavity wall, so the closer's continuity with the main wall insulation and DPC is important.

• Cavity insulation: the closer continues the wall's insulation line up to the opening
• DPC: the closer's vertical DPC strip ties into the wall's main damp-proof course
• Door frame: fixes to or against the closer at the reveal