What is it?
A short length of concrete fill placed at the very base of a cavity wall, below ground level, closing off the bottom of the cavity between the two masonry leaves.
What does it do?
Below ground, an open cavity would just be a void collecting soil, debris and water with nothing to stop it: the infill closes that off, ties both masonry leaves structurally to the foundation, and gives them a solid bearing to build up from. It's laid with a slight fall towards the external face, so any water that does collect in the cavity is directed back out rather than towards the building.
Where is it used?
How to specify
Specified simply as a lean-mix concrete fill to the depth shown on a typical cavity wall detail. Noting "lean mix cavity infill" on the drawing is normally all a builder needs, since this is a standard detail rather than something engineered case by case.
Interacting elements
- Foundation: the infill sits on top of the foundation, filling the cavity above it
- Footing Blockwork / Facing brick: both leaves bear on top of the infill
- DPC: sits at least 225mm above the infill, at the point the damp-proof course crosses the wall