What air bricks do
Houses with suspended timber floors — most of Brent's pre-war housing — have a void between the floorboards and the ground. Air bricks in the outside walls let air move through that void and stop the joists from rotting. Blocking them causes damp and decay, sometimes serious and expensive.
Why they let rodents in
- Old clay air bricks with holes large enough for mice to pass through
- Cracked or broken grilles, often from ground-level knocks or frost
- Grilles removed and never replaced after building work
- Air bricks buried by raised patios or flowerbeds, with gaps around them
- Cavity vents that connect straight into the wall cavity
A mouse needs only about 6mm, and a young rat around 15mm. Many older air bricks are well within both.
How to proof an air brick without blocking it
Replace broken air bricks with sound ones, and where the holes are large, fit a rodent-proof cover: a metal grille or plate with fine mesh, fixed securely over the opening. Choose one designed for the job, so it still gives enough free airflow for the floor. Plastic insect-mesh covers are too soft for rats.
Check the airflow afterwards
Fine mesh collects cobwebs and leaves. Brush covers clean from time to time, and do not let soil, patios or planters rise above the air brick. If you have had damp problems, get advice on ventilation before changing anything.
Is the air brick really the route?
Look for smear marks, gnawing and droppings at the air brick itself, and for disturbed soil or burrows below it. If an air brick is sound and there are still rodents under the floor, the drains may be to blame — see can rats enter through drains. Telling a live route from an old one explains the signs.
Air bricks in Brent's older streets
In the Victorian and Edwardian terraces of Kensal Green, Harlesden and Queen's Park, air bricks are often original, over a century old and at pavement level where they get damaged.
Getting it done
Fitting covers to damaged air bricks is typical of the small jobs our rodent proofing service covers, at £180 for up to one hour — book it here. If rodents are under the floor now, start with rat control or mouse control, and read where rats nest.
