No. Air bricks ventilate the void under suspended timber floors, and blocking them lets moisture build up underneath, which can lead to wet rot, dry rot and woodworm. If draughts are a problem, seal and insulate the floor from inside instead.
In winter, people get down on their hands and knees, feel cold air coming through the floor and decide the air bricks are the problem. So they stuff them with rags, cover them with tape or put a plant pot in front of them. I understand the logic, but it’s one of the worst things you can do to an older house with timber floors.
What air bricks are for
If your ground floor is timber, it sits over a void. The ground underneath gives off moisture all the time. Air bricks in the outside walls let air flow through the void to carry that moisture away. Without that flow, the humidity under the floor climbs, the timbers absorb moisture, and you’re creating ideal conditions for rot and woodworm.
Some air bricks serve other purposes, such as ventilating rooms with gas appliances. Blocking those can be dangerous. If you’re not sure what an air brick serves, find out before touching it.
Signs they’re blocked or not working
- Soil, paving, gravel or plants covering them outside.
- Painted over, rendered over or full of cobwebs and debris.
- Old clay air bricks with very small holes that are mostly clogged.
- Air bricks only on one side of the house, so there’s no cross-flow.
Better ways to deal with draughts
- Seal gaps between floorboards and under skirtings from inside.
- Insulate between the joists, using a method that keeps the void below ventilated. Done properly, this makes rooms warmer without stopping the airflow underneath.
- Put down a good underlay and carpet, or seal the boards.
- Fit draught-proof covers to unused fireplaces with a small vent, rather than blocking chimneys completely.
Keeping them working
- Keep the ground well below air brick level, and use periscope vents where levels are high.
- Clean them out once a year.
- Replace broken air bricks, and fit mesh where needed to keep vermin out.
- Make sure new paths, patios and extensions don’t cover them.
Your floor will be cold whether the air bricks are open or not, if it isn’t insulated. Insulate the floor, not the air bricks.
When to call a specialist
If you've had air bricks blocked for a while, or your floors feel soft or smell musty, have the subfloor and timbers checked. Book a survey with All Dry on 01226 287181 or email info@alldrydampproofing.com.
Listen on The Damp Show
Frequently asked questions
Is it OK to cover air bricks in winter?
No, they need to stay clear all year to keep the subfloor dry.
Can air bricks be below ground level?
They shouldn't be; periscope vents can be used where ground levels are high.
How do I stop draughts through the floor without blocking air bricks?
Seal and insulate the floor from inside while keeping the void ventilated.