How do I check and clean an air vent or airbrick?

Airbricks are the most consistently misunderstood feature of a house. They look like a source of draughts and are frequently blocked deliberately, which causes exactly the problem the house was built to avoid.

Safety

Step by step

1. Find out what vents you have.Walk the whole perimeter and note every airbrick, usually just below floor level on a suspended timber floor. Also look for wall vents inside, trickle vents in windows and vents serving appliances.
2. Understand what they are for.Airbricks ventilate the void beneath a suspended timber floor. Moving air keeps the joists and floorboards dry. Without it, moisture builds up and causes rot and damp — this is the whole reason they exist.
3. Never block one.Not with foam, not with a brick, not for winter. It is a very common and very expensive mistake, and it causes far more damp than the draught it removes.
4. Check ground level against them.Soil, gravel, a raised patio, decking or a new path can bury an airbrick or leave it below ground level. Dig back so there is clear air in front of it and below the damp-proof course.
5. Clear plants and debris.Shrubs growing against the wall, leaves accumulating, a wheelie bin standing in front. Anything within a few centimetres restricts the airflow considerably.
6. Check for render or paint over them.Rendering and painting frequently seals airbricks partially or completely. Look closely — a rendered-over airbrick is not obvious and it is a common finding in a damp survey.
7. Clean them out with a brush and a vacuum.A stiff brush and a narrow vacuum nozzle. Cobwebs, leaf litter, mortar droppings and old insulation all restrict them and it takes a minute each.
8. Check inside the void where you can.Lifting a floorboard or looking through an access hatch. Rubble, old insulation and debris in the void can block the path even when the airbricks themselves are clear.
9. Replace broken or missing ones.Clay or plastic airbricks are inexpensive and straightforward to replace. A missing one lets rodents into the void, which is its own problem.
10. Fit a periscope vent through insulation.Where cavity wall insulation or an extension has interrupted the path, a telescopic or periscope vent carries the air through. This is the correct answer rather than accepting a blocked vent.
11. Check there are enough of them.They should be reasonably spaced along each wall, with cross-ventilation from one side to the other. A void with airbricks on only one wall does not ventilate properly.
12. Leave appliance vents entirely alone.A vent serving a gas fire, boiler or solid fuel appliance is a combustion air supply. Blocking or restricting it is dangerous. If unsure what a vent serves, ask a Gas Safe engineer.
13. Deal with draughts a different way.If the floor is draughty, insulate under it and seal the gaps between floorboards. That addresses the draught while keeping the void ventilated.
14. Check them annually.Autumn, when leaves accumulate. It takes ten minutes round the whole house and it is among the highest-value maintenance checks there is.

Tips

• Walk the perimeter once and photograph each airbrick. It makes the annual check a two-minute comparison.
• A blocked airbrick is a far more expensive problem than a cold floor. Insulate under the floor instead.
• Look specifically for render and paint over them. It is the blockage people never notice.

Common mistakes

• Blocking airbricks to stop draughts — The void then holds moisture, and rot in the joists and floorboards follows. It causes far more damage than the draught it removes, and it is a common finding in damp surveys.
• Raising ground level over an airbrick — A new patio, path or raised bed can bury a vent and bridge the damp-proof course at the same time. Keep the ground clear and below the DPC.

If it doesn't work

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