Can Rats Enter Through Air Bricks and Ventilation Openings?

What Air Bricks Are For

They ventilate the void under a suspended timber floor. Air moving through that void keeps the timbers dry; without it you get damp, and eventually rot in the joists and floorboards.

That is the constraint on everything that follows. An air brick cannot simply be filled in, and anyone who offers to block one to stop rodents is trading a pest problem for a much more expensive building one.

How They Fail

Older clay air bricks crack and lose sections, leaving a hole several centimetres across. Plastic ones become brittle and break. Some have been rendered over during past work and then cracked. Some are missing entirely, leaving a rectangular hole straight into the void.

Ground levels are the other half. Where a path, patio or border has been raised over the years, an air brick can end up at or below ground level, which makes it both useless for ventilation and easy to reach.

How to Check Yours

Walk the whole perimeter, including behind bins, under the boiler flue, behind planters and along the side return that nobody looks at. Count them, and look at each one closely rather than from standing height.

You are looking for missing sections, cracks, gaps at the edges where the mortar has gone, and any that are blocked by soil or vegetation. Smear marks around an opening mean it is in use, not just available.

The Right Fix

Replace or cover with a purpose-made rodent-resistant air brick or a stainless mesh grille fitted over the opening, sized to keep the airflow. Fix it properly to the brickwork rather than pushing mesh into the hole, which rats pull out.

Where the ground has been raised, the proper answer is a periscope vent or lowering the ground level, not a blocked brick. And never expanding foam, chicken wire or a plastic cover with large openings.

The Other Ventilation Openings

Tumble dryer and extract vents through an external wall, which frequently have a flap that no longer closes. Boiler flue penetrations with a gap around the pipe. Soffit and eaves vents at roof level. Wall vents in old kitchens and bathrooms. Cavity wall weep holes, which are mouse-sized rather than rat-sized but still count.

All of them can be meshed without losing their function. Rodent proofing is £180 for up to an hour and covers rats, mice and squirrels — and it comes after treatment, never while there is still activity inside.