Air bricks on the internal layer of the external wall.
Redecorating and ive noticed airbricks are on the inside wall of the external wall of my house. They have also been boarded up (with plywood) by im guessing the old owner. But since redecorating one room i have noticed mould starting to form where the airbrick is so some moisture must be getting through it.
My question is do i need the airbricks on the internal wall. Or could i just silcone them up and then cover it again, to hopefully prevent the moisture getting through?
Advice from 3 local tradespeople
At Quality Roofing & Guttering Ltd, we see this issue regularly. Air bricks should not normally vent directly into a living space – they are designed to ventilate a cavity wall or sub-floor, not the internal room.
You should not silicone or permanently seal an air brick without first confirming what it is ventilating, as this can cause damp or rot elsewhere. Mould usually indicates condensation, poor external detailing, or a defective air brick.
The correct fix is to ensure the air brick vents correctly to the cavity or sub-floor, often using a proper internal sleeve or by repairing the external wall and air brick. An inspection is recommended before covering anything over.
Good question! Airbricks are usually there to provide ventilation—often to ventilate underfloor spaces or cavity walls to prevent damp and condensation.
Since yours are on the internal side of an external wall and boarded up, it sounds like:
They may have been original ventilation points that the previous owner blocked, possibly because of drafts or other issues.
Blocking them might reduce airflow, which can cause moisture build-up and mould — ironically making damp problems worse.
If you seal them completely with silicone and cover them, you might stop airflow but could trap moisture instead, potentially making the mould problem worse over time.
What to do:
First, try to identify what those airbricks ventilate—usually underfloor or cavity.
If they are still needed for ventilation, it’s best to unblock them and improve airflow, possibly by fitting ventilated airbrick covers that prevent rain and pests but allow air through.
If the airbricks are redundant or not connected to anything critical, you might be able to seal them, but it’s safest to get a professional damp specialist or surveyor to check first.
In short: Don’t just seal them up without knowing their purpose—good ventilation is key to preventing moisture and mould.
Airbricks must remain unobstructed to ensure adequate ventilation and prevent moisture accumulation, thereby mitigating mold growth.
