Air bricks and cavity walls

11 Dec 2015
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United Kingdom
I have a 1930's semi-detached house with a cellar that is slightly damp, I understand that this is ok because it is below the DPC.

I have air bricks at ground level on the outside of my cavity wall. The air brick is not sleeved through the cavity wall. The air can flow into the open cavity and through an air brick sized gap in the inner wall to the cellar.

Does this sound right? Is the air supposed to circulate around the cavity, the cellar or both?

There is not great access to the air brick area from the inside of the house as a floor joist sits right up against it, so retro fitting a sleeve would be difficult. There is however enough room to get a tube from a expanding foam can into the cavity, would it be a good idea to put some foam into the cavity around the air brick to stop air circulating through the cavity?

There is no cavity insulation and British Gas say it cannot be installed because of the position of the DPC in relation to the cellar.

My house has been extended and one original cavity outside wall is now an internal wall. The pitched roof has also been extended.

In the attic the top of the cavity on this wall is now exposed and open, see photo, should I close the cavity in the attic, if so how?


The reasons for asking, keeping the house warmer and we have a mouse problem in the attic. I think that mice are getting into the cavity, possibly through the air bricks and up through the wall to the attic.
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Hi Maymo,
Why don't you attach a sketch so it is easier to understand which wall you are referring to and which face of the original property had been extended.

Do not seal the air brick, it is necessary for good ventilation.

As for the attic gap, I would simply put down wooden flooring to cover the gap but it would be easier to understand the ventilation aspect if I can see a diagram of the different walls.

Air bricks need to be sleeved. If you can't slot a clay or plastic liner in, you can make one from some cement board such as undercloak used for roofing - and silicone the joints.

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