Cavity wall that seems to be open to the outside.

[1954baby]

We have an extension room with a cavity wall and the inside wall is very cold. I drilled a 5" hole in the inside wall just at the concrete floor line. Inside the cavity is very cold and there is a draught. The cavity extends to about 6" lower than the internal floor. It is damp, if not wet, down in the cavity. So, there must be a way for air to get in. We replaced the ceiling in this room and the top of the cavity is sealed so, the air must be coming in from outside.

Can't see anywhere outside where air can get in.

Any ideas?

 

[AronSearle]

Any windows or doors, purpends, is the top of the cavity blocked?

May be lots of paths for air, and plenty of little gaps where it is apparently sealed, air pressure and temperature differences will cause air movement to seem fairly strong.

Why not just get cavity insulation?

 

[1954baby]

I was, in a previous house, wary of cavity wall insulation. It was a long time ago but there were concerns when it first came out about condensation and rodents.

SC

 

[AronSearle]

It won't contribute to condensation, it will help to prevent it.

It may be bad for water penetration in a few high exposure locations, with certain types of insulation (cavities exist for a reason). polystyrene beads are your safest bet as they still allow water drainage. A good company will advise you on the suitability of it being done. Given your situation I can't see why not.

Can't comment on rodents, not aware personally it is a big issue?

 

[lbzbean]

They use smoke machines to find holes in leaky cars - if you have a decent hole you should be able to rig something up.

 

[KenGMac]

1954baby, hi

Does the extension have any external air bricks fitted? to provide under floor ventilation.

At times the air brick is not ducted over the cavity, thus air entering the external air brick will simply get into the cavity

Ken.