Removal of blown fibre cavity wall insulation to help with damp issues

[Rich_R]

Hello All,

 

First post here and looking for some advice. We just bought a circa 1930's brick-built semi-detached house in Leeds. We knew from a Level 3 survey that it had some damp issues so were able to negotiate about £20k off the asking price. A full damp survey confirmed the damp is pretty extensive on the ground floor, but generally not present on the first floor (some minor issues around a leaking chimney but these are being addressed). The construction is fairly standard cavity wall (looks like 75mm gap) and the house is made from what looks like engineering bricks so good solid bricks.

 

The damp survey recommends that we have the cavity wall insulation (looks like white fibres) removed from at least one external wall (where the worst of the damp is), in the lounge. We've removed all the flooring in this room already, as some of the joist ends are rotten and need replacing. I can reach inside the cavity where the air bricks are and about 500mm+ above ground level the blown fibre feels okay (not damp), but around airbrick level and below it starts to get a bit damp, and then in the lower section of the cavity it is noticeably damp, and also the bottom 100mm or so of the cavities are filled with broken mortar, brick rubble etc, which is also very damp.

 

My questions are:

1) For the blown fibre insulation, is it possible to just remove *some* of it at the lower levels and leave the rest higher up? if we remove say 500mm up from the bottom of the cavity (also clearing out the cavity of any debris etc). We intended to put 50-100mm of Kingspan on the inside of this wall so this will insulate it, but we need to remove at least some of the cavity wall fibre as it's bridging moisture across the cavity. I'm not sure if there will be issues with most of it being left in the wall and taken out a 500mm "layer" at the bottom. If we did this, won't the higher up fibre just migrate down the wall over time and fill the cavity again? Is there anyway to prevent this, if needed?

 

2) I've done some research on how cavity wall fibre insulation is removed and it doesn't look too hard. Remove some bricks, remove as much insulation as you can get to, put bricks back, remove some more bricks a bit further along, rinse and repeat until done. We've got some reasonable building skills in the family (we've renovated several houses before, done basic bricklaying etc). Is this a job a good non-professional can do? Mostly I'm concerned about the structural integrity of the wall if we start removing and then replacing bricks. I can't see an issue as long as we're careful but just want to get a second opinion.

 

3) Since we have the floors up in the house, I think we could do (2) internally. That is, remove the bricks sections from the internal cavity wall rather than externally. This means we won't have to be as neat and tidy with the finishing when putting the bricks back. I can't see any issues with this but again just wanted to double-check that this is okay to do, and there's no reason for having to do it externally, given we have convenient access to both sides of the wall at the moment.

Thanks in advance for any advice! 🙂

Edited March 31 by Rich_R