Mould in Roof space - bad insulation install.

19 Nov 2006
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United Kingdom
Hi all, I have a query I can't seem to find the answer for yet:

Story so far: We have a 1930's granite chalet style house (first floor is slated hipped roof with dormer windows at front). We moved in over a year ago and as the house is next to a busy road we had someone install sound proofing in the attic space between rafters and joists, this seemed to work quite well and damped down a lot of noise from passing trucks etc. However, recently I was up there and knocked off one of the Rockwool panels accidently and was horrified to find mould and damp timbers. I went round the rest of the rafter bays and found about 80% of them had mould and damp.

I also found that the installer had shoved the old fibreglass insulation down each bay thereby blocking any airflow up to the attic from the soffits below.
He had left a 70mm gap between the Rockwool (RW3 I think) and the underside of roof, but had tightly pushed the rockwool up against the vertical ridgeboard in the apex of roof. As there are no ridge vents there was no way any air was going to flow through the roof.
I've since dried the area out with a dehumidifier and started cleaning with P0lycell 3in1 Mould killer.

My question is can I (or get the installer back) to reinstate the insulation without the blockages in the eaves and leave say 100mm gap at the top of the insulation near ridge to allow air to flow from one side of the roof to other?
Also, as the roof is hipped all sides it forms a pyramid shape with long ridge, thus leaving 4 corners with about 4 bays each corner that form a point that cannot get ventilated, should these be left open or reinstated with rockwool sniped at top again with say 100mm gap? Would there be enough airflow through the roofspace to ventilate these corners?

I've also noticed there don't appear to be any soffit vents, so I'm assuming any gaps along the soffits were enough to keep the roof ventilated before being blocked up. Should I be considering soffit vents and high level slate vents and if so how many? We were also going to install insulation between the joists at lower level (i.e. above ground floor rooms), there is a gap between the granite outer wall and lath & plaster inner wall, is it safe to lay insulation over this gap and up to the edge of the wall (keeping the soffits clear)?

So, to sum up, we were looking for insulation of the attic, eaves and voids (both acoustic and thermal - very cold in winter) but need to consider ventilation.

The installer said he would come back to take a look after the roof has dried out, so just after some advice I can use to get him to do the job correctly (which he should've done in the first place).

TIA for any advice and apologies for long post...
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Particularly the bits about the corners in hipped roof and the gap between walls (we're about to put insulation between joists here as it so cold in rooms below).


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