Mould inside external walls

hessodreamy

I've been noticing mould accumulating in rooms with external walls. I'm getting the cavity insulation looked at which might help with some walls but for other rooms I'm not sure what to do.

Here's the front bedroom. Mould on the wall behind some drawers:



Also some mould on the ceiling (which I've cleaned off now but circled in this picture:


These 2 points relate to these points outside:


Is it likely to be normal room moisture not being able to escape? Should I avoid having drawers next to an outside wall? Is it likely there's a leak in the tiles or flashing? 

I'm also looking at getting trickle vents installed in the windows. How much would that help?

ThisIsWeird

I suspect a combination of two things - lack of insulation in these two areas, meaning they will be the two coldest spots in that room - and, for the wall, having a unit close to it will reduce ventilating air flow across it which would otherwise help to keep it dry.

I can't see easy access to either wall section from behind, so the solution would be to either add a layer of rigid insulation to the inside surfaces, something like Thermal Plasterboard, or to first remove the existing p'board to gain access to behind, and filling between the studs with rigid insulation before over-boarding.

If you do the whole of that external wall, you should notice a much easier bedroom to heat up. I'd insulate the flat bay ceiling too.

Lorian

Plus use and extractor fans rigorously in showers and kitchen. Get a cheap hygrometer and dehumidify or ventilate to keep relative humidity below 60%.

FreeBear

ThisIsWeird said:

I suspect a combination of two things - lack of insulation in these two areas, meaning they will be the two coldest spots in that room - and, for the wall, having a unit close to it will reduce ventilating air flow across it which would otherwise help to keep it dry.

I can't see easy access to either wall section from behind, so the solution would be to either add a layer of rigid insulation to the inside surfaces, something like Thermal Plasterboard, or to first remove the existing p'board to gain access to behind, and filling between the studs with rigid insulation before over-boarding.

If you do the whole of that external wall, you should notice a much easier bedroom to heat up. I'd insulate the flat bay ceiling too.

Walls under an upstairs bay are often stud construction with a little bit of insulation in the void if you are lucky. Judging by the style of the bay, I'd hazard a guess at this being a 1940-50 building. So internally, lath & lime plaster on the bay wall. Knock that off, insert 50mm Celotex boards between the studs and use plenty of expanding foam to seal any gaps with a foam gun. Screw a 50mm wide batten to the uppermost stud and stick a 65mm thick sheet of insulated plasterboard (use PIR/PUR rather than XPS) under the batten. Give it a skim of Thistle, and paint. You could go thicker and get a decent width for a window sill (150mm is about the limit).

Skirting & laminate flooring will need to be removed, and if you can extend the insulation down below the floorboards, that will reduce cold spots forming in that area. The double socket could be put in to a flush mount back box - Depending on how much slack is in the cables, placed a little higher on the wall.

Ceiling could be tackled from outside, but that would need scaffolding to do it safely. From the inside, rip down the plaster (along with laths if used). Follow the same process as used on the wall.

hessodreamy

Thanks for the info, all. I'm in the process of redecorating and plastering anyway. The plasterboard under the window started to come away when I took the skirting off so I decided to go the whole hog and rip off everything under the window to get some good insulation in (there was none). Also going to not keep a set of drawers there! 

ThisIsWeird

hessodreamy said:

Thanks for the info, all. I'm in the process of redecorating and plastering anyway. The plasterboard under the window started to come away when I took the skirting off so I decided to go the whole hog and rip off everything under the window to get some good insulation in (there was none). Also going to not keep a set of drawers there! 

Good move.

If you'd like to show some photos of the exposed wall, folk on here can guide you further if you need.