Insulating wall under bay windows

[Sikes]

Hello all

Looking for any advice for an insulation idea I've had for my Edwardian house. The wall under our bay window in the bedroom suffers from condensation. Its thinner than the other external walls (stone and brick). The room is usually heated but cant always ventilate as we live on a main road (i.e light sleepers). To stop warm air condensing on the wall I thought about putting a wooden rectangular frame on the wall, putting insulation in it (not sure what) and then covering with tongue and groove cladding. Does this sound like it would work or is a very wrong way to go about it?

 

[Abi Cott]

Welcome to the forum.

Sounds like it would work to me, but it's not a job I've tackled myself so let's see if bumping this attracts someone more knowledgeable.

 

[paulc]

Just finished insulating a solid brick wall here. Fixed 2x1 battens to the walls vertically at two foot centres. Placed a full sheet of PUR sheet up, and then screwed horizontal battens over the top on st 16" centres (again. 2x1 battens). The spaces then filled with more PUR sheet cut to size. Any gaps were filled with expanding foam and all joints taped with aluminium foil. Finished off with plasterboard.

The 1" gap between the brickwork and insulation is ventilated to the loft space and air can get up from the bottom via a gap in the joists. So hopefully, if any condensation does form, it will have a path to dissipate.

Insulating under a bay needs a little more thought, as ideally, the insulation needs to bridge the gap under the window boards. If you don't, a cold spot will form just inside the window causing condensation and perhaps premature rotting of the boards.

 

[Crazycacti]

Got this to do myself soon. My plan is to use a lime/hemp/perlite mix and wet plaster direct. The other thing i'll be ensuring is that the air brick flow goes fully into the subfloor and no chance at getting up any gaps and putting even a small amount of cold air on the wall as that will in time cause issues. From what I see in properties with damp/cold bays, this seems to be the problem a lot of the time. Often hidden by plasterboard.

 

[MatthewC]

Is this wall breathable? I would expect an Edwardian house to have been built with lime rather than cement. It sounds as though it might not be breathable and the condensation is on something like gypsum, in which case I would think that making the wall breathable would largely fix the problem.

Failing that then improving the ventilation would help - two people in a room for eight hours would produce a lot of moisture which has to go somewhere - an issue with most modern boxes which are airtight!

 

[Sikes]

Is this wall breathable? I would expect an Edwardian house to have been built with lime rather than cement. It sounds as though it might not be breathable and the condensation is on something like gypsum, in which case I would think that making the wall breathable would largely fix the problem.

Its not breathable. We knew nothing about how a house of this age needed to breathe until we had finished the upstairs (working downwards). The previous owner had had all of the walls covered in artex (and I mean every wall in the house). We removed this in the bedroom and had the walls covered in gypsum. We've learnt our lesson as we are in the process of removing cement from the internal walls downstairs (one room has been lime plastered). I suppose the best solution might be to go back to our bedroom and take the gypsum off. We are getting more air in, the previous owner hadn't opened some windows in 15 years (don't ask :roll: ).

 

[MatthewC]

Artex? On EVERY wall? Aaaaaaaaarrrrrrrgh!