Insulating bay window walls

14 Nov 2012
Reaction score
United Kingdom
Hi all, I've been reading posts on this site for a while but this is my first message..

Our house is a 3-bed 1930s south-east-london semi with solid walls and we get pretty bad mould on the inside of the first floor bay window. (similar on the ground floor, though not quite as bad)

The bay wall in question is about 2.5m wide by about 1m high. It sits beneath new-ish UPVC double glazing without trickle vents. And had a small-ish radiator in the middle of it.

I've taken off the radiator and I reckon without moving the pipes to it I've got about 15-18mm to add some insualtion to the wall behind the radiator before refitting and redecorating it.

The aim of this bit of work would be purely to stop further condensation & mould on the wall rather than make much of a difference to total house insulation.

What I've got in mind is to put 10mm square vertical battens on the wall, some kind of insulating material - TBC (just air maybe.. recommendations welcome!) - between the battens, vapour barrier sheet on top of that (sealed on all sides), 5 mm ply on top of that then a plaster skim, paint and refit radiator.

What do people think? Will this 1. be warm enough to reduce condensation (and therefore mould) and 2. be an adequate design to prevent internal condensation that causes problems that I can't see?

Sponsored Links
I'd take everything back to the brick and then attach some insulated plasterbord as thick as it will fit. This shoudl solve everything as products such as Gyproc Super have a built in vapour barrier.

I'd normally fix it on 25x50mm battenns but for such a small area you might get away with dabbing it straight on.
Thanks. I should have added that the bay walls are curved - or I'd definitely just use an off the shelf insulated plasterboard. Taking back to the brick would give me a bit more room though.
Sponsored Links
Waste of time and money, you need better ventilation to prevent condensation.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local