Stud Wall insulation

[gremlin_95]

Hello all,

I have got some spare 40mm Celotex sheets left from a previous project and was wondering if there would be any benefit gained in using them for the stud walls in the converted loft.

The said walls are already insulated with 100mm mineral wool in between the studs and I'd prefer to leave that in place.

The Celotex would have to go on top of the existing insulation/over the studs provided there is nothing wrong with doing this? Is this a reasonable thought or have I gone completely mad? ;)

Cheers,

[fred]

In article , gremlin_95 writes

No problem, that's a perfectly normal way to do it, particularly if there is a need for extra high insulation where insulating over the studwork avoids the problem of cold bridging due to heat passing through the studs.

Prob easiest to tack the Celotex in place using the odd screw with a penny washer under the head to stop it putting through, screwed just flush, then you'll need plasterboard over the top to get a decent finish. Fix the PB through the celotex into the studs using extra long plasterboard screws as they wont tear up the PB paper like normal screws. Easier to find the studs first and draw a line down the celotex and a little over at the ends to still be visible when you offer up the PB.

[gremlin_95]

Hi Fred, thank you for your reply.

Perhaps I should have made it clear that this stud wall is pre-existing and it already has PB covering the insulation. I was thinking of fixing the Celotex above this PB and then boarding it again but I can't really afford to lose that much space and it would be quite a lot of upheaval.

There is access *behind* the stud walls so the plan was to put the Celotex over the studs/insulation from behind.

[fred]

I did wonder :-)

Yes, that will work but the difficulty may be in getting the rigid board behind without chopping them into tiny pieces, they wont bend. Get some foil tape (cheap at toolstation) to re-tape the joints when reassembling. Make absolutely sure that you can't get any draughts circulating on the room side of the celotex between it and the fibreglass or it will be a wasted effort. Less risk of this if the fibreglass is filled to full depth or you can hand stuff a bit of extra fibreglass in at the edges or use foam but the gaps may be a bit large, say at the bottom where the joists meet the studs.

[fred]

In article , fred writes

Sorry, forgot to mention that the screw with penny washer under the head is again the easiest way to fix.

[gremlin_95]

There is actually quite a lot of room behind the stud walls which is used for storage, the boards are not the 2400x1200 size; they are 1200 x

450 so getting behind in one piece isn't a problem. I have plenty of tape and expanding foam left over from the previous project so I *should* be OK.

OOI, could I insulate the roof part of a bay window from the inside? The whole house has external wall insulation but the front lounge with the bay window is still a bit cooler.

[fred]

In article , gremlin_95 writes

I don't see why not but the ceiling may not be the most significant loss and so may not be worth the effort. Maybe calculate the area of glass, area of wall under the glass and compare it to the area that you will insulate. I'd expect you to be losing more through the glass.

In IR thermometer would be a good toy to play with to see what is the coldest surface around there as that will likely be losing most. You can measure the surface temp of the glass by adding a bit of insulating tape to the pane and then targeting that. A 20mm sq piece is fine if you place the lens hole in contact with it.

If you do go ahead then you will need some sort of surface finish under the insulation (PB or ply). I tried cutting corners in putting up some celotex in a utility and not plasterboarding it over and despite taking great care to get all the joints smooth and level it is very noticeable (to me) that it is a bodge.

[chris French]

In message , fred writes

I think it's one of those jobs that's worth doing as part of something else, but not necessarily otherwise.

So I did ours in our old house when they we being skimmed, as I was overboarding the ceiling anyway. worth looking at the walls as well. Our downstairs one was single skin brick IIRC (certainly solid anyway) and the upstairs was tile hung over a wodden frame, lathe and plaster inside

[gremlin_95]

Cheers, I will get some reading with my IR thermometer this weekend.

[gremlin_95]

I can imagine, wish I had thought of it when it was being decorated.

The walls are 9 inch solid walls, the whole house used to be quite cool and require the heating to be on for ages to keep it warm, however the whole house has been insulated externally with 90mm EPS boards and this has made the place a lot warmer and allowed me to run the CH at lower temperatures :)