Insulating bay

Looking for advice on thermal insulation, needs to be fairly non messy.

I've a 1930's semi detached house that's got bay windows, the downstairs is fine, cavity wall under the window and the cavity is filled with insulation but upstairs it seems to be a plaster lath construction with the outside being roof tiles nailed to some kind of frame over a waterproof membrame.

Given the horrific rise in energy costs I'm trying to insulate and draught proof as much as possible and wondered if anyone could give some advice on how to insulate this sort of mess?

Preferably without resorting to ripping it all out and starting again if possible so some kind of internal fixing insulation. The interior of the bay isn't really seen but I'd like to be able to decorate over it.

I'm thinking some sort of polystyrene or expanded foam sheet?

Reply to
Clint
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Could you drill holes on the inside and have it filled with blown fibre ? You may be able to locate the vertical studs with a detector to get the holes in the right places. That how I had my tile hung walls done, from the inside, but they are ordinary cavity, not lathes.

Andy C

Reply to
Andy Cap

Hi,

The best answer is celotex (which is a brand name, but the actual material is manufactured by many others: Celotex, BallyTherm, Kingspan).

Twice the efficiency of glass wool depth for depth, easy to work with.

I did my bays, but I ripped the ceilings off and installed between the rafters. Even 2" thick of the stuff prevents snow melting on the lead above.

If you don't want to tak ethe ceilings out, you could put 1", 2" or 3" thickness onto the existing bay ceiling depending how much height you re happy to lose.

Then put a sheet of plasterboard over that and repaint.

You can fix the celotext into the existing rafters with screws and large spreader washers (sold for the job, usually plastic, sometimes metal, about

3cm diameter.

Then screw the plasterboard with suitably long plasterboard screws through the whole lot again into the rafters.

You can also fix with PU foam adhesive but in this case you will have to suppport everything for 30-60 minutes while it sets.

As another option, you can buy a premade plasterboard/celotext composite (Kingspan I think).

Wickes sell celotex in small quantites and half sheets.

HTH

Tim

Reply to
Tim Watts

I assume you wish to insulate the bay wall under the window, not the ceiling above? I have a similar 1930's semi, with the same arrangement. Upstairs the wall was the same thickness as the uPVC window, no sill on the inside. I created a wooden frame by screwing 50mmx50mm timber to the inside of the bay, 6 straight sections make up the bay shape, then filled with rockwool insulation, and fitted plasterboard over the top. (I also fitted an MDF window sill screwed to the frame, plasterboard between underside of sill and floor). Skimmed over the joints and decorated.

End result much warmer. If doing the job again I'd use Celotex or similar for it's superior insulating properties over rockwool.

Reply to
AlanD

In article , AlanD writes

These days I'd be inclined to glue an inch of celotex inside and then face that with some 6mm MDF, again fixing with glue[1]. Some light caulk type filling should give a good finish in short order and seal any gaps against draughts.

[1] Using one of the 'sticks like' variants
Reply to
fred

I'd avoid polystyrene foam, in a fire its a killer. PIR foam is much safer, insulates better, and of course costs more.

NT

Reply to
NT

Agreed, for this application glued on foam would be sufficient, and not leave insulation bridges.

Reply to
AlanD

I don't think there's a cavity to fill, I think it's just a single skin and not even of brick, rather a thin wooden construction with tiles hung on the outside and plastered on the inside :(

Reply to
CJ

Good point, I mentioned polystyrene as I didn't really know how else to describe what I wanted but thanks, yes, definitely a bad choice

Reply to
CJ

What you want is polyisocyanurate

NT

Reply to
NT

I assumed that was what he meant by PIR

cost that means in my DIY book 'passive infra red' as applied to automatic light switches.

Reply to
The Natural Philosopher

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