dryling with insulation inbetween studs

I'm just about to embark on this, builder has fabricated the stud wall with

3 x 2 set just off the 13" brick wall. Perceived wisdom is to squeeze the 65mm celotexlike boards in between the studs and flush with them and fix plasterboard over this. This makes sense in that the plasterboard gains some support and is what the insulation manufacturer recommends. From an insulation point of view wouldn't it make sense to have an thinner air gap either side of the insulation as the thinner gap would be less likely to transfer heat by convection currents?

AJH

Reply to
andrew
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I would think the insulation value of the air-gap will be insignificant compared to 65mm celotex.

However with celotex, you pay pretty much for thickness - so not much price-difference between 25mm plus 40mm, and 65mm. But two layers would mean you can install a continuous layer behind the studs (or ideally, the whole lot, if you can afford the loss of room-space).

(I'm assuming you're insulating a solid masonry wall).

Extra space in the depth of the studs also useful for cable routing.

Reply to
dom

In article , andrew writes

Sounds good.

Nope, air movement undermines insulation. Make sure there is no path for air from the cold (brick) side of the insulation to warm (plasterboard) side. This is normally done with wide foil tape to cover joints and small gaps with expanding foam to fill larger gaps.

Def don't do what some hired 'friends' did to a chum's installation, used misc offcuts to make up insulation in panels, free to rattle and with nothing sealing the gaps. Air was free to move around the whole lot, negating the insulation.

Watch out for any gaps top and bottom that might allow cold air to pass to the inevitable small (hopefully tiny gap) between the insulation PB.

Make sure that the insulation is well fixed in place, you don't want to use a plasterboard fixing in the future for a shelf and find yourself pushing the insulation backwards.

Reply to
fred

Thinner than what? You get far more resulting insulation with no gaps for air to blow through. If you're using rigid boards, use foam to fill any little gaps.

NT

Reply to
Tabby

I was not meaning gaps front to back, this will all be well sealed.

The recommended method is Brick : airspace : insulation : plasterboard.

In my case there will be a >10mm air space.

I was wondering if better insulation effect would be had by

brick : >5mm airspace : insulation : 5mm air space : plasterboard.

The builder insisted on the stud work because the old brick wall was so badly pocked and spalled that the time truing each plasterboard with dot and dab would have increased labour cost more than the cost of the stud wall.

AJH

Reply to
andrew

Ah! Yes, your way would give more insulation, but the amount of difference it makes is fairly trivial once you've got a good layer of celotext in there. I'd do as you suggest only if it doesnt increase labour.

Celotex around R=3D1 per inch, so maybe R2 if you put 2" up. Air cavities, I forget, 0.12 or something, so about 6% difference.

NT

Reply to
Tabby

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