DIY Doctor

Insulation order for single brick airgap distance

Postby MWCDE » Sun Jun 07, 2020 11:28 am

Hi all.

I've been looking at converting our detached garage into something of a play house for our son. Nothing too major but I keep reading different ways of doing the insulation.

It's a new build (2018) detached garage with single brick and slab floor. BPM is visible two bricks up from floor. I'm assuming a DPM is also under the slab somewhere.

The way the garage is built is that it's not square, it's got breeze block corners and middle posts so its going to require some off spaced\shaped design work at the edges which is fine.

What my plan is to...

DPM 1000 gauge between anything that touches either brick or slab.

Treated CLS 38x63mm for the batten frame floor.
CLS 38x63mm for the rest of the frame.

Integrated breathable membrane between the brick and the frame (Question - What distance does this need to be from the brick for the air gap?

50MM Kingspan to fill the batten frame. (is this enough?)
Plasterboard the frame.

I could use 38x89mm CLS timber which allows the use of 75mm Kingspan.

Does this sound ok?
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Simply Build It

Postby B4Less » Tue Jan 12, 2021 8:49 am

It's good that you can see the DPM as that means your floor is watertight and that the DPM is under the floor. You should use a proper DPC membrane for anything that touches the concrete or block. Although the 1000g DPM is similar, DPC is better. If you need something to cover the floor then use DPM but no real need as it seems to be already there. Another layer of DPM could just trap moisture. Typically a 50mm air gap is required in a cavity. I would fix the breather membrane to the inside leaf of the timber-frame in the cavity. 50mm PIR (Kingspan, Celotex, Ecotherm etc) is enough. But the more the better. Also depends on what is under the concrete floor. If there is nothing under the concrete floor then I would go 75 to 100mm at least. Other than that I would say you are on the right track.
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