Insulating single skin wall - garage conversion

[Notch7]

Here's the principle.

You would use polythene vertically and across the floor, and lap and tape the joint as shown. You are making a floating floor, so ignore the joists, and just butt up to the frame.

I'm confused that you mention using a breather membrane. Was that to be used instead of polythene? If so you will need to construct the frame first and then staple the membrane to the back then fix the frame. Awkward. And strictly, if using membrane you would need a minimum 25mm vented cavity for it to work. I suppose you could have the membrane tight up the back of the wall, but it's a bit non standard, and you'll need to be careful with the detailing. You'll also need to fit a strip of polythene to the frame first, which will lap the floor DPM after the frame is fitted, and then the membrane over the top of the polythene.

Hi Woody, that seems like a good method, would BC be happy with that detailing in your experience?

The way youve detailed the DPM has to work, in my mind, as any water ingress or condensation can only run down to the floor and get trapped below the DP

I ask because I am doing similar in the autumn and if I could avoid a cavity, I would as space is awfully tight for the bathroom room.

cheers Notch

 

[0Floz0]

Here's the principle.

You would use polythene vertically and across the floor, and lap and tape the joint as shown. You are making a floating floor, so ignore the joists, and just butt up to the frame.

I'm confused that you mention using a breather membrane. Was that to be used instead of polythene? If so you will need to construct the frame first and then staple the membrane to the back then fix the frame. Awkward. And strictly, if using membrane you would need a minimum 25mm vented cavity for it to work. I suppose you could have the membrane tight up the back of the wall, but it's a bit non standard, and you'll need to be careful with the detailing. You'll also need to fit a strip of polythene to the frame first, which will lap the floor DPM after the frame is fitted, and then the membrane over the top of the polythene.

Thanks that’s really useful.

Well the building regs chap said that because I’m putting a timber frame against single skin wall it needs a breathable membrane to let any moisture in the wood frame out. He said I can’t use polythene. I’ve got a gap of about 20mm. Between the frame and the wall. Think membrane is about 3mm so it’ll be more like 17mm.

 

[Mr Chibs]

3mm thick membrane... what is it, the one I was thinking of is more like thin card?

Are you talking tanking? as I didn't think that was breathable.

 

[0Floz0]

3mm thick membrane... what is it, the one I was thinking of is more like thin card?

Are you talking tanking? as I didn't think that was breathable.

It’s tyvek house wrap

 

[Mr Chibs]

Don't think you'll find it's 3mm thick, its like paper, I've got half a roll in the garage.

 

[0Floz0]

Don't think you'll find it's 3mm thick, its like paper, I've got half a roll in the garage.

Ah you’re right. Must have been reading a different spec product.