breathable membrane

[tatydt99]

Hi I have just had a shed put up and I'm getting ready to insulate it. But I'm not sure what to do with the breathable membrane.
I know now it should of been put on under the cladding but the company that built it didn't have that as an extra.
So I'm thinking about putting some 25mm battens on the inside to make an air gap and attaching it to them does that sound right.

I have seen a couple of ways to put it on and I'm not sure what one is correct in-between the uprights or over them I have added a picture of both ways.

Thanks for any help

 

[erikhar]

Really annoying that the installation company did not have that as an option!

I am no expert in this area, but I have been exploring options and doing a lot of reading on the same subject as I have an older building with the same situation. On the insulation - yes sounds like you are on the right track - are you going to use a foam type board or a rockwool type? I would say that if you use a foam type board (the type with a silver coating) then your membrane issues are less critical from the perspective of keeping the insulation dry - but your measurements will need to be spot on to get a good tight fit.

Regarding the membrane - most people recommend removing the cladding but suspect you don't want to do that (neither do I) - I would say your second option of over the uprights seems to be the best as it really reduces the chance of any ingress through the wood or any gaps that might open up - I would go with this option especially if you are going to invest in a high quality interior finish.

That said - it would be good to hear from anyone on here with longer experience in such matters.

 

[harryc]

I wouldn’t bother with the membrane, just put your battens up between the vertical joists and use pir insulation, use expanding foam where you have gaps and remember to cover your joists with aluminium foil to stop thermal bridging.

Cover the lot with osb board and you have a excellent barrier preventing moisture inside the shed condensing behind the insulation.

 

[Fitzroy]

In a traditional build the breather membrane prevents drafts from the outside and keeps any rain that penetrates the cladding off of the insulation and fabric of the building. In your situation both solutions help with drafts, but the back of the stud work will be exposed to any penetrating water, so the membrane doesn’t help there. It will keep your insulation dry in both cases but I’d only be bothered about that if I were using rock wool or similar. With PIR (Kingspan) I’d just batten the air gap on the cladding side and foam the gaps around any board.
Fitz.

 

[Fitzroy]

your bigger challenge will be the roof. You’ll need to ensure ventilation into the cavity above the insulation.
Fitz.

 

[mikej460]

After the insulation is in you will also need to staple a vapour barrier across all studs and rafters i.e. on the warm side, overlap all joins by 100mm and tape together. You can get this from Screwfix

 

[Sheptonphil]

Or use OSB boards, as they act as vapour barrier and provide an excellent medium to hang all manner of things from.