shed insulation

[David729]

I have an 8' by 5' wooden shed which I plan to insulate. It's constructed of tongue & groove and the studs inside are 1.75 inches (45mm) deep.

I don't want to make it much smaller inside so I'm thinking of putting the insulating material between the studs and then screwing plywood onto the studs. From reading earlier threads I see that I need to leave a ventilated airgap between the insulation and the t&g. Is it realistic to accommodate reasonable insulation and an airgap within the 45mm depth of the studs? I was thinking of using some sort of kingspan type boards.

Thanks

David

 

[JimLoskot]

why would you need a gap?
I would of thought if you put a vapour barrier both sides of the insulation it would be fine.
Why are you insulating it? it pretty pointless unless you are heating it

 

[David729]

It will need to be heated in winter it when I am working in it and at other times I want to keep the inside above freezing point. I've read elsewhere that it's better to have an air gap between the wood and the insulation to allow any penetrating moisture evaporate, but maybe that was only when using mineral wool and won't be necessary with kingspan etc.

 

[freddiemercurystwin]

You ought to retain an air gap behind the T&G so that it does not rot, theoretically this gap should be open at the top and bottom (though it will probably have enough gaps in it to allow ventilation). Normally you would fit a breathable membrane over the studs before you fit the T&G; to keep the studs dry and preventing them from rotting. However as your T&G is already in-situ you cannot do this and how you can suspend such a membrane away from the T&G would also be difficult. So preventing your studs from getting damp will be impossible but as long as you don't expect the shed to last 50 years you'll be OK.

So if it were me I would be fitting say 30-35mm Kingspan flush with the studs (foil facing inwards) and then tape over the joints/across the studs with foil tape, then fit your ply over this. This is about as good as you'll achieve without losing any space internally or removing the T&G.

 

[David729]

Thanks for that, very helpful. I'll give the studs a good coating of preservative to try and delay rot. When you say 'foil facing inwards' I take it you mean facing the inside of the shed?

 

[freddiemercurystwin]

yes

 

[jpjsavage]

And can anyone recommend a suitable breathable membrane for this project? I'm doing something similar and I'm confused about the various types.

 

[freddiemercurystwin]

How are you going to keep the vapour barrier in position? To be effective it needs to go between the studs and the T&G.

Haven't we been here before?