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I have a shed framed with 2x2 batons, clad with 17mm Cedar. I want to insulate it to use it as an office. I have read good things about celotex GA4000 and its cheap.
The diagrams on the celotex website show a cavity in the diagrams. Is this necessary or not, because the thinnest board is 50mm and my walls are only 50mm thick (without adding more depth to the walls, more wood, more cost).
Do i need to add a damp membrane at any point?
the gap is to allow air movement and prevent conduction.
When you dry line the walls you could always stand the board off the stud with some strips of 12mm ply.
TBH for a shed though, I wouldnt worry.
I used 3x2 on mine so have an 1/2 inch space on each side of the insulation. I didnt use a membrane.
BTW you can get xtratherm in 40mm too, which will be nearly as effective and would give you the gap.
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Stoner? Why did you decide not to use a membrane? Is it recommended?
Why did you decide not to use a membrane?
because it's just a shed. I get no water ingress and there's plenty of air movement behind the featherboard. On the gable end of the barn, that's a different matter.
Final question. If you had of used a membrane, where would it have gone?
That shed has brick walls, isnt a shed defined as a free standing building needing no planning permission? Did you need permission for that Stoner? Just thinking ahead
membrane goes on outer face of stud, underneath cladding. Ensure that the membrane finishes outside of your lowest damp ingress point - for me, that would mean hanging below the top of the highest brick. For you it might be hanging past the slab/floor.
Start at the bottom so that you can overlap as you go up, like a roof tile.
RD - yep PP for that one as part of whole barn build works.
the gap is to allow air movement and prevent conduction.
Nah, it means the circulating air can get the moisture out that condenses on the boards - if anything a drafty gap increases thermal losses.
I love this forum.
😳 meant absorption of water, not conduction ....
what your looking at is interstitial condensation, i think the simplest way to understand what is happening is to imagine a glass filled with a cold drink from the fridge or a bathroom window. You find a sharp change in the air temperature at the surface which results in the air being unable to carry the moisture resulting in condensation.
What you are trying to do is control this condensation so that it i does no damage. This can be done via a cold or warm construction just a matter of the correct amount of insulation to ensure the dew point temperature is in the right place in relation to the structure.
I would allow a 25mm gap between the boarding and the insulation so that you have a free space for air movement. If shiplap then I don't see any need for a membrane behind but if feater edge then it would be adviseable.
Can't remember off hand which insualtion code is which but there are three or four that all all the same insulation just different codes. I think it was the general floor one that comes in 30mm or so.. could be worth a pop