Must a breathable membrane on a timber wall have an air gap?

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I have done a lot of searching on this forum but have not found a definitive answer so I hope someone can put me right.

I have built a timber summerhouse/log cabin using 28mm thick T&G wall planks. it is double glazed.

The Roof and floor I am happy with and both are insulated and finished.


I want to line the walls with plasterboard (top half the walls) and T&G Cladding (bottom half of the walls) its going to be a pub of sorts.

Is the best course of action, working out to in:-

Outer T&G wall planks
Breathable membrane
Insulation (between battens I will fit)
Vapour barrier on top of battens
Internal cladding / Plasterboard

do I really need an air gap between the breathable membrane and the outer wall planks? just this will mean losing even more space inside cabin as I will already be losing around 50-70mm with the above arrangement.

My main requirement is to avoid is dampness and condensation, I don't want mould on the plaster board as I want to wallpaper it. heat retention is a close secondary requirement.


thanks!
 
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Not clear about the wall construction - is it done with vertical timber studs?
 
The inner or outer wall?

Outer is horizontal 28mm thick T&G planks interlocked onto one another like a lot of 'log cabins'
Inner will be plaster board and cladding onto battens.

I'd assume they would need to be horizontal for the cladding to attach to.

Cheers
 
If you mean a gap between membrane and sheathing the answer is no. The membrane is normally fixed direct to the sheathing with stainless steel staples or similar.

Crossed with your last post - the above is a different construction.

I don't think any breather membrane is designed to work in the position you propose. It sounds to me like you would need to batten the t&g boards and then membrane, then insulation. but the battened gap between membrane and boards will need to be vented.
 
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Hi,

not sure what you mean John but hopefully these pics may explain better.

the cabin I have is constructed like the one in the image attached.

I want to create an interior similar to the image attached. Plasterboard or ply upper half of the wall to be plastered or wallpapered and a T&G cladding on the bottom half.

The final image is what I was hoping would be ok. My concern is does there need to be an air gap between the outer wall in this diagram and the 'red' breathable membrane with this particular setup?

thanks again
 
So a membrane does require an air gap hence the battens in the last posters mail.

Cladding - battens - membrane (the air gap being between the battens and the cladding)
 
So a membrane does require an air gap hence the battens in the last posters mail.

Cladding - battens - membrane (the air gap being between the battens and the cladding)
Yes. Requires battened air gap on the outer between membrane and cladding but not on the inner which would normally be membrane tacked to sheathing.
 
I have come across this form of construction of interlocking planks and it suffers from an inbuilt problem. The problem is as the boards rest one on the other, expansion/contraction of the wood due to its water content, causes the height of the walls to change with humidity. With conventional wooden buildings the external planking has provision for the change of the wood dimensions.
The suppliers actually say not to fix vertical supports inside the walls or the walls will buckle.
The other problem is with "short" planks, like between a window and the door as the planks are floating about.
My son in law has a garage with windows and a side door in it and the door has never fitted properly, because the door can not be fixed to the side planking, so it moves about. As far as I can see it needs metal straps with slotted holes fixed to the inside of the planking, so it can only move vertically and not sideways.
I would never buy one.
Frank
 

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