# Should I use Building Fabric Behind Larch Weatherboarding?



## davethebb (19 May 2022)

My build is 100 x 50 stud work, 95mm PIR between, and 11osb on the outside (glued and screw in place). The PIR will be tapped on the inside and eventually there will be cladding (probably 9mm ply) on the inside.

The outside of the 11mm OSB will be battened vertically and the horizontal weatherboard cladding fixed to this. Is there any benefit in wrapping the walls in building fabric?


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## Jones (19 May 2022)

Not really needed the OSB sheathing is a vapour barrier anyway and will be ok if some water gets behind the cladding and on to it as long as the cavity is ventilated. You could have missed out the OSB and saved a bit of cash.


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## eribaMotters (19 May 2022)

davethebb said:


> My build is 100 x 50 stud work, 95mm PIR between, and 11osb on the outside (glued and screw in place). The PIR will be tapped on the inside and eventually there will be cladding (probably 9mm ply) on the inside.
> 
> The outside of the 11mm OSB will be battened vertically and the horizontal weatherboard cladding fixed to this. Is there any benefit in wrapping the walls in building fabric?


I do like to hear when a job is being done correctly.

Colin


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## Jameshow (19 May 2022)

You could put the osb inside and fabric outside??


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## Fitzroy (19 May 2022)

If you can make the change as Jameshow mentions with OSB inside and fabric outside that would be the optimal solution.


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## MikeJhn (20 May 2022)

Look up "Canadian Rain Wall" for the definitive solution to a wooden building's construction.


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## Br5d (20 May 2022)

It really depends on how long you want it to last. Breather membrane will help protect the osb from water damage.


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## Jones (20 May 2022)

Br5d said:


> It really depends on how long you want it to last. Breather membrane will help protect the osb from water damage.


Or equally it may hold water against the OSB, when it's laid directly on boards not spaced off with battens this is more likely to happen. Cavity venting as per Canadian thing is important to reduce moisture in the cavity, insect mesh to the top and bottom is worthwhile to keep wasps out.


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## Lard (20 May 2022)

I don’t think I’d be using, or trusting, OSB as a vapour barrier, especially if used externally.

Counter batten and ventilated space for me every time.


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## PeterSH (20 May 2022)

I would use OSB 11mm on the inside and that is your vapour barrier. Not 100% but close enough for the workshop.

Then insulation between the studs.

Then wrap the outside of the stud work with a breather membrane which lets any trapped moisture escape.

Then batten and clad but not OSB on the outside as it's not breathable.


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## Molynoox (20 May 2022)

Anther added advantage of OSB on inside is it's easier to attach stuff to it.
No need for pattresses.
Martin


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