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I'm building a garden room and I want to attach a breathable membrane directly to the exterior side of my studs using staples and then cover it in some sort of exterior grade plywood sheathing, which will be the finished surface (painted of course).

Are there any issues in doing this as most applications I see have the breather membrane attached to OSB and then cross battered and cladded.

isherwood
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Fony Tinlay
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  • Is this going to be a "unfinished" room without interior walls or HVAC? – JPhi1618 Mar 17 '20 at 17:20
  • is there insulation in the walls? is there an interior wall covering? – Ack Mar 17 '20 at 18:17
  • Will have PIR insulation between studs, an airtight membrane and then plasterboard walls. There will be no internal partitions and will probably use electrical heaters to heat and a ductless ventilation/heat recovery solution. – Fony Tinlay Mar 17 '20 at 18:46

1 Answers1

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I'm not an expert on this but based on what I know about breathable membranes in building construction I don't think you would want to have the membrane on the interior side of the OSB or plywood sheeting. I'm also not sure why you would want to do that.
The problem is that these membranes are water-proof but vapor-permeable. With the OSB between the membrane and the weather you're probably going to have moisture issues and probably mold/mildew problems in the OSB or plywood. So you'd be defeating one of the main advantages of the membrane.

I believe you want to make sure it's attached to the exterior side of the OSB.

Edit
I'm responding to your comment in my answer so I can include a picture.
Most exterior cladding or siding allows air to circulate under it to solve this problem.
enter image description here

If you install plywood in place of siding over the membrane I do think you will still have the moisture issue. You need a space for air circulation.

Second edit

If you attach the membrane to the studs and then cross-batten over the membrane and into the studs and then the plywood/OSB that would give you room for air circulation but structurally I see it causing problems since I don't see the membrane having the structural integrity to properly support the plywood/OSB.

HoneyDo
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  • I agree. See discussions on https://diy.stackexchange.com/questions/186472/how-important-is-tyvek-house-wrap-for-a-house-with-metal-siding/186479?noredirect=1#comment328327_186479. – SteveSh Mar 17 '20 at 15:48
  • Would you not have the same moisture issues between the cladding and membrane anyway? The only reason is cost saving, I'd be putting OSB | membrane | Plywood. By removing the OSB i'd be able to invest the savings elsewhere. – Fony Tinlay Mar 17 '20 at 16:36
  • do not cross batten between the studs and the sheathing as the sheathing is your the source of lateral support and needs to be attached directly to the studs – Ack Mar 17 '20 at 18:15
  • Yeah I'd kinda figured as much regarding the battens creating a circulation void, something similar to the flat roof ventilation. The lateral support had completely slipped my mind, I've been staring at drawings too long. – Fony Tinlay Mar 17 '20 at 18:48