breathable membrane for garden room

[jonnypron]

Hi, I need some advice if possible on the best type of membrane for a timber framed structure for a garden office.

I was going to have the stud wall, membrane, battens, then ply cladding sealed with Osmo oil. Parts of the cladding might be open joint cladding with vertical battens, but am aware some of the membrane behind will be visible in the shadow gap, so need black membrane without all the branded writing all over it.

Heard Tyvek is a bit overpriced as it's the one everyone goes for / knows about, but isn't necessarily the best.

I am also unsure if the flat roof (1:60 pitch) requires membrane? Was intending on cold roof with the insulation between rafters, then air gap, then OSB and EPDM on top.... Maybe Vapour barrier before plaster ceiling or at least use foil backed insulation instead.

Any advice much appreciated.

Thanks

 

[John D v2.0]

Are you using a tried and tested design for the walls and roof or designing yourself? Of you get the wrong membrane in the wrong place you can cause problems rather than solving them.
Your external membrane shouldn't be directly exposed to the weather so whether it is branded or white shouldn't matter. The sun will eventually destroy it.
You would need to cover the gaps in your cladding somehow to protect it, perhaps a batten at the gap, but I'm not a pro.
If you've a ventilated cold roof you would have a membrane on top, it's basically stopping water coming in and is also the waterproof layer (ie felt or fiberglass). Any water that gets through the insulation from inside would evaporate due to the ventilation before it condensed anywhere.
If you have a high risk room such as bathroom it might need something inside.
Normally you'd do a warm roof to avoid thermal bridging through the joists, but I guess you've ruled it out on head height? Consider putting insulation under as well as between the joists.
Good luck!

 

[jonnypron]

Are you using a tried and tested design for the walls and roof or designing yourself? Of you get the wrong membrane in the wrong place you can cause problems rather than solving them.
Your external membrane shouldn't be directly exposed to the weather so whether it is branded or white shouldn't matter. The sun will eventually destroy it.
You would need to cover the gaps in your cladding somehow to protect it, perhaps a batten at the gap, but I'm not a pro.
If you've a ventilated cold roof you would have a membrane on top, it's basically stopping water coming in and is also the waterproof layer (ie felt or fiberglass). Any water that gets through the insulation from inside would evaporate due to the ventilation before it condensed anywhere.
If you have a high risk room such as bathroom it might need something inside.
Normally you'd do a warm roof to avoid thermal bridging through the joists, but I guess you've ruled it out on head height? Consider putting insulation under as well as between the joists.
Good luck!

Thanks for your help. I am doing a cold roof, but might put insulation under the joists i.e. before the plasterboard on the warm side, but warm roof will just take up too much height.

I wasn't intending on putting membrane above the rafters, just the OSB and EPDM directly on top of that? I've just followed some diagrams from other structural plans? The only other thing I'm unsure of is, as you say, where to finish the membrane where the sides meet the roof? do you overlap it with the EPDM flashing kit over that?

What system is used where I've seen vertical battens with gaps i.e. open joint cladding, with the membrane visible underneath in the gaps? you can often see the horizontal counter battens in this setup as well?

 

[John D v2.0]

Yes the OSB and edpm will be a good external barrier. You only do another barrier if the outer layer isn't weather tight eg tiles.
Regarding the edge detail, you might be able to get answers from the roofing forum here.
Regarding the vertical cladding, I know what you mean, perhaps some membranes are specified to be UV resistant, edit here's one http://www.dupont.co.uk/products-an...ucts/tyvek-uv-facade-rainscreen-cladding.html

 

[jonnypron]

Yes the OSB and edpm will be a good external barrier. You only do another barrier if the outer layer isn't weather tight eg tiles.
Regarding the edge detail, you might be able to get answers from the roofing forum here.
Regarding the vertical cladding, I know what you mean, perhaps some membranes are specified to be UV resistant, edit here's one http://www.dupont.co.uk/products-an...ucts/tyvek-uv-facade-rainscreen-cladding.html

Thanks for advice. Didn't think about UV requirements... that must be the way it's done. Will think about posting in the roofing forum for specifics about the edging detail. Thanks again.

 

[John D v2.0]

No problem, sounds like an interesting project! Have fun!

 

[John D v2.0]

Sorry just realised we are in the roofing area, thought this was building! Wait and someone will answer soon I'm sure!

 

[jonnypron]

Not sure if anyone has any experience with Klober Permo Frame Breathable Membrane but have just ordered some from https://www.aboutroofing.com/permo-frame-breathable-membrane-50mtr-x-1-5mtr.html and it's unbranded? Not sure which side is the external i.e. cladding side and which is the insulation / stud wall side. I want to be sure it's the correct membrane as all the photos show it being branded.

Also am unsure of the overlap as some have tape or marks on them. Would 300mm overlap suffice?

Thanks in advance.