wall questions (timber, insulation, breathable membrane)

[KevGillan]

Hi all

I'm building a shed/workshop, about 3x4m with a timber frame on top of a layer of concrete blocks. Just wondering about wall construction.
What I'm thinking is:
- 100mm timber frame
- internal plywood/osb boards
- then insulation (perhaps 50mm celotex)
- then a breathable membrane
- then cedar cladding (vertical board and batten style)

So, the questions are really about the membrane. Is it really necessary? Can I just staple it onto the timber frame? Should there be an air space between cladding and membrane or between insulation and membrane? Are horizontal overlaps better than vertical ones?
Also, membranes that are specifically for walls (eg Tyvek) seem to be more expensive than roof ones. Can I use something like Vent 3 Light instead?
(http://www.cromar.uk.com/cromar-roofing-products/roofing-membranes/vent3light.html)

I don't want to go OTT on spending as this is an occasional use space, but I do want it to last and be usable in winter.

Any help much appreciated.

Cheers
Kev

 

[Alastairreid]

From the outside in.

Cladding..horizontal!

25x50mm battens,,vertical

building paper

9mm wbp ply

100mm studwork

100mm full fill insulation

vapour barrier

Internal finish.

 

[KevGillan]

Okay, thanks Alastair - sounds thorough.

So the vapour barrier is non-breathable? (I'll probably have enough visqueen left over on the roll from the dpm - suitable?)

I had hoped that decent cladding + membrane would mean no need for external ply. The vertical thing (not sure if board and batten is the right term) is inspired by Norwegian construction. Here's a couple of pics of a boathouse I saw being built.

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• KevGillan
• 26 Apr 2013
• 1

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• KevGillan
• 26 Apr 2013
• 1

Cheers.

 

[MJPlastering]

Hi I'm building a timber frame building for a granny flat etc, it's being built out of 4 x 2 treated timber and I'm going to timber clad the exterior in 27mm cladding, my question is on the exterior do I fix a breathable membran to my 4x2 then my osb board & then my cladding in what order do I fix the outside in I will be using 100mm celotex in between the stud work on the inside

 

[Alastairreid]

From the outside working in.

Cladding fixed to battens then builders paper stapled to the plywood.

Insulation between the studs, vapour barrier over the studs internally followed by whatever you are using for the internal finish.

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• Alastairreid
• 17 Jan 2015
• 3

 

[MJPlastering]

Vapour barrier do you mean breathable membrane or is that builders paper thank you Martin

 

[MJPlastering]

Have you got any reconmended breathable membrane to use for my timber building please

 

[Alastairreid]

Vapour barrier on the inside to help prevent the passage of moisture from within the building migrating into the fabric. 500 guage visqueen

http://www.visqueenbuilding.co.uk/ourproducts_details.asp?productid=35

Builders paper fixed to the ply.

http://www.novia.co.uk/building_paper_bs1521.html

or

http://www.insulationexpress.co.uk/Breather-Membrane/Dupont-Tyvek-Housewrap-Breather-Membrane.htm

 

[BLP]

Hi all,

Just joined the forum as I am building a garden office. I am using the method you suggest for walls Alastair.

Cladding..horizontal!

25x50mm battens,,vertical

building paper

9mm wbp ply (What do you think about substituting this for OSB3 9mm?)

100mm studwork

100mm full fill insulation

vapour barrier

Internal finish.

I am wondering when I get to the ceiling/roof, do I apply the same principal?
I will be putting joists and the breathable felt, purlins and corrugated sheets for roof, which I will insulate with same full-fill. Should I also put Vapour barrier on ceiling behind my internal finish (plasterboard/plaster), or should the ceiling have a breathable layer to let rising condensation through. I have read/heard that sealing in the entire space completely is not good as there is nowhere for the condensation to escape.
I will have trickle vents in the patio doors but not sure if this is enough?

Cheers,

Ben

 

[AronSearle]

Roofs should have vapour barrier on the warm side, ventilation on the cold side (so behind your corrugated sheets).

So typically corrugated sheets, battens for creating a ventilated airspace, breathable felt yadayada.

 

[BLP]

Thanks Aaron, so basically the same principal as the walls. I guess any condensation will be dealt with by having opening windows and using trickle vents etc.

Cheers,

Ben

 

[Alastairreid]

You dont need a membrane at ceiling level, just make sure there is plenty of cross ventilation in the roof space.

 

[BLP]

Thanks for that Alistair.

I was not going to put in a seperate ceiling but use the pitched underside of ther roof as the ceiling, if this is the case, there will only be ventilation between the purlins underneath the corrugated outer roof. Would it be best to use a membrane in that instance?

I could have a flat ceiling and a seperate pitched roof, with a cavity between, but it seems like a lof of extra unneccesary work.

Thanks for advice on full-fill insulation too.

Cheers,

Ben

 

[Alastairreid]

Yes you would install a vcl in a vaulted ceiling.

 

[tony1851]

Vapour barrier do you mean breathable membrane or is that builders paper thank you Martin

A vapour barrier (more correctly termed a 'vapour control layer') should not be breathable because that would defeat the object. Its purpose is to stop
moist air from penetrating the insulation and condensing on the cold side.
For a shed/office, 500g polythene sheeting would do (the proprietory products are more expensive).