Timber Framed Garage Advice

17 Feb 2008
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United Kingdom
Hi there,

I am going to build a timber framed garage on my concrete slab with upvc coated metal cladding on the outside walls and roof. I am just trying to clear up in my head the construction of the walls/roof. Can somebody advise if this is correct or if there is parts missing, starting internally:

1) Fireproof plasterboard (will be welding in garage)

2) 100mm Stud wall (400 centres) with rockwool or insulation board

3) Exterior grade plywood

4) Breathable membrane

5) Upvc coated metal cladding

I have read some sites where there is a membrane behind the plasterboard too, is this required ?

Also can someone advise the thickness of exterior plywood i should use (needs to take my weight on roof :)

Thanks in advance for any help

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Fire check plasterboard will require jointing and skimming, and will then be forever getting knocked/holed/dented in a garage.

Consider using ply sheets instead, which will be just as good in terms of fire resistance

Normally there may be a vapour check layer (polythene) behind the plasterboard - if you use rockwool, but not if you use foil-coated insulation board. But as a garage it's not that important
Agree with woody, used ply on my garage interior with a clear fireproof coating.
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Plywood it is then.

The slab isnt actualy in yet, the frame will be attached to the blockwork which will be the form for the slab, what would be the best method mounting to this? I was thinking about using bricks with holes in for the top row and mortaring some threaded bar vertically so that i can bolt the frame down onto it. Is that a bit overkill ? should it just be plugged and screwed into blockwork ? The garage is to be 6.2 x 3.2m external.


but not if you use foil-coated insulation board.

As said, for a garage it won't really matter. But if you use foil coated insulation between the studs, the vapour barrier becomes more not less important, as vapour cannot pass throught the insulation, it will pass between the studs, and specificly gaps between the studs and insulation (you will never have a complete seal).

If you are putting a metal sheet cladding onto plywood, i would recomend using a membrane that includes a fuzzy layer, can't think what the stuff is called, but it looks like velcro. (it allows condensation that occours on the underside of the metal, to flow down)

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