Hi all Just hoping for some advice on a shed we'll be building in the next few months. I haven't done anything like it before although I think it's well within my skill set, but there's always doubt. It's a 5500x3000mm shed with a flat roof (approx. 4 degree pitch), build on an existing concrete foundation of that size. Height will be 2200mm on shortest side and 2400mm tallest (long sides). walls 47x75mm (2x3) frame, 600mm centres with noggins approx every 1200mm. Waterproof membrane and tantalised feather board externally and 11mm OSB internally. Roof 47x100mm (2x4) beams, with 18mm OSB externally covered with EPDM. I've been recommended to use marine ply on roof instead of OSB but is that overkill? It's much more expensive. Fixings 100mm nails for all framing but not sure about size of fixings to secure frame to foundation. I'm thinking rawlplugs but how big? My major concern is whether 47x75 will be enough for the walls? Other advice I've found online seems to range from that being absolutely fine, to not using anything less than 47x100mm for all framing.
It all looks fairly fine to me. 3x2's for the walls is fine, especially if lined with OSB - personally I'd use 9mm, and for a shed roof OSB is also fine - do remember to leave 3mm between the sheets. What are you going to use it for? if it's unheated storage then a VCL on the outside is fine. If you are going to heat it, then the VCL goes on the inside, then insulation and then a breathable membrane on the outside under the cladding. Once you heat it, you have to think more about condensation control. Think about the joint between wall and concrete pad. Ideally the cladding should come down over the edge of the pad to stop water running through the joint. If you can't do that, then you have to think about the possibility of water pooling on the edge of the pad and either running under the wall base or continually soaking the timber. A solution to this is to run a course of brick/block around the edge of the pad and then build the wall up from that - the cladding can then pass over the timber/brick joint. You could even raise the level of the floor by half a brick thickness of fresh concrete over a VCL inside the perimeter brick to help keep the floor dry. It all depends what your existing concrete pad actually is. You could use frame fixings to secure the wall to the base, - lots of solutions. Personally I'd use 80 and 100mm screws for the framing - more controllable than trying to wack 100mm nails in to a springy frame.
Thanks for your response. Glad to hear I'm on the right track. I'm going to be using it as a workshop but there'll be no heating system, probably just an electric heater for winter. I'll look into a VCL. As for the pad, we're fortunate that it's raised above ground level by a decent amount so I do have the opportunity to overlap the cladding. We were planning on putting a damp course layer between the frame and the pad.
You’ve described pretty well exactly how my workshop is built, and it came out great. I discovered (googled) that the OSB is a fairly good Vapor barrier on its own, I caulked the gaps. I did use a breathable membrane on the outside of the studs and rafters. Filled the cavity with loft roll. Added 1” tile battens over the studs and fixed the cladding to these. That construction keeps the insulation in place, and leaves a 1” ventilation gap for the cladding.
That's very generous, I'll definitely take you up on that. Am I being blind or is there no way to send PMs here?
Yes. and definitely if have OSB over them. But if you want to go up to 4x2s it will make it even more solid
I'd put the osb on the inside. You'll have to batten for the featherboard anyway, just gives a cleaner interior, and you can fix anything wherever you want.
@Rosso - y that's what he plans - when I said "over" I meant over the inside - its the stability and strength the OSB adds that is important