SimonD Posted May 16, 2021 Share Posted May 16, 2021 1 hour ago, Marvin said: Outside to inside: Cladding Batten Tyvek Thin ply Studwork Insulation and services in studwork. Plastic sheeting Internal finish say plasterboard or ply or OSB. There are discussions about the plastic required by building regs but not mandatory for sheds If you build up as the OP, using plywood or osb sheathing on the inside of the frame, you don't need an additional vcl as the sheathing does this job and then you just need a breather membrane on the outside, this is particularly the case if you're using a vapour open insulation. AFAIA there is not requirement in building regs that you have to have a plastic vapour control layer, it depends on your buildup. You simply need to ensure that the internal side of the wall is sufficiently less vapour permeable than the outside. 1 hour ago, Omnibuswoman said: thank you. Should I put a layer of plastic sheeting between the ply and the stud, or just tape up the ply joins? No, you don't need an extra layer of plastic between the ply and the stud as you're using a different wall buildup than is being suggested by @Marvin who is suggesting a traditionale wall buildup. You are using what is called a reverse wall. If you decide to put your plywood on the outside of the timber frame instead, then you would need a plastic sheet. With your buildup, taping the joints is fine. If you want independent reference, have a look at this article that explains the differences in wall buildup and why. https://www.architectsjournal.co.uk/archive/the-breathing-wall-is-a-simple-concept-but-often-confused-by-linking-it-only-to-particular-wall-constructions-all-timber-walls-breathe 1 Link to comment Share on other sites More sharing options...
Omnibuswoman Posted May 25, 2021 Author Share Posted May 25, 2021 Quick update, and bit of a panic about the roof.... We have three of the walls done now - 1750mm studs (2x4s) with top and sole plate, fixed into the blocks with hammerfix screws. Overall height is 2310mm which feels generous for my height (1.6m) and even adequate for HWMBO. So far so good... We are going to move on to the front wall today, but I have started thinking about the roof and panicking that my design isn't sound... The workshop is 6.5m long and 4.6m wide. I had planned a ridge plate (2x10) with 2x6 rafters coming up to meet it, covered in 18mm ply. I ordered two 3.6m lengths of 2x10 for the ridge plate. I started looking at how to fix them together, and then had a panic about the roof design not being sufficient and collapsing in and killing us all.... So now I'm considering whether to do an almost flat roof by adding an extra top plate on the right hand side, and running timbers across the 4.6m width sloping down slightly to the left hand side. I spent a lot of last night looking at roof trusses and the design of trusses, but it looks quite difficult to get right, and I'm still worried about the roof falling in. Any and all thoughts will be hugely appreciated!! Photos of progress to date attached... Link to comment Share on other sites More sharing options...
jamieled Posted May 25, 2021 Share Posted May 25, 2021 Have you looked at the online timber roof span calculators? They obviously come with a bit of a caveat around the assumed loads but if you know your roof makeup you should be able to adjust if necessary and it might give you the confidence in your roof strength/assumed timber size. Something like: https://www.timberbeamcalculator.co.uk/span-table/flat-roof-joists?load=1&class=C16 1 Link to comment Share on other sites More sharing options...
SimonD Posted May 25, 2021 Share Posted May 25, 2021 Well done, great progress. You can join your separate ridge beams using a scarf joint. There's a very neat video on it by Skillbuilder - Cutting a scarf joint for a carpenters roof - which is a self locking version, although you can use a simpler 'straight' cut which is bonded or mechanically fixed. You will need to some pretty hefty timbers to span your 4.6m flat. If you're looking for a vaulted ceiling, it may be worth looking at plywood gussets as ridge rafter ties, which you can make . Otherwise, if you have the head room, adding ties across the span at wall plate level is pretty straight forwards and probably a safer best. You don't need to build roof trusses so to speak. Here are a couple of links you might find useful: Article: https://www.finehomebuilding.com/project-guides/framing/how-it-works-collar-and-rafter-ties Video: Plywood Ridge Rafter Ties Verses Conventional Roof Framing For Small Sheds - Building Better Roofs HTH 1 Link to comment Share on other sites More sharing options...
joe90 Posted May 25, 2021 Share Posted May 25, 2021 Or use I joists https://elliotts.uk/i-joist-faqs 1 Link to comment Share on other sites More sharing options...
Omnibuswoman Posted May 25, 2021 Author Share Posted May 25, 2021 Thank you all. I am on-site now but will review these suggestions tonight when we finish. We are working on our corner posts now and I’m delighted to find everything is perfectly aligned and square ? 2 Link to comment Share on other sites More sharing options...
Omnibuswoman Posted May 25, 2021 Author Share Posted May 25, 2021 Problem solved, courtesy of Ali Dymock's amazing YouTube videos and the span tables linked to above. We need 10x2s for the 4.6m span, and will put in some noggins for stability/to better support the roof. 18mm ply on top, with EPDM over that. It actually looks achievable now, although we only have until the end of the day on Monday which might be a challenge. I can see that Ali Dymock left his garden room wrapped in tyvek membrane all winter, so if we run out of time to do the cladding it won't be the end of the world as we can return to it later on. Where would I be if not for the buildhubbers?!! 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 25, 2021 Share Posted May 25, 2021 Mine's been wrapped in membrane since the start of last winter. Perfectly fine and I'm only now continuing with the cladding which I'm doing 'in my spare time', so probably be 'part-wrapped' for 3 more winters at this rate Seriously consider some of the closed cell spray-on insulation kits to boost draught-proofing and insulation in both the roof and the walls Quick, easy and effective. Wish I had done mine ? May well attempt a retro fit somehow if I can inject from inside..... 1 Link to comment Share on other sites More sharing options...
TonyT Posted May 25, 2021 Share Posted May 25, 2021 My house wrap was only guaranteed for something like 4 months exposure to UV Tyvec house wrap I think from memory. Link to comment Share on other sites More sharing options...
Omnibuswoman Posted June 13, 2021 Author Share Posted June 13, 2021 Another roof-related panic question: when we fit the roof ply (today), does each sheet need to be in contact with a joist/rafter at each corner - ie do the edges of the sheets need to sit at the joist centres just as the wall ply did?? we’ve added external noggins of 22cm which throws my beautiful calculations out as to starting at the front corner and working back in whole sheets. If I do that, the edges won’t be at centres because I’ve added 22cm on the front…. Link to comment Share on other sites More sharing options...
Omnibuswoman Posted June 13, 2021 Author Share Posted June 13, 2021 Picture of front noggins 1 Link to comment Share on other sites More sharing options...
Onoff Posted June 13, 2021 Share Posted June 13, 2021 (edited) Deffo support the ply edges on joist centrelines. Even more important on the roof than the walls. You'll have to add a nom 220mm ply strip along the front. Have you already bought your roof covering and taken that into account? (I'd have extended the overhang a good full board at least and had a bit of an overhang supported by posts. Great for a bit of craft spraying etc out side. Shade too from full ?). Enough room for an outside rocking chair and somewhere to rest the shotgun is good! ? Edited June 13, 2021 by Onoff 1 Link to comment Share on other sites More sharing options...
Omnibuswoman Posted June 13, 2021 Author Share Posted June 13, 2021 ? Thanks! weve limited the overhang as our house will have a stoop for rocking chairs and shoguns ? Link to comment Share on other sites More sharing options...
TonyT Posted June 13, 2021 Share Posted June 13, 2021 Either cut the plywood to land on existing supports or add extra supports. probably quicker to cut the ply. 1 Link to comment Share on other sites More sharing options...
Omnibuswoman Posted June 13, 2021 Author Share Posted June 13, 2021 We only need to take 15-30cm off the four front and four back sheets to be able to land on a joist centre, so that’s the plan. So far so good. Link to comment Share on other sites More sharing options...
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