Crofter Posted June 9, 2016 Share Posted June 9, 2016 42 degree pitched roof, 6x2 rafters 3.8m long at 600 centres, and then boarded with 11mm OSB as sarking. The sarking is doing a good job of stiffening everything up, but should I install a dwang to support the edge of the sheet? I know that with 22mm timber sarking you obviously don't. It seems a bit weird to have an unsupported sheet edge, though. I don't want any movement across the join between sheets, in case that damages the membrane which is going on next. Just wondering if a dwang would normally be fitted, and if so can this just be a little bit of batten? Thanks Link to comment Share on other sites More sharing options...
Tennentslager Posted June 9, 2016 Share Posted June 9, 2016 Do you mean at the verge? Have you fitted a barge board? Link to comment Share on other sites More sharing options...
ProDave Posted June 9, 2016 Share Posted June 9, 2016 No dwangs in my roof and none specified on the drawings. P.S a question out of curiosity, why choose 42 degree pitch? 45 degrees is SO much easier for marking out and cutting. Link to comment Share on other sites More sharing options...
Tennentslager Posted June 9, 2016 Share Posted June 9, 2016 Had a look at your pic on the blog. I'm assuming you have the OSB overhanging the verge by 2/300mm and its a raw edge . Mine was 22mm osb but I screwed 4*2 @ 200 centres under the osb to give the verge a finished edge. Most roofs don't need this as they have a ladder rafters detail. Link to comment Share on other sites More sharing options...
Crofter Posted June 9, 2016 Author Share Posted June 9, 2016 1 hour ago, Tennentslager said: Do you mean at the verge? Have you fitted a barge board? No, not there- the sarking stops at the edge of walls, but when the roof covering goes on it will overhang a bit and I'll make up a barge board to support that. That's some way in the future, though. 1 hour ago, ProDave said: No dwangs in my roof and none specified on the drawings. P.S a question out of curiosity, why choose 42 degree pitch? 45 degrees is SO much easier for marking out and cutting. Thanks, I remember you had 11mm osb sarking so if it's good enough for you... I am considering gluing some strips of osb scrap onto the underside, just to bridge the gap between adjacent boards, and more than anything else to help prevent rainwater getting in through the 3mm gaps that I have dutifuly left between each board. Link to comment Share on other sites More sharing options...
ProDave Posted June 9, 2016 Share Posted June 9, 2016 No, mine has 100mm thick wood fibre board as the "sarking" and extra insulation. Then 9mm osb goes on the inside (to hold the insulation in) before the service void and plasterboard. Which membrane are you using? if it's the VP400 that I have, it's as tough as old boots and you won't tear thart. 1 Link to comment Share on other sites More sharing options...
Crofter Posted June 9, 2016 Author Share Posted June 9, 2016 I'm looking up the BBA certs of different membranes. The VP400 is not cheap but so far it is clearly the toughest available. For the extra hundred quid or so it might well be worth going for it, as I don't know how long it will be exposed for. Building a roof entirely on your own takes quite a lot of time!! Link to comment Share on other sites More sharing options...
ProDave Posted June 9, 2016 Share Posted June 9, 2016 My garage roof has been exposed with nothing more than the VP400 for 8 months now. Not a drop of a leak even over winter. Once I get the cladding and render finished I will be tiling that. The roof of our sun room will be left exposed even longer so that one I have also sheeted over with some left over DPM to give another layer of protection to the VP400 Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 27, 2016 Share Posted June 27, 2016 What's the full title of the vp400 dave? When the shedshop is finally built, I'll be wanting to concentrate on the interior and had planned to leave the outside just membraned, prob for one full season. If yours is holding up in the Highlands then I'm all ears. Do you know roughly how much per roll / per m2 it costs please? Edit. Does yours have nail penetrations thorough it for fixing? How have you held it down and remained watertight etc. Link to comment Share on other sites More sharing options...
ProDave Posted June 27, 2016 Share Posted June 27, 2016 All it says on it is "Protect VP400 plus" It's held down with the counter battens (vertical battens that follow the line of each rafter) and long screws (long screws needed as they have to pass through the 50mm counter battens, then the 100mm wod fibre before they reach the rafters, so 200mm screws used) So any penetrations are under the counter battens where it's not normally wet and so far no leakage. Link to comment Share on other sites More sharing options...
Nickfromwales Posted June 28, 2016 Share Posted June 28, 2016 Cheers Link to comment Share on other sites More sharing options...
Crofter Posted August 9, 2016 Author Share Posted August 9, 2016 Just by way on an update, I used Cromar Vent 3 Pro (the vent 3 comes in various different thicknesses) and am so far very impressed. Despite some horrendous weather recently, it has stayed put and no sign of leaks. Like Dave, I installed it vertically so the counterbattens run over every overlap. It is pretty tough stuff, as I found out when the first 8m length I was trying to tack down by myself was whipped out of my hands by the wind as soon as I had put the first nail in; it ended up flying like a banner and hanging on by that one nail which did not show any signs of stretching or tearing out. Link to comment Share on other sites More sharing options...
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