Do not understand why you want shiplap boarding on top of commons. You will have 4 couples with your TDAs, but would suggest couple every other rafter, unless of course you want ceiling of some sort, then couple every rafter with 47x100 at 400mm centres with 50x175mm mid span binder hung on TDAs. Triangulate and brace whole roof with 25x100 to underside of rafters above and below purlin. With no ends and high wind, whole roof could move. ![]() Strap bressummer down well to stanchions with twisted heavy duty restraint each side. Ditto to purlin.Įven though your run of rafter is a good length, it is still possible to make up TDAs with spliced joints to reduce length of main rafters. for your birdsmouth to match plane of T.D.As. but you will need to add blocking plate to bressummer in between T.D.As to obtain H.A.P. Purlin would need to be somewhere in region of 75x225mm.With the centre span purlin you can reduce your common rafters down to 50x100 and use two lengths 50x100 either overlapped or scarfed on top of purlin. ![]() One each end and two intermediates to support purlin. Your next problem is you have no end walls to support purlin, This can be overcome the old fashioned way, by making up 4 number half TDA trusses with stub toe for building in. Say 22.5 degree pitch, length of rafter will be from top cut to plumb cut at seat 4.208m long and even working on 50x150 rafters at 400mm centres, they will need a purlin mid span.Ĥ.208 plus overhang makes length of commons 4.5m long, which length you will find hard to source. Pitch will be at your discretion, and depending on what type of tile you are using, could be anywhere between 22.5 and 45 degrees You need two, 50xx225mm bolted together with bulldog connectors to form wooden bressummer stood on edge and oblique scarf jointed over each intermediate post with 1.350x100x100 concrete spur bolted front and back, to support wooden bressummer over the 8.600 run length.Īfter saying that, would feel a lot happier with 100mm box section with plate top and bottom. ![]() No other supporting walls except wall you intend to lean against.įirstly, one intermediate post would be insufficient, would suggest two number at approx 2.150 centres. Two concrete posts, one each end, and intention of fitting wooden post in centre. Guidance is based on overall length 8.6metre, and overall span 4metre with 200mm overhang. Sizes are all based on max dead load 0.75kNM2. Simon, Read your last post and, feel that this roof is way beyond what you will manage, however will try to elaborate on the advice already given, and explain your problems, but remember we are talking U.K regulations.
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