![]() it'll have 'proper' joints that tighten as it dries. splits big enough you could get your hand in them in some cases. In other words, if there is a 1 1/2 ridge board nailed into the wall, and the width of the lean to is 96, then the run will be 94 1/2 ( 96 1 1/2. splits big enough you could get your hand in them in some cases. How to Calculate a Lean to Rafter The run for a lean to shed rafter ending into a wall should account for the ridge board nailed into the wall where the tops of the rafters rest into. Consider what impact that shrinkage will have on junctions, joints and interfaces. If the 250mm x 300mm are also to be green oak, the 300mm dimm will end up being 288mm ish. Therefore 125mm square sections will end up being more like 120mm when dried. You will end up with a 4% change in dimension for the timbers. ![]() FSP for oak is 28% and in-situ you will end up at about 12%. Any old bit of timber won't do.Ī note on shrinkage, you will get a 1% change in width and thickness (not length) for every 4% change in moisture content between fibre saturation point and dry in service. Make sure the engineer uses a grade that you can actually get. UK grown European oak can be graded to D40, but French grown European oak can only be graded to D30. Have a look around to see what grades you can get locally. Really, the easiest thing is going to be to get a structural engineer to run the numbers. Unfortunately the TRADA software is only available to paying members. ![]() wet) to ensure it is strong enough during the initial drying out phase (wet wood is weaker than dry wood). These span tables are the equivalent of other industry-standard span tables and are calculated to the same standards. These spans were calculated using our purlin calculation engine. ![]() This span table is to the format and methodology given in BS 5268-7.6. Green oak needs to be designed at UC3 (Use Class 3, i.e. Click on a span to generate a full calculation (you can adjust the exact span and slope). However, i believe it only covers UC1 and UC2. TRADA have a span tables tool kit for members which will allow any sizes and hardwood grades to be spec'd. ![]()
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