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Foot Cut (given) 40.05º
Plumb Cut = 49.95º = (180-(40.05+90))
SOH CAH TOA
Rise of Roof (we’ll need later)
Tan 40.05º = Rise of Roof ÷ 1430
Rise of Roof = Tan 40.05º x 1430
Rise of Roof = 0.84058 x 1430
Rise of Roof = 1202mm
True Length Common Rafter
Cos 40.05º = 1430 ÷ TL Common Rafter
TL Common Rafter = 1430 ÷ Cos 40.05
TL Common Rafter = 1430 ÷ 0.76548
TL Common Rafter = 1868mm
Setting Out
Actual Length Common Rafter = True Length + Allowance at ridge + Allowance at eaves
It is best to draw full size the allowance at the ridge and the allowance or overhang at the eaves and add these to your True Length to get the actual length for your cutting list.
Pattern Rafter; cut a pair of rafters, check these, then use them as patterns for cutting the remainder. this way all the common rafters will be the same.
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