If you want to add on a rafter foot (overhang) add this to your rafter length. All roofs excluding the Saltbox and Polygon apply the width of the building rather than the common rafter run as well as the total overhang along with the. This calculator is to be used as an estimating tool only. Click the button to calculate the stock size needed for this job. Calculation set out Rafter run external width between the wall plates divided by two. Click the button to calculate the stock size needed for this job. Rafter Stock Size Calculator Input the rafter span (on the flat), eave overhang and pitch of the roof. Multiply this factor by your run which gives your rafter length. Input the rafter span (on the flat), eave overhang and pitch of the roof. Just multiply the rise or run by the appropriate rafter length factor corresponding to your roof pitch.įor example, if your roof pitch is 30ﹾ and your run is 2.4m then reading from the table the rafter length factor is 1.15. Common Rafter BuilderUsing Common Rafter Builder is quick and easy, just enter the- Roof pitch or rise- Run length- Overhang lengthThen the app will. There is a useful table below for your convenience. Rafter length = 2.4 ÷ cos(45°) = 3.39m to 2 d.p.Īny modern mobile phone will be able to perform these calculations. Rafter length = Run ÷ cos θ = Rise ÷ sin θįor example. Using a bit of trigonometry you can find the rafter length using the following equations. Method 2 - You know the roof pitch, θ, and the rise or the run. The eagle-eyed will have spoted this is another example of a 3-4-5 triangle.
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