How To Frame Hip Roofs 2

Basic Construction And Carpentry Techniques Home

Hip Rafter and Overhang Line Length Calculations

The line length of common and hip rafters can be calculated by using the dimensions shown in figure 2 and the Frederickson Metric Framing Square rafter table. Line lengths lie between two working points. The line length of the common rafter is calculated first. Run = span of 6400 mm divided by 2 = 3200 mm. The common rafter unit of run length is 250 mm. The number of units of  run for the common rafter is = 3200 mm divided by 250 mm = 12.8. The unit of length of the common rafter with a 150/250 slope is 291.5mm. The line length of the common rafter in figure 2 is 291.5 mm times 12.8 =  3731.2 mm.

The length of a hip rafter unit run is 353.6 mm. The Pythagorean theorem is used to calculate the hip rafter unit run shown on the Frederickson Metric Framing Square rafter table. The rounded square root of 250^2 + 250^2 = 353.6 mm.

The hip unit run of 353.6 mm and unit rise of 150 mm is used to calculate the unit line length of the hip rafter shown on the rafter table. The Pythagorean calculation shows that the square root of 150^2 + 353.6^2 = 384.1 mm. 384.1 mm is the unit line length of the hip rafter.  384.1 mm times 12.8 = 4916.48 mm rounded  to 4916 mm is the line length of the hip rafter. 12.8 is the number of units of run for the common rafter and hip rafter.

The line length of the overhang  is calculated the same as the line length of the hip. The projection of 800 mm divided by 250 mm = 3.2 units of run. 384.1 mm times 3.2 = 1229.12 mm rounded to 1229 mm is the line length of the overhang.

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Note: If you are having trouble fitting the hip roof components together, check to make sure the roof is plumb, level and square before you redo your measurements and cuts.

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Written and maintained by
Ronald Hunter

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