How To Frame Gable Roofs 1

Using The Pythagorean Theorem To Frame Roofs

Roof framing is based on the Pythagorean theorem which is the square root of the Rise^2 + Run^2 = hypotenuse^2. Note ^2 means squared. The Frederickson metric framing square, and imperial framing squares, can be used to lay out all of the ceiling joist and rafter cuts. See the Frederickson Metric Framing Square rise and run units on figure 32. A building plan roof slope of 3 in 5, will have a rise of 3 and a run (or base) of 5. The hypotenuse or line length, will be the square root of 3^2 + 5^2 =  5.83^2 approximately or 5.83. In metric terms, the roof slope 3/5 can be described as 150 mm in 250 mm or 150 to 250 or 150/250. 250 is the constant run measurement for the Frederickson metric square.

Figure 32  The Frederickson Metric Framing Square

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1.Framing Gable Roofs: Roof Framing Is Based On The Pythagorean Theorem.
2.Framing Gable Roofs: Layout The Ceiling Joists.
3.Framing Gable Roofs: Cut The Ceiling Joist To The Slope Of The Rafter.
4.Framing Gable Roofs: Gable Roof Components.
5.Framing Gable Roofs: Calculate The Length Of A Common Rafter.
6.Framing Gable Roofs: Mark Plumb Lines For Ridge, Birdsmouth And Overhang.
7.Framing Gable Roofs: Adjust The Rafter To The Size Of The Ridge Board.
8.Framing Gable Roofs: Layout & Cut The Rafter Birdsmouth.
9.Framing Gable Roofs: Calculate Length Of The Rafter Overhang & Cut Excess.
10.Framing Gable Roofs: Layout The Collar Ties.
11.Framing Gable Roofs: Calculate The Gable End Stud Lengths & Adjustments.
12.Framing Gable Roofs: Calculate Gable End Stud Length By Ratio & Proportion.

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Written and maintained by
Ronald Hunter

All images and text are copyright Ronald Hunter 2005 to 2011