Gable rake length and siding waste — the rake is the hypotenuse, and every course is cut at its angle
The rake (sloped edge) is the hypotenuse — √(run² + rise²) = 16.8 ft, not the 30 ft width — so size rake fascia and trim from it. And because every course is cut at the rake angle, gable siding wastes 12–15% (up to 25–30% on steep or narrow gables), more than a flat wall.
What this diagram shows
A gable triangle inside its bounding rectangle showing two things a gable take-off turns on. First, the rake — the sloped edge of the gable — is the hypotenuse of the run-and-rise triangle, equal to the square root of the run squared plus the rise squared. For a 15-foot run and 7.5-foot rise that is 16.8 feet, longer than it looks, and it is what you measure rake fascia, frieze board, and trim from, not the 30-foot horizontal width; a standard gable has two rakes. Second, the corners of the bounding rectangle outside the triangle are shaded as waste, because every horizontal siding course meets the sloped rake at an angle and gets cut off. Gable siding therefore wastes more than a flat wall: budget 12 to 15 percent for lap or board siding, and up to 25 to 30 percent on steep or narrow-exposure gables.
Gable Area Calculator
Free gable area calculator: get the square footage of a gable end from width and roof pitch or peak height, plus rake trim length and siding waste.
