Traditional Architecture

How to Figure Roof Pitch on a New Building

In some cases, a homeowner that is having a new home constructed may have reservations about the pitch of the roof that is shown on the construction plans. The plans demonstrate opposing rafters growing to a summit at the ridge since they’ll be installed by the contractor. A pair of numbers nearby indicate the pitch, like 4 and 12. To figure a different pitch, or any roof pitch, use a method that’s used by contractors and roof framers. After figuring a pitch, ask the contractor to put in a mock rafter assembly with two opposing rafters.

Measure the length of two adjoining exterior walls from end to end. With few exceptions, rafters attach at the top of opposing longer walls and climb to the ridge at the middle point of the wall. Notice the length of the shorter outside wall.

Divide the length of the shorter wall in half. The result is the “run” of a rafter in the attachment at the top of the long wall to the ridge board. For this instance, the brief wall is 20 feet from end to end, and the run of every opposing rafter is 10 feet. Proceed to figure the growth of the rafters and pitch of a roof.

Put a piece of framing timber, like a two-by-six or two-by-eight, flat atop a pair of sawhorses. Put a framing square flat on the board, with the outer corner in which the long and short legs of the square match, facing toward you.

Align the 12-inch mark on the longer leg at the edge of the board that is closest to you. Align the 4-inch markers on the shorter leg at precisely the exact same edge of the board. Understand the second number in a pair of numbers which define the pitch of a roof is always 12. To put it differently, if the pitch is 4 and 12, a rafter rises 4 inches for every 12 inches measured straight in from the outer end of the brief wall. For this instance where the run is 10 feet, the top ends of opposing rafters at the ridge board will be 40 inches over the top of the brief wall at the middle point.

Figure a different roof pitch to use when the contractor builds a pair of rafters for evaluation of the pitch. To do this, use 1 hand to hold the longer leg of the square in place with the 12-inch mark at the edge of the board. Move the brief leg toward you and also align the 5-inch mark at the edge of the board. Use the outer edge of the brief leg for a guide, and mark a line across the surface of the board, using a carpenter’s pencil. The line represents a 5 and 12 pitch.

Request the contractor to lower the ends of two rafters at the 5 and 12 pitch. Following the contractor builds the mock pair of opposing rafters at the construction, evaluate the pitch. Notice a 5 and 12 pitch is steeper than the 4 and 12 pitch shown on the plans since the height at the ridge is now 50 inches.

Use the exact same process to mark a plank at a 5 1/2 and 12 pitch or greater. Request the contractor to construct pairs of opposing rafters until you decide the pitch which looks best.

See related