How Does Roof Framing Geometry Work

A gable is a triangle formed by a sloping roof.

How does roof framing geometry work.

Includes result for hip valley factor slope factor and the roof slope in degrees. This will the first point of the rafter measurement line using the results of your rafter length calculation measure from this point along the rafter measurement. One major factor to consider on a hip roof is that there is often very little peak or ridge area at the top of the roof. When a piece of lumber is added to a carpenter s square it becomes a right triangle.

The rise or height of the roof at its peak is the altitude of the triangle. If you add an eaves overhang dimension then the amount the rafter sticks passed the wall will be added to the rafter length. And the line length measurement from the roof peak to the building wall is the hypotenuse. In the following section we ll cover some of the more common roof and rafter terms you ll need.

To measure a 10 20 roof pitch place the 10 on the tongue and the 20 on the body. Using i joists requires the same basic understanding of rafter layout and roof design. The run or half the building span is the base of the triangle. A sketchup model helps clarify how various rafters and framing components are assembled in an off angle hip and valley configuration.

Within the roofing industry there are two basic types of roof framing. Roof framing terms are related to the parts of a triangle. The longer leg of the framing square is called the body and the shorter one leg is called the tongue. Refer to the figure as you study the terms discussed in the next paragraphs.

From one end of the rafter material using a speed square or framing square mark an x in 12 angle on the rafter and cut it measure down y height from the long point of the rafter cut and make a mark. Generally used for roof framing but i joists are increasingly common see chapter 13 engineered wood. The two types of roof framing. Explore framing complexities that result when roofs of two different pitches intersect.

Truss roof framing is cov ered in section 17 4. Learn more about off angle roof framing. Your work as a builder. The framing of a basic gable roof is based on a right angle triangle and the various roof framing components fit the triangle.

Roof features associated with basic roof framing terms are shown in figure 2 2. This and following chapters describe roof framing using con ventional lumber. However a four sided roof is usually a hip roof. Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement.