How Does Roof Framing Geometry Work

Refer to the figure as you study the terms discussed in the next paragraphs.

How does roof framing geometry work.

Roof framing rafter layout. Your work as a builder. A gable is a triangle formed by a sloping roof. Learn more about off angle roof framing.

If you add an eaves overhang dimension then the amount the rafter sticks passed the wall will be added to the rafter length. However a four sided roof is usually a hip roof. A sketchup model helps clarify how various rafters and framing components are assembled in an off angle hip and valley configuration. Using i joists requires the same basic understanding of rafter layout and roof design.

Roof framing terms are related to the parts of a triangle. The rise or height of the roof at its peak is the altitude of the triangle. The two types of roof framing. The longer leg of the framing square is called the body and the shorter one leg is called the tongue.

When you think of a roof that just has a front and a back that is usually a gable roof. 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. To measure a 10 20 roof pitch place the 10 on the tongue and the 20 on the body. Truss roof framing is cov ered in section 17 4.

Roof features associated with basic roof framing terms are shown in figure 2 2. 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. Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement. The run or half the building span is the base of the triangle.

Generally used for roof framing but i joists are increasingly common see chapter 13 engineered wood. The framing of a basic gable roof is based on a right angle triangle and the various roof framing components fit the triangle. Includes result for hip valley factor slope factor and the roof slope in degrees. In the following section we ll cover some of the more common roof and rafter terms you ll need.

When a piece of lumber is added to a carpenter s square it becomes a right triangle. This and following chapters describe roof framing using con ventional lumber. Explore framing complexities that result when roofs of two different pitches intersect. Within the roofing industry there are two basic types of roof framing.