Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement.
How does roof framing geometry work.
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.
Using i joists requires the same basic understanding of rafter layout and roof design.
However a four sided roof is usually a hip roof.
When you think of a roof that just has a front and a back that is usually a gable roof.
In order to do roof framing properly it is important to understand the unique shape and dimensions of your roof since these will greatly impact the geometry of the roof frame.
This and following chapters describe roof framing using con ventional lumber.
Explore framing complexities that result when roofs of two different pitches intersect.
To measure a 10 20 roof pitch place the 10 on the tongue and the 20 on the body.
Roof framing rafter layout.
Learn more about off angle roof framing.
A sketchup model helps clarify how various rafters and framing components are assembled in an off angle hip and valley configuration.
If you add an eaves overhang dimension then the amount the rafter sticks passed the wall will be added to the rafter length.
Generally used for roof framing but i joists are increasingly common see chapter 13 engineered wood.
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.
And the line length measurement from the roof peak to the building wall is the hypotenuse.
The longer leg of the framing square is called the body and the shorter one leg is called the tongue.
Roof framing terms are related to the parts of a triangle.
Roof features associated with basic roof framing terms are shown in figure 2 2.
The framing of a basic gable roof is based on a right angle triangle and the various roof framing components fit the triangle.
The rise or height of the roof at its peak is the altitude of the triangle.
Your work as a builder.
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.
Refer to the figure as you study the terms discussed in the next paragraphs.
Within the roofing industry there are two basic types of roof framing.
The run or half the building span is the base of the triangle.
A gable is a triangle formed by a sloping roof.
