Roof slope may be given on a drawing by showing a slope ratio diagram or fractional pitch indication. The slope diagram, Fig 1-4 represents the ratio between the rise and run of the roof. The fractional pitch is calculated using the following formula. Pitch=Rise/Run
Roof slope may be also be shown using an angular dimension. However, this method is seldom used because it is difficult to measure as accurately as either of the other methods. A roof with a 45 degree slope has a 12:12 or ? pitch. There are several common roof pitches used in residential home construction. When designing a roof for your new home, try to use on of the standard roof pitches.