The slope of a roof is often referred to as the pitch. The slope, or pitch, of the roof is determined by the vertical rise in inches for every horizontal twelve inch (12") length (called the "run"). A roof with x rise/12 run slope means that for every 12 inches horizontally (run), it rises x inches.

Generally, roofing types and roofing products are typically divided up into two primary categories, steep slope roofing and low slope roofing.  Sometimes steep slope roofing is also referred to as “residential roofing” due to the fact that most single family homes in the U.S. are constructed with some sort of pitch or slope to the roof.  Just as steep slope roofing is often referred to as residential roofing, the term low slope roofing is oftentimes synonymous with “commercial roofing”.  Again, this is due to the fact that, predominantly, commercial buildings have “flat” roof designs.
 

If we were to classify roofing slopes more specifically, the list below contains the common roof slopes and the terms which classify them.  However, in general terms, low slope roofs (commercial roofs) are those below 2/12 or 3/12 while steep slope roofing would consists of roof pitches above either 2/12 or 3/12 and higher.

 

      Flat Roof: 2:12

      Low Slope: 2:12-4:12

      Conventional Slope Roof: 4:12-9:12

      Higher Slopes:  9:12 - 20:12

      Steep Slope: 21:12 and higher

Roof slope is a very important aspect and it is considered the primary factor in roof design. The slope of a roof has an effect on the interior volume of a building, the drainage, the style, and the material used for covering. For example, if you notice water collecting on the roof the problem is probably related to the slope. The style is affected too because the framing of the roof changes the slope.

Steep slope roofing products are generally more visually appealing because they are critical aesthetic components for residential construction where the roof can consist of 40% of the exterior visual appearance of a home.  Steep slope roofing also generally lasts longer than low slope roofing because the systems shed water much more efficiently and generally are subject to less direct U/V activity.

For more information, please visit CertainTeed’s roofing products page.