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Choosing the Best Material for the Slope of Your Roof

The slope of your roof is a key aspect of your roofing system and is the primary element in your home’s roof design. Roofing types are generally divided into two groups, steep slope roofing and low slope roofing. Due to the fact that most American homes are framed with a steep slope roof design, steep slope roofing is widely referred to as “residential roofing.” Conversely, low slope roofing is commonly referred to as “commercial roofing” due to the predominant use of flat roof designs on commercial buildings.

Whether steep or low, the slope of a roof influences the interior volume of a building, the drainage, the style and – most importantly – the roofing material used.

Steep & Low Slope Roofing
This home has both a steep slope roof, and a low slope porch roof, covered with rolled roofing (Image provided by CertainTeed)

What is roof slope?

The slope, or pitch of a roof is determined by “rise over run” referring to the roof’s vertical rise in inches for every twelve inches of horizontal length (the run). As an example, a roof with four inches of rise for every 12 inches of run has a slope of 4/12 or 4:12. See the list below for some common roof types and their associated slopes:

  • 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 or higher

Steep Slope Roofing Products

With the roof consisting of 40% of the exterior visual appearance of a residential home, steep slope roofing products tend to be more ascetically pleasing. The longevity of steep slope roofing products is typically better than that of it’s counterpart. This is due to more efficient drainage and less direct UV exposure.

Low Slope Roofing Products

Low slope roofing products are also used for residential construction. Residential low slope roofing can be separated into two categories: large flat roof applications such as apartment complexes, and smaller applications such as residential porches.

For larger residential low slope roofing applications, CertainTeed has a great line of products and systems available. Among the products and systems available are the BUR (Built-Up Roofing) systems, APP Modified Bitumen systems, and SBS Modified Bitumen systems, including Cool Roofing and Energy Star compliant products that may qualify for federal tax rebates when installed for residential use.

For smaller residential low slope roofing applications such as porches and garage transitions, CertainTeed offers the Flintlastic® SA, self-adhering SBS modified bitumen roofing system. Flintastic SO products are easy to install and are available in vast array of colors to coordinate with any shingle color. CertainTeed Flintastic SA products provide homeowners with an elegant coordinated roofing design, creating a seamless transition from steep to low slope.