Asphalt Shingles: Understanding Its Limits on Low-Slope Roofs

Asphalt shingles are one of the most popular roofing materials in the United States. They are affordable, durable, and available in a wide range of colors and styles. However, asphalt shingles are not suitable for roofs with a slope of less than 2/12. In this article, we will explain why shingles cannot be installed on low-slope roofs and provide examples of alternative roofing materials that are better suited for this type of application.

What is roof slope?

Roof slope, also known as roof pitch, is the angle at which a roof surface rises relative to its horizontal base. It is usually expressed as a ratio of the rise (height) to the run (horizontal distance). For example, a roof with a slope of 4/12 rises 4 inches for every 12 inches of horizontal distance.

Why can’t shingles be installed on a low-slope roof?

The main reason that shingles cannot be installed on a roof with a slope of less than 2/12 is that they are not designed to withstand the water infiltration that can occur on low-slope roofs. Here are some specific reasons why:

Water resistance: Shingles are designed to shed water quickly, but on a low-slope roof, water can collect and pool, which can lead to leaks and other water-related problems. Shingles installed on a low-slope roof may not be able to shed water effectively, which can increase the risk of water infiltration.

Wind resistance: In addition to water resistance, roofs also need to be able to withstand high winds. Shingles are designed to be installed on roofs with a minimum slope of 2/12 to ensure that they are securely fastened and able to withstand wind uplift.

Manufacturer’s warranty: Most shingle manufacturers require that their products be installed on roofs with a minimum slope of 2/12 in order to qualify for their warranty. If you install shingles on a low-slope roof, you may void the warranty and be responsible for any repair or replacement costs.

Alternative roofing materials for low-slope roofs

If your roof has a slope of less than 2/12, there are alternative roofing materials that are better suited for this type of application. Here are some examples:

Built-up roofing (BUR): BUR is a traditional low-slope roofing material that consists of multiple layers of asphalt and felt. BUR is a time-tested and reliable roofing system that is known for its durability and long lifespan.

Modified bitumen: Modified bitumen is a type of asphalt roofing material that has been modified with synthetic rubber or plastic. It is available in a variety of colors and styles and is known for its flexibility and resistance to weathering.

TPO roofing: Thermoplastic olefin (TPO) roofing is a single-ply roofing material that is becoming increasingly popular for low-slope applications. TPO roofing is known for its energy efficiency, ease of installation, and long lifespan.

Shingles cannot be installed on roofs with a slope of less than 2/12 due to their inability to withstand the water infiltration and wind uplift that can occur on low-slope roofs.

If your roof has a low slope, there are alternative roofing materials that are better suited for this type of application, such as built-up roofing, modified bitumen, or TPO roofing.

It’s always a good idea to consult with a professional roofer to determine the best roofing material for your specific slope and needs.


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