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  • Writer's pictureLAST STOP ROOFING

Why Shingles Aren't the Right Fit for Low-Slope and Flat Roofs

Updated: Nov 28, 2023

When it comes to roofing, one size does not fit all. Shingles, the go-to roofing material for many residential projects, may be a popular choice, but they're not suitable for every roof type. One area where shingles often fall short is on low-slope or flat roofs. In this blog post, we'll delve into the reasons why installing shingles on such roofs can be a risky decision, potentially leading to a host of problems and costly repairs down the line.

What is a low slope or flat roof?

Roof pitch is the steepness (angle) of your roof or certain roof facets. Roof pitch is a ratio calculated by the number of inches or feet it rises vertically for every 12 inches or feet it extends horizontally.

For example, a roof with a 6/12 pitch will be 6 inches (or feet) up for every 12 inches (feet) out.

With that in mind, a roof is considered low slope when the roof’s pitch is below a 2:12.

This means your roof is low slope if its pitch is less than 2 vertical units (inches or feet) up for every 12 horizontal units out. In general, it should be pretty obvious if your roof or a roof facet is low slope.

If you’re still unsure, don’t risk your safety by getting on a ladder to measure your pitch; you’ll learn your pitch after an inspection by a qualified roofing contractor for your roof repair or replacement.

Why shouldn’t you put shingles on a low slope or flat roof?

Now that you know what’s considered a low slope roof, you’re ready to learn why you shouldn’t install shingles on them. According to shingle manufacturers and/or per codes, a low slope (or flat) roof is not steep enough for shingles to be installed on it.

These are the main reasons you’d never want to install shingles on your flat roof...

  • Inadequate Water Drainage: Shingles are designed for roofs with a steeper pitch, allowing water to flow down and away. On low-slope or flat roofs, water drainage becomes a significant challenge. Shingles are not equipped to handle standing water, which can lead to ponding. Ponding water can, over time, compromise the integrity of the shingles, causing leaks and water damage.

  • Material Compatibility: Shingles are typically made of asphalt, a material that can be susceptible to damage from the UV rays of the sun. On a low-slope or flat roof, where the sun hits more directly, shingles are exposed to more intense sunlight, leading to faster degradation. Other roofing materials, such as single-ply membranes, are better suited for these conditions.

  • Wind Uplift Concerns: Shingles may not be the best choice for areas prone to high winds. On flat or low-slope roofs, wind uplift forces are more significant, and traditional shingles may not be adequately secured. This can result in shingle damage or, in extreme cases, complete roof failure.

  • Limited Sealing Capability: Shingles rely on gravity for water to flow downward. On a low-slope or flat roof, the lack of pitch can lead to water infiltrating beneath the shingles. While underlayment is used as a secondary barrier, it may not provide foolproof protection against water infiltration.

  • Shortened Lifespan: Shingles are not designed to endure the challenges posed by low-slope or flat roofs. The combination of inadequate drainage, increased UV exposure, and potential wind damage can significantly shorten the lifespan of shingles in these conditions. This means more frequent replacements and increased maintenance costs over time.

So why would a roofing contractor recommend installing shingles on your low slope or flat roof?

Now you know why you shouldn’t install shingles on your low slope or flat roof, but why would you consider this in the first place?

Most of the time it’s because a roofing contractor has recommend it. This could be because of a lack of knowledge on his part, but its not usually done by accident.

If a roofing contractor is willing to install shingles on your low slope or flat roof it is more than likely to lower their overhead costs so their estimate will be cheaper than the competition, and therefore they will hopefully win your business.

While shingles are a popular and cost-effective roofing choice for many homes, they are not universally suitable. Low-slope or flat roofs present unique challenges that shingles are ill-equipped to handle. To ensure the longevity and effectiveness of your roof, it's crucial to choose a roofing material that aligns with the specific characteristics of your roof. Consulting with a professional roofer and exploring alternative materials, such as single-ply membranes or built-up roofing, can help you make an informed decision that protects your investment and guards against potential issues in the long run. Remember, the right roofing material is the first line of defense for your home, and choosing wisely can save you headaches and expenses down the road.

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