Why Should You Not Install Shingles on a Low Slope or Flat Roof?

Why Should You Not Install Shingles on a Low Slope or Flat Roof?

When it comes to roofing, homeowners and contractors alike face the challenge of selecting the right materials and installation methods for different types of roofs. While asphalt shingles are one of the most popular roofing materials in the industry, they are primarily designed for sloped roofs. This brings us to an important question: why should you not install shingles on a low slope or flat roof? The answer lies in the unique characteristics of low-slope and flat roofs compared to traditional steeper pitched roofs.

In this comprehensive blog post, we will explore why shingles are not ideal for low-slope or flat roofs, the potential risks associated with their use in these applications, and the best roofing materials to consider instead. We will also dive into the challenges these roof types pose to proper installation and maintenance. Understanding these factors will help homeowners make informed decisions when it comes to roofing projects, preventing costly repairs or premature roof failure.

What is a Low-Slope or Flat Roof?

Before we dive into the reasons why shingles are not the best option for low-slope or flat roofs, let’s first define what these types of roofs are.

A low-slope roof is typically defined as having a pitch (or angle) between 1/4 inch to 3 inches of rise for every foot of horizontal distance. Essentially, it has a slight slope that is not steep, but still noticeable. Low-slope roofs are often found on modern homes, commercial buildings, and certain types of extensions or additions. These roofs still have enough of a slope to allow for drainage, but the angle is much more gentle compared to a traditional, steep-pitched roof.

On the other hand, a flat roof appears to be completely level or horizontal, although it may have a very slight pitch (usually less than 1/4 inch per foot). These roofs are commonly found on commercial buildings or homes with a modern, minimalist design. Flat roofs are built to accommodate drainage, but since they lack a noticeable slope, the drainage may not be as efficient as that of a sloped roof.

Why Shingles Are Not Ideal for Low-Slope or Flat Roofs

Now that we understand what low-slope and flat roofs are, let’s discuss why asphalt shingles, which are typically used on steep-pitched roofs, may not be suitable for these types of roofing systems.

1. Inadequate Drainage

One of the most significant problems with installing shingles on a low-slope or flat roof is the lack of effective drainage. Asphalt shingles are designed to shed water down a sloped surface, allowing rain, snow, and other moisture to flow off the roof. On low-slope and flat roofs, however, there is not enough of a pitch to facilitate proper drainage.

When water does not drain properly from a roof, it can accumulate on the surface. Over time, this standing water can lead to a variety of issues, including:

• Water Leaks: The accumulation of water increases the risk of leaks. As moisture collects on the roof, it can seep beneath the shingles, eventually infiltrating the underlying roofing materials and the building’s structure.
• Mold and Mildew Growth: Moisture that remains on the roof for extended periods can encourage the growth of mold and mildew. These microorganisms can damage both the roof and the interior of the building, leading to costly repairs and health concerns.
• Roof Deterioration: Standing water can cause shingles to become soft, brittle, or even warped. This can weaken the shingles and reduce their lifespan, leading to premature roof failure.

Asphalt shingles are not designed to handle such prolonged exposure to standing water, which makes them an unsuitable choice for low-slope and flat roofs.

2. Lack of Sealant and Water Resistance

Another reason asphalt shingles are not appropriate for low-slope or flat roofs is that they rely on gravity to help shed water. As mentioned earlier, shingles are installed with overlapping layers that allow water to flow down the roof. On a flat or low-slope roof, however, this natural water-shedding process does not work as effectively.

While some asphalt shingles come with a sealant to improve waterproofing, the lack of slope means that water can sit longer on the surface. This increases the chance of water getting beneath the shingles. Over time, this can lead to a breakdown of the roofing material, causing gaps, cracks, or other damage. Furthermore, without a sufficient slope to encourage drainage, the shingles cannot perform as they were intended, and the roof will be left vulnerable to leaks and water infiltration.

3. Wind Uplift

Wind uplift is the force that wind exerts on the surface of the roof, especially during storms or high winds. In sloped roofs, the angle of the shingles helps to resist wind uplift by allowing the wind to flow smoothly over the surface. However, on flat or low-slope roofs, the shingles have less resistance to wind, which can cause them to lift or even become detached.

Without proper wind resistance, shingles may be blown off or loosened, leaving the roof exposed to further damage. Wind-driven rain can also penetrate beneath the shingles, further increasing the risk of leaks and water damage. Flat and low-slope roofs are more prone to these issues, and asphalt shingles simply aren’t built to withstand the forces of wind uplift in these situations.

4. Shortened Lifespan of Shingles

Even if shingles are installed on a low-slope or flat roof, they will not perform as well or last as long as they would on a steeper pitch. Asphalt shingles are designed to endure the elements, but they are not built to withstand constant exposure to the challenges posed by low-slope and flat roofs. Over time, the lack of drainage, wind uplift, and moisture infiltration can cause the shingles to degrade, crack, or become dislodged.

The lifespan of asphalt shingles on a low-slope or flat roof is significantly shorter than that of shingles on a steep-pitched roof. While a typical asphalt shingle roof may last 20-30 years, you may find yourself replacing your roof much sooner if you install shingles on a low-slope or flat roof.

5. Costly Repairs and Maintenance

Installing shingles on a low-slope or flat roof can lead to more frequent repairs and maintenance, which can quickly add up in terms of costs. Shingles may require re-sealing, replacement, or even a complete roof replacement sooner than expected.

Additionally, maintenance on a low-slope or flat roof is generally more complex and expensive. The contractor will need to regularly inspect the roof for signs of leaks, mold, water pooling, or other damage. In many cases, it’s more cost-effective in the long run to install a roofing system designed for low-slope or flat roofs, such as a flat roof membrane or modified bitumen roofing system, rather than attempting to make asphalt shingles work.

Best Roofing Materials for Low-Slope or Flat Roofs

Given the challenges that shingles pose on low-slope and flat roofs, it’s important to explore other roofing materials that are better suited for these types of roofs. Let’s take a look at some of the best options for low-slope and flat roof installations.

1. TPO (Thermoplastic Olefin) Roofing

TPO is a popular roofing material for low-slope and flat roofs, particularly in commercial buildings. TPO is a single-ply roofing membrane that is highly resistant to UV rays, chemicals, and punctures. TPO roofing provides excellent waterproofing and is highly durable, making it an ideal choice for flat and low-slope roofs.

2. EPDM (Ethylene Propylene Diene Monomer) Roofing

EPDM is another single-ply roofing material commonly used for flat roofs. EPDM is a rubber-based membrane that is extremely resistant to weathering and UV damage. It also provides superior waterproofing and is flexible enough to handle the expansion and contraction of the roof due to temperature changes.

3. Modified Bitumen Roofing

Modified bitumen roofing is a type of asphalt-based roofing that is specifically designed for low-slope and flat roofs. It is applied in multiple layers and can be either torch-applied, self-adhesive, or cold-applied. Modified bitumen is more flexible and durable than traditional asphalt shingles, making it a better option for flat roofs.

4. PVC (Polyvinyl Chloride) Roofing

PVC roofing is another type of single-ply membrane roofing system that is well-suited for low-slope and flat roofs. PVC roofing is highly resistant to water, fire, and chemicals, making it a durable and long-lasting option. It is also energy-efficient, as it reflects UV rays and reduces the amount of heat absorbed by the roof.

Conclusion

Installing asphalt shingles on a low-slope or flat roof may seem like an easy and cost-effective solution, but it presents a number of challenges that could lead to long-term problems. From inadequate drainage and water resistance to wind uplift and shortened lifespan, asphalt shingles simply aren’t built to handle the unique demands of low-slope and flat roofs. These issues can lead to costly repairs, frequent maintenance, and premature roof failure.

Instead, homeowners with low-slope or flat roofs should consider roofing materials that are specifically designed for these types of roofs. TPO, EPDM, modified bitumen, and PVC roofing systems are all excellent options that offer superior durability, water resistance, and long-term performance.

By choosing the right roofing material for your low-slope or flat roof, you’ll be able to ensure a longer-lasting, more reliable roof that will protect your home for years to come. Always consult with a professional roofing contractor to determine the best solution for your roofing needs and make sure you’re getting the most out of your roof investment.