Why you shouldn't install shingles on a low slope roof

The most commonly used roofing material on the market today is asphalt shingles for residential roofs. But there are certain situations or areas where shingles shouldn’t be installed. One of these areas is a low slope or flat roof.

Unfortunately, I still see shingles installed on a low slope roof.

Not only is this a problem for the shingles themselves, but also the warranties that protect your investment. That’s why you need to know why you shouldn't install shingles on a low slope roof.

For over 20 years, the team at Trapala Construction has helped homeowners make good home improvement choices with unbiased and honest information.

Let's take a look, and I’ll help you understand the “why” behind not using shingles for low slope roofing.

Example of flat roof with membrane

What is considered a low slope or flat roof?

Roof pitch is the steepness (or 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. It should be pretty obvious if your roof or a roof facet is low slope; just take a look at the picture above.

But, if you’re unsure, don’t risk your safety by getting on your roof to measure its pitch. You’ll learn your roof’s pitch after our inspection.

Why shouldn't you install shingles on a low slope or flat roof?

Now that you know what’s considered a low slope roof, let's understand why you shouldn’t install shingles on them.

Water sitting on shingles

The reason for this is that shingles aren’t meant to have sitting water on them. Because a low slope or flat roof isn't steep enough for water to flow down to the gutters, this leaves pools of water sitting on the shingles.

This drastically shortens an asphalt shingle's lifespan and creates a leak if there are nail pops or other problems in the area. No matter what, shingles shouldn’t be installed on anything less than a 2:12 pitch.

Not only will this result in problems, but the manufacturer also won’t warranty the area because the installation instructions weren’t followed.

Why would you install shingles on a flat roof in the first place?

Buyer beware. Now you know why you shouldn’t install shingles on a low slope or flat roof. But why would you consider doing this in the first place?

Most of the time it’s because a roofing contractor recommends it. This could be a mistake or lack of knowledge, but it’s not always done by accident unfortunately.

If a roofing contractor is willing to install shingles on a low slope or flat roof, it’s most likely to lower their prices to win your business. 

For example, installing a membrane roof system on a low slope or flat roof costs around $20.00 to $30.00 per square foot; that's the first picture above. For comparison, it’ll cost around $10.00 per square foot for architectural asphalt shingles (the picture with the standing water on the roof).

This is a big difference in price between the two roofing materials. So, it can be tempting to go with the cheaper overall price.

But if you install asphalt shingles on a flat or low slope roof, you’ll actually end up spending more money in the long run. I understand pricing is a huge decision-making factor for most homeowners.

However, you’re setting your investment up for failure by going with the roofing material that isn't recommended for your roof type.

In Conclusion

We are happy to give you a free inspection and quote and can advise you on your best possible options for low slope roofs or any roof for that matter. We'll help you consider your budget, the necessity of the repair or replacement, and the right materials for the situation. Contact us today and we will help you make the best choices to protect your investment.