Asphalt shingles are the most commonly used roofing material in the country. But there are certain situations where they can’t be installed.
One of these situations has to do with a low slope roof pitch. So, that begs the question, “What’s the minimum roof pitch for asphalt shingles?”
For over 30 years, the team at Bill Ragan Roofing has helped thousands of homeowners in the Nashville area find the right roofing material that fits their budget and situation. Now we want to do the same for you.
We’ll begin this article with a quick overview of what roof pitch is. After that, we’ll get to the minimum roof pitch for asphalt shingles and the reasons why you can’t use them on a low slope pitch.
To finish this article off, you’ll learn the 4 best roofing materials for a low slope or flat roof since shingles won’t be an option. And at the very end, you’ll get a complete roof replacement guide that gives you all the information you need to know about a replacement.
What is roof pitch?
Roof pitch is simply the steepness (angle) of your roof. It’s in the form of a ratio that’s 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 4/12 pitch will be 4 inches (or feet) up for every 12 inches (feet) out. Be aware; I don’t recommend trying to get on your roof to measure its pitch.
The minimum roof pitch for shingles is a 2:12 pitch. If your roof is less than 2 vertical units (inches or feet) up for every 12 horizontal units out, it’s considered low slope.
But why can’t you put shingles on a low slope or flat roof?
Shingles aren’t meant to hold or have sitting water on them. Because of this, the shingle manufacturer’s installation instructions and building codes state you can’t install asphalt shingles on a roof with a pitch below 2:12.
You might think you can avoid problems by ignoring the installation instructions to save money. Not only will the shingles not do their job properly, but the manufacturer also won’t stand behind their product because the installation instructions weren’t followed.
But if they were willing to ignore installation instructions, I guarantee they won’t stand behind their work. No matter what, don’t install asphalt shingles if your roof’s pitch is below a 2:12.
The 4 best roof systems for a low slope or flat roof
Now you know you can’t install asphalt shingles on a low slope or flat roof. But if you can use shingles, what materials can you use?
Below we give you the best roofing materials for a low slope or flat roof.
1. TPO membrane roof
TPO (thermoplastic polyolefin) is a single-ply white membrane used in both commercial and residential roofing. Because TPO is a white membrane, it reflects heat instead of absorbing it.
If you have a flat roof or a low-slope dormer over a bedroom, TPO is a great option because it’ll keep the room below cooler. But if you have a window that looks over the membrane, you need to consider how dirty the white will get.
This isn’t a big deal, but it’s just something to keep in mind when choosing your roofing material. As long as it’s installed properly, you can expect to get 25 years out of a TPO membrane flat roof.
2. PVC membrane roof
PVC (polyvinyl chloride) is also a single-ply white membrane used in commercial and residential roofing. Because PVC is white, it’s a great choice for any flat or low slope over a living space or bedroom.
PVC and TPO are also very similar in their characteristics besides their chemical make-up. Even the installation process is pretty much the same.
The only major difference is that PVC is slightly more flexible and has been around longer than TPO. Like TPO, you can expect to get 25 years out of a PVC flat roof as long as it’s installed properly.
3. EPDM membrane roof
EPDM (ethylene propylene diene monomer) is a synthetic rubber black membrane commonly used mostly in commercial roofing and medical facilities. While it’s used mostly for commercial properties, EPDM is still used in residential roofing.
Because it’s a black membrane, I wouldn’t recommend using it over a bedroom or living space because it’ll absorb the heat. However, EPDM is a great option for a flat roof over a garage or another non-living space.
The black membrane also won’t get as dirty as a white membrane if you can see it from a window. EPDM is extremely durable and is basically like having a bulletproof rubber roof system.
Because of this durability, you can expect to get 25 to 30 years out of a fully adhered 0.060 thickness EPDM flat roof.
4. Standing seam metal roof
A standing seam metal roof system is a series of metal panels that are locked together at the seams or seamed mechanically. This allows for panels to expand and contract freely when the metal panels go through thermal expansion.
A standing seam metal roof is a great roofing material for a flat roof. It has better aesthetics with more color options and is longer-lasting than the membrane roof systems.
As long as it’s properly installed and your attic is adequately ventilated, there’s no reason you shouldn’t get at least 30 years out of your standing seam metal flat roof. Under the ideal conditions, a standing seam metal flat roof could last for 50 years.
But this extra life and aesthetics comes at a higher price and is more expensive than all 3 types of roof membranes.
The guide you need for your roof replacement
Now you know the 4 best roofing materials for a low slope or flat roof. If you have a roof that’s 2:12 or steeper, you’re good to go with your asphalt shingle installation.
But before you do, there’s a lot you need to know/learn for your upcoming roofing project. Wouldn’t it be great if things like cost, roofing material options, the components that make up a roof, and more were all in one place?
If your answer is yes, then we have just the guide you need. The Complete Guide to Purchasing a Roof has all the information you need for your roof replacement and ensures you make all the right buying decisions.
Don’t go into the roof replacement process blind; get your free buyer’s guide below.
The team at Bill Ragan Roofing has provided high-quality roofing services to residents in Nashville, Brentwood, Franklin, and other surrounding Middle Tennessee areas since 1990. We’ve provided thousands of homeowners with an experience rare in the roofing industry, and we know we can do the same for you.