Do you have a low slope or flat roof facet? Are you trying to decide if you can install asphalt shingles on it, but don't know the minimum roof pitch required?
Asphalt shingles are the most commonly used roofing material in the United States. But there are certain situations where they aren't the recommended choice.
And one of the most common reasons 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 35 years, Bill Ragan Roofing has helped thousands of homeowners in the Nashville area find the right roofing material that fits their budget and situation. Now, I want to do the same for you, whether you're a customer or not..
By the end of this article, you'll learn the answers to:
Roof pitch is simply the steepness (angle) of your roof. Roof slope is also used, but pitch is the term used by the roofing industry.
A roof’s pitch is measured as a ratio by the number of inches or feet a roof rises vertically for every 12 inches or feet it extends horizontally. For example, a roof that is 6 inches (or feet) up for every 12 inches (feet) out is a 6/12 pitch.
Roof pitches can go anywhere from flat to almost fully vertical. However, it’s also possible for a roof to have multiple pitches.
The minimum roof pitch for asphalt shingles is a 2:12 pitch. This is based on codes set forth by the 2018 International Residential Code, the standardized building code book.
The first one is based on roof pitch itself.
According to code R905.2.2: Slope |
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Asphalt shingles shall be used only on roof slopes of 2 units vertical in 12 units horizontal (2:12) or greater. For roof slopes from 2:12 up to 4:12, double underlayment is required. |
This code means that if a roof has a pitch (slope) below 2:12, it’s not steep enough, per the shingle manufacturers or codes, to put shingles on it. While the first code has to do with pitch itself, the second one is actually about following manufacturer installation instructions.
According to code R905.1: Roof Covering Application |
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Roof coverings (roofing materials) shall be applied in accordance with applicable provisions of this section and the manufacturer’s installation instructions. |
Asphalt shingles aren’t meant to hold or have sitting water on them, so manufacturer’s state that asphalt shingles cannot be installed on a roof with a pitch below 2:12. Now, if they do allow it, there's usually very strict adherences that most installers don't know without training.
So, asphalt shingles can't be installed on a pitch below 2:12. You may think these codes are pointless, and plenty of roofers ignore it (more on this next).
However, installing asphalt shingles on a low slope roof creates some very big problems.
Asphalt shingles aren’t meant to handle sitting water. Well, on a low slope or flat pitch, water ponds on the asphalt shingles.
Sitting water will find it's way to leak into your home, especially if nail pops or other problems are in the area. If there's aren't immediate issues, water will eventually get underneath the roofing materials.
If a leak isn't bad enough, the sitting water also shortens the asphalt shingles’ lifespan.
If asphalt shingles are installed on a roof pitch below a 2:12. the roof is technically improperly installed. When your shingles aren't installed correctly, any material warranty from the manufacturer is voided.
The manufacturer simply won’t stand behind their products if they weren’t installed per the instructions to function correctly. All they have to say is that the shingles can't do their job properly because the installation instructions weren’t followed.
This leaves you with no recourse if there’s an actual problem with the shingles themselves. If voiding your material warranties isn't bad enough, but insurance also won’t cover an improperly installed roof in the event of storm damage.
A reputable roofer knows not to install shingles on a roof with a 2:12 pitch or less, and will guide you on making the right material choice. However, there are plenty of bad roofing companies that do it to lower their prices.
For labor and materials, asphalt shingles (depending on the type) cost around $4.50 to $8.50 per square foot. On the other hand, specific flat or low slope materials cost anywhere from $12.00 to $17.00 per square foot.
This is a big price difference, which is why some companies ignore to win business. Now, you may think potential problems are worth saving money.
And even if there are problems, you have your roofing contractor’s workmanship warranty to fall back on. However, I can pretty much guarantee they won’t stand behind their work if they aren't willing to follow simple installation instructions.
Now you know all there is to know about why the minimum roof pitch for asphalt shingles is a 2:12 pitch. You can obviously still just do it.
However, it's not worth the problems that come with an improperly installed roof. But if you can't use shingles, what materials can you use?
There are multiple materials specifically made for low slope or flat roofing. However, there are some that are best for residential purposes.
That's why I wrote another breaking down the top flat and low slope roofing materials you should consider.
Check out 4 Best Roofing Materials for a Low Pitch Roof to learn which flat and low slope roofing material is right for you.