Do you have a low slope or flat roof section of your roof? Are you trying to decide if you can install asphalt shingles on the low slope or flat area like the rest of the roof?
Asphalt shingles are the most commonly used roofing material on the market. However, there are certain situations or areas where installing shingles isn't necessarily the best thing.
And one of these areas is a low slope or flat roofing section. Unfortunately, I still see it all the time.
So, can you install shingles on a low slope or flat roof? If not, why?
For over 35 years, Bill Ragan Roofing has helped homeowners avoid being taken advantage of with educating them on the complexities of the roofing industry. Because of this, I’ll break down what you need to know about installing shingles on a low slope or flat.
By the end of this article, you'll learn:
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.
(Asphalt shingles on a 3/12 roof pitch)
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.
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 an inspection by a local roofing contractor for your roof replacement.
No, you shouldn't install shingles on a low slope or flat roof. In fact, the minimum roof pitch for asphalt shingles is a 2:12 pitch per codes set forth by the 2018 International Residential Code.
The first code specifically has to do with the minimum pitch required for asphalt shingles.
"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 codes, to put shingles on it. However, adding two layers of underlayment is a loophole to get around this code.
While the first code has to do with pitch itself, the second one is actually about following manufacturer installation instructions.
Per code R905.1: Roof Covering Application:
"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. Just like the double underlayment loophole, some manufacturers allow shingles on a low slope roof.
However, doing so usually requires very strict adherences that most installers don't know about without training.
At this point, you know asphalt shingles can't be installed on a pitch below 2:12. Now, 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 can create 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 eventually 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.
Sitting or ponding water leading to leaks is one thing, but it can also shorten the lifespan of asphalt shingles. This is especially true when it comes to debris building up from leaves, sticks, or anything else that falls on the roof.
The debris becomes oversaturated the longer it sits, which continues a cycle of building up, drying out, and become wet again. This damages and shortens the lifespan of the shingles below.
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, insurance also won’t cover an improperly installed roof in the event of storm damage.
Even though asphalt shingles shouldn't be installed on a low slope or flat roof, it still happens. And 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 usually done by accident. 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.
Not only is this a shady sales tactic, but it’s also a huge red flag when comparing multiple estimates. For example, installing a membrane roof system on a low slope or flat roof costs around $12.00 to $17.00 per square foot.
For comparison, it’ll cost around $5.00 per to $7.00 square foot for architectural asphalt shingles. This is a big difference in price, 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 contractor who recommends installing asphalt shingles on a low slope or flat roof to win your business.
After reading this article, you know you shouldn’t install shingles on a low slope or flat roof and the reasons why. You also know to look out for a roofing contractor trying to lower their prices by installing shingles instead of one of the appropriate low slope or flat roofing.
But if you can’t use the most common roofing material option on the market for a low slope or flat roof, what can you use? To answer this question, I wrote another article breaking down the best low slope roofing materials.
Check out The 4 Best Materials for a Flat Roof (& How Much They Cost) to find the right roofing material for your flat or low slope roof replacement.