Every roofer comes across low-slope roofs in their career, but homeowners may not know exactly what a low-slope roof is. When it comes to low-slope roofs, it’s all about the pitch. 

The usual slope for asphalt shingles is a 4” or greater vertical rise for every 12” of horizontal run along the roof, generally denoted as a 4/12 pitch.

A slope of 3” vertically per foot (3/12) is considered low but may be acceptable if a double layer of roofing underlayment is used. Some building codes allow as low as a 2” rise per foot slope with asphalt shingles if additional steps are taken.

However, for a roof pitch any less than 3/12, you should use a roofing material specifically designed for low-slope or flat roofs rather than traditional asphalt shingles.

Minimum Roof Slope Requirements To Use Asphalt Shingles

The slope or pitch of your roof refers to how steeply inclined it is. Roof slope is measured by the vertical rise over the horizontal run, and proper slope allows water to drain effectively off the roof.

Most asphalt shingle manufacturers specify a 4/12 pitch as the minimum for their products in installation instructions. This 4/12 pitch or greater allows for adequate drainage. However, some building codes allow for 3/12 or even 2/12 if additional underlayment is used. For a roof pitch this low, manufacturers and building codes don’t recommend asphalt shingles because of the risk of failure, which can encourage water damage. Using shingles on a low-slope roof typically leads to problems like increased leaks, shorter shingle life, and less durability.

Minimum Slopes for Asphalt Shingles

  • 4/12 or greater: Required by manufacturers for warranty coverage
  • 3/12: May be allowed with extra underlayment
  • 2/12 or less: Too low for asphalt shingles

Using Extra Underlayment on a Low-Slope Roof

On slightly steeper pitched roofs from 3/12 to 4/12, building codes often require double underlayment. This involves overlapping two layers of roofing felt to provide extra leak protection. An ice barrier membrane or water shield should be used on all roofs, but this is especially true of low-slope roofs, which are more susceptible to ice dams. The added underlayment improves drainage and prevents wind-driven rain from getting underneath the shingles. This may allow certain roofs down to a 3/12 pitch to use asphalt shingles.

However, no amount of extra underlayment can compensate for a roof pitch below 2/12. The slope is simply too minimal for asphalt shingles to drain properly.

Shingle Alternatives for Low-Slope Roofs

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For roofs with less than a 3/12 pitch, specialized low-slope roofing materials are recommended rather than asphalt shingles.

Examples of these materials include:

  • Ethylene propylene diene terpolymer (EPDM) rubber roofing
  • Thermoplastic polyolefin (TPO) roof membrane
  • Spray polyurethane foam
  • Elastomeric acrylic coatings
  • Styrene-butadiene-styrene (SBS) and atactic polypropylene (APP) modified bitumen membranes

These types of roofing materials are specifically designed to withstand water, expansion, and contraction, as well as provide durable waterproof protection on flat or low-pitched roofs. Other low-slope roof system options include PVC, metal roofing like standing seam, or rolled roofing. Installing one of these commercial-grade flat roofing products is the best way to ensure your low-slope roof section is properly sealed and leak-free for its full lifespan.

Protecting Your Low-Slope Roof

I recommend getting bids from qualified commercial roofing contractors who specialize in flat roof installation and roof replacement. They can advise the most effective and durable flat roof covering solution for your low-pitch roof section. Be sure to ask about the durability, warranty, and workmanship guarantees the roofers provide on flat roof systems and materials.

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So, Is Using Asphalt Shingles Acceptable on a Low-Slope Roof?

In summary, while asphalt shingles may be used on slightly pitched roofs down to a 3/12 or 2/12 slope, in most cases, I don’t recommend them for roof pitches any lower.

Anything less is too minimal for reliable performance from standard asphalt shingles. To properly waterproof and avoid leaks on a low-slope roof section, you need specialized flat roofing materials designed for low or no-pitch applications. Take time to research qualified flat roofing contractors in your area to ensure your low-pitch roof is properly sealed and protected long-term.

FAQs About Low-Slope Roofs

What roof slope is considered low?

Most manufacturers specify 4/12 as the minimum pitch for asphalt shingles in their installation instructions. However, anything under 3/12 is considered a low-slope roof.

Can asphalt shingles be installed on a flat roof?

No, you can’t install asphalt shingles on a flat roof. True flat roofs with no pitch require a flat roofing system, not shingles.

What underlayment should you use on a low-pitch shingle roof?

For low slopes, double underlayment is often required, including an ice barrier membrane or water shield.

How long do low-slope roofs last?

Properly installed flat roofing systems can last 15–30 years or more. Standard asphalt shingles will likely fail prematurely on low-slope roofs.

Should I hire a roofer or general contractor for a flat roof?

For best results, hire a roofer who specializes in commercial flat roofing installation and roof replacement.

Editorial Contributors
avatar for Doug Sluga

Doug Sluga

Doug Sluga is a professional roofer and carpenter with ten years of experience in residential and commercial construction. His expertise spans the breadth of the roofing trade from minor repairs to laying shingles to framing trusses. These days he spends most of his time writing about roofing and the roofing industry.

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Lori Zaino

Lori Zaino is a freelance writer and editor based in Madrid, Spain. With nearly two decades of editorial experience, she’s written and edited for publications like Forbes, CNN, Insider, NBC, Newsweek, The Points Guy, The Infatuation, and many others. Having just completed her first home renovation, she’s more interested in home improvements than ever, dedicated to bringing you fresh and accurate content to help you update your living spaces.

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