What Do You Need to Know About Roofing on a Steep Slope?

Do you have an unusually steep roof and worry that the roofing material you choose could start pulling apart, slipping, or failing under its own weight? Are you concerned that replacing a 12/12-or-steeper roof could already cost more because of the extra labor and safety requirements—only to find out later that your roofer installed a material that wasn’t well suited for such an extreme slope?

At RoofSmart, we’ve repaired and replaced hundreds of steep-slope roofs throughout the Greater Seattle area, and we’ve seen firsthand that materials that perform well on a standard roof don’t always perform the same way on an extreme pitch. The material’s weight, construction, fastening requirements, water runoff, and even your gutter system all become more important when your roof is this steep.

In this article, I’ll explain which roofing materials we recommend and which ones we would avoid on roofs with a 12/12 pitch or steeper. I’ll also cover the additional installation and safety requirements that can make these projects take longer, why some asphalt shingles are better suited to steep slopes than others, and how your roof’s pitch can affect your gutters and gutter guards.

What’s the worst roofing material to install on a steep-slope roof?

Typically, asphalt shingles can have a lot of problems on a steep slope. Here are the styles of shingles you should definitely avoid on a steep roof:

• Heavy shingles (like thick luxury or designer shingles)
• Extremely thin architectural shingles
• 3-tab shingles
• Slate or tile

On a roof with a very steep slope, heavier asphalt shingles should be avoided because they can delaminate and start to pull apart under their own weight over time while they are sitting on the roof.

The heavier the shingle, the more pressure on the sealant. Think of it like a heavy sweater stretching on a cheap hanger. They’re not designed to sit on the hanger and be pulled down like that. Eventually, the sweater will be ruined, just like your roof.

An example of that is the now-discontinued GAF Grand Canyon. Unfortunately, for some reason, there was more than one house with a steep slope where I saw this shingle in particular fall apart. I haven’t seen any GAF shingles have the same frequency of delamination issues since it has been discontinued

On the other hand, even though thin architectural shingles and 3-tab shingles weigh less than heavy shingles, they do not have enough structural integrity to stay together at a steep angle. They’re more likely to fall apart.

You can add slate or tile, but the big issue there on a steep slope is the weight. The material itself will hold up fine on the roof, but you’ll need to hire an engineer to make sure that the roof and walls are properly reinforced for the weight of slate or tile. It will be a very expensive roof installation.

Note: For the purposes of this article, anything that is 12/12 or steeper is considered a steep-slope roof. This is important to clarify because some manufacturers consider a 4/12 slope to be steep. But we’d consider that to be more of a standard slope.

Here's what different roof slopes look like from 1/12 all the way to 18/12:

Image from Kentucky Metal Roofing

What’s the best roofing material to install on a steep-slope roof?

There are some roofing materials that work well on a steep slope. Here are the top options:

• Metal: An excellent choice for steep roofs because it is lightweight but still very strong. The panels are secured together with screws, so you don’t have to worry about them falling apart.
• Premium Cedar Shake: This is the ideal steep-slope roofing material because it drains quickly and prevents rot. It is not at risk of failure from water because the slope is so steep that the water just runs right off. It’s actually at a much lower risk of water damage when the roof is steeper. When cedar shake is able to stay dry, it lasts a long time.
• Asphalt Shingles: Pick a standard architectural shingle for the right balance of weight and quality shingle construction.
• Example: One example of this is the Owens Corning Duration shingle. It is a great option because of the SureNail strip technology it’s built with, which provides superior reinforcement. On other shingles, the nail strip is so small that it’s difficult to hit the nails on it every time.

Best and Worst Roofing Materials for Steep-Slope Roofs

Are there different requirements for roofers installing roofs on a steep slope?

Every roofing material has different installation requirements, but it’s usually a matter of following the manufacturer’s installation instructions. In some cases, it’s the same for a steep slope, while other times there are additional requirements.

For example, some of the asphalt shingle manufacturers will say you need to get the nail exactly in the nail strip, and you need to hand seal the shingles. To hand seal the shingles, the roofer adds a quarter-sized dollop of roofing cement on each of the corners.

So, you can imagine how much more time this would take. Pretty much all steep-slope roofing jobs take around two times longer due to additional installation requirements and safety needs. Roofers usually have to set up scaffolding and navigate it to access the roof rather than walking directly on the roof like they would on a less steep slope.

Does having a steep-slope roof affect your gutters?

On a steep slope, larger gutters may be needed if your new roof material significantly increases water runoff speed. This is usually only needed if you install a metal roof because the water shoots right off of those.

Another important factor to consider is that most gutter guards fail on steep slopes because they cannot handle large amounts of water hitting them all at once. We have seen MasterShield gutter guards be very successful on steep-slope roofs, though.

This is what MasterShield looks like installed on the roof:

How does roof pitch affect your Seattle roof replacement?

If your roof has a 12/12 pitch or steeper, choosing a roofing material isn’t just about appearance, price, or expected lifespan. The extreme angle can affect how certain shingles perform, how quickly water leaves the roof, which gutters and gutter guards will work, and how your roofing contractor needs to approach the installation.

As we’ve seen on steep Seattle-area roofs, material choice matters. Heavy designer shingles can put additional stress on their sealant and construction, while very thin shingles may lack the structural integrity you want at an extreme angle. Metal, premium cedar, and properly selected architectural asphalt shingles can be better suited to these roofs, but each still comes with its own installation requirements.

Your roof pitch can also affect the complexity and cost of the project. A steep roof may require scaffolding, additional safety precautions, hand sealing, and more labor, which is why these projects can take significantly longer than a standard roof replacement.

Read our article “What Is Roof Pitch and Why Does It Matter on My Seattle Home?” to learn how roof pitch is measured and how it can influence your roofing materials, installation, cost, and overall roof performance.