Do you feel like your contractor is speaking a different language when they talk about pitch ratios? Are you planning to replace your roof but aren’t sure how to choose the right material for your slope?
Roof pitch isn’t just a builder’s term; it directly affects the material you should use, how long your roof will last, and what kind of damage you could be facing in Seattle’s damp climate.
At RoofSmart, we understand that it can be difficult to figure out all of the factors you need to consider when choosing the right roofing material for your home. We help hundreds of customers every year to find their perfect roof material based on their needs, budget, and roof slope.
In this article, you’ll learn exactly what roof pitch is, how to measure it, why it matters, and which roofing materials are best for each type.
Whether you have a flat, low-slope, regular, or steep roof, you’ll walk away knowing how to protect your home (and your wallet) from unnecessary damage.
What is roof pitch?
Roof pitch is how steep the roof is. It is calculated by using the rise and run of the roof. So, for example, if you have a roof with a 2:12 pitch, that means for every 12 feet the roof rises a total of 2 feet.
Here’s an example of what the different roof pitches look like:
Image from Kentucky Metal Roofing
Roof pitch is divided into 4 categories:
- Flat roofing: Completely flat to 2:12 pitch
- Low-slope roofing: 2:12 to 4:12
- Regular roofing: 4:12 to 12:12
- Steep roofing: Higher than 12:12
What happens if my flat or low-slope roof has the wrong material?
So, why does knowing your roof pitch matter? Can’t you just slap some asphalt shingles on any roof and call it a day?
Well, technically, you can if you don’t care how long your roof will last. However, in a rainy, wet area like Seattle, it’s important to make sure that your roof material is set up to protect your home from water getting in and causing damage. Knowing your roof’s pitch can help you pick the right material.
Most homes in the Seattle area have a regular slope (4:12 to 12:12). If your home falls into this category, then you can expect standard roof materials (like asphalt shingles or metal panels) to protect your roof.
But not all roof materials are designed to work on every roof pitch. For example, asphalt shingles don’t protect your home properly on a flat or low-slope roof. Without the help of gravity to pull water off the roof, asphalt shingles can wear down and let water in.
If you put the wrong type of roof on your Seattle home, it can lead to these issues:
- Leaks
- Mold
- Water damage
- Rotting wood
These are all issues that can happen for years before you even notice. The worst part? This kind of damage isn’t covered by warranties or insurance, so you’ll have to pay thousands of dollars to repair your roof.
Which roof material is best for flat or low-slope roofs in Seattle?
Because flat and low-sloped roofs are so susceptible to leaks, there are special materials that you can use. Your options include:
- PVC: This is a similar material to a pool liner. It has a plastic base, making it light and flexible. It is installed on the roof using a heat gun.
- Torch down: This material is made of modified bitumen. It basically looks like one big asphalt shingle, and can come with or without a granule layer on top. It is installed using a torch gun.
- TPO: This is a similar material to PVC, but it has a rubber base instead of plastic and is more affordable. It is also installed using a heat gun.
- EPDM: This is another rubber-based product, but it is the least flexible of all the options. It can only be installed in warm weather (otherwise it will be too brittle and break). It sticks to the roof using an adhesive.
- Metal roofing (this is only for low-slope roofs): Metal roofing can be used on low-slope roofs if it goes through the process of mechanical seaming, which reseals the seams to make the roof extra waterproof. This is a good option if you want great protection and are looking for something fancier than the standard flat roof material options.
Flat roof materials are adhered to the roof using adhesive or heat. This means that there are no nails in the top layer that can become potential leak points (unlike an asphalt shingle roof, which has hundreds of nails all over). This way, the roof is sealed completely from water, even when it pools up.
You can put flat roof materials on regular or low-slope roofs, but it’s not common. This usually only happens when your roof has multiple slopes.
A well-known example is the Tacoma Dome, which has a wide range of slopes but is covered in a flat roof material.
Image from Western Wood Structures
What happens if my steep slope roof has the wrong material?
Asphalt shingles also don’t work very well on a steep roof (12:12 pitch or higher) because the asphalt shingles are so heavy that they pull down and tear at the nail points. Eventually, the shingle will fall off completely.
This is the perfect place for rain or moisture to get in, leading to leaks and water damage in the roof.
Shingles have a special nailing requirement on a very steep slope. You're supposed to put more nails in a specific pattern, and then you're also supposed to take like a quarter-inch dab of sealant and put it at the lower corners of the tabs on every single shingle.
But it'll still fail because that dab of sealant will get hotter in direct sun even though it's underneath the shingle. It's almost like a sauna rock hidden underneath, and so the heat gets transferred into the sealant more than the shingle.
This leads to blistering, which also causes the shingle to fail and leak.
Which roof material is best for regular and steep pitch roofs?
You can use pretty much any roof material on a regular slope roof. Common options for Seattle area homeowners include:
- Asphalt shingles
- Metal roofing
- Euroshield
Other options that aren’t as common (because they’re more expensive) include:
- Cedar shake
- Tile
- Slate
For a steep roof, we recommend something that gets lightweight or screwed in, like:
- Metal
- Cedar shake
- Euroshield
- Slate (these are held up with hooks on the bottom, so they’re very secure)
How Do You Make Sure You Hire the Right Roofer for Your Roof Pitch?
Understanding your roof pitch is just one part of the equation. The other? Making sure the person installing or repairing your roof actually knows what they’re doing, especially on Seattle’s flat or low-slope homes.
The wrong pitch paired with the wrong material can cause years of hidden damage. But even the right material won’t protect your home if it's installed incorrectly.
That’s why the smartest next step is to download our Qualified Roofer Checklist. It will show you exactly what to look for (and ask about) when hiring a roofer—so you can avoid costly mistakes, premature leaks, and shady workmanship.
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