If you’ve been thinking about having a roof replacement, you may have heard some different terms thrown around. A hip roof, gable roof, mansard roof, gambrel roof, or shed roof all refer to different roof geometries, or shapes. Metal roofing, double underlayment, slate shingles, asphalt shingles, and similar options refer to roofing materials. But what about roof pitch and slope? Where do they come into play for your roofing system?
When you start hearing roof slope, roof rise, and roof’s pitch referred to, it’s the angle of your roof that is in question. Though roofing materials can vary in price and roof geometry can impact complexity, why does a different roof pitch impact your final quote for a roof replacement? Let’s start by defining what roof pitch is, then get into how your roof’s pitch can impact your overall project cost. Though many contractors use the terms roof pitch and roof slope interchangeably, there is a difference. Roof slope is the entire rise of the roof as a ratio to the entire run of the roof, which the roof pitch refers to the ratio of a specific section of roof.
What is a Roof Pitch?
A roof pitch is a combination of the roof rise over the roof run, or the loss or gain of height compared to the length of the base. Though you could measure the peak and the distance from the peak to the edge of the eaves, most builders will measure the number of inches of roof rise in one foot. As an example, a roof that is 4′ higher at the peak and 12′ to the edge of the roof will have a rise of 4:12 and will also measure 4″ higher over each horizontal foot of run to the edge.
All roofs have at least a minimum slope, even a flat roof, because otherwise, water will not drain off of the surface, causing problems with water damage and leaks. But why does a pitched roof have a different price depending on whether it’s a high-pitched roof or a flat roof? There are two factors that will impact this cost, which are discussed further below.
Common Roof Pitches
There are several common types of roof slopes and roof pitches that are commonly found on residential homes:
Flat Roof
A flat roof has almost no roof slope at all, though it must have a minimum roof pitch to drain instead of building up puddles and pools that can lead to leakage. This type of roof is usually only used in very dry areas where there is low rainfall, or on some multi-family or commercial buildings where the ability to build in a drainage system is more feasible. These structures typically have a tar-pitch roofing material or membrane system, with a slope that can go as low as 1/8″:12″ up to 1/2″:12″.
Low Slope Roof
To be defined as a low-slope roof, the pitch of your roof must be 3:12 or lower, though not as low as a flat roof. At this slope, it’s fairly easy for workers to put on a new roof, and it will require much lower amounts of material. Once you hit 2:12 and higher, you can use asphalt shingles, provided that you double underlayment layers in the process to prevent leaks up to 4:12. At 2.5:12, you can add the use of metal sheet roofing and clay tiles as an option. However, a low slope roof will also not shed water as quickly and easily, which can be problematic in hurricane season in South Carolina, and a somewhat higher pitch is recommended.
Medium Slope Roof
Extending from 4:12 to 9:12, a moderate-slope roof can use asphalt shingles with a single layer of underlayment, with the usual caveat of a double layer at eaves, peaks, and valleys for extra protection. Clay tiles and metal roofing can also be used through this range, providing excellent protection and a faster rate of rain run-off, making leaks and roof repairs less likely. However, with all roof slopes, it’s important to follow manufacturer minimum slops for a material, even if your local codes allow the material in general to be installed at a lower slope.
Steep Slope Roof
Once you pass 9:12, you’re in steep slope territory. Because the angle is harder to work on, roof jacks may be required to hold work platforms in place to provide additional protection against slip and fall accidents.
How to find the Pitch of your Roof
If you’re curious about the pitch on your roof, you can use a tape measure to measure into the peak, then from the lower edge to the height of the peak. If you have 5′ of vertical height (60″) across 10′ of horizontal distance (120″), you’ll have 6″ of rise to 12″ of run, or a 6:12 moderate pitch.
However, if you do decide to try to measure your roof’s slope or pitch, it’s very important that you have adequate safety measures in place. This should include a sturdy and adequately tall ladder, a spotter, and a safety harness at a minimum. This way, you’ll be able to protect yourself from harm while taking measurements. Never stand on the top rung of a ladder, always tie off your safety harness to a solid structure at the peak or other side of your roof, and always make sure someone is aware of your location if you can’t have a spotter with you as you’re undertaking the work.
Roof Pitch – Factors to Consider
The first aspect is the area. To start, a flat roof on a 20′ by 20′ structure will have just a touch over 400 square feet of roof surface, referred to in roofing as 4 squares. If you go to a lower pitch 3:12 pitch roof, which will be 30″ tall at a 10′ horizontal distance at the middle of the roof, each side of a roof with simple geometry will be longer, totaling 412.3 square feet. A medium-pitch roof of 6/12 will have 447.2 square feet and be 60″ tall in the center, and a steep roof pitch of 12:12 will have a 45-degree angle and require 565.7 square feet of roofing. If your roof has a much higher pitch, such as an A-frame construction with an 18:12 pitch, it will require 721.1 square feet of roofing material. Most residential roofs will fall somewhere between a flat roof and a 9:12 pitch, though there are exceptions. It’s much more common to see flat roofs and extreme angles on industrial buildings.
However, beyond the area, which will require more material to complete as the steepness of the roof increases, there’s also the difficulty of putting a new roof on a steep pitch. Roofs tend to be relatively walkable up to about a 6:12 pitch and become more difficult after that point. Low-pitch roofs are much easier to roof, requiring only ladders to the edge of the roof, and the workers can then walk on the roof surface while working. However, a higher vertical distance at the peak makes a steeper roof, which makes it harder for workers to walk on the roof and increases the risk of injury. As the vertical distance increases compared to the horizontal span, additional structure is needed to work safely. One example is a worker on an A-frame with an 18:12 pitch, who slipped and landed hard where the addition on the home had a roof of a different pitch. Though he only fell a few feet, he tore his Achilles tendon at the top of his heel, requiring surgery and loss of work for several weeks. If he had been on a lower-pitch roof, he wouldn’t have caught his foot on the high-pitch roof on landing and caused such a significant tear. Steeper pitch roofs also make roof maintenance and roof repair more difficult.
You may also experience different roof pitches based on your roof’s construction. A garage may have a 3:12 pitch, while the rest of the house has a higher 9:23 pitch with dormers to provide additional headroom in a second half story. An addition on an A-frame, as described in our injury example above, may move away from the 18:12 pitch to a simple 4;12 pitch that is much easier to work on. Your roofing company will help you with determining the overall slope of your roof to take these aspects into account when creating an estimate.
As you can see, the pitch and slope of your roof can have a strong impact on the cost of your roof, and in many situations, lower isn’t always better, especially in the heavy rains of hurricane country. If you’ve had issues with a flat or low-pitch roof and want to consider adding a higher pitch to your roof to improve water shedding or have a higher-pitch roof that needs new roof material installed, Leverage Roofing can help you. Please contact us today to get started.