What is the Difference Between a Pitched and a Sloped Roof?
The difference between a pitched and gently sloped roof can amount to quite a bit in terms of roofing materials and ease of repair. Roof pitch can determine whether one type of roof covering, say composite shingles, will work or if the pitch is below a certain amount, you might have to use a single ply membrane system, like Duro-Last.
But What is Roof Pitch Anyway?
Here is where your math comes in. When someone remarks on the pitch of a roof, they are referring to the angle, slant or slope of your roof. A roof with the least pitch would be a flat roof.
The pitch is measured by a simple formula. Wikihow.com gives a detailed explanation of the formula for roof pitch. Simply put, the pitch is determined by taking a level (18” to 20”) and a measuring tape into your attic (if you have one) and placing it against the bottom of a roof rafter, holding it so it is absolutely level. Make sure you can see the 12” mark on your level. Take your measuring tape at that 12” mark and measure up vertically, to the underside of the rafter. That number, whatever it is, will determine the rise of your roof. If your tape measures 4” the pitch formula is 4:12, which makes it a low-slope.
Categories describing roof pitch are loosely defined by the slope:
- Flat– That may actually be a misnomer, because no roof is completely flat, since they need to have a slight angle to enable rainwater to drain off the roof. Still, they can get away with a minimum pitch of only ½:12 inches to 1:12 inches, with proper drainage techniques.
- Low-slope–Low-slope roofs also require may special attention to techniques and materials to promote proper drainage and prevent leaks. You can access flat and low-slope roofs and they are easy to walk on, but most of them shouldn’t be walked on by people who don’t know what they are doing, as the roofing materials themselves can be damaged by too much foot traffic. Low slopes are much less efficient at allowing the run-off of rain and snow. Low slopes have a pitch of between 1:12 to 4:12 inches.
- Medium-slope– This slope is the most common. You’ll see them in the flatlands and on the hillsides. They provide both ease of access, stability and enough of a downslope for runoff. Their pitch is between 4:12 to 9:12 but the most familiar have a slope of 6:12.
- Steep-slope– Roofs with steeper slopes often require extra fasteners and can be very challenging or even impossible to walk on. We don’t see many buildings with severely steep sloped roofs in the San Francisco Bay area. They are more common in certain climates in Europe. They can add a decorative charm to a home but cost more to install and maintain. A steep slope is any pitch above 9:12.
Roof pitch can be a health and safety issue on homes in geographic areas that experience heavy snow and rain. A steep slope to a roof makes it more difficult for wet snow to accumulate and put undue stress on your roof. That isn’t an issue in the Mediterranean micro-climates of the San Francisco Bay Area.
However, heavy rains, like those we experienced in Marin County in late 2018, pooled and accumulated on a flat commercial roof on the Home Goods store in San Rafael causing it to collapse. The store remained closed for almost a full year.
Knowing something about roof pitch will come in handy when envisioning that addition, or remodeling job for your home or even something as simple as choosing the right skylight for installation.
The Professional Roofers at Booth And Little are Here To Answer Your Questions
If you are designing a home improvement project that involves roofing or planning a rainy-day fund for a reroofing project, the team at Booth and Little Roofing are happy to discuss your roofing questions. Contact us today for all your roofing needs.