If you’re planning to make changes to the roof of your home such as adding an extension, installing features (like skylights), or cutting new rake boards, it will be necessary to calculate the correct roof pitch.
Also called the roof angle, the roof pitch is defined as the numerical measure of the steepness of a roof, or the ratio of the rise of the roof to the horizontal span. You can calculate the roof pitch by the number of inches that it rises vertically for every 12 inches that it extends horizontally. As such, a 7/12 or 7-in-12 roof pitch means that the roof rises 7 inches for 12 inches that it runs horizontally.
There is no single set standard for roof pitch across the country, but contractors typically refer to thresholds when figuring out what to charge for roof installation. A low pitched roof, for example, falls within the range of 2:12 and 4:12. Medium pitch would be between 4:12 and 9:12. Anything that is 9:12 and up will then be considered a steep slope.
How to determine the typical roof pitch for your home
There is a simple way to compute your house’s roof pitch, from inside your attic. Using a pencil, a tape measure, and an 18- or 24-inch level, measure 12 inches from one end of the level and mark the spot first. Afterwards, in the attic, place one end of the level against a roof rafter’s bottom, making sure to hold it completely level. Next, measure vertically from the 12-inch mark you made on the level, straight up to the rafter’s underside. The measurement you get is the number of inches that the roof rises in 12 inches.
You can also calculate the roof pitch from the top of the roof. Place the level at any point on the roof’s angled slope. When you’re sure that the level is steady, measure 12 inches. From that 12-inch mark, measure down to the roof’s surface. If you get a distance from the level to the roof of, say, 5 inches, then the roof pitch is 5:12.
If you’re having a roof installed, keep in mind that costs go up as the roof pitch becomes steeper. This is because contractors will need specialized equipment to put steep-pitched roofs into place, and this task can mean additional safety risks for the workers, so that will have to factored into the expenses.
There’s good news, though; having a steeper pitch means that water and ice flows off the roof better instead of sitting on the roof and potentially causing damage over time. A steep pitch can then actually be considered a good home improvement investment.