A roof’s pitch is an important consideration when planning many kinds of home improvement projects. Knowing the pitch of your home’s roof can be very useful when installing skylights, designing an addition, or creating new rake boards. Read on to learn a safe and simple way to determine the pitch of your roof from within your attic.

Understanding Roof Pitch

Roof pitch is essentially the slope created by the roof rafter. It is often expressed as a ratio between the rise and the run in the form of x by 12 (x:12). We can generally divide roofs into the following main categories: Flat roofs: Flat roofs are really not perfectly flat; they actually need a small slope to keep water from pooling. Generally, these types of roofs will have a pitch ranging from 1/2:12 to 2:12. Low pitched roofs: These roofs have a pitch below 4:12. These types of roofs can be difficult to maintain, since they require special materials to prevent leaks. Conventional roofs: Most roofs have a pitch ranging from 4:12 to 9:12. They are the easiest types of roofs to construct and are also safer to walk on. High-pitched roofs: Higher-pitched roofs often demand additional fasteners and have drastic pitches that can be up to 21:12.

Calculating Roof Pitch

Roof pitch is generally calculated from the same mathematical formula used to describe a right triangle. If you’re handy with math, you can use these equations to find the length of the rafter in relation to the slope:
  • rafter² = run² + rise²
  • rise / run = pitch, where the pitch is expressed in a percentage
  • pitch = tan (angle), where the angle is the roof pitch shown in degrees
If you would like to find the roof pitch in the form of x:12, just calculate the pitch and use 12 for the run length; “x” will be the value displayed as the rise.

An Easier Way to Determine Roof Pitch

If all that sounds too complicated, there is a simpler method. To measure your roof pitch from within your attic, you will need a tape measure, an 18- or 24-inch level, and a pencil.
  • Start by measuring 12 inches from one side of your 18- or 24-inch level and make a mark.
  • Next, enter your attic and place the end of the level up against the very bottom of a roof rafter.
  • Measure vertically, starting from the 12-inch mark on the level going straight up to the very underside of the rafter.
calculating roof pitch The pitch or angle of a roof is essentially calculated by measuring the inches it vertically rises for every one foot it extends horizontally. For instance, a roof that rises 3 inches for every 1 foot of horizontal run has a 3-in-12 pitch, since there are 12 inches in one foot. With the above method, the measurement you end up with will be the number of inches the roof rises per every 12 inches.

What’s the Best Pitch for a Roof?

The best pitch for a roof depends on the type of roof you prefer. If you prefer a sleek, contemporary style, you might want a flatter roof with a pitch of 1:40. For a Gothic type of style, the rafters should equal the span, while an Elizabethan design would require the span to be shorter than the rafters. In snowy regions, your roof pitch should be at least 10/12, so snow will be able to shed. In very windy areas, roof pitch should be between 4/12 and 6/12.

Other Things to Consider

Knowing your roof pitch is important because it helps in determining the correct type of roofing system. It also helps determine the appropriate type of materials to use for a variety of home improvement projects. Furthermore, an accurate measurement of your roof pitch is an important way to assess the complexity of a roof’s design that helps roofers go about their work. If you aren’t sure how to measure your roof pitch or just want to make sure your measurements are accurate, it’s a good idea to consult a reputable contractor. Established more than two decades ago, National Home Improvement has helped countless homeowners with a wide variety of home repair and improvement projects. Committed to consistency, integrity and quality, our seasoned team will work with you each step of the way to turn your vision into a beautiful reality.