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.
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.
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
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.
