A roof’s pitch determines the steepness of the roof of a building and is an important factor to consider, especially when it comes to roof repair or installation. Understanding the measurement of your roof’s angle will allow you to determine what roofing material will be the most effective for your home’s protection and how efficiently it sheds weather like rain or snow.
What is Roof Pitch?
Roof slope and roof pitch are two terms that are often used interchangeably, but they are not the same. The slope of a roof is used to refer to the rise of the roof by the run of the roof, which is the distance from the edge of the roof to the center of the roof, as opposed to span, which extends the full length or width of the home. Slope is typically represented as inches per foot or as a ratio like 3:12 or 4:12 and can also be written as 3/12 or 4/12.
The steepness of a roof, or its pitch, uses measurements based on the entire roof span and is determined by calculating the ratio between the roof’s rise to the roof’s span (distance from one side of the building to the other). Roof pitch is expressed as a ratio of the roof’s vertical rise to its horizontal span, or run. For example a 4/12 roof pitch means that the roof rises 4 inches for every 12 inches it runs.
The higher the first number (the rise) in the ratio, the steeper the roof; the second number in the equation is the horizontal area measured. A 4/12 roof pitch angle is about 18.4° which is a fairly common low to medium pitch. Generally speaking, anything under 3/12 is considered a low pitch roof, and anything above 6/12 is a steep roof pitch and becomes much harder to walk on, install and repair.
Why is Roof Pitch Important?
All types of roofs are pitched to some degree to ensure effective drainage. A steeper roof pitch helps your home shed water, snow and even debris more quickly and areas that have high annual snowfall for example often have building codes with minimal roof pitch details. A home with a more flat roof exposed to snow and ice build up risks permanent structural damage and even roof collapse.
If your home is in an area prone to high winds, you’d want to consider a lower roof pitch because high winds can do more damage to steep roofs as the wind hits them more directly. The pitch of your roof also determines what type of roofing materials can be used. Commonly used materials including slate and asphalt shingles depend on gravity to prevent water from intruding through the overlaps and work more efficiently with steeper roofs.
Since steep roofs have a larger surface area they need more materials to build and will cost more than installing a gently-sloped roof. You will also need to use special safety measures like shinglers and roof brackets when installing or repairing steeper roofs. Unless your climate or style demands a higher pitch, lower pitch roofs are easier and safer to work on and more cost effective making them increasingly popular.
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