Understanding your roof’s pitch is vital when it comes to home maintenance, planning renovations, or installing new roofing. The pitch – or angle – of your roof affects how the building copes with rainwater, wind, and the weight of snow. And, crucially, roof pitch affects the overall look and style of your home.
What Is Roof Pitch?
Roof pitch means the steepness of a roof. Usually expressed as a ratio or angle, the roof pitch measures how much the roof rises vertically over a horizontal span, in a triangle. This is called the “run.”
What Is Roof Slope?
Roof slope and roof pitch are terms that are often used interchangeably, but these are technically different things.
Roof slope: Simply the steepness of a roof, calculated as the vertical rise over the horizontal distance, without involving angles or ratios
Roof pitch: A ratio or angle based on the steepness of the roof slope
While the slope is a straightforward measurement, roof pitch helps determine the best materials and design features for your roof.
Types of Roof Pitch
The pitch of a roof is generally one of two types: low-slope or steep-slope.
Low-Slope Roof
Generally speaking, a low-slope roof has a pitch of 2:12 or less. This means that the roof rises two inches for every 12 inches of horizontal run, like a relatively flat triangle.
Low-slope roofs are typical on commercial buildings. While more susceptible to water pooling on the surface, materials like rubber membranes, tar, and gravel can help prevent leaks. They also require more maintenance as they collect debris and moisture.
These roofs are easier to walk on and can easily fit solar panels or air conditioning units.
Steep Slope Roof
A steep-slope roof, on the other hand, has a pitch greater than 4:12 – think of a steep triangle. These roofs are common among residential homes.
Steep-slope roofs offer better drainage and last longer with less maintenance. They allow water, snow, and debris to run off more easily than low-slope roofs.
However, the steep angle makes these kinds of roofs more challenging and costly. They require more labour and materials and are often made from shingles, tiles, or metal.
How to Work Out Your Roof Pitch
There are several ways to calculate roof pitch.
1. Measure From the Roof
One way to calculate the pitch of a roof is by measuring it directly:
- Place a level flat on the roof surface horizontally
- Measure a set horizontal distance
- Measure the vertical rise from the roof surface at the end of the level to the bottom of the roof surface
Remember to be safe and take necessary precautions if you’re climbing on the roof to measure the pitch angle – especially on steeper roofs. It’s best to avoid climbing a sloped roof in winter or wet weather.
2. Measure From the Attic
If accessing the roof is challenging or dangerous, here’s a method for measuring roof pitch from inside the attic:
- Place a level horizontally against one of your roof rafters
- Measure a set distance (12 inches again) along the rafter from the attic floor upwards
- Measure the vertical rise at the 12-inch mark
3. Measure the Total Rise and Run
To calculate the total rise and run of your roof, measure the total height of the roof from the ridge – the topmost point – to the base and the total horizontal span.
Divide the height by the span to get your roof slope.
Measuring roof slope is useful when calculating the capacity of your roof to bear weight. This is important to make sure you use the right materials for your roof.
4. Measure With a Speed Square
- Place the speed square against the roof surface
- Rotate it until the bubble level is horizontal
- Read the pitch from the corresponding markings on the speed square
Speed squares are quick for getting an accurate reading, and are go-to tools for professional roofers.
How to Calculate Roof Pitch in a Ratio
Roof pitch is most commonly expressed as a ratio of rise over run – for example, a roof with a 6:12 pitch rises six inches vertically for every 12 inches of horizontal run. Understanding ratios are particularly useful when discussing roofing materials with a professional or planning a project.
Here’s how to calculate your roof angle in a ratio:
- Measure the vertical rise of your roof
- Measure the horizontal run
- Divide the rise by the run to get a ratio like 6:12 or 4:12
How to Calculate Roof Pitch in Degrees
Another method of calculating roof pitch is to measure the angle in degrees.
To do this, you’ll need trigonometry. Once you’ve measured the rise and run, apply the following formula:
Roof Pitch (in degrees) = arctangent (rise/run)
Use a calculator to find the arctangent. Rounded to two decimal points, this is your roof pitch in degrees.
For example, if the rise is six inches and the run is 12 inches, the roof pitch in degrees is approximately 26.57°.
You can also use an online roof pitch calculator to convert a ratio to degrees.
Standard Roof Pitches
The minimum standard roof pitch for residential roofs is generally around 4:12, which is a relatively flat roof. Steeply pitched roofs might have a maximum patch around 9:12.
Flat roofs are suited to areas with little rain or snow-prone regions. A steeper pitch works well in areas with more rainfall and snowfall, as it allows for faster runoff.
Understanding Roof Pitch
Understanding how to calculate your roof pitch and angles is a key skill for any homeowner. It’s especially important for those planning renovations or roofing repairs and calculating roofing costs.
Whether you’re dealing with low-pitched roofs or a steep pitch, knowing how to measure and calculate pitch can save you time, money, and future headaches. You’ll be better prepared to select materials, hire contractors, and maintain your roof effectively.
FAQs
What Is the Standard Pitch for a Roof?
The standard roof pitch for residential homes typically ranges between 20 to 25 degrees, which means a ratio of around 4:12 to 5:12. However, this can vary depending on the design, local building codes, and weather conditions.
What Is the Best Pitch for a Roof?
There’s no one-size-fits-all roof pitch, as it depends on your location and needs. For areas with heavy rainfall or snow, a steeper pitch (above 6:12) will improve water runoff. A low-sloped roof is suitable in warmer, drier climates.