How to calculate roof pitch

Few property owners realize just how important the pitch of the roof over their heads is to their overall safety, particularly in areas where heavy snowfalls are commonplace.

Roof pitch is the measurement that defines the slant of a roof – the steeper the pitch, the better the runoff of water and snow.

People who live in areas that experience heavy snowstorms in winter, like Massachusetts, know that a roof can collapse under the weight of snow. That is why their state government has published guidelines on ways in which to clear snow from rooftops. The guidelines state that low-pitched roofs “are at greater risk of buckling under heavy snow and ice accumulations”.

That is why the pitch of a roof is so important. A steeply pitched roof will prevent snow from settling down on top of your home because of its runoff.

If you are building a new home in cold winter area, seriously consider using wood shake shingles on the roof. They are resilient in winter weather conditions. Wood shake shingles are thicker than either metal or asphalt shingle roofing and are impact-resistant to ensure the safety and integrity of a building.

Before we broach the method used to calculate roof pitch, let us clear up some existing anomalies regarding “pitch” and “slope”. These two terms have different meanings.

The pitch                                            

According to the National Association of Certified Home Inspectors (NACHI), the pitch is the measurement of the slant of the roof. In other words, the steepness or slope. Pitch is measured in inches and expressed as a ratio of the vertical rise to the roof’s horizontal span. It is measured in inches and expressed as a ratio.

The slope

Slope refers to the distance between the length of a roof. The slope is measured from the top plates of the two exterior walls. The length of a roof is also known to as a run.  The run, too, is expressed as a ratio and this horizontal area is measured as 12 inches or one foot.

Explanation

If the pitch is 10, and the slope is 12 – 10:12 – it means that the roof rises 10 inches for every 12 inches of the roof. This type of pitch is an example of a steeply sloped roof.

Pitch roof categories

Flat roof

No roof is entirely flat and has a slight angle to allow water to drain off the surface. Expressed in inches, they have a pitch of between ½:12 to 1:12.

Low-slope roof

Low-slope roofs may be easy to walk on but are less efficient for runoff of snow and water. They have a slop of between 1:12 to 4:12.

Medium-slope

You can work on a ratio of between 4:12 to 9:12 for a medium-slop roof. In mathematical terms, these ratios are expressed as 1:3 and 3:4. The most common medium-slope roofs have pitches of 6:12. These are a good balance for runoff and easy access.

Steep-slope

A steep-slope is a pitch of 9:12 or more.

Slope gradients overview

Many homeowners opt for properties with a steep pitch roof. Not only are the angled shapes aesthetically pleasing but, because of the gradient, can be described as “a safe roof over your head”. This type of roof ensures runoff of snow and water and should not collapse during heavy snowfalls. However, a steep pitch roof costs more to build because the spans are larger, requiring more material than less sloped counterparts. A high-pitch roof also requires the services of skilled labor.

In areas with more temperate weather, such as the Southwest, low-pitch roofs provide satisfactory cover. These roofs are popular on ranch homes. Metal and concrete shingles are popular choices for low-pitch roofs.

Calculating the pitch

What you will need

  • Measuring tape
  • A large carpenter’s level
  • A ladder
  • Using a tape measure, measure 12 inches on a large carpenter’s level and mark the 12-inch line.
  • Now, place the ladder against the wall at the gable end of the house.
  • Climb to the top of the roof.
  • Place the carpenter’s level against the gable trim. You must lay it flat against the side of the house.
  • Use the measuring tape measure from the 12-inch mark on your level up to the bottom edge of the gable trim. This number you arrive at is the rise.
  • Rise measurements are written as “# in 12”. This is the pitch of the roof. If the rise is 4 inches, the roof’s pitch is 4 in 12 (4:12)

Pitch measurements

You will need to calculate the area of the roof to calculate the pitch.

Single pitch

A pitched roof has a gradient over 15 degrees – the higher the pitch, the larger the size of the roof area. Although a high pitch roof requires more material,  it allows easy drainage of snow and water.

Double pitch

A double pitch is a roof that forms a ridge (the pitch) in the middle and runs in two different directions.

Selecting roofing materials

Asphalt Shingles

Asphalt shingles are the overall popular choice for most residential properties. They are budget-friendly, easy to install and versatile. These shingles have a lifespan of 15 – 20 years and adapt well to all climates, hot or cold. Asphalt shingles also have good waterproofing qualities.

Slate shingles

Slate roof shingles are not only resistant to rot, but also offer a lifetime of service of around 100 years. A disadvantage is that these shingles are heavy and therefore not suitable in cold climes with high snowfalls.

Wood shake shingles

Wood shake shingles are a popular choice in areas with heavy snowfalls. They are “green-friendly” and have a lifespan of 30+ years.

Metal shingles

Although metal shingles require installation by professionals, they are light-weight, environmentally friendly and are easy to maintain.

Conclusion

The number one rule for any homeowner is a safe roof over their heads. Choose your roof materials wisely to meet both budgetary constraints and years of carefree service.

References :

www.safeharborroofingandsiding.com

https://www.prestigeroofinglv.com/what-is-roof-pitch/https://www.pjfitz.com/diy/roofing-installation/calculate-roof-area/