Roof slope is a measurement of a roof’s steepness or incline. It’s expressed as a ratio between the vertical rise of the roof (in inches) for every 12 inches of horizontal run. It can be written in a couple of ways, such as 4/12 or 4:12. Both mean that the roof rises 4 inches for every 12 inches of run.
Roofs that have a slope below 3:12 are considered flat or low slope. Conventional roofs have slopes from 4:12 to 9:12 and are standard for most homes. Steep-slope roofs are defined as roofs with a slope greater than 9:12.
How is roof slope measured?
The most accurate way to measure the slope of a roof is from the unfinished attic or anywhere you can access the underside of the roof deck. You’ll need a level and a tape measure. Mark 12 inches from one end of the level. Place it so it touches the roof decking material and hold it level. Measure from the 12-inch mark on the level to the roof deck. That distance is the roof rise. The slope is the ratio of that rise to the run (12 inches in this case).
To measure the roof slope from the roof, you’ll need a board or other flat surface to lay across the shingles. Using the same level with a 12-inch mark, place a corner on the flat surface and hold it level. Measure the distance from the 12-inch mark to the flat surface to determine the rise.
You can also use smartphone apps to determine the roof slope by laying your phone on the roof surface.
Why is roof slope important?
The slope of your roof is important for several reasons:
- Amount of drainage required – Steeper roofs can easily shed water and snow, while lower slope roofs need more drainage to help prevent water backing up and causing leaks. Roof drains can be installed on low-slope roofs to improve localized drainage and prevent ponding.
- Roofing materials – Most residential homes have conventional slopes, and asphalt shingles are designed to shed water, so they provide sufficient protection. Low-slope roofs, however, require waterproof roofing materials because they often have standing water. Vinyl, plastic, and rubber materials are used to create membranes that provide a waterproof seal on low-slope roofs.
- Aesthetics – Roof slope is a key component in determining your home’s architectural style and appearance. Steep slopes are often found on Gothic or chalet-style homes, while low slopes are common on more modern designs.
- Roof materials and installation costs – Steeper sloped roofs require more materials than lower slopes. Also, due to the increased safety risks when working on steeply sloped roofs, you may have to pay more for roof installation.
The team at New Roofs is here to help, no matter how steep your roof slope is. If it’s time to replace your home’s roof, contact our team or use our instant quote tool, which uses satellite imagery to determine your roof’s size and slope.