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Minimum Slope For An Asphalt Roof

Shingles of all types need to have a slope to function properly. The minimum slope for an asphalt shingle roof pitch is 2:12, meaning that for every two units of vertical for every 12 units horizontal. That works out to about nine degrees if that works better for you. A shingle roof can have a failure no matter how good a job the installer did. This minimum slope requirement can be found in the roof installation instructions for almost every manufacturer and in many building codes. 

What Is Roof Slope?

Roof slopes are defined as a ratio of rise-over-run.  If the rise of the roof slope is 2 inches when measured 12 inches along the bottom of a horizontal roof, the roof slope is then 2 inches of rise per 12 inches of run. You can measure the roof slope on the bottom side of the roof deck at an easily accessible point such as the rake, using a tape measure and simple geometry. Alternatively, there are also apps you can get on your phone that can help, but shingle manufacturers distribute convenient pitch estimator cards which provide a quick way to estimate the slope.

A roof pitch estimator can help you determine if your roof slope is likely too low for shingles. The majority of the homes in the U.S have typically been constructed with a slope between about 4:12 and 9:12. Roofs at the lower end of the range between 2/12 – 6/12 are relatively easy to walk and work on. As always proper safety equipment and precautions must be followed when working on any roof. Steeper roofs “show” the shingles better, and are therefore better suited to premium designer styles. Shingles on a steeper roof also tend to weather at a slower rate due to their favorable angle to the sun’s rays.

Low Sloped Asphalt Roof Shingle Installation

 

Asphalt shingles are an effective roof covering material for sloped roofs that can be successfully used on slopes as low as 2:12. With respect to shingle application, roof slopes from 2:12 to less than 6:12 are called “low slope” roofs, while roof slopes of 6:12 or greater are called considered to be standard slopes.  Asphalt shingles should never be applied to roof slopes below 2:12, this is lower than the minimum slope of a metal roof so ensure to check the different minimums for each roof material.

When installing asphalt shingles on a low slope roof, after the manufacturer’s application instruction has been completed, an extra underlayment with a specific method for application is required. As it is a lower slope, these styled roofs have a tendency to allow more water to enter, primarily because of severe ice dams and harsh rain. The need for underlayment increases to help enhance the water shedding element of the roof system.