The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles.
Minimum roof angle for shingles.
A shingle roof like this north dallas garage in the photo above may have a failure no matter how good a job the installer did.
How roof pitch determines suitable roofing systems.
Flat and nearly flat roofs a pitch of 1 in 12 or 2 in 12 cannot be covered with shingles or shakes of any material since there is not enough angle to combat the danger of blow off.
The highest degree possible is a 45 degree roof which is a 12 12 pitch roof.
Shingles of all types need to have a slope to function properly.
The requirements for an asphalt shingles roof are contained in the international building code.
Mineral surfaced roll roofing minimum roof slope roof pitch r905 5 2.
The following table provides the minimum required allowable roof slope for each type of roofing material mentioned in the code.
The standard for roof pitch is 4 12 though a 2 12 is completely fine for most structures.
These are also the most common pitches for shed roofs.
For simplicity sake every degree of pitch is roughly 4 75 degrees.
That works out to about nine degrees if that works better for you.
This means for every 12 horizontal units the roof must rise a minimum of 3 vertical units.
The asphalt shingle manufactures recommend that you install asphalt shingles on a recommended minimum of 4 in 12 or greater however most manufactures will warrant their shingles down to a 2 in 12 pitch if the recommended installation method is used.
The minimum pitch for shingles is 1 6 which is equivalent to 4 inches rise to 24 inches run.
Determine the minimum slope of the roof based on the roofing material.
Metal roof shingles minimum roof slope roof pitch r905 4 2.
The 2 12 number is rise over run or two units of vertical for every 12 units horizontal.
Again the most important consideration is the weather.
What is the minimum slope for an asphalt shingle roof.
Installation on roof slopes below a 2 in 12 pitch is not recommended at all.
The minimum requirement is 2 12.
Metal roof shingles can only be installed on roof slopes of 3 12 or greater 25 slope.
Use a handy tool like snow load calculator to help you determine if your roof can handle the weight of snow based on its pitch.
Any roof from 4 12 to 9 12 is considered an ordinary angle for a roof.
The minimum roof slope allowed by code for any type of roof is in 12 applicable only to coal tar pitch roof systems.
