The pitch of the roof is determined by the vertical rise in inches for every horizontal twelve inch length.
Minimum roof angle for rain.
Flat roof slope minimum according to the international building code the typical built up flat roof that uses tar or asphalt goes by the guideline that for every foot 12 inches of a flat roof a minimum of inch must step up or down.
The minimum pitch for a roof is 1 4 12 which translates to 1 4 inch rise to 12 inches of run.
As a general rule gutter slope is set at 1 4 inch per 10 feet of guttering.
For example if you have 30 feet of guttering the calculation is 1 4 x 3 0 75 i e.
This means the downspout end of the gutter should be set 3 4 of an inch lower than the other end.
Minimum slope for asphalt shingles the requirements for an asphalt shingles roof are contained in the international building code.
Pitch is a measure of the steepness of a roof.
A 4 12 is a roof slope that rises by 4 inches for every 12 inches across.
However you can only use this pitch with built up roofing or specialized synthetic roofing.
If the gutter continues around a corner cut the appropriate angle typically 45 degrees on that end.
A flat roof would have a 2 12 pitch while the average roof pitch would be between 4 12 and 9 12.
I reckon that rain is about 45 degrees.
Going with a 6 12 roof slope instead of 7 12 will work slightly better in terms of minimizing the overall wind uplift pressures while also adequately mitigating for any wind driven rain issues and retaining the profile of a true single story structure from the wind uplift mitigation perspective.
A reputable roofing contractor will be familiar with the pitch required by these codes.
The only logical answer is that the rain must come down somewhere so once in every 100 years the rain comes down onyour building.
This forms an angle of 18 5 between the horizontal section and the roof and creates a gentle incline that is seen as a midpoint between a low pitch and medium pitch roof.
According to this code the minimum slope for asphalt shingles is 17 degrees or two vertical units to twelve units in the horizontal.
This is the basis for calculating the angle which is approximately a 1 19 degree slope.