A ratio is the most common way of expressing roof pitch or roof slope but degrees are also possible.
Minimum pitch for roof trusses.
The minimum pitch for a roof is 1 4 12 which translates to 1 4 inch rise to 12 inches of run.
If a roof slope rises say 4 inches when measured 12 inches along the bottom of a horizontal roof truss the roof slope is said to be 4 12.
Difference in slope between the top and bottom chords is at least 3 12 or the bottom chord pitch is no more than half the top chord pitch.
I e 4 inches of rise per 12 inches one foot of run.
Flat the most economical flat truss for a roof is provided when the depth of the truss in inches is approximately equal to 7 of the span in inches.
Roof pitch is the measurement of roof steepness.
So if your roof rises 4 inches for every 12 inches of horizontal length then the pitch of your roof is expressed as 4 12.
It will use the current cost of wooden rafters based on the average price found at home improvement stores.
This online truss calculator will determine the all in cost of your truss based on key inputs related to the pitch width and overhang of your roof.
The minimum roof pitch for shedding snow is around 30 or a 6 12 or 7 12 slope although this is not a definite as the material of your roof the direction of the snow and wind are some factors that can affect whether or not snow will slide as roofs of as little as 10 have been reported to shed snow.
The run or the base number is 12 inches.
This table is considerably more useful that the one that was in the previous 1990 edition of the regulations as not only maximum truss spans are indicated but also the allowable and recommended pitch of the roof and the member sizes and grades of timber that are specified in sans 1783 2.
For example a slope of 6 12 means for every 12 inches of horizontal distance the slope of the roof will rise 6 inches vertically.
The chief reason for having a roof pitch is to redirect water and snow away from the roof and avoid any percolation that might result from stagnation of water on the roof.
The minimum roof pitch is also subject to the standards set forth by the various building codes used in the respective regions.
The picture below shows the pitch of a 7 12 roof slope meaning that for 12 of horizontal measurement roof run the vertical measurement roof rise is 7.
Importance of a roof pitch.
However roof pitch is technically measured and defined differently.
Note that roof pitch is sometimes used in parallel with roof slope.
However you can only use this pitch with built up roofing or specialized synthetic roofing.
Pitch slope the pitch or slope is the incline of the roof expressed as a fraction describing the rise over the run.
