The area of a roof can be determined from the area covered by the building to the outside of the walls and taking in to account the pitch of the roof by adding on a percentage depending on the pitch. A method is shown at the web link below along with a table of the percentages to be allowed.
Providing the roof covers the same surface area in plan view (looking down from above it, i.e. the ground area covered), then the rain landing on it will be the same. In other words, a high pitched roof would have to be bigger to cover the same plan view surface area as a low pitched roof. For a given area covered by a roof, the pitch of the roof won't matter. If the pitch is so steep that the rain flows off it so fast that your gutters can't cope, then you will lose the rain and fail to collect it. What you need to maximise is the ground area covered by roof. This will maximise the rain you can collect.
Yes, shingled areas should be at least 4/12.
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A single pitch roof is basically a flat roof with a pitch (or angle), usually to allow water to run off. This differs from a double pitch roof /\ that is what you commonly see.
Roof pitch is measured in "rise over run". In other words, how many inches does the roof rise vertically in 12" of horizontal run. If a roof rises 4" in 12" of run, you have a 4/12 roof pitch.
Roof pitch is measured in "rise over run". In other words, how many inches does the roof rise vertically in 12" of horizontal run. If a roof rises 4" in 12" of run, you have a 4/12 roof pitch.
Roof pitch is rise and run. So if you have a 4/12 pitch, for every foot of run the roof rises 4 inches.
The pitch of the roof.
A 12/12 is 45 degrees. If you set a 45 degree piece of wood on the roof it should be level.
roof pitch 14.9 degrees, or roof pitch 26.6%
In general, talking about roof pitch, I have never heard or read about this term being used. Roof pitch is measured when you start at the leading edge of a roof and measure towards the center of the house too 12 feet. Pitch is measured from a imaginary parallel level line at the 12 foot mark, how many feet high the roof is at 12 feet is the pitch of a roof. If your roof is at 4 feet high at the 12 foot mark then the phrase would be- a 4/12 pitch.