I do not see any ambiguity in their documentation regarding the minimum roof pitch or any other limitations of their recommendations.
Minimum roof pitch for standard shingles.
Mineral surfaced roll roofing requires a minimum roof pitch of 1 12 or greater.
The standard of lower pitch actually ranges between 1 12 to 5 12.
Normal roof slope for typical installation.
Asphalt shingles continue to be the most widely installed roof covering option in north america.
The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles.
The recommended minimum roof pitch for shingles is 2 12 or simply two units of vertical rise to every twelve units of horizontal span.
Pitch is measured in inches of vertical rise of the roof over one foot 12 inches of horizontal run.
Roofing material or system.
9 46 built up roof asphalt.
Minimum required slope x in 12 minimum required slope degrees asphalt shingles.
Normal shingle installation is allowed for all roofs with a pitch of 4 12 and above.
5 12 to 12 12 pitch.
So a 4 12 pitch roof rises 4 inches for every 12 inches of horizontal run.
These shingles are appropriate for pitches as low as 4 12 pitch all the way up to a 12 12 pitch.
The minimum pitch is typically 3 12 meaning the roof should rise 3 inches for every 12 inches of horizontal foot.
If 4 12 and above is normal and 2 12 is minimum what about properties with roofs in between the two such as a 3 12 pitched roof.
Metal roof shingles require a minimum roof pitch of 3 12 or greater.
Think of them as taking the middle road in terms of roof pitch not too flat not too steep.
Manufacturers of asphalt shingles recommend a pitch of 4 12 or more but the absolute minimum pitch is 2 12.
The minimum pitch for shingles is 1 6 which is equivalent to 4 inches rise to 24 inches run.
18 43 asphalt shingles with special underlayment requirements 2 in 12.
The minimum pitch for a standing seam metal roof is 1 4 or 3 inches rise to 12 inches run.
Anything above that will require you to put out higher cost because they are already considered as higher pitch.
As you state the roofing manufacturers provide minimum roof pitches of 2 degrees lysaght trimdek and stramit monoclad even with long run lengths.
However it is regrettable that many installers usually ignore this requirement due to the desire for a quick installation process.
In 12 0 25 in 12 1 19 built up roof coal tar pitch.
Slate and slate type shingles require a minimum roof pitch of 4 12 or greater.