What is the min. roof pitch for asphalt arch. shingles in NY

[sarecco]

Long Island, NY 2nd floor addition: I have a 6/12 pitch with arch. asphalt shingles. I want to make the room larger by extending the roof another 8ft or so. What is the minimum pitch allowable? or is there a formula that EX: for every 1 foot of pitch you gain or loose (x-ft of horizontal run)?

[Richard A Hetzel]

3 on 12 is the absolute minimum for shingles, and that requires special measures like double felt underlayment, or full coverage of waterproofing shingle underlayment. A more practical minimum is 3 1/2 on 12, and better yet is 4 on 12.