If the width of the building is 12 feet and you use a pitch of 5" rise per foot of run then you may get away with 14' rafters and have about a 6-8" over hang!!! Take a 16' piece of strapping and see what length of rafter you need!!!<br /><br />Also you may have to think about any windows on the side of the building that you are attaching to!! You may be limited to your roof height!!!<br /><br />When using regular roof shingles I wouldn't use less then the 5" rise for water run off!!!<br /><br />When fiquring your pitch and using 5" per foot of run, take 5x12= 60" or 5 feet from your top plate is where the top of your rafter height will be on the existing exterior wall<br /><br />Exsample: 5" pitch in 12 feet= 60"<br /> 4" pitch in 12 feet= 48"<br /><br />Any less then a 4" pitch then you need either a rubber roof or double coverage asphalt!!! <br /><br />When repeling water I wouldn't use less then 5" pitch!! <br /><br />12' wide with 2' eave is 14' ya know. you need to figure how much pitch you want. probably not matching your house roof is what you're hoping for, to save space/wood. get someone up there with some nylon string to look at what you want. put a post out on the outside edge and look at the roof angle with the string to figure your roof. if you're tieing into the other roof, then you already know it won't be the same pitch, unless you're dropping the floor of the addition. <br /><br />you probably should not go less than 4/12(4'rise/12'length)<br /><br />hint: a2 + b2 = c2{sq} (14ft overhang sqrd + 4'8" high sqrd)<br />168x168=28224<br />56x56=3136<br />28224+3136=31360<br />31360sqroot=177.08754<br />177.0875/12=14.757295<br />14'8" rafter length(if it were tied in at edge of other roof, which ain't happening)
