A. Corresponding Editor Paul Fisette replies: The CABO One and Two Family Dwelling Code permits the installation of asphalt shingles on roofs with a slope as low as 2/12 if the shingles are double-coverage, self-sealing versions.
Shingles that are not self-sealing must be hand-sealed with asphalt roofing cement. This low-slope application requires a double layer of #15 felt underlayment, cemented together, for a distance extending from the eaves up to a point 24 inches inside the interior wall line of the building. For the rest of the roof slope, the felt underlayment...
to read the full article.