The minimum pitch for an asphalt shingled roof is a two in 12 pitch, meaning for every 12 inches of ceiling the roof rises two inches. The ideal asphalt shingled roof has a slope greater than a four in 12 pitch, which is an incline greater than 18 degrees.
The National Roofing Contractors Association recommends applying an underlayment material over the roof wood decking before laying asphalt shingles. Asphalt saturated roofing felt is one of the most common underlayments. Low-pitch roofs require two layers of 15-pound felt for proper asphalt shingle installation. A second option is to install an ice and water membrane underlayment.