Low Slope Roof Asphalt Shingles

What is the minimum slope for an asphalt shingle roof.

Low slope roof asphalt shingles.

A 3 per foot slope is considered low but may be acceptable if a double layer of felt is used. The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. Because of the non absorbent nature of asphalt the shingles themselves provide an element of waterproofing which is why they work well for low slopes. Some building codes allow as low as a 2 slope with asphalt shingles if additional steps are taken.

Cover the entire low sloped roof area with a self adhered modified bituminous membrane that will act as an ice and water. The acceptable underlayment installation options for low slopes are described in the canadian standards association asphalt shingle application standard csa a123 51 as follows. When combined with the proper underlayment materials and application they are an excellent solution for a low slope roof with a pitch between 2 12 to 4 12. The usual slope for asphalt shingles is a 4 or greater rise for every horizontal foot of run.

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. Shingles that are not self sealing must be hand sealed with asphalt roofing cement.