Best Roofing for Low-Slope Porches and Additions

This is a two-ply, peel-and-stick SBS modified bitumen system: a base sheet and a granule-surfaced cap sheet. GAF says its LIBERTY system protects low-slope areas such as porches, garages, carports and sheds, on slopes between 1/4:12 and 3:12 and roof areas of about 2,500 square feet or less. CertainTeed's Flintlastic SA is built for the same jobs and goes on without mops or torches. Mule-Hide makes a self-adhering SA-SBS cap sheet as well.

The granule surface is what makes it the best fit on most houses. LIBERTY's cap sheet comes in nine colors designed to complement GAF Timberline shingles, including Weathered Wood, Pewter Gray and Black, and Flintlastic SA Cap comes in 11 colors to go with popular shingles. As a complete two-ply system, GAF says LIBERTY passes Class 4 impact-resistance testing.

The limit is temperature. GAF's ideal installation range for LIBERTY is 45°F to 95°F, and CertainTeed sells a cold lap tape, Arctic Edge, that boosts adhesion down to 35°F.

EPDM is a rubber membrane with a long record on low-slope roofs. For houses, the self-adhering versions are the practical choice. Mule-Hide's Self-Adhering EPDM is a nominal 60-mil sheet with a pressure-sensitive adhesive already on the back, in black or white-on-black.

Mule-Hide now sells it in 5-by-40-foot rolls, about 80 pounds, that fit in a pickup, and calls them a convenient option for residential low-slope roofs. It's eligible for warranties of up to 20 years. What it doesn't have is a shingle-matching color, which is why we rank it behind modified bitumen on a porch that faces the street.

TPO is a heat-weldable single-ply membrane, and like EPDM it comes in self-adhering form. Mule-Hide's Self-Adhering TPO is polyester-reinforced, 60 or 80 mil, in white, gray or tan, and can't be installed below 25°F.

On a small porch it's usually more product than the job needs. Mule-Hide's self-adhering TPO comes 10 or 12 feet wide and needs a segmented weighted roller, and its specification calls for at least one layer of approved insulation over a plywood deck on a reroof after tear-off. On a bigger addition, those are ordinary steps.

Standing seam metal can go surprisingly low, but only the right panel. Code allows standing seam systems down to 1/4:12, and some panels are rated that low: Central States' Central-Loc, Central Seam Plus and Central Span, and Metal Sales' Seam-Loc 24 and Snap-Loc 24. Metal Sales' Magna-Loc is rated to 1/2:12.

Many common residential panels are not. Central States' Central Snap is rated to 1:12 and Horizon-Loc to 3:12. Metal Sales' Vertical Seam is rated to 1:12 over a solid deck but 3:12 over open framing, and its exposed-fastener residential panels need 3:12. Ask for the specific panel's minimum slope in writing.

Shingles can go on a low slope, but not a very low one. Michigan's residential code allows asphalt shingles only at 2:12 and steeper, and requires double underlayment from 2:12 up to 4:12. GAF's own instructions say its shingles must be installed at 2:12 or greater, with leak barrier at the eaves extending 24 inches past the inside wall line and the whole deck covered with two layers of roof deck protection. GAF also warns not to shorten the shingle exposure to make up for the low slope.

CertainTeed goes further for snow country. Its Landmark instructions require WinterGuard or VYCOR waterproofing underlayment, or an equivalent, over the entire deck on slopes from 2:12 to under 4:12. Two layers of felt are only an acceptable substitute in areas not prone to snow or ice, which rules them out here. CertainTeed also covers residential low-slope roofing under a separate limited warranty, so ask which one applies.