Note: On a low-slope roof, if you don't see nails, you're probably looking at modified bitumen, not roll roofing.
- Roll roofing can be installed parallel to the eaves or to the rakes.
- Roof sheathing: minimum 3/8”
- Class C (lowest) fire rating.
- No underlayment necessary
- 6”min. end lap. 2” min. horizontal lap.
The lifespan of roll roofing varies with quality and the homesite environmental elements to which it is exposed.
Roll roofing is manufactured using basically the same materials and methods as asphalt shingles. A fiberglass mat is embedded in asphalt and coated with ceramic granules on the weather surface and powdered stone on the back side. Two things affect quality:
- The quality and thickness of the fiberglass mat. Lower quality, thinner mats will be less resistant to damage from impact from things like hail, falling tree limbs, ice falling from overhanging roofs, etc.
- The quality of the asphalt. For both shingles and roll roofing, powdered stone (called “filler) is added to the asphalt to improve durability and also to reduce costs. The use of excessive amounts of filler will reduce quality and lower resistance to thermal cracking caused by expansion and contraction caused by thermal cycling (heating and cooling).
Thermal cycling: Thermal cycling is the term used to describe materials exposed to sunlight heating up and expanding during the day and cooling off and contracting at night. Greater temperature differentials between day and night will cause more extreme thermal cycling that will shorten the lifespan of both asphalt shingles and roll roofing.
Basically, roll roofing installed on a roof in Death Valley will have a lifespan different from a home in Maine!