Asphalt roll roofing or membrane is a roofing material commonly used for buildings that feature a low sloped roof pitch in North America. The material is based on the same materials used in asphalt shingles; an organic felt or fiberglass mat, saturated with asphalt, and faced with granular stone aggregate.
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Overview
Roll roofing is usually restricted to a lightweight mat compared to shingles, as it must be rolled for shipment. Rolls are typically 36 inches (91 cm) by 33 feet (10 m) in size. Due to its light weight compared to shingles, roll roofing is regarded as an inexpensive, temporary material. Its wide width makes it vulnerable to temperature-induced shrinkage and tearing as it expands and contracts.
Other names for this material are "asphalt prepared roofing, asphaltic felt, cold-process roofing, prepared roofing, rolled roofing, rolled strip roofing, roofing felt, sanded bituminous felt, saturated felt, self-finished roofing felt."
Roll roofing is normally applied parallel to the eaves from the bottom of the roof upwards, lapping each new roll in the same manner as shingles. Its use is restricted to roofs with a pitch of less than 2:12. To avoid penetrating the exposed membrane with nails, adhesive or "lap cement" must be used at the bottom edge to keep it from being lifted by the wind. The upper edge of the roll is nailed and covered by the next roll.
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Uses
The main uses are:
- for outbuildings
- on flat roofs on houses in the UK, a low cost limited life roofing method
- as a backup water catching & wind stopping layer under roofing slates & tiles
Types
Several variations of bitumen roofing felt are available.
- Single coverage thicknesses range from 55 to 90 pounds per square (100 sq. ft.) for single-coverage
- Double coverage range from 110 to 140 pounds per square.
Fibre content:
- mixed rag fibre - lowest cost, shortest life
- all plastic fibres
- fibreglass - longest lived
Bitumen:
- bitumen - stiffens & hardens in winter, cracks in time
- modified bitumen - stays supple in winter, lasts better
Underside:
- Uncoated - most common, applied with adhesive or nails
- Self-adhesive - simpler to apply
- Torchable - applied by torching the underside, which partly melts and glues the sheet. (Most roofing felt is torchable.)
Topping:
- Sand - low cost
- Stone waste - prettier, better life expectancy. Only used on capsheet.
- Uncoated - used as undersheet
Double coverage:
Application methods
- Glue in place with bitumen/solvent mix
- Nail in place - relies on the clout nail head being driven slightly under the surface for a pressure seal. Waterproofing not quite perfect, a water durable timber layer is used under the felt, usually OSB or ply. Most common method on sheds.
- Hot bitumen
- Torch on - underside of felt melted with a torch and pressed in place
Source of the article : Wikipedia
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