Asphalt roll roofing

Roofers applying commercial grade "torch-applied" modified bitumen roll roofing.

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.^[1]

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.^[2] 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."^[3]

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.^[4]

Uses

This roll roofing on the roof was applied vertically and is in very poor condition.

Horizontally applied roll roofing on a ruined log cabin. Image: American Historic Building Survey

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.^[5]

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

References

↑ "What is roll roofing?". All About Roofing. Asphalt Roofing Manufacturers Association. 2009. Retrieved 2009-06-18.
↑ "Mineral Surfaced Roll". Owens Corning Roofing. 2009. Retrieved 2009-06-18.
↑ "cold-process roofing." McGraw-Hill Dictionary of Architecture and Construction. 2003. The McGraw-Hill Companies, Inc. 20 Dec. 2013 http://encyclopedia2.thefreedictionary.com/cold-process+roofing
↑ "2" and 4" Selvedged Mineral Surface Roll Roofing Application Instructions" (PDF). Owens Corning Roofing and Asphalt, Inc. 2008. Retrieved 2009-06-18.
↑ DeCristoforo, R. J.. Housebuilding: a-do-it-yourself guide. Rev. & updated ed. New York: Sterling Pub., 2007. 295. Print.