10.2 Built-Up Roofing & Modified Bitumen: Materials, Application, Kettles & Torch Safety

Code Requirements

Both are installed per the code and the manufacturer's instructions. For reroofing, R908.1 does not require raising an existing roof to 1/4:12 if it already provides positive drainage, meaning drainage within 48 hours of precipitation.

Built-Up Roofing

A BUR is built from layers of ply sheets (usually fiberglass felts) laminated with hot asphalt or coal tar, over a base sheet, and finished with a flood coat and aggregate, a mineral-surfaced cap sheet, or a coating. Redundant plies make it durable, but it is labor-intensive and involves hot materials.

Roofing Asphalt Types (ASTM D312)

Using too soft an asphalt on a slope lets plies slide. Too hard an asphalt on a dead-level roof can crack. The roof manufacturer's specification sets the type.

Equiviscous Temperature (EVT)

Asphalt must be applied hot enough to flow into a thin, even interply layer:

• EVT is the temperature at which the asphalt reaches the target viscosity: about 125 centipoise for mop application and about 75 centipoise for mechanical spreader application. The EVT appears on the asphalt packaging or bill of lading.
• Apply within about ±25°F of the EVT at the point of application. Asphalt that is too cold goes on thick and bonds poorly. Asphalt that is too hot runs thin and can starve the plies.
• Never heat asphalt to its flash point. Industry guidance calls for staying well below it, and the kettle rules below still apply.

Modified Bitumen

Modified bitumen sheets are asphalt blended with polymers and reinforced with polyester or glass mats.

Two-ply systems of base sheet plus granule-surfaced cap sheet are common. Self-adhered SBS systems avoid both open flame and hot kettles, which makes them attractive for occupied homes.

Michigan's Tar Kettle Rules (MIOSHA Part 24)

• A qualified operator attends a fired kettle at all times, stays on the ground, and remains close enough for immediate attention.
• The kettle has a working temperature gauge and a close-fitting, hinged lid that can smother a fire.
• Extinguishers: dry powder, at least 40 pounds total, placed 10 to 25 feet from the kettle, with no unit under 10 pounds.
• Placement: at least 20 feet from combustible materials unless separated by a fire-resistant blanket, at least 10 feet from a structure that rises above the kettle, and not on a building without MIOSHA's permission.
• A fuel tank closer than 10 feet must be shielded by a rigid noncombustible barrier.
• Hoisting equipment must support 3 times the load, and no one may stand under hoisted material.

Torch Safety

Torch-applied roofing causes serious fires when crews torch into cavities, onto wood, or near combustible insulation.

• Never torch directly on combustible decks, nailers, insulation, or into openings, gaps, or flutes. Use a base sheet the manufacturer approves, which may be nailed or self-adhered, and use non-torch methods, such as self-adhered or cold-applied flashing, at walls and penetrations where flame could reach hidden combustibles.
• Extinguishers: a 10-B unit within 50 feet where more than 5 pounds of flammable gas is in use (MIOSHA Part 18). Keep additional extinguishers at the work area.
• Fire watch: NRCA's CERTA torch-safety program requires a fire watch for at least 2 hours after the last torch is shut off. The watch often uses an infrared thermometer to find hidden heat.
• Store LP-gas cylinders safely, with the valves closed when not in use, and keep hoses in good condition.

Removing Old Built-Up Roofs

• Older BUR felts and coatings may contain asbestos. Test before removal. Under MIOSHA Part 602 (29 CFR 1926.1101), removing asbestos-containing BUR with a power roof cutter requires collecting dust with a HEPA dust collector or HEPA vacuuming along the cut line. Material may not be dropped or thrown, and rooftop air intakes must be isolated or shut down.
• Coal tar pitch is a carcinogen and skin irritant. Follow the SDS for PPE.
• Do not reinstall aggregate surfacing (R908.5). Wet or damaged insulation found during removal should be replaced.