Torch-Down Roof: Pros, Fire Risks and Safer Options

It covers houses with flat or low-sloped roofs under the 2025 California codes, in force since January 1, 2026. It doesn't price the work or predict how long a roof will last. All the flat-roof systems are compared in flat roof options for Los Angeles homes, and whether an existing built-up roof should be repaired or replaced is in hot mop roof: repair or replace.

• needs a design slope of at least 1/4 inch per foot (2%);
• is made to ASTM standards for SBS-modified sheets (D6162, D6163, D6164) and APP-modified sheets (D6222, D6223), among others;
• can go over a base sheet meeting ASTM D1970 or D4601;
• has its wind resistance tested to FM 4474, UL 580 or UL 1897, and is installed to the manufacturer's instructions.

Which sheets get a torch depends on the product. In CertainTeed's modified bitumen line, for example, the APP sheets are torch-applied, while the SBS sheets come in versions for hot asphalt, cold adhesive, self-adhering and torch application. In CertainTeed's handbook, every system starts with a base sheet over the substrate, mechanically fastened on a nailable deck, with the torched plies and the cap sheet above it.

• No kettle. The asphalt that bonds each sheet is already on its back, so there's no hot-asphalt kettle on the ground and no mopping on the roof.
• Laps fused into one membrane. Heat melts both sheets at each lap. In CertainTeed's handbook, enough heat shows as a uniform bead of melted compound, 1/4 to 1/2 inch, along the edge of the lap; an unbonded area is lifted and torched again, never sealed by torching the top of the sheet.
• A long record. NRCA describes torch-applied sheets as used successfully and safely since the late 1970s, and safe when roof decks, membranes and details are designed and installed with fire safety in mind.
• Cool-rated cap sheets exist. On a low-sloped re-roof that has to meet California's cool-roof values, the cap sheet's own Cool Roof Rating Council rating, or a coating, carries the requirement.

• Wood decks. In its 2019 roofing manual, NRCA stopped recommending torch-applied sheets over combustible roof decks, even with a thermal-barrier insulation layer over the deck, and advised considering other methods, such as cold adhesive, instead. NRCA concluded that the fire risk of torching over wood decks outweighs the advantages. On a wood-framed house, the roof deck is plywood, OSB or boards.
• Flashings and penetrations. In a 2018 bulletin, the Ontario Industrial Roofing Contractors Association said most torch fires start at roof flashings and penetrations, fewer in the field of the roof.
• What insurers see. In a 2023 bulletin on the CERTA program, the insurer CNA wrote that most recent claims came from lapses in basic practice: an improper fire watch, torch use near HVAC equipment or open ducts, and not noticing a wood substrate.

CERTA, the Certified Roofing Torch Applicator program run by NRCA, sets the industry's own rules for those spots. Among them:

• never torch directly onto combustible material, and identify and protect plywood, OSB, wood, wood fiberboard and other combustible parts;
• never torch where the path of the flame can't be seen, including flashings, corners, curbs, voids, expansion joints and small penetrations; use torch-and-flop, an indirect method in which the sheet is heated away from the substrate and then laid in place, or cold adhesive or hot asphalt there instead;
• at flashings, a direct torch only with a single-burner detail torch of 105,000 Btu or less, over an air-impermeable backer layer;
• clean lint and grease out of exhaust vents before torching;
• where an owner insists on torching over a wood deck, at least 2 inches of stone wool insulation or a cement or gypsum board over the deck first, then an air-impermeable layer, before any torched sheet.

The code's own checks are worth knowing as a homeowner: before the work starts, someone has to confirm the area is clear of combustibles or protected and that openings are covered (3504.3.1), and a "Caution: hot work in progress, stay clear" sign goes up where others can walk into the area (3503.6). CertainTeed's handbook also keeps propane tanks upright, secured and at least 10 feet from the torch flame, with tanks not in use stored on the ground.

• Cold-applied. SBS sheets set in cold adhesive; NRCA names cold adhesive as the alternative to consider over wood decks.
• Self-adhered. SBS sheets with a self-adhering back, pressed into place with a roller.
• Hot-mopped. SBS sheets set in hot asphalt, which brings the kettle back under the fire code's kettle rules.
• At the edges. Where torched sheets are used in the field, CERTA's list for flashings: torch-and-flop, cold adhesive or hot asphalt.

Other flat-roof systems avoid a flame altogether: single-ply membranes welded with hot air, spray foam and coatings. They're compared in flat roof options for Los Angeles homes.

1. Which permit? Whether the fire department's hot-work permit is in the job, along with the building permit.
2. What's the deck, and what goes on it first? On wood, how the torched sheets are kept off it, or whether a cold-applied or self-adhered system is proposed instead.
3. How are the edges done? Walls, curbs, vents, drains and corners: torch-and-flop, cold adhesive, self-adhered sheet, hot asphalt, or a detail torch over a backer.
4. How long is the fire watch, and where? The code's 30 minutes, CERTA's 2 hours or more, and whether the attic is checked.
5. Which cap sheet? The product, its CRRC rating if the cool-roof rule applies, and the manufacturer's warranty.

Code sections, rules and figures on this page come from the primary sources below. Codes, local requirements and product terms change; each was verified October 9, 2026.

1. California Residential Code 2025, Chapter 9, Roof Assemblies (R905.11)
2. California Fire Code 2025, Chapter 1 (105.5.25), Chapter 2 (definitions), Chapter 33 (3305.10) and Chapter 35 (3503, 3504)
3. Mark S. Graham, "New torch-safety guidelines," Professional Roofing (NRCA), February 2019
4. CNA and NRCA, CERTA – NRCA Certified Roofing Torch Applicator Program, risk control bulletin, 2023
5. CertainTeed, Flintlastic Modified Bitumen Application Handbook, third edition (2016), copy published by a distributor
6. California Energy Commission, 2025 Building Energy Efficiency Standards (Title 24, Part 6), CEC-400-2025-010, section 150.2(b)1I