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Under One Roof

Canadian Roofing Reference Manual

1.5.3. Torching

The following are some safety tips when using a torch.

  • Use well-built durable products that feature safety devices and are listed by Underwriters Laboratories of Canada (ULC) and approved by the Canadian Gas Association (CGA).
  • Follow the manufacturer’s safety and operating instructions provided with the torch system.
  • Check all equipment for wear. Repair and/or replace as necessary.
  • Use soap solution or leak detection liquid to test for gas leaks before lighting, then check for proper operation of the torch.
  • Check all fittings and other equipment on the applications equipment for leakage.
  • Be sure that torching equipment is in good working order and that the cylinder valves are clean.
  • Stop work and shut off flame if propane odour is detected.
  • Stop work and make repairs if a propane leak occurs.
  • Keep the flame of the torch at least 3 m (10 ft) from other crew members.
  • Protect your equipment: Store it in a tool box.
  • Do not use matches or cigarette lighter to test for gas leaks.
  • Containers which hold or may have held flammable material must be kept clear of the torch or other heat sources.
  • Do not use equipment that has been damaged or that needs repair.

Each building is different and each roof design presents a different set of challenges to the roofing contractor. The applicator of modified bitumen systems must adapt their standard safety procedures to meet the special requirements of the current job. However, roofers should follow the basic rules presented in these pages.

The crew leader should take extra care when working on the modified bitumen roofing job. The supervisor shall conduct a fire watch after all torches have been extinguished. As required by the National Fire Code, fire watches must be completed during any “hot” work and for a minimum number of hours following completion of work. The delay will help guard against a smoulder fire going undetected at the end of the work day. Check for potential “hot spots”, especially at cants, wall flashings, and around penetrations such as vent pipes, intake vents, and skylights. The underside of the roof deck should be inspected, whenever possible. A hand-held infrared thermometer or infra-red camera is typically required for detecting hot spots during the fire watch.

Applicators must take special care when torching at flashings, corners, or voids in the roof deck. Never torch directly at these locations. Always torch the membrane and then adhere it to the corner or joint.

  • Install metal flashing on penetrations or flashing with tight fitting felt collar before torching.
  • Shut down air conditioning units, exhaust fans and air intake fans in the work area at the roof control.
  • Do not work in an enclosed area where gas can accumulate.


  • If the substrate  material to be torched over  is plywood, OSB, or the material cannot    be confirmed as non-combustible, it is required that a thermal barrier, such as perlite asphaltic board, fiberglass or mineral wool insulation or gypsum board be installed before torching.
  • Fill any voids, holes or gaps in the substrate with non-combustible insulation, such as perlite or mineral wool.
  • Install a base ply or a layer of roof insulation, acceptable to the membrane manufacturer to separate polyurethane or polyisocyanurate roof insulation from the modified sheet and the torch.
  • Do not torch to wood fibre insulation, a cant strip, non-primed wood or any flammable material.

Torching Methods

  • Follow manufacturer’s recommendations on torching to insulation and cover board surface.
  • Shield air conditioning units and other protrusions when using the torch around them.
  • Heat the membrane away from air conditioning units, fans, soil pipes and all other protrusions. Care must be taken to avoid flame being pulled into the building interior.
  • Use caution when torching near pipes in the event there is suction present.
  • Do not torch anything you cannot see such as under air conditioning units or behind  counter flashing.
  • Do not torch near gas lines or near electric wires (such as around roof top equipment, etc.).
  • Do not torch around flammable vents or plastic projections.
  • Do not point the torch into corners of roof edges where dried wood or fibre may ignite (such as wood blocking or cant strip).
  • Do not point the torch under rooftop equipment.
  • Do not point the torch down open roof penetrations.
  • Do not point the torch at low flashings where there is an overhang  and flame could  get up under the counter flashing, such as around skylights or prefabricated curbs with fibreboard sidewall insulation.
  • Do not apply modified bitumen products directly over exposed conduits or pipes lying on the roof deck.
  • Avoid prolonged contact with heat sensitive metals such as lead, as overheating of these metals could ignite underlying flammable services.
  • Do not lay an operating torch directly onto the membranes. There is a danger both of fire and of damaging the membrane.
  • Do not lay an operating torch on an open penetration on the roof. If the penetration is part of an air intake system, the flames could be sucked into the building.


  • Carefully follow safety directions listed here  in  after  when  using  torches  and  torch equipment in accordance with manufacturers’ specifications, notices and documentation.
  • Wear protective gloves, long sleeve shirts, full length pants and security footwear. Do not wear synthetic fabrics. Remove all clothing that comes in contact with solvents.
  • Torches used to weld roof membranes can produce temperatures beyond 1093ºC (2000ºF).
  • Avoid all contact with temperature sensitive materials such as lead and plastic materials.
  • All employees, other than the torch operator, must be at least 900 mm (3 ft) from the open flame.
  • Never use torch(es):
  • When substrate(s) have been recently covered with solvent based products.
  • Near any combustible materials.
  • Close to containers containing flammable liquids or materials.
  • Directly on combustible substrate or insulations.
  • Avoid presence on inflammable materials near open flame. Apply products only on
  • clean, dry surfaces, free of debris, grease, dust and solvents.
  • Do not direct the torch through open roof penetrations.
  • Keep in mind that the flame can travel over long distances, through and beyond small openings. Take proper preventive safety measures.
  • Attach the torch to the fuel tank using a pressure regulator calibrated to the manufacturer’s design pressure. The regulator should be equipped with a rupture check valve.
  • Never leave a lit torch unattended for any reason.
  • When torch is not in use, always place it on its support, with head aiming upwards.
  • At all times and especially when leaving job-site, make sure that there is no smoldering or concealed fire. Job planning must allow for employee presence on the roof for the duration of the fire watch.
  • When the torch is no longer in use, the fuel tank valve must be shut first, then activate
  • the torch so as to completely evacuate the rubber hose of its propane.