How to Use a Roofing Torch Safely: Kit, Cylinders, Lighting, Flame and Fire Watch
A professional tool with a real fire risk. Check the kit, secure the cylinder, control the flame, and watch the roof after the torch is off.
- Professional
- 20 minutes to set up and check
- Updated
The short answer
A roofing torch burns propane to heat modified bitumen sheet so it bonds to the roof. Inspect the hose, regulator and torch, leak-test the connections, keep the cylinder upright and secured, light with the valve barely open, keep the flame on the roll and never on combustible surfaces, have extinguishers within reach, and keep a fire watch after the last flame. Confirm the fire watch period with your insurer and the local authority.
A roofing torch is a propane burner on a long handle that heats the underside of a torch-on membrane until the asphalt melts and bonds to the surface below. It is fast and produces a strong, well-adhered roof. It is also the highest fire-risk task in residential roofing. The flame reaches well over 1,000 degrees Celsius, and heat travels through flashing, vents and gaps into wall cavities and attics, where it can smoulder for hours before it shows.
This guide covers the torch kit, how to check and set it up, how to light it and control the flame, how to use it near details, and the fire watch that comes after. It does not replace training, a written fire plan, or the requirements of your insurer and the local authority. For how the membrane itself is applied, see torch-on roofing explained, how to install a torch-on cap sheet and torch-on laps and seams.
Tools
- Roofing torch with a long handle and a wide flame head
- Propane regulator rated for the torch
- Hose rated for propane, with matching fittings
- Propane cylinder in good condition
- Leak test solution
- Two fire extinguishers rated for roofing work
- Metal heat shield or flashing shield
Materials
- Modified bitumen torch-on membrane
- Heat resistant gloves
- Water source or a hose ready for the ground
- Fire watch log and a written torch plan
Safety first
- Torch-applied roofing is hot work. Flame and melted asphalt sit close to wood decking, insulation and wall framing, and fires often start inside a wall or eave where the flame cannot be seen. Do not use a torch unless you are trained.
- Have a fire extinguisher rated for the job within reach, and commonly a second one. Industry practice calls for two. Check the current requirements with your insurer and the authority having jurisdiction.
- Keep a fire watch after the last flame. RCABC practice calls for at least one hour, and NFPA 241 and the NRCA CERTA torch safety program call for at least two hours. Some insurers and sites require more, and the roof underside should be checked as well as the top.
- Keep propane cylinders upright, secured and out of the sun and away from the flame. Never lay a cylinder down, never use a damaged or rusty one and never use a leaking hose or fitting.
- Never leave a lit torch unattended, and never point the flame at a person, a wall, a vent or bare wood.
Step by Step
Step 1: Plan the job and set up fire protection first
Look for anything that can burn or carry heat: wood blocking, cedar siding, soffit vents, open eaves, gaps around pipes, vents and curbs, dry leaves and debris. Plan how each will be protected. A sheet metal shield behind the flame, a wet blanket or a non-combustible board can block the heat. Mark the areas where you will use a different method, such as cold-applied adhesive, near wood.
Extinguishers should be full, inspected and of the type the plan names, commonly pressurized water or ABC units. Place them at the work area, not on the ground, where it takes a minute to reach them. Have a hose or water source ready and know where the nearest exit from the roof is.
Watch out: Check with your insurer before torching. Many policies and building owners restrict or ban open flame roofing.
Step 2: Inspect the torch, hose and regulator
Look along the hose for cracks, cuts, bulges and soft spots, and check the fittings for corrosion and damaged threads. The regulator must be rated for the torch and set up for propane. The torch head should be clean, with no blocked holes. A kit that has been dropped, burned or left in a hot truck should be checked carefully, and replaced if in doubt. Do not use duct tape or any repair on a hose.
Step 3: Place and secure the propane cylinder
Propane cylinders must be used upright so the valve sees vapour rather than liquid. Chain or strap the cylinder to a solid point or use a stand. Keep it upwind of the work where you can, away from hot membrane rolls and out of the sun. Never store a cylinder in a vehicle or an enclosed space. Many crews keep the cylinder on the ground and run the hose up, which reduces the risk of a cylinder sliding off a slope.
Check the cylinder for dents, rust, damage to the valve and the test date stamped on the collar. Do not use a damaged cylinder.
Step 4: Connect the regulator and leak test the system
Make sure the threads are clean and engage properly. Propane fittings are left-handed on some connections, so do not force them. Open the cylinder valve slowly, then spray or brush soapy leak solution on each joint. Bubbles mean a leak. Close the valve and fix or replace the part. Do not look for leaks with a flame.
If you smell gas, close the cylinder valve, stop work and remove all ignition sources.
Step 5: Light the torch and set the flame
Light with a striker or an igniter, never a lighter held close to the head. Start with the valve slightly open and increase slowly. The flame should be blue with a stable shape. A flame that roars, lifts off the nozzle or gives a yellow tip needs the regulator and valve adjusted. Set the regulator to the pressure the torch manual specifies, not higher.
Keep your body to the side of the torch, not in line with the flame or the hose.
Step 6: Work the flame on the roll, not on the roof details
The aim is to melt the asphalt so a small bead of molten bitumen flows ahead of the roll and then bonds. Too little heat leaves the roll unbonded. Too much burns the membrane and can ignite the deck. Keep the torch moving and watch the colour change of the film on the roll. Detail work near walls, curbs, vents and penetrations needs a shield and a lower flame, see torch-on parapet flashing and torch-on penetrations.
Never aim the flame into a gap, a vent or a void. The heat can pass through to the framing and start a fire you cannot see.
Step 7: Shut down correctly at every break
Closing the cylinder valve first removes the fuel at the source, and the remaining gas in the hose burns out. Then close the torch valve. At breaks, disconnect or at least close the cylinder, and place the torch on a safe, non-combustible surface. Lunch is a common time for accidents, so treat it like the end of the day.
Step 8: Keep a fire watch and check the roof after the last flame
A fire can start long after the flame is out. RCABC practice calls for a responsible person to watch the work area for at least one hour after the torches are out, and NFPA 241 and the NRCA CERTA torch safety program call for at least two hours, with checks of the attic or underside. Insurers often require a longer period, and some require a follow-up check later in the afternoon. Follow the strictest requirement that applies.
Use a heat-sensing method where allowed, and check the eaves, the soffits, the wall cavities and any penetrations. Write down the time the torch was out and the time the watch ended.
Step 9: Store the kit safely
Never leave cylinders in a closed truck cab or in the sun. Wipe the torch head and inspect it after use. A torch that coughs, flashes back or burns unevenly should be serviced before it is used again.
Propane Cylinder Handling
Transport cylinders upright, secured and with the valve closed and capped. Do not store them in a vehicle cab or in a hot enclosed space. Keep them away from ignition sources, and check the test date on the collar. Do not refill a cylinder yourself, and do not use one that is rusted, dented or has a damaged valve. Regulations for transporting and storing propane exist at provincial and federal levels, so check the current requirements for your work.
Where Torch-On Is Not Appropriate
Torch application is a poor choice over combustible decks without a proper base, near old wood framing, in buildings with open soffits or gaps in the wall assembly, and in tight areas where the flame cannot be controlled. Cold-applied and self-adhered systems exist for these situations, see torch-on roofing explained and the membrane choices for flat roofs.
Common Mistakes
- No fire watch, or a short one. Most torch fires begin well after the flame is out.
- Flame aimed into gaps and vents. Heat travels into the wall or attic and smoulders.
- Lying a cylinder down or using a damaged one.
- Leaving a lit torch on the roof during a break.
- Skipping the leak test. A leak at the regulator or hose is a fire waiting for a spark.
- Not having extinguishers within reach, or having them empty or the wrong type.
When to Call a Professional
Torch work should be done by trained professionals with a written plan, an insurer who knows about it and a fire watch. If you are not trained, do not attempt it. There are other membrane systems that do not use an open flame, and they are usually a better choice for a homeowner project.
If an area near the work smokes, smells of burning or feels hot after the torch is off, call 911 first, then the contractor. Do not assume it will stop on its own.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Replacement service or the towns we cover.
How to Use a Roofing Torch Safely: Questions
How long is the fire watch after torch-on roofing?
It depends on the standard that applies. RCABC practice calls for a responsible person to watch the work area for at least one hour after the torches are out. NFPA 241 and the NRCA CERTA torch safety program call for at least two hours, including checks of the underside. Many insurers require more, so use the strictest requirement that applies.
How many fire extinguishers do you need for torch roofing?
Industry guidance commonly calls for at least two extinguishers within easy reach of the torch work, of a rating suitable for a roof fire. Insurers and building owners may specify more or a particular type. Keep them full, inspected and at the work area, not on the ground, and know how to use them before you light the torch.
Do propane cylinders go on the roof for torch-on roofing?
Practice varies. Some crews keep the cylinder on the ground and run a hose up, which avoids a cylinder sliding off a slope. Others place it on the roof on a flat, secured stand. Either way, it must be upright, secured, shaded and away from the flame, and the hose must be protected from damage.
What order do you shut down a roofing torch?
Close the cylinder valve first and let the gas in the hose burn off, then close the torch valve. This removes the fuel at the source and leaves no pressurized gas in the hose. Never leave the cylinder open or the torch lit and unattended, and treat breaks the same as the end of the day.
Is torch-on roofing safe for a house?
It can be done safely by trained crews with a fire plan, extinguishers and a fire watch, but the risk is real because the flame is close to wood decking and wall framing. Many homeowners insurers restrict it. Other systems such as self-adhered or cold-applied membranes avoid open flame and may be a better fit.
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This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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