Torchdown roofing installation instructions

Updated February 21, 2017

Torchdown roofing is a flat roofing application that is extremely effective at waterproofing and is very durable. The roofing comes in rolls which are heated with a torch to activate the adhesive as it is unrolled. Torch down roofing requires a base material such as felt or water shield as the material protects the roof surface as the torch down material is applied. This also acts as a secondary precaution from leaking. This roofing system is fairly simple to apply, but some simple tricks-of-the-trade will make this roofing system last several decades.

Lay the underlayment sheeting down over the roof surface. Apply adhesive to the roof surface and slowly unroll the underlayment onto the roof. Work all of the ripples and creases out with a broom or squeegee. This is very important so that the torchdown roofing material adheres properly. This underlayment is a combination of rubber and fibreglass and is extremely heavy and durable. Wait 12 hours before starting the torch down roofing process.

Measure the length of the torchdown roofing rolls. Measure this distance from the edge of one side of the roof, subtract 12 inches for over lap, and make a mark. Repeat this action down the roof so you have several marks as references. Give one end of chalk line to your roofing partner and have them hold one end on a mark on the end of the roof. Go to the other end, line up the string of the chalk line on the mark, and snap the chalk line making a reference line for the torchdown roofing to roll out along. Measure from this chalk line the length of the roof and repeat the process of making reference lines until you have performed this for the entire roof. Do not subtract 12 inches for each roll for the rest of the chalk lines. Instead, subtract 2 inches as this is an appropriate overlap between rolls.

Place the torchdown roofing on the end of the roof. Using the propane torch to heat up the material being very careful not to ignite the base material. Slowly unroll the as you heat the underside with the propane torch. Heating along the roll and rolling that portion out is a time consuming process, but is fully adhering to the roof surface for maximum bonding. Use your foot to make sure that the edges of the torchdown are fully adhered to the surface.

Place the torchdown flashing pieces around the penetrations on the roof. Fold them back and apply heat from the torch. Slowly unfold the pieces around the flashing using a masonry trowel to push the edges to make sure that they adhere properly.

Fold back the edges or the torch down roofing along the roof to expose the underlayment. Use adhesive to secure the underlayment to the eaves making sure to stretch the material as tight as possible. Let the adhesive dry for 12 hours.

Heat the roof edges up with the propane torch and fold the edges over the sides of the roof. Use a masons trowel to make sure that the roofing fully adheres to the surface.


When using the torch, move quickly never stopping in one place with the torch. This will cause undulations in the roofing and will defeat the water proofing ability of the roofing surface. It is extremely important not to apply fire to the surface of the torchdown roofing as this will ruin the surface. Only apply heat to the underside of the roll. If the roof has parapet wall (short walls on the edge of the roof), the roofing material for both the underlayment and the torchdown roofing needs to extend up the wall, onto op the wall and over the edge about 2 inches. A flashing cap will be installed over the top of this that will protect the edges of the torchdown roofing.


Always use caution when working on high surfaces. Use extreme caution when applying torch down roofing systems so that you do not accidentally cause a fire.

Things You'll Need

  • Measuring tape
  • Pencil
  • Propane torch
  • Hammer
  • Roofing nails
  • Chalk line
  • Underlayment sheeting
  • Torchdown roll roofing
  • Masons trowel
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About the Author

Adam Yeomans has been writing professionally since 2010, with his work appearing on websites such as eHow. He works in the construction industry as a builder and as an energy efficiency consultant.