Torch Down Roofing Explained


The roofing industry is complex and varied. Not only are there different kinds of buildings (industrial, commercial, and residential, for example) with different styles of roofs (flat, pitched), there are also myriad materials used in the construction of these roofs.  Applying, installing, maintaining, and repairing roofs requires specialized training and experience depending on the type of roof.  One type of common roofing application is known as a torch down roof.  But, what is torch down roofing and when is it used?  Let’s take a closer look.

Let’s start with a simple definition.  Torch down, or torch on roofing is a type of roof that utilizes sheets of modified bitumen that are essentially “burned” onto a roofing surface using a propane torch.  This heating process adheres the bitumen roofing materials onto the surface of the roof, and given the right conditions and temperatures, the layers are sealed together to create a waterproof surface.

Bitumen is essentially asphalt combined with rubber or plastic.  Torch down roofs using modified bitumen are well suited to seasonal climates as these roofs will expand and contract without being damaged.  Not only do these roofing systems withstand extreme temperatures (both hot and cold), but torch down roofs maintain durability even in the face of fluctuating temperatures.

Torch down roofing systems may feature either two- or three-layers of modified bitumen, and they are one of the most common roofing systems for flat roofs.  Still, there are several components of torch down roofing systems.  Indeed, torch down roofing systems feature a vapour barrier, insulation, asphalt or adhesive, base sheets, overlay boards, cap sheets, base flashing, and cap flashing.  Each of these components helps to ensure the integrity and weatherproof features of your roof.

  • Insulation is critical to maintaining internal building temperatures even as weather changes.
  • The vapour barrier prevents condensation and problems such as mould or mildew which are associated with excess moisture.
  • Overlay provides a level surface on which the torch down roofing membrane is applied.
  • A base sheet refers to the initial layer of modified bitumen applied directly to the overlay.
  • Cap sheets are the outermost membrane which is applied to the base sheet.
  • Flashing is applied around roofing features such as vents, HVAC, and other penetrations.

As mentioned, one of the primary benefits of a torch down roofing system is its ability to provide weather protection even in changing climates as these systems expand and contract with weather temperatures.  This means the durability of torch down roofing is hard to beat.  Likewise, torch down roofing holds up well in wet climates or those climates with snow as the waterproof barrier prevents water damage to underlying structures.  Finally, torch down roofing systems are resistant to UV damage and also reflect heat from the sun for improved energy efficiency.