What is Torch Down Roofing?

Updated: Aug 14, 2020

Torch down roofing, also known as “torch on roofing,” is so named because it requires an open-flame propane torch during installation. In this method, sheets of modified bitumen are rolled onto the roof, a roofing professional then uses a hand-held propane torch to heat the material that adheres to the surface. Once the layers reach the right temperature, seams are melted together to create a waterproof seal. Torch down roofing’s uniquely watertight surface makes it a great choice for homes with flat or slightly sloped roof, wherever water damage is a serious concern.

There are a few different types of torch down roofing including two-layer and three-layer systems. The membrane layers of a torch down roof are made of an asphalt compound called bitumen that is modified with either rubber or plastic. There are two main types of modified bitumen membrane used to create torch down roofing material: Atactic Polypropylene (APP) and Styrene Butadiene Styrene (SBS). Modified bitumen can expand and contract without melting or cracking due to its flexibility and high tolerance for both heat and cold.

  • A two-layer torch down roof consists of one base sheet and one smooth cap sheet.

  • A three-layer torch down roof features the same base and cap sheets, as well as an additional cap sheet with a granulated surface.

Two-layer torch down roofing may cost less to install, but it doesn’t last as long and doesn’t offer as many benefits. The granulated cap layer of a three-layer roof adds to the roof’s energy efficiency, fire resistance, curb appeal and durability. With that in mind, torch down roofing comes with a number of benefits as well as downsides to consider when deciding if this roofing system is right for your property.


  • Water Resistance: The first job of any roof is to keep water out of the building below. With flat roofs, this job becomes much harder to do, especially in regions where snow builds up on the roof. Heat-sealed seams and ultra-waterproof membranes make torch down roofing one of the most highly water-resistant flat roof systems, preventing water from collecting and pooling on the roof and promotes drainage.

  • Flexibility and Durability: The modified bitumen sheets expand and contract as the temperature changes without cracking or splitting. Where other roofing materials are rigid and may be damaged by changing temperatures, torch down roofing works well in any climate. It also has a consistent thickness (about 3-4 mm) across the entire roof, unlike other roofing materials that may vary in thickness.

  • Lifespan: The lifespan of a torch down roof is one of its main selling points, at 15 to 20 years. Torch down roofing is more long-lasting than some other types of flat roof systems due to its flexibility in hot and cold temperatures, as well as its resistance to water damage.

  • Fire Resistance: Especially with a granulated cap layer, torch down roofing can be highly fire-resistant. However, there can be some risk of fire hazards, which are described below.

  • Easy Repairs: Torch down roofing is very easy to repair when compared to other roofing materials. Because it rolls on and can be sealed relatively quickly, the process is less intensive and less expensive than installing or fixing other types of roofs.


  • Fire Hazard: The primary downside of torch down roofing is due to the method of application using an open flame. As a construction material, modified bitumen is highly fire resistant. However, if overheated during the installation process, the compound can break down and become flammable. Additional flammable materials, such as the wood frame of a house, residual sawdust from construction or repairs, or dry foliage, add to the potentially hazardous nature of torch down roof application. Working with a professional, licensed, and highly trained roofing contractor makes the process relatively risk-free. Torch down roofing is not a safe DIY project!

  • Seam Failure: Inadequately sealed seams can naturally result in roof leaks. This is less common with a three-layer roof but may still occur. If this does happen, a repair to seal the roofing seam is relatively quick and easy.

  • Trapped Water: It is possible for water to get trapped between the layers of rolled roofing during installation or repair. For this reason, torch down roofing should only be applied or repaired during dry conditions.

  • Not Resistant to Scuffs and Tears: A torch down roof may be highly flexible and durable, but it isn’t impervious to scratching and tearing. The waterproof seal of a torch down roof is essential to its performance, but if it gets torn or scuffed, the roof system is compromised. This can be avoided with regular roof maintenance, inspection, and minor repairs when needed.

  • Disadvantages of a Flat Roof: As a flat roof system, torch down roofs must be highly water resistant and durable. However, even with the most durable system, you must maintain and inspect your flat roof regularly. Flat roofs are more prone to pooling water and piling snow, as well as built-up debris. If you have a flat roof, make sure you have it inspected by a certified roofing professional to make sure it is stable enough to withstand torch down roof application as well as everyday wear and tear.

  • Cost: The cost of a torch down roof varies between contractors and across different materials. With higher-quality torch down roll roofing, you may have to pay a little bit more at installation, but you will also get a longer-lasting roof that will end up saving you money in the end.

Torch down roofing is a great choice for flat and slightly-pitched roofs due to its water resistance and flexibility. This roofing system must be installed by a roofing professional and isn’t something you can take on as a DIY project. However, if you want a roof that is long-lasting, highly durable, and easy to repair, torch down may be a good option.

While you consider what type of roof will work best for your property, contact us for a professional inspection and free roofing estimate on any work or repairs that may be required. Call us today at (310) 903-0536 to schedule an inspection and determine the right materials and services for you.

Southland Roofing Inc. is committed to providing premier service at the right price. Serving Los Angeles and Orange County, we pride ourselves on safety, efficiency, and competitive pricing as we revolutionize the roofing industry. Contact us today to find out how we can serve all your roofing needs.

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