Two-Layer and Three-Layer Torch Down Roof Systems


Torch down roofing, also known as “torch on roofing,” is a popular choice for flat and slightly sloped roofs. This type of roofing involves the application of modified bitumen membranes using a propane torch. The installation process creates a watertight seal, making torch down roofing an ideal option where water damage is a concern.

The watertight seal provided by torch down roofing makes it particularly suitable for homes with flat roofs. However, it’s important to consider whether torch down roofing is the right choice for your specific needs. In this article, we will explore the components of a torch down roofing system, its advantages and disadvantages, and help you make an informed decision.

What is Torch Down Roofing Material?

torch down roofing material

Torch down roofing material comes in the form of rolled sheets. During installation, each sheet is unrolled and applied individually. The sheets are composed of several membranes stacked and adhered together. The layers of torch down roofing material include:

  • Layer 1: Thermo-fusible film
  • Layer 2: Modified bitumen
  • Layer 3: Reinforced polyester
  • Layer 4: Modified bitumen
  • Layer 5: Granulated mineral surface (for three-layer roofs)

Modified bitumen, a compound made of asphalt mixed with a plastic or rubber additive, forms the second and fourth layers of each sheet. There are two main types of modified bitumen membranes used in torch down roofing: Atactic Polypropylene (APP) and Styrene Butadiene Styrene (SBS).

  • Atactic Polypropylene (APP) is a plastic material that offers flexibility and performs well in different temperature ranges.
  • Styrene Butadiene Styrene (SBS) is a rubber material that also provides flexibility and has a lower melting point than APP membranes. SBS membranes can be used in torch-down, self-adhering, and cold-processed roofing systems.

Torch Down Roof Application

Both two-layer and three-layer torch down roof systems follow the same installation process. Here are the steps involved:

Step 1: Attach insulation.

Insulation is essential for flat or low-sloped roofs, especially in colder climates. It can be attached using screws and plates or adhered with glue, depending on the roof deck and other factors.

Step 2: Lay down a moisture barrier.

A vapor barrier is placed on top of the insulation to prevent condensation within the roofing system.

Step 3: Install the overlay board.

An overlay board is placed as a support surface for the torch-down membranes. Precise installation is necessary to ensure a level roof and proper water drainage.

Step 4: Apply the base sheet.

The first layer of torch down roofing material, known as the base sheet, is applied. It is attached to the overlay board using either a heat fusing method or adhesive.

Step 5: Apply the cap sheet.

The second layer of torch down roofing material, called the smooth cap sheet, is applied. The heated cap sheet is pressed onto the base sheet, creating a watertight seal. For a two-layer roof, this is the final layer of rolled roofing material. For a three-layer roof, an additional cap sheet with a granulated surface is applied in the same way.

Step 6: Install flashing.

Flashing is applied around any roof features that penetrate the surface to ensure proper waterproofing.

Benefits of Torch Down Roll Roofing

roofing benefits

Torch down roofing offers various advantages, making it a popular choice for many homeowners. Here are some benefits to consider:

Water resistance

Torch down roofing provides a highly water-resistant solution for flat roofs. The heat-sealed seams and waterproof membranes prevent water from pooling or causing damage.

Flexibility and durability

The flexibility of torch down roofing allows it to expand and contract with temperature changes without cracking or splitting. This durability ensures a longer-lasting roof compared to other materials.

Energy efficiency

Torch down roofing, especially with the added cap layer in three-layer systems, provides protection against UV rays and heat. This helps lower cooling bills in hot weather.


With a lifespan of 15 to 20 years, torch down roofing is a long-lasting option. Its resistance to water damage and flexibility in different temperatures contribute to its longevity.

Fire resistance

Torch down roofing, especially with a granulated cap layer, offers high fire resistance.

Less harmful fumes

Compared to other roofing materials, torch down roofing emits fewer harmful fumes during installation.

Easy repairs

Repairing torch down roofing is relatively simple compared to other materials. The rolling application allows for quick and cost-effective repairs when needed.

Disadvantages of Torch Down Roofing

roofing disadvantages

While torch down roofing offers many advantages, there are also some potential disadvantages to consider:

Fire hazard

The application of torch down roofing involves an open flame and, therefore, always carries a fire hazard risk. Professional installation by a licensed roofing contractor ensures safety precautions are taken.

Seam failure

Incomplete sealing of seams can lead to roof leaks. This is less common with three-layer roofs but can still occur. Seam repairs are relatively quick and straightforward.

Trapped water

During installation or repair, water may become trapped between the layers of rolled roofing. Therefore, torch-on roofing should only be applied or repaired under dry conditions.

Not resistant to scuffs and tears

Torch down roofing can be prone to scratching and tearing. Regular maintenance, inspection, and minor repairs can prevent damage to the waterproof seal.

Disadvantages of a flat roof

Flat roofs, including torch down roofing systems, require regular maintenance and inspection due to the potential for pooled water, snow buildup, and debris accumulation.

Is Torch Down Roofing Right for You?

roofing decision

A torch-down roof system is well-suited for slightly pitched roofs where flexibility and water resistance are essential. It withstands various weather conditions, including high and low temperatures, heavy rain, and snow buildup. Professional installation by a roofing contractor is necessary, as it is not a DIY project.

If you desire a long-lasting, durable, and easy-to-repair roof for your flat roof, torch down roofing may be an excellent option. Contact an experienced torch-down roofing contractor near you to discuss your specific needs and receive a free quote.

If you’re in Maryland, Washington D.C., or Northern Virginia and looking for a torch down roof, our team of torch-on roofing experts is here to help. Get a free quote today!

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