Torch Down Roofing Manual: Lifespan, Costs, Installation, Benefits, and Risks

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Torch Down Roofing Manual: Lifespan, Costs, Installation, Benefits, and Risks

Torch Down Roofing Manual: Lifespan, Costs, Installation, Benefits, and Risks

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Torch down roofing is one of the most common roofing systems used up until today, and it’s especially popular for commercial roofs.

One of the main benefits of a torch down roof is protecting your roof from water leaks and UV rays. Still, a torch down roof, despite its wide benefits, isn’t always the best option.

It’s worth noting the risks involved during the installation process and the costs associated with it.

For this reason, we’ve created this guide to share everything we’ve learned about torch down roofing and how it can help you decide whether it’s the right option for you.

What is Torch Down Roofing?

From the name “torch down,” a torch down roofing is the process of applying multiple layers of modified bitumen with an open-flame propane torch.

Once the material is hot enough, it adheres to the roof’s surface, and finally, the seams are melted together to create a watertight seal.

You’ll find two types of torch down roofing in the market: two-layer and three-layer systems.

Types of Torch Down Roof Systems

Two-Layer Torch Down Roofing

Two-layer systems have a base layer and a cap sheet or torch-on layer. While two-layer systems are easier to install and cost less, they also don’t last as long as three-layer roofing systems.

Three-Layer Torch Down Roofing

A notable difference between two-layer and three-layer roofing systems is the additional cap sheet or torch-on layer.

For two-layer torch down roofing, the cap sheet uses a smooth layer, while a three-layer torch down roof has a smooth layer and granular layer.

Yes – three-layer torch down roofing is more costly and difficult to install, but it also comes with a wider range of benefits, lasts longer, and provides more protection.

Roofing Materials Used in a Torch Down Roof

To gain a clearer understanding of torch down roofing, let’s dive into the roofing materials used to install one.

Modified Bitumen

Modified bitumen is the main roofing material used in torch down roofing. It consists of a waterproof membrane embedded in a thick asphalt layer, and it’s also highly flexible.

The high-quality resins combined with rubber additives allow the asphalt layer to expand and contract rather than crack under stress.

Additionally, it provides a secure watertight seal and weatherproofing for better protection of your roof.

You can also easily bond modified bitumen to metal flashings while keeping the bond intact.

The high flexibility and durability of modified bitumen in torch down roofing is what makes it an attractive choice and a success for many.

Depending on your roofing contractor, the type of modified bitumen used varies. There are two types available: Styrene Butadiene Styrene (SBS) and Atactic Polypropylene (AP).

Styrene Butadiene Styrene (SBS)

A type of rubber used in modified bitumen with a low melting point and high flexibility. SBS [R] are suitable choices for torch down roofing, cold-processed, and self-adhering roof systems.

Atactic Polypropylene (AP)

A type of plastic used in modified bitumen, although it has a higher melting point than SBS. It’s also flexible and can withstand both low and high temperatures.

Thermo-fusible Film

This will act as your first layer of underlayment applied in a torch down roofing installation.

Overlay Board

Installing an overlay board is useful for supporting the torch down roofing membrane. Installing the overlay board comes after your roofing professional installs the thermo-fusible film and vapor barrier.

Vapor Barrier

The vapor barrier is also a sheet of underlayment like your thermo-fusible film and protects your roof from moisture damage or issues. [R]

Granular Cap Sheet

For a three-layer torch down roofing system, a granulated layer is added along with a smooth cap sheet to enhance your roof’s protection and sealing.

Two-layer torch down roofing systems will only have a smooth cap sheet, thus reducing your roof’s lifespan and durability.


For roofs with vents or HVAC designs, metal flashing is required to protect any features on your roof’s surface, including chimneys, skylights, etc.

In torch down roofing, a self-adhering modified bitumen is applied as the first layer of flashing. Once this layer has been successfully installed, metal flashing is applied above the bitumen layer.

What Is the Life Expectancy of a Torch Down Roof?

The average lifespan of torch down roofing system is 15 years, at most.

That being said, this is evident for two-layer torch down roofs, while three-layered systems will last about 2o to 30% more, with a maximum life expectancy of 20 years.

You can extend the lifespan of your torch down roof with proper maintenance. Ultimately, choosing between two-layer or three-layer depends on your budget.

Can You Walk on a Torch Down Roof?

Yes, it’s safe to walk on a torch down roof; however, you should always perform annual checkups on the conditions of your roof.

Regardless of how durable a roofing system may be, neglecting proper maintenance and care will always lead to higher risk.

How Are Torch Down Roofing Systems Installed?

When consulting a roofing professional about installing a torch down roof, these 6 steps will help you gain an understanding of the proper installation process to ensure its success.

Step 1: Apply Insulation

Insulation is a vital roofing material for every roof, especially for flat or low-slope roofs. Insulation is applied either through glue or through screws and plates.

The method of application depends on the type of roof, along with several factors.

Step 2: Install a Vapor/Moisture Barrier

As mentioned earlier, a vapor barrier is crucial to enhance protection against water or moisture damage.

Step 3: Install An Overlay/Cover Board

As mentioned earlier, a vapor barrier is crucial to enhance protection against water or moisture damage. An overlay board acts as a support system upon applying the torch roof membrane. When installing an overlay board, make sure the board is installed precisely.

An improper installation can lead to a roof that isn’t leveled, which causes water to pool and damage your roof structure.

Step 4: Install Base Sheet

Your base sheet is the first layer of torch down membrane material. Roofing professionals will attach the base sheet to the overlay board using an adhesive or heat-infused method.

Step 5: Install Cap Sheet

The cap sheet serves as the second or final layer for a two-layer torch down roof. First, the cap sheet is rolled out on top of the base sheet. Using a torch, heat is applied to fuse the cap and base sheet.

This fusion is what provides a watertight seal for your roof. For a three-layer torch down roof, the installation process is the same except that a third granular layer is applied.

Step 6: Apply Metal Flashing

The finishing touches will be to apply metal flashing  around your roof. This will further enhance the sealing and water leak prevention in your roof.

Benefits of Installing a Torch Down Roofing System

Waterproofing & Weatherproofing

One of the most appealing benefits of torch down roofing is its resistance to water damage and weather elements, such as pooling water and snow buildup.

For flat roofs, standing or pooling water is a common issue. A properly installed torch down roof promotes effective drainage and prevents further damage from snow buildup.

To date, torch down roofing is one of the most highly water-resistant roofing systems in the market.

UV Rays Protection

Prolonged exposure to heat can damage your roofing structure and increase its susceptibility to punctures or holes.

For a three-layer torch down roof, UV ray protection is further enhanced thanks to the added cap layer. Furthermore, this increases the energy efficiency of your roof, making it more beneficial for humid areas.

Life Expectancy

Compared to most roofing systems, the life expectancy of torch down roofing is relatively higher, lasting between 15 to 20 years.


First, the bitumen material used in torch down roofing expands and contracts when the temperature changes, making it flexible and less prone to structural damage and cracks.

Torch down roofing is also suitable for any climate and has a consistent thickness, which adds conformity to your roof. In effect, this provides durability to the overall structure.

Easy Maintenance

Sealing the layers in torch down roofing is relatively easier to do than most roofing systems. Repair costs are also slightly cheaper, and labor isn’t as intensive, too.

Minimized Harmful Fumes

Torch down roofing isn’t completely free of harmful fumes; however, it emits a lot less than a hot-mopped roofing system.

Risks of Installing a Torch Down Roofing System

Vulnerable to Tears

Scratches and tears are potential risks of a torch down roofing system. If the waterproof seal is scuffed or torn, this can compromise the entire roofing structure.

Fire Hazard

Since torch down roofing is installed using an open-flame torch, this poses a fire hazard and can be dangerous if mishandled.

If you notice any flammable debris in the area during the installation, it’s urgent you remove these first before starting the installation.

Also, should the modified bitumen overheat, the compound can break down and become a highly flammable material.

Flat Roof Vulnerability

The main concern with a flat roof is its susceptibility to snow or water buildup.

Without proper maintenance and considering everyday wear and tear, flat roofs require a roof system that’s durable and has high water-resistance.

Meticulous Installation

Torch down roofing requires precision and considerable experience.

Improper installations lead to seam failure and trapped water, which results in roof leaks and less protection against weather elements.

Further down, we explain in detail how to make sure you find a contractor you can trust to install your Torch Down Roof.

How Much Does It Cost to Install a Torch Down Roof?

Torch down roofing isn’t the cheapest. Depending on your roofing contractor, the lowest you might pay is $365 for a 1,200 square feet roof. Higher quality materials can bump this price to $460.

If you want to use premium materials, costs can range from $850 to $1000. Granted, it’s not exactly budget-friendly; however, it’s well worth the costs if you want durable roofing that will last longer.


How to Properly Maintain Torch Down Roofing?

Even with the best roofing materials, the longevity of your roof ultimately depends on how well you maintain it. That being said, here are a few tips for maintaining torch down roofing:

  1. Have your roof re-sealed every 4 to 5 years.
  2. Check your attic once a month for any leaks, holes, or punctures.
  3. Remove any debris or water & snow buildup as soon as possible.
  4. When doing an annual or monthly checkup, check your gutter, flashing, and any area around your vents, chimneys, or skylight for any damage that needs immediate repair.

Are There Any Alternatives to Torch Down Roofing?

Some alternatives include TPO roofing, EPDM roofing, and PVC roofing. Among the three, the best alternative would be PVC roofing (read about the pros and cons here).

EPDM roofing has been around for a long time, and even at a budget-friendly price, the main concern with EPDM is durability and lifespan.

TPO is considerably better than EPDM, in some ways. It’s also price-friendly; however, TPO is fairly new in the market, so installations may vary. As a result, so does the quality.

PVC roofing uses a hard plastic roofing material that offers durability that’s stronger than both EPDM and TPO roofing systems. It also has a decent lifespan and isn’t as labor-intensive. The only drawback is the price.

Read more for a full break down of PVC vs TPO here.

Is Torch Down Roofing Suitable for Flat Roofs?

Although torch down roofing is a flat roof system, it’s not recommended if your roof is completely flat.

Of course, that doesn’t mean you should neglect or ignore installing a torch down roof.

In cases like these, it’s crucial to talk to several roofing contractors and ask for their advice before making a decision.

Is Torch Down Roofing the Best Type of Roofing for You?

If versatility and water-resistance is your primary goal, a torch down roof will suit you well.

It’s best to install a torch down roof in dry conditions to prevent improper sealing or mishaps during the installation.

Finally, a torch down system is ideal for slightly pitched roofs. If your roof has a pitch between 1/4:12 and 1:12, this makes your roof an ideal candidate.

Finding the Right Roofing Contractors for the Job

Finding the right roofing contractors for the job requires considerable time and patience. You can’t limit yourself to just one roofing professional.

We recommend collecting as much feedback and research on various roofing contractors in an area and then narrow your choices to the contractor that can fulfill your needs the most.

You can do this by reading google reviews, calling local roofing supply companies and talking to your city’s zoning department to identify who has the best reputation.

One tip we can give when choosing the right roofing contractor is to ensure they’re certified torch applicators.

Roofing professionals can receive the Certified Roofing Torch Applicator (CERTA) safety training program through the National Roofing Contractors Association (NRCA).

Final Words

Torch down systems provide excellent waterproofing and can last as long as 20 years or more given the right maintenance practices and using a manufacturer that has a great roofing warranty.

Combined with its versatility, durability, and protection against various weather elements, it’s a clear sign why these roofing types are preferred by many.

Should you decide to install one, we highly recommend going for three-layer torch down systems if you want the most value and benefits for your roof.

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