Last Updated on December 15, 2025 by SampleBoard
Torch-down roofing or “torch on roofing” is a process where modified bitumen sheets are laid out on the roof and then a hand-held propane torch is used to heat the material and make it bond with the roof permanently.
The use of the open-flame propane torch gives it the name – torch down roof.
The bitumen used is modified with plastic or rubber. This ensures that it will be able to expand and contract without causing any damage.
You will find torch-down roofs usually in homes that have flat roofs or those that are slightly sloped. It doesn’t work for homes having steep-pitched roofs.
Standard shingles offer good water drainage. But in a flat roof where there is no slope, the water will collect on the roof and find its way through crevices and cracks, causing damage.
A torch-down roof will prevent this as there is watertight sealing between the sheets of bitumen.
Advantages of Torch Down Roofing
There are many advantages to why this roofing solution has become so popular.
Saves Energy
Light-colored or white bitumen sheets will reflect sunlight and as a result, the rooms will be cooler. Your home will be more energy efficient.
Durable and Lightweight
The bitumen sheets are lightweight. They are also strong. Your home will be protected from the elements. The roof will last for many years.
Easy to Maintain
There is very little maintenance work. You just have to clear the debris from time to time.
Fire and Leak Resistant
There won’t be any water leaks as the roofing system comes with an excellent seal. It is also fire-resistant.
Low Installation Cost
The roofing cost ranges between $4 and $7.50 per square foot, which is lower than tile or metal roofs.
disadvantages of Torch Down Roofing
Does not work for angled roofs
Torch-down roofs do not work for roofs having a steep pitch. Professionals recommend them for roofs having a pitch between 5:12 and 2:12.
The impact may damage the roof
The material is resistant to UV, fire, and water. But hail or a falling tree branch can cause damage. They may create holes in the roof. These holes can however be patched very easily.
Seam failure
Improperly sealed seams can cause roof leaks. This usually happens with two-layer torch-down roofs. Once again, you will be able to fix the issue easily.
Torch-Down Roofing Cost
For an American home, the average total cost to install a torch-down roof may vary between $4,400 and $15,000. Making the average cost install $4 and $7.50 per square foot.
Contractors will give you the quote based on your roof’s square footage, so it is best to focus on the cost per square foot.
Why does the cost of torch-down roof installation vary between $4 and $7.50 per square foot? Various factors will determine the cost, such as:
Number of layers
You can install a two-layer or a three-layer torch-down roof. The cost will be less for a two-layered roof. However, the roof’s life span will be longer if you go for three layers.
Roof size
The size of your roof will significantly impact the price. You will need material for sloped and larger roofs, which means a higher cost.
Quality of the roofing material
You can select SBS or APP-modified bitumen. The choice will affect the price significantly.
Here are some more factors you should consider when replacing your roof.
Materials Used In Torch-Down Roofing
The membranes in torch-down roofing have layers that are made from different materials.
Modified bitumen is the main material, which is present in the second and fourth layers. The bitumen is mixed with rubber or plastic.
- APP or Atactic Polypropylene – This is a type of flexible plastic that works both in low and high-temperature conditions.
- SBS or Styrene Butadiene Styrene – It is a synthetic and flexible rubber. The melting point is lower than AAP, which makes it a good choice for cold-processed roofing, self-adhering, and torch-down roofing. It works well for those living in cold-weather places.
There is also a bottom layer in the membrane made of thermo-fusible film, a top layer of granulated minerals, and a layer of reinforced polyester.
Components and Layers
There are various components used in the roofing, depending on whether you install a two-layer or a three-layer torch-down system.
In a two-layer torch-down roof, you will need a base sheet and a cap sheet. On the other hand, in a three-layer system, there will be two cap sheets and a base sheet.
One cap sheet will be granular, while the other is smooth. A three-layer system is more fire-resistant, more durable, and more energy efficient.
Insulation
The first layer is insulation. It is either screwed or adhered with glue to the roof deck. This is an important layer for flat roofs as heat escapes more quickly.
The Vapor Barrier
This is the second layer. Low-slope and flat roofs collect water and snow. A vapor barrier will solve the moisture and condensation problems and also provide underlayment.
Overlay Board
The roofing professional will keep this board over the vapor barrier to support the roofing membrane.
If it is not laid down correctly, then it can cause “ponding”, a condition where the roof is not leveled correctly. Water can be collected as a result.
Base Sheet
This is the first bitumen membrane layer. This layer can be installed in many ways. Usually, the contractor will roll out the membrane.
A gas torch having an open flame will be used for melting the rolls to the overlay board. Another heat-fusing method or adhesive can also be used.
Cap Sheet
Once the base sheet is installed, it is time for the smooth cap sheet.
The torch will be used again to heat the cap sheet’s bottom part and fuse it to the base layer so that a watertight seal is formed for a two-layer system.
For a three-layer torch-down roof, another cap sheet with a granulated surface will be installed.
Flashing
In most roofs, you will find features that penetrate the roof. In torch-down roofing, a self-adhering modified bitumen membrane will be installed and a layer of metal flashing will be placed on its top.
A torch-down roof will last for many years as it is extremely durable, especially when you install a three-layer roof.
They also cost less compared to many other roofing solutions. But remember, you may have to get a permit, depending on the laws of your municipality, which may cost between $100 and $1000.
The cost also varies depending on the season and demand. Roof installation will cost you more in the fall and less in the winter because of the upswings and downswings in demand.
Torch-down roofs are excellent for flat and slightly perched roofs. They are best installed by professionals. Avoid trying to install the roof yourself.
