Flat Roofing

Flat Roofing with Torch Down

San Diego Residential Flat Roofing With Torch Down Roofing

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A flat roof is a roof with a pitch of 10° or less. It is more common to see flat roofs on industrial buildings or apartment complexes. But in San Diego it is not unusual to see flat roofs on modern style homes or on structures like carports, patios, or add-ons. The temperate weather in places like Del Mar, Encinitas, and Mission Beach means that flat roofs don’t have to contend with problems like snow and ice build up.

Shingle and tile roofing systems are designed for roofs with enough of a slope for the water to easily drain off. Since flat roofs don’t drain as quickly, you need materials and a roofing installation system designed especially for flat roofing.

Some of the most common flat roofing methods include:

  • Torch down roofing
  • Built-up roof (BUR), hot mop rock, or tar
  • Rubber membrane (EPDM Rubber Roof)
  • Spray polyurethane foam roof
  • Thermoplastic membrane flat roof (PVC or TPO)

In our over 29 years of business, we have found that torch down roofing performs the best on homes in areas like San Diego. In fact, we are seeing torch down roofing replace most of the BUR roofing systems.

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What is Torch Down Roofing?

Torch down roofing is known by many names – modified bitumen, rubberized asphalt, torch on roofing, or granulated cap sheet. This roofing system uses sheets of modified bitumen that are applied to the roof using a propane torch. The torch melts the asphalt and as it cools, it creates a watertight seal on your roof. Sheets are laid down to overlap, allowing the seams to melt together.

Modified bitumen membrane or sheets come in big rolls. The sheets are made up of multiple layers of material including a thermo-fusible film, modified bitumen, reinforced polyester, and a granulated mineral surface.

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Advantages of Torch Down Roofing

Watertight Seal

Flat roofs have to be particularly good at keeping water out. Their small slope makes it easier for water to pool up on the roof. This is where torch down roofing really shines. In fact, it is one of the most water-resistant flat roofing systems available. The sheets of modified bitumen are waterproof and when melted together and on the roof, they form a watertight seal. In comparison, the gravel on BUR roofs can trap water and make it harder for it to evaporate.

Easy Repairs

It is easier to find and fix leaks on a torch down roof than on any other flat roofing system. The sheets of modified bitumen are easy to roll on and seal up. And you don’t need to remove the gravel or other materials around an area to find a leak.

Performs Well in Heat and Cold

The sheets of modified bitumen are very flexible. This allows them to expand and contract in the heat and cold without cracking or splitting. They are also resistant to damage caused by UV rays.

Less Vulnerable to Punctures

The embedded granules on the cap sheet make it more resistant to punctures or other damage.

No Loose Gravel

The gravel used on hot mop tar roofing systems (BUR) can move and fall off over time. Wind, rain, vibration, moving cable wires, and even cats using the gravel as kitty litter can knock the gravel loose. This exposes areas of the roof membrane, which decreases the life expectancy of the roof system.


The combination of the embedded granules and the water-tight seal creates a roof with a life expectancy of 15 to 20 years.


The granulated mineral surface helps reflect heat off the roof, saving you money in A/C costs.


The embedded granules make torch down roofing very fire resistant. We use Dibiten modified bitumen with a Class A fire rating.


With BUR roofing systems, the gravel can add hundreds of pounds to your roof. If your roof isn’t built to sustain this weight, you can have problems. Modified bitumen sheets weigh much less and you don’t have to reinforce your roof.

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Flat Roofing

What are the Best Materials for Flat Roofing?

At TR Construction, we use a three-layer torch down roof system. It performs significantly better than two-layer torch down roofing systems. You can find self-adhering roofing sheets that are easier to install, but they are more prone to failure if the seams come loose.

A three-layer torch down roof system consists of a base sheet, a smooth cap sheet, and a top cap sheet with a granulated surface. The granular top sheet makes your roof more durable, energy-efficient, fire-resistant, and aesthetic.

We use Dibiten APP Modified Bitumen Membrane, which uses a 90 lb. granulated cap sheet. Dibiten uses slate for the granular surface membranes because it is lighter weight and the slate granules lay flat – making for better adhesion and easier application. Dibiten has an exceptional reputation and is known for producing top-quality roofing material. See the available colors and styles.

How Do You Install Torch Down Roofing?

Torch down roofing is definitely not a DIY job. It needs to be installed by a professional roofer who has the proper insurance. Because it uses an open flame, you want a roofing expert who knows what they are doing and who follows safety guidelines.

The roofer should also be an expert in flat roof draining. Flat roofs are actually not completely flat. They have to have enough of a slope so that the water drains off. If the roof doesn’t drain appropriately, water can pool up and damage your roof.

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How Long Does a Flat Roof Last?

Your torch down roof should last between 15 and 20 years if installed correctly and with quality materials. Things that can reduce the life of your roof include:

  • Seam Failure: If the seams have not been sealed completely, water can get trapped between the sheets of the modified bitumen. This is less common when a three-layer roof is installed by an experienced roofer.
  • Wet Conditions During Install: During the installation, the area should be completely dry. You do not want water to get trapped in between the layers while installing the roof. This can cause mold and water damage.
  • Tears: Torch down roofing is designed to be durable, but it can still be torn. This can happen when walking on top of it or if something scrapes against your roof.
  • Improper Drainage: Gutters and drainage are important for any roof, but especially for flat roofs. Leaving standing water on your roof can increase your risk for leaks, weaken your roof’s membrane, and add a lot of weight to your roof. Water is heavy – only one gallon of water weighs over 8 pounds!
  • Neglect: It is very important to have your flat roof regularly inspected for potential problems. Make sure you keep it free of any pooling water or debris. Gutters should also be cleaned frequently.

How Do You Repair a Leaking Flat Roof?

Flat roofs need more maintenance and are more susceptible to leaks. Small problems can become big problems fast.

On older San Diego homes, it is common to see hot mop rock or BUR systems with gravel applied over tar. Unfortunately, we have found that things like wind, rain, and vibrations move the gravel over time. This exposes the roof to the elements and decreases its life expectancy. And before we can find the leak, we need to remove a lot of the existing roofing materials.

Torch down roofs are easier to repair because you don’t have to remove a lot of gravel and material to spot and fix the problem. We generally don’t repair BUR roofs but recommend you replace your roof with a torch down roof.

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How Much is a Flat Roof Replacement?

Flat roofs are cheaper to install, but they also don’t last as long as a sloped roof. When researching flat roof replacement cost, the price will depend on the following factors:

  • Size of your roof
  • Type of roofing system you choose
  • Quality and availability of the materials
  • The current condition of your roof and if there are any drainage issues
  • The complexity of your roof

To get a detailed quote of how much it would cost to replace your flat roof, contact us to get a free, no-pressure estimate. An experienced roofer will carefully examine your roof and take the time to explain what needs to be done. Our specialized divisions in remodelingroofingelectricalsolar, and painting can also help with any repairs or modifications you need. Our divisions are designed to work seamlessly together so you don’t have to worry about coordinating with multiple contractors.

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Torch Down Roofing With Modified Bitumen