Roofing 101 Series: Hot Mop vs. Torch On

Written by Apartment Management Magazine on . Posted in Blog

Which Is Right for Your Roof

Authored by Steve Pinkus, Owner of Royal Roofing Company

For your flat or low slope roof, there are more re-roofing options available now than ever. Choosing what’s right for you can be overwhelming if you’re not prepared.

Picking a roof can feel harder to do than picking just one ice cream topping at a shop with unlimited options. Unlike dessert, your roof can cost thousands of dollars, and you’ll have to stick with it for 5, 10, or even 15 or more years.

Two of the most popular flat re-roofing options are “hot mop” and “torch on” systems. But which should you pick if two contractors quote two different options? Each has unique benefits, but if you are uninformed, you could choose the wrong roofing system and end up with a lemon of a roof — or worse.

What is Hot Mop Roofing?

Hot mop roofing is one of the oldest and most trusted ways to repair or replace your flat roof. The two-part name comes from the 400 degree Fahrenheit, liquid “hot” asphalt tar that is applied to the roof using a large “mop.”

While the details have changed over the years, the fundamentals remain the same: repeating layers of fiberglass felt and hot tar are applied to create an impenetrable shield for your roof. Over time, other nicknames for hot mop roofing emerged, including a “built-up” roof, named after the many layers of felt and tar that are built as part of the process. And just like making a lasagna, the more layers there are, the stronger it is. Redundancy improves its protection, making it the longest lasting roof system and why 70% of all the roof systems installed nowadays are hot mop.

The many advantages of hot mop roofing are why it has long been the most popular flat roofing system. These include, among others:

  • Durability and weather resistance
  • Low maintenance
  • Long warranties available
  • Affordability

With that, there are also important considerations for a hot mop roof. The application requires trained roofers that can not only apply it correctly, but that can also protect themselves and your building against the risks of the hot tar. Hot tar also has an iconic smell that can bother some people, so accommodations for building owners and tenants may be needed. With that in mind, hot mop roofing continues to be #1 for many reasons.

What is Torch On Roofing?

Torch on roofing, also called torch down roofing, is another low slope roofing system that is considered an alternative to hot mop roofing. Rather than combining the felt and tar “ingredients” while your roof is being installed, the layers for a torch on roof are made in a factory and delivered in single rolled sheets of material.

If you were wondering, “Well then how does the roll stick to the roof?” you’re about to learn. An open-flame propane torch is used to melt the tar in the rolls. Immediately after, it is rolled out onto the roof, and its seams melt together to create a waterproof seal.

Keep in mind that this isn’t a hand-held torch like what you may have used to toast marshmallows or have seen used to make crème brulée. These are high powered flames that work on an industrial level, and with great power comes great responsibility for safety.

When used appropriately over non-combustible decking like concrete or metal, torch on roofing can be a great roofing solution. Rubbery additives make it highly resistant to punctures, it is a great insulator, and the cap sheet — or top layer — is protective against damaging UV rays similar to traditional hot mop roofs. If you only have a small area to patch or if it’s in an area that’s difficult to access with a hot tar kettle, a torch on system can be a solution that is not overly labor intensive and stays watertight for years, but likely not decades.

Aside from the higher cost, when should you not go with a torch down roof job? With the risk of flash fires being so high, there are several instances to avoid torch down roofing, and you need an experienced and trusted roofing contractor to advise you appropriately. Your roof can catch on fire during the process, but perhaps even more scary than that, the flame can penetrate your roof and cause smoldering in attic space that builds for hours before actually flaming up. This can effectively create a ticking time bomb that lights up after the contractor has left for the day.

Despite torched down roofing being banned for use with combustible wood structures in New York and 36 other states, some unethical roofers — if you can even call them that — still trick countless customers into using them in the wrong situations to make extra money.

No matter what roofing system you choose, it is only as good as the roofer installing it. Reach out to Royal Roofing Company for a free consultation regardless of if you are just getting started or already have other bids in hand.

About the Author

Roofing 101 is a pioneering educational resource focused on empowering property owners and managers to make informed choices for their roofing needs. For residential and commercial buildings alike, Roofing 101 levels the playing field by revealing the closely-guarded insights most contractors choose not to disclose to their customers. By sharing decades of experience through this platform, the Roofing 101 team fosters better service, happier customers, and cost savings across the roofing industry.

Roofing 101 is provided by Royal Roofing Company and led by Owner and industry veteran Steve Pinkus. Whether you’re getting started or already have bids in hand, you should include Royal Roofing Company in every roofing project. Royal Roofing Company has stayed in continuous business for nearly 40 years in Southern California under the same license. That’s because they only hire the “best of the best” roofers and use the finest quality materials. They maintain the highest level of business integrity, as proven by their 38-year CSLB license that stands without a single violation, citation, or disciplinary action.

For more resources or to schedule your free estimate, visit, call their office at 562-928-1200, or reach out to Steve directly at 213-305-0277 and Mention “Roofing 101” to your Royal Roofing Company specialist to receive an exclusive 10% discount on your roof up to -$1,000.