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Can a Flat Roof Be Repaired?

September , 2022 | 8 min. read

By Nicole Corson

warehouse with flat roof

A roofing contractor never wants to admit that sometimes, roofing projects can be difficult. Our egos are oftentimes as vast as our skill sets, but we all still have to acknowledge that a flat roof repair can be tricky. Very tricky. If you’re the proud owner of a flat roof, sorry to say, but you’re already at a disadvantage. The water doesn’t drain off of your roof as fast as a steep slope roof. Let’s say you spring a leak. With the roof being flat, the water could be coming in from further away than where the leak is showing up on your ceiling, making it harder to detect and repair, even for the experts.

Here at RoofCrafters, we’ve been repairing and replacing commercial and residential flat roofs for over 28 years. We have seen some of the worst flat roof leaks, and have also been able to make solid repairs and save our clients time and money by extending the life of their existing flat roof system that was either leaking due to installation errors or suffering from minor damages. 

To determine if a flat roof can be repaired, we first need to discuss some of the most common types of flat materials. In this article, we will cover single-ply flat roofing, modified bitumen flat roofing, and hot tar flat roofing. We will also cover what kind of condition it takes to be able to make repairs to these commonly used flat roof systems. By the end of the article, you’ll be ready for the flat roof repair big leagues. Okay, maybe not quite that far in one article, but you will go from rookie to semi-pro in all things flat roof repair related. So, let’s hit the field rookie!


Top 3 Flat Roofing Materials & How to Repair Them


flat roof roofcrafters being repaired

  • Single-ply roofing (TPO, PVC & EPDM roofing)

  • Modified bitumen (rubber roofing)

  • Built-up roof (hot tar roofing)

1. Single-Ply Flat Roofing Repairs (TPO, PVC & EPDM) 

Single-ply roofing is one of the most popular roofing materials used on commercial and residential flat roofs. They come in different thicknesses, and you might even have your local roofing contractor ask you, “do you want a 45 mil or 60 mil roof?” The higher the number the thicker the product. The thicker the product the longer the manufacturer warranties the flat roof material.

Can a single-ply flat roof be repaired? The short answer is yes, and it is the easiest of the 3 flat roof materials to repair. If, and only if the material has any useful life remaining. To repair this roof system we have to clean it free of all debris and bond the new repair materials to the older roofing. 

Single-ply TPO and PVC roof is made up of 3 layers. A base layer, the scrim layer (reinforced woven fiber layer), and thickness over the scrim layer, which is the top layer. This top layer protects the scrim layer from the sun’s harmful UV rays.

If this top layer, which is called the thickness of the scrim, is deteriorated, your roofer will not be able to weld the new repair material to the old roof. This is what will determine if your flat TPO or PVC roof can be repaired.

EPDM commercial flat roof

An EPDM roof typically comes in a 45 or 60-mil thick membrane too. The difference is the laps and flashings are glued or seam taped together instead of welded like TPO or PVC.  Once an EPDM roof reaches the end of its lifespan it begins to shrink. This shrinkage or movement makes repairing an old EPDM roof nearly impossible. 

Notice I did not say impossible. Nearly impossible, to be fair, a repair on an older EPDM roof should be thought of as “buying time” and not expected to last very long whatsoever. The good news is that if any of the 3 mentioned single-ply materials are in decent shape then they are very repairable and the repair done properly can be expected to last as long as the materials last.

Now that you know about single-ply roofing and the conditions needed to make flat roof repairs with each material let's discuss the second most popular flat roofing material, modified bitumen.

2. Modified Bitumen Flat Roof Repair (Rubber Roofs or Mod-Bit Roofs)

I like to say a Modified bitumen roof is the second generation of flat roofing. Built-up or hot tar is the OG of the flat roofing world and we will discuss that next. Mod-bit became popular because unlike the hot tar roof that requires setting up a hot tar kettle, which alone is a full-time and dangerous job in itself. Modified bitumen roofs can be installed with hot tar but the most popular installation methods are without the hot tar. 

Here are 4 main installation methods.

torching mod-bit flat roof roll

  1. Hot tar applied
  2. Cold tar applied
  3. Torch applied
  4. Self-adhered


With 4 methods of installation and two primary finishes, smooth and granule surface, you may already see where we are going. First, like single-ply roofs, the condition of the top layer is important. Yes, this roof has to be installed with multiple layers. 2 layers are the minimum and it can be more depending on the warranty desired. If the materials on the top layer have passed their useful life, attempting to get a new mod-bit to adhere to an older worn-out mod-bit material will be almost impossible. 

Again, I did not say impossible. I am optimistic, but keep in mind that a repair, if your local roofing contractor will attempt it, will be very short-lived.  Once these rubber roofs get old, they expand and contract so much that the new materials used for the repair won't stick to the shifting old rubber roof materials for very long.

modified bitumen flat roofing

Now on the flip side, if the materials have useful life remaining, a roofer with experience in modified bitumen roofing or even an ole hot tar roofer will be highly capable of stopping a leak by doing a minor repair for you.  The most important thing to make a repair successful on a modified bitumen roof is to properly prep the area being repaired. 

Because modified bitumen is an asphalt-based product, the preparation is typically done by cleaning the area and then applying asphalt primer to the area that needs repairing. Next, we would install the new mod-bit patch over the leaking area. This priming process will help to allow the new mod-bit roofing to bond to the older mod-bit roofing that has weathered from the sun. This primer is also required to be applied to any metal flashing that the mod-bit roofing needs to be adhered to. 

So, can a modified bitumen roof be repaired? It depends, the short answer is yes but the condition of the existing roof will ultimately determine that. And the experience or skill set of the roofer you hire will ultimately determine the long answer to this question.

Now that we have covered repairing single-ply and modified bitumen flat roofing and you are semi-pro at both. Let’s talk about the “OG” of flat roofing, build-up, or as most old-school roofers like to call it, “hot tar” roofing.

3. Can a Built-Up Roof or Hot Tar Roof Be Repaired?

That is a great question. A built-up roof can be your best friend or your worst nightmare. There are so many variations or layers of materials. Layering the materials is how it got called a built-up roof. The roof is built-up by layering plies of fiberglass rolls of roofing and hot tar between each layer. And this is only a short explanation of how it gets installed. The basics of a hot tar roof.

RoofCrafters-commercial built up roofing

Again, the top layer is going to be what determines if it can be repaired successfully. Oftentimes the top layer is a flood coat of hot asphalt (tar) with rocks put in the tar while it is still 450 to 500 degrees. A hot tar roof with a rock finish makes for a challenging repair for a very experienced roofer. But it can be done if there is useful life left in the flat roof system. Now, if it has a granule surface cap sheet as a finish layer or an asphalt flood coat, it is a much more manageable repair. Either way, the existing materials that will need to be repaired need to have some useful life left to make a repair that will last any length of time.

Can I Repair My Flat Roof?

Now that you are officially a semi-pro flat roof repair consultant, on single-ply, modified bitumen, and built-up roofing, you have a better understanding of if they can be repaired, and how the repairs will be executed. At the end of the day, it will largely depend on the specific type of flat roof you have, the type of damage done to your roof, and the extent of that damage.

In order to be certain, your best bet is to get in touch with a local roofing contractor and have them come out for an inspection. They’ll be able to assess the damage with you, walk you through your next steps, and decide if a flat roof repair is possible. 

If this article has you feeling a new sense of hope regarding your flat roof repair efforts, go ahead and schedule your inspection with RoofCrafters today, and one of our experts will give you an honest inspection to see what your insurance will cover. In the meantime, browse the extensive resources listed in our learning center. We recommend reading, "How Long Do Roof Repairs Last" so that you can better understand the lifespan of your roof repair.

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Nicole Corson

At RoofCrafters, our mission is to provide job opportunities for others to thrive and grow while making a meaningful impact within our communities.