Modified Bitumen vs. Built-Up Roof: Which to Choose?

Modified Bitumen vs. Built-Up Roof: Which to Choose?

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If you are planning on building a new roof for your home or commercial property, you need to use the proper roofing method for your circumstances. Two extremely common options in today’s world include modified bitumen and the built-up roofing system.

Both of these roofing systems are somewhat related to each other, but there are some key differences between them that you need to be aware of. We’re going to compare these two roofing systems with each other to figure out which one is best for your needs.

What Is a Modified Bitumen Roof?

Let’s first talk about modified bitumen roofing, which is often said to be some of the most durable roofing around. This system is characterized by the use of many roofing materials to create layers.

These layers consist of modified bitumen, which is made out of plastic, rubber, and asphalt. We then also have various layers of fiberglass, plastic, asphalt, and rubber. These all come together to create a flexible yet durable waterproof membrane that is very resistant to impacts, weather, and more.

Exactly which materials are used to create these layers depends on the exact application in question. Here, you can have as few as two layers or many more. Furthermore, this is a type of roofing method that has been in use for well over 100 years, and it is most often used for commercial roofs, specifically for flat and semi-flat roofs.

Some of the biggest advantages of modified bitumen roofs are that they are very durable, strong, long-lasting, and resilient, with the biggest drawback being ease of installation.

Although some sources might tell you that modified bitumen roofing can be installed on your own, it’s still a very difficult process and usually requires professional installation.

This is especially the case because the process can be extremely dangerous, as there are torches and scorching hot materials involved. Installing a modified bitumen roof is also time-consuming, not to mention that if one of these roofs requires maintenance, the process is quite intensive.

What Is a Built-Up Roof?

We then have the built-up roof, simply known as the BUR. This is another roofing system that is commonly used for low-pitched and flat roofs. Just like with modified bitumen roofing, here you see several layers of material combined to form one solid layer.

Although the process has changed over time, BUR roofing has been around for well over 100 years, just like modified bitumen roofing. This is one of the top choices for flat roofs due to some of the factors that we’ll discuss below.

Built-up roofs have at least three materials, which include ply sheets, layers of asphalt or bitumen, and a surfacing material like gravel or stone.

However, modern installations may see many more layers, including a deck surface, rigid roof insulation, asphalt, a cover board, a ply sheet, more asphalt, and sometimes even a reflective roof coating to allow for great heat dissipation.

What is interesting to note is that a BUR roof can be applied hot or cold, unlike modified bitumen roofing, which has to be applied hot. A BUR roof is often seen as very beneficial because it will have great energy efficiency, the aggregate is fire-resistant, and the different layers create good leak resistance, among other benefits.

Modified Bitumen vs. Built-Up Roof: What Are the Differences?

Now that we know what both modified bitumen roofs and built-up roofs are, let’s take a closer look at the differences between them.

Durability and Longevity

Although this may be seen as more of a similarity than a difference, it is worth mentioning that both of these roofing systems are considered to be very durable.

Both are said to have very high impact resistance, they are fairly tear, UV, and fire-resistant, and more.

Additionally, these two systems allow for good traffic resistance in the event that people walk over the roofs a lot. Both are also quite durable, as they are said to last for about 30 years or even longer.

That said, longevity may depend on the exact materials used, particularly as far as modified bitumen is concerned. If top-quality materials are used, modified bitumen may last slightly longer.

Ease of Installation

Although modified bitumen roofs are generally considered somewhat difficult to install, it appears as though the process is still a bit simpler than with BUR roofing systems. Yes, both of these roofing systems involve installing multiple layers of a wide variety of materials.

However, although we aren’t going to go into great detail here, the process with BUR roofing systems is a little more complex, especially because of the materials being used. The modified bitumen roof is just a bit easier to install, and on that note, also somewhat easier to maintain.

Energy Costs

Although both of these roofing materials are fairly good in terms of energy costs, BUR roofing tends to be a little better. The reason for this is that modern BUR roofs usually have a reflective layer installed on the exterior, which allows for great UV resistance.

This helps reflect a lot of the UV rays back from the roof, therefore greatly reducing cooling costs during the summer. That said, modified bitumen roofs are not terrible on this front, as they do reflect some sunlight, just not nearly as much.

Water Leaks

While both of these roofing systems are pretty good in terms of preventing water from leaking, BUR roofs often make it much harder to find the source of leaks, and it can also make it hard to even see that there are leaks in the first place.

The longer leaks are left untreated, the bigger the problem becomes. Although this is sometimes also an issue with modified bitumen roofing, it’s usually not quite as severe.

Fire Issues

Something else to consider with modified bitumen roofing is that if the torch-down method is used, there is a certain risk of a fire starting. Furthermore, although this roofing system is fire-resistant, this resistance will decrease over time. BUR roofs, on the other hand, tend to be much more fire-resistant for a longer period of time.

Overall Cost of Installation

Modified bitumen roofs should cost you around $5 per square foot to install, whereas BUR roofs tend to be even more cost-effective.

Modified Bitumen vs. Built-Up Roof: Which One Should You Use?

Admittedly, these two roofing systems are very similar. One of the main differences to consider is that modified bitumen is likely a bit more durable, but also slightly more expensive.

That said, if we take energy savings into account, over the long run, BUR roofs become even more cost-effective. However, they are also more difficult to install and maintain, and they have issues in regard to water leaks.


Now that you know what makes these two types of roofs different from each other, you can make an informed decision as to which one is best for your specific needs.