The Pros And Cons Of Built-Up Commercial Roofing

One of the most common options for commercial roofing is built-up roofing or BUR. BUR is ideal for low-slope roofs and is made of alternating layers of bitumen and reinforced fabric made of fiberglass or organic material topped with a layer of aggregate. The aggregate layer is typically gravel or stone. The bitumen can be installed in either hot or cold processes. Built-up roofing has several major advantages on the right roof but can create problems if installed in less than ideal conditions on a roof that isn't right for BUR. Here are the major pros and cons of built-up roofing in commercial applications.



Commercial buildings have a higher risk of fire damage than residential homes simply because commercial buildings often contain activities and machinery that present a greater fire danger, particularly in the industrial and manufacturing industries. That's why it's so important that commercial buildings have highly fire-resistant roofing. One of the major advantages of built-up roofing is that the gravel layer on top is extremely fire resistant and that's more than an advantage—it's essential.


One of the greatest characteristics of a built-up roof is that it's very durable with a long lifespan. Roofers estimate that the lifespan of a BUR will be five times the amount of plies or layers installed. So factoring in the average number of layers put down on a built-up roof, they typically have an average lifespan of between 15 and 30 years, though it's not uncommon for a well-built and meticulously maintained BUR to last up to 40 years.


When properly installed, a built-up roof is watertight. The bitumen layers underneath the aggregate create a tight seal with no seams. Because seams are the most common causes of leaks on most other types of roofing, a well-maintained BUR can stay watertight for many years without ever springing a leak.

Easy To Repair

BUR requires regular maintenance in order to ensure that there is no pooling water and that the membrane layers are always properly covered by aggregate. However, if any problems should arise, it's very easy to repair by cutting away the problem areas and then simply adding more membrane and bitumen layers.

Impact Resistant

The multi-layer roofing system with membrane and bitumen layers and aggregate top make BUR very impact-resistant. Falling branches, hail, or any other debris won't easily damage it.


Only Low Slopes

One of the major disadvantages of built-up roofing is that it can only be installed on low-slope roofs. In fact, buildings codes dictate that BUR can only be installed on a roof with a 1/4:12 minimum slope. That rules out many commercial roofs in areas with harsh winters and heavy snowfall that require steep slopes. BUR roofs are best in areas with mild climates.


Another disadvantage of a built-up roof is the physical weight of the material. Because it's a roofing option with a heavier load, it can only be installed on roofs that have the support structure to handle the weight of the bitumen layers and aggregate.

Regular Maintenance

Another downside of BUR is that it must be regularly maintained. If the aggregate layer ever recedes enough to allow the membrane through, harmful UV rays will cause damage and degradation. It must also be checked regularly for proper water drainage because any water buildup and pooling can break down the materials and cause leaking. The best time to do this is after a period of severe wet weather.

Installation Safety

If installed using hot bitumen, the fumes from the process can be toxic and therefore hazardous to the roofers performing the installation. It's essential that only experienced roofers using the proper safety gear install BUR.

For more information, contact a local roofing company, like Drey Roofing.