Built-up roofing is one of the most popular roofing materials for commercial buildings with flat or low-slope roofs, and for good reason. When properly constructed by a high-quality commercial built-up roofing contractor, built-up roofing (or BUR) is incredibly durable and long-lasting, especially compared to most single-ply roofing membranes.

Unfortunately, while built-up roofing is extremely tough, it is not invulnerable. Over time you may notice your building's built-up roof developing large, shallow bumps. These are known as 'blisters', and while they are usually harmless, serious blistering problems may require professional repairs.

What Are Blisters In Built-Up Roofing?

Built-up roofing is a multi-layered roofing product, which consists of several sheets of reinforced fabric sandwiched between alternating layers of bitumen-rich asphalt. This unique structure is strong, durable, and completely watertight.

However, when a built-up roof has been in use for many years, the asphalt within the built-up roof may start to lose its adhesive properties, allowing the layers of fabric to separate slightly. During hot weather, the air trapped between these layers of separating fabric can expand, forcing the layers above the air pocket upwards and creating a blister.

Should Built-Up Roofing Blisters Be Repaired?

Blistering in single-ply roofing membranes is generally seen as a serious problem, and in many cases, the entire membrane must be replaced. Built-up roofing's multi-layered structure means that blistering is less of an issue. Most blisters in built-up roofing can be safely ignored, as they do not significantly impact the roof's overall durability or water-tightness.

If you want to have blisters removed for purely aesthetic reasons, a commercial built-up roofing contractor can effect swift repairs. Once the blisters are pierced to remove their air content, the blistered section of roof is coated with another layer of fabric and asphalt, and weighed down with gravel ballast. These repairs are quick, inexpensive, and reliable. 

There are are a few situations where blisters in built-up roofing must be urgently repaired to prevent more serious damage. If any of the following problems apply to your building's built-up roof, call in a commercial built-up roofing contractor to repair your roof as soon as possible:

Blisters Are Very Large

If a blister grows to more than few feet in diameter, it may place significant expansion strain on a large section of the built-up roof. This can pull the fibers of the fabric layers apart, reducing their water-tightness and causing leaks. These large blisters can usually be repaired without replacing the entire roof.

Blisters Are Cracked

Large blisters can also crack the roof's top layer of asphalt, allowing moisture to leak into the roof's inner structure. Internal moisture damage can shorten the lifespan of any built-up roof, and may cause problems with damp inside your commercial building. Cracked blisters should be professionally repaired as quickly as possible to prevent long term damage.

Blisters Block Access To Rooftop Infrastructure

Blisters in built-up roofs should never be stepped on, as this can cause them to burst. If blisters are blocking access to important rooftop machinery, such as roof-mounted air conditioning systems, having them professionally repaired will prevent accidental damage.

For more information, contact a built-up roofing contractor today.