As we continue to explore the basics of commercial roofing in our “What is a Substrate?” series, this blog will answer the question, “What is Built Up Roofing (BUR)?”
BUR is a system of specialized roofing materials that are layered and sealed with asphalt or other industrial adhesives. It is placed on a building’s flat or low-slope roofing structure and can be covered in aggregate material such as crushed stone or pebbles.
This blog will focus mainly on gravel BUR’s major advantages and disadvantages. We will explain how a Progressive Materials silicone roof coating restoration can help an aging BUR system.
One advantage of BUR is its lifespan. While it has a shorter expected life than some other substrates such as concrete, a BUR system can be expected to last about five years per layer. This makes it possible to get 20 to 30 years out of a built-up roof system.
Additionally, the strength in its multiple layers can help make BUR more resistant to a variety of weathering elements, such as fire, water, and even UV rays.
Gravel built-up roofs also provide great impact resistance. The aggregate material on top can shield and protect BUR from things like hail damage and falling branches.
A disadvantage before the roof is even completed is that the multiple layers on a built-up roof can create a lengthy installation process. That will result in higher labor costs.
Once completed, a built-up roof can suffer cracks over time. Imperfections in the roofing materials and normal weathering can result in these cracks. Cold temperatures, especially, can reduce the lifespan of a BUR system.
Those cracks can create another problem.
Finding a crack in a rubber roof such as EPDM can be relatively easy. Finding a crack in a gravel-covered, multi-layered BUR surface is often extremely tough. This makes repairs on a BUR system difficult.
Additionally, heat or moisture under the top layer of roofing or roofing seal can cause BUR blisters. A BUR system also can be susceptible to wind and water damage, depending on the roofing materials and installation process.
How PM can help
Replacing or restoring a gravel built-up roof has historically been a major challenge. In the past, it took back-breaking labor to remove the tar and gravel. Now, PM’s SL-800 Surface Leveling Silicone is designed for use on gravel BUR. After vacuuming off any loose rock, SL-800 can be applied to fill in cracks and gaps and provide a smoother surface for your silicone top coat.
Under the old application method, rocky or bubbled surfaces made achieving a seamless membrane difficult as silicone found its way to the bottom of these cracks and crevices. SL 800 – a surface-leveling silicone that helps flatten rocky or bumpy roofs — creates a smooth surface. The top coat can then be applied while keeping costs down for the client.
Additionally, PM silicone won’t crack or deteriorate even if it’s constantly exposed to sunlight. Our silicone reflects nearly 90% of UV rays on a commercial building’s flat roof. That limits the damaging affect those rays will have on your building. This will also lower your building’s internal temperature.
While moisture can cause BUR blisters and further damage a roof, that isn’t a problem with properly installed silicone roof coatings. A silicone coating creates a seamless membrane on your roof that moisture will not penetrate. That protects your roof structure and building contents from leaks that might be seen on other buildings.
We would like to point out that a coal tar pitch BUR system should not be coated with silicone. Coal tar pitch is a roof type that is constantly re-emulsifying. Every day when the temperature increases, the tar returns to its liquid form, resealing cracks and holes. This is a fantastic roofing system because it is self-healing, but when it is coated, the silicone will tear as the substrate moves beneath it. Any roofing system that is unsettled, intentionally or unintentionally, is not a candidate for a silicone roof coating.
In conclusion, we agree that built-up roofs are a good choice for a commercial building’s low-slope or flat roof. They do fail, however, and PM silicone can strengthen and add life to your roof.
To learn more about our company and roof coatings, please visit pmsilicone.com.