The problem with gravel is that there are still spaces where UV can penetrate, damaging the roof over time. Another problem with gravel is that it heats up in direct sunlight. As the gravel heats up, it eventually sinks into the tar. Any foot traffic can result in damage of the roof as the gravel that has embedded into the warm tar can penetrate through the layers eventually causing leaks.

BUR roofs also tend to crack or “alligator” as they get older, due to extensive UV exposure and low elongation properties of the asphalt, allowing water to penetrate the system causing blisters, cracks and leaks. Even with its faults, a traditional tar and gravel roof can last for over twenty years if installed properly.

Modified bitumen

Modified bitumen or torch down systems are applied by using a propane torch to heat up the underside of the roll of modified bitumen to adhere it to the roof. This process is highly dangerous and has resulted in many buildings catching on fire causing multi millions of dollars in damage.

Some municipalities have outlawed the use of such systems. Torch down systems also have seams making them prone to leaks. They have limited reflectivity as their white granular system is actually grey and not white. Warranties on these type of roof systems is typically five to ten years.

TPO

Newer flat roof systems like TPO (Thermoplastic Polyolefin) or single ply membrane roofs have been developed as a lighter, whiter, cost effective roof system. The bonus of these roofs is they do not contribute to the Urban Heat Island Effect and they are easily installed.

The downside is that TPO is not much thicker than a credit card, making it prone to damage and leaks, especially where the seams have been welded together. Most manufacturers of TPO have very strict policies regarding foot traffic, making it very difficult for tradespeople working on HVAC units and solar installations up on a roof.
Warranty on a TPO is pro-rated and worded in a way that coverage becomes very minimal. TPO remains largely unproven in real world applications as its formulation has been changed several times over the years.

Greener roofing

In the next few years, we will be experiencing a shift to roof systems that are friendlier to our environment. We are already seeing such progress with flat roofing systems that are using plant and cool roof technologies.

Cool roof systems do not allow transfer of the suns’ heat energy to penetrate into the building, making a cooler environment to work in. Cool roofs can reflect as much as 90 per cent of the sun’s damaging UV rays back into the atmosphere, as compared to the five to 26 per cent of a traditional asphalt roof.

TOUGHROOF, an example of a cool roof, is a multi-layered seamless hot asphalt system that takes the best qualities of all existing roof systems and makes them better. The gravel that would be typically used on an asphalt roof to reflect some of the sun’s UV is now replaced with a highly reflective white coating that actually protects the highly elastic rubberized asphalt from breaking down. As long as UV doesn’t get to the tar layers, it will last forever.

The only layer of this roof system that wears is the top white coating. After time this white coating will become dull due to prolonged periods of UV and environmental dust but the roof underneath will never need to be replaced, saving space in our landfills.

The white coating can be re-applied around ten to 15 years after installation. With this re-application of the top coat, the warranty is then renewed again until the next application time. The white coating is installed at a fraction of the cost of a new roof, saving the building owner a lot of money over time and saving our landfills.

White or cool roofs that are highly reflective will offer both immediate and long term savings in energy costs as well.

Paul Peic can be reached at 416.841.7873 or at http://www.toughroof.com.