For decades, ballast-covered flat roofs were some of the longest lasting and most reliable options available for commercial buildings. However, advancements in flat roofing materials now make ballasted assemblies less than ideal in most cases. It's no longer mandatory that you cover certain types of roofing membranes just to prevent damage to them. These three disadvantages of ballasted roofs may inspire you to choose an exposed membrane commercial roof instead.
It's true that ballasted roofs tend to cost less to install at first than exposed membrane roofs. This is because a thinner and less durable membrane is used under the protective layer of gravel or crushed stone. However, the cost of maintaining the roof is higher over time when ballast is used. The weight of ballast shortens the lifespan of the membrane so it needs replacement more often, while the ballast itself also needs replacement when it breaks down into rock dust or blows off of the roof. Since the ballast must be carefully removed by hand each time the roof is inspected or repaired, labor costs for hiring roofing professionals are also much higher for a ballasted assembly.
Adding inches of heavy gravel to a building's roof increases the total weight pushing down on the structure, and each commercial roof has a specific limit to the amount of roof weight it can bear. Yet without heavy enough gravel, the wind picks up the ballast material and scatters it off of the roof. Wind scouring can leave the membrane exposed, which increases the chances of wind lifting and leaks during future storms. You must carefully design the parapets around the roof's edge and use just the right ballast to make sure high winds don't affect your roof. Eliminating the ballast material prevents winds from being an issue since exposed membranes are firmly attached to the roof's deck with adhesive or fasteners and bars.
Finally, covering the roofing membrane in a thick layer of ballast makes it hard to see what's happening below the surface. When a leak or tear is suspected, the roofing professionals must rake and shovel the material away while taking care to prevent further damage to the membrane as they work. Even if you can see down through the gravel when it is first installed, dirt and debris quickly fill in any gaps between pieces of stone to block your view. You may have to pay for more expensive methods, such as thermal imaging, just to get an accurate inspection. There is also a greater chance for damage if an inspector moves some ballast and forgets to replace it since exposing a covered membrane leaves it vulnerable to damage.
Contact a roofing contractor such as Art Construction of NW FL LLC for more information on ballasted roofs.