TAKING ROOF WEIGHT INTO ACCOUNT
Often overlooked when comparing various roof types is the weight of each option. Your roof weight can be a major factor to consider depending on the structure of your building. During construction you have architects determining structural loads and other factors, but in a re-roofing application some building owners don’t consult an architect.
There are usually no problems with roof weight, but if your building was originally built with a very lightweight roof system in mind, it likely isn’t advisable to put a very heavy roofing system on during your re-roofing project.
Lighter Roofing Systems
Metal panel roofs, while the metal itself can be rather heavy, are a light system overall because of their simplicity and their few components. Single-ply roofs are also typically a light roofing system depending on the board underlayment used. The insulation board used is often very light, making this a safe bet if roof weight is a concern of yours. In retrofit applications, roof coating systems are also very lightweight. They add virtually no weight to the existing roof. The only limitation structurally is ensuring that the existing roof is structurally sound. Whereas other systems would tear out the existing roof, coatings go directly over it and therefore it must be in good condition structurally.
Heavier Roofing Systems
Other roofing systems place a lot more load on the structure of your building. Concrete roofs, for example, while becoming less common in the last 10-15 years, are a very heavy roofing system should you encounter one or consider one for your building. Built-up roofs are also heavy due to their many layers. Any roofing system that includes gravel, such as a ballasted roof, will also be very heavy. These systems are often planned at new construction and are less likely in retrofit applications, but it still often pays to understand the limitations of each.
Every roofing system is different, and therefore each system puts different stress on your building under the roof weight. Before planning any roofing project, consider the weight of the new roofing system. Then, you can determine if your building can handle the new load.