BUR: Time-Tested Roof Systems with New Relevance Mike Silvers, CPRC, Owner, Silvers Systems, Inc. and FRSA Director of Technical Services
The terms “sustainability,” “efficiency” and “green” (good for the environment) are very often used in our industry these days. The color of the roof can seem to be more important than how well it keeps water out or resists wind uplift and, just as importantly, how long it lasts. But please don’t confuse how long it lasts with how long the warranty is. But I digress. Certainly the first question, when considering sustainability, should be how long something will last in the first place? Then, how can I extend the life and for how long? Built up roofs (BUR) and their offspring, modified bitumen roofs, have been a staple of the roofing industry since before it was called an industry. Many roofing contractors and manufacturers still swear by these systems. Why is that? Some may say it’s because we’re old fashioned and don’t like change. In fairness, there is probably some truth to that. But like many things that endure, there is a reason. To put it quite simply: they work and work well. But with all the new technology and the advent of single-ply systems in particular, are they still needed? At this point, there are simply not enough fair comparisons available to conclude that they are not. The most prevalently used single plies have not been around long enough to know. We do see extended life in many single-ply systems that have used the same composition or formula long enough to observe them fairly. But keep in mind, there are many built-up roofs in Florida that have been in service for not just 20 years but 30, 40 and more and there are a lot of 22
FLORIDA ROOFING | November 2020
them. These are primarily multi-ply, gravel-surfaced roofs. We also see some of the original APP (atactic polypropylene) modified bitumen systems that are more than 30 years old still in service. For these roofs to last this long, they required some degree of maintenance, but you might be surprised, in a few cases, just how little. One of the reasons these systems last so long is the basic materials they are comprised of: asphalt and, in fewer cases, coal tar bitumens. Just as importantly, they are usually made up of multiple layers or plies and, in the best cases, multiple waterproofing layers. In all cases, they are made up of bitumens and a reinforcing layer or layers. In Florida, with our brutal environmental conditions, it is great to have some portion of your waterproofing protected from not only the sun but also from our constant wet-dry cycle, both of which are very detrimental to any constantly exposed material. This is one of the reasons why properly installed gravel-surfaced BURs have proven to be so durable and thereby sustainable. They have a sacrificial layer of bitumen (flood coat) that helps to protect the waterproofing layers. The gravel in turn protects the sacrificial bitumen. Some disadvantages of gravel-surfaced roofs are that they are not good substrates for coatings and should only be used where the possibility of wind-borne debris from gravel has been considered. Granule-surfaced modified bitumen membranes provide a very similar protection, just less of it. The granule surface on a BUR cap sheet is also similar, but
