Roofing Systems: How Your Choices Have Changed

Back in 1964, Max Baker of the National Research Council of Canada’s Division of Building Research published a digest on new roofing systems. Each digest in that series dealt with just one topic relating to one aspect of building research. This month, let’s look back at Digest 49, published in 1964, when the first generation of single-ply flexible roofing was just gaining traction.

Emerging Developments in 1964
Roofing professionals had to learn a new vocabulary. Beyond bituminous roofing, which had been dominant up to that date, the market now featured elastomeric materials such as neoprene, silicone, butyl and chlorobutyl rubber, polyisobutylene, Hypalon, and Tedlar, and thermoplastics such as polyvinylchloride (PVC), chlorinated polyethylene (CPE), ethylene vinyl acetate (EVA), and ketone ethylene ester (KEE). Polymeric modifications to asphalt and coal tar pitch (MB) also emerged.

Many of these polymeric systems were non-reinforced or internally reinforced with scrim, or in some cases used a backing such as fleece. New techniques for attachment, such as ballasted and mechanically attached systems, joined the fully adhered bituminous roof systems.

Several manufacturers of roofing in this generation relied upon Weatherometers to accelerate the weather process, since the products were new and were expected to last for 15-20 years. From personal experience, polyisobutylene worked well in the Weatherometer, but not on actual roofs.

In many cases, the new products were already in service in Europe, where the price of petroleum was much higher than in the U.S.  These new polymeric products were in most cases just a single layer of membrane, while most MB membranes were two-ply. As Baker points out in his textbook:

Some of the advantages claimed for most new materials are lightness, high elasticity, resistance to traffic, high chemical and weather resistance, ease of application on complicated slopes, ease of repair, and for many of the products one or even several or all of these advantages apply.

 Factors that exist for new as well as for old materials, however, are often forgotten or ignored and these include building movement, construction moisture, the effect of trapping moisture, and construction conditions in relation to workmanship. New materials often introduce new factors such as dependence on thin layers of adhesive to provide water tightness at narrow joints, and often a level of perfection in application that may not always be easy to obtain.

By 1972, the roofing industry recognized that these factors required more education and hands-on exposure, with the introduction of the Built-up Roofing Systems Institute (BURSI),

later changed to the Better Understanding of Roofing Institute. Many manufacturers followed suite, leading to the formation of the Roofing Industry Educational Institute (RIEI) in 1979. In addition to the Asphalt Roofing Manufacturers Association, SPRI was formed in 1981 to represent sheet membrane and related component suppliers. By the time Baker’s book was published in 1980, there were available in Canada at least 100 different roofing products that might be described as new.

Emerging Developments in 2014