As one of the most critical features of a building, roofs first served the sole purpose of protecting the structure and its interior spaces, furnishings, and occupants from the elements. Today’s roofs serve a greater purpose than simply sheltering a building’s occupants, thanks to advances in product technology.
Looking Back
The flat roofs of more than a century ago used to be covered in corrugated iron or straight-run bitumen (thick layers of hot liquid spread across the roof and left to dry).
Early composition or built-up roofing (BUR) often featured layers of heavy paper covered with pine tar and sprinkled with sand. In 1847, Cincinnati entrepreneurs Samuel M. Warren and Cyrus M. Warren replaced costly pine pitch with coal tar and later found a natural asphalt that could be combined with petroleum tar to produce a roofing pitch, according to From Asbestos to Zinc: Roofing for Historic Buildings, a report from the Technical Services Branch of the National Park Service.
Asphalt products evolved out of mid-19th-century composition roofing. In the last quarter of that century, manufacturers assembled built-up roofing’s site-layered components to produce long strips of factory-assembled “ready roofing” (better known today as “roll roofing”). The first asphalt shingles were produced in 1903, according to the National Park Service report.
Up until 25 years ago, asphalt products dominated the roofing industry, says Bill Good, executive vice president at the Rosemont, IL-based National Roofing Contractors Association.
The market began to shift around 1980, a benchmark year according to Good. The quest for higher-performance buildings at lower cost had begun.
While single-ply roofing started appearing on low-slope commercial roofs in the 1960s, a marked revolution of such products took flight in the 1980s.
“We began to see the real emergence in the marketplace of prefabricated, single-membrane roofs - EPDM, polyvinyl chloride (PVC), and thermal plastic polyolefin (PPO),” Good says. “At the same time, the asphalt roofing market began to produce modified-bitumen roofing that combines a pre-manufactured, rolled asphalt-based good with the elements of single-ply technology. It can be applied in single- or two-layer construction.”
What’s Hot Now
Today, BUR has slipped to just 25-percent market share as preferences toward single-ply roofing increase. Single-ply roofing makes up as much as 55 percent of the roofing marketplace, according to Good.
Good notes that the emergence of energy-friendly and environmentally friendly products has been the “real trend” for the past 5 years. “We’re having a lot of discussion in the industry [regarding] roofs that are reflective and emissive - roofs that keep buildings cool,” he says, adding that the move in this direction is “partly voluntary and partly by mandate.”
Highly reÂÂflective roofs - in shades of white, brown, and gray - reduce ambient temperature in a building by reflecting solar energy away from the structure. This, in turn, reduces the cooling load and ultimately provides a greater degree of energy efficiency in a building, not to mention a healthier budget.
“We’re at this wonderful place in the transformation,” Good points out. “We’re not only doing a good thing, but we also can make it economically worthwhile. You can pay for these roofs much faster than something that’s there just to keep the water out of the building.”
Another trend that has emerged is green roofs. The planting media and plants replace traditional roofing components such as gravel ballast and shingles or tiles. Each system varies with respect to the number of layers and layer placement, but all green roofs have a single- or multi-ply layer, a drainage system, growing media, and plants that cover the entire roof surface.
These systems help boost a building’s energy efficiency, provide oxygen to the environment, and also absorb stormwater run-off. “They’re still relatively expensive,” Good says. “But, if they are used in a big-enough development project, you might be able to eliminate the need for retention ponds.”
The Road Ahead
The move toward user-friendly, environmentally friendly, and energy-efficient products continues to drive technological milestones in roofing.
Good predicts increased reliance on metal roofs in the future, and says that the industry is also seeing the first generation of commercial roofs with photovoltaic cells embedded in PVC membranes. This expensive technology remains under development, although real-life applications do exist.
Robin Suttell, based in Cleveland, is contributing editor at Buildings magazine.
