The Latest Trends in Roofing Materials

Jeff Evans

Fresh out of college with a degree in Construction Administration, I began my roofing career in 1977 with a roofing contractor who specialized in a new revolutionary product, a single-ply ballasted roof membrane. Knowing very little about roofing in general, I was moderately successful in selling the new fangled membrane to my customers, because they were fed up with the perceived performance problems of built-up roofing, the other roofing option at the time.

The roofing landscape has changed quite dramatically since then, and in fact continues to change on an almost daily basis. Over the past 20 years, single-plies have progressed from a new revolutionary product to having a significant share of the roofing market, albeit with some missteps along the way.

The built-up roofing industry, out of favor for awhile because of real and perceived performance problems, has re-established its viability in the market as a capable performer. It has done so by improving its base components and has developed better flashing and accessory products. Built-up roofing manufacturers and contractors have also done a better job of educating the roof buying public of long known design principals, such as eliminating ponding water, to reduce the inappropriate use of built-up materials.

For those facility managers, engineers, etc, purchasing roofs in today's market there are two words that best describe the state of the industry, Choice and Change.

Today's Choices

Compared to the 1970's, when the only real decisions the buyer of a new roof had to make was how many plies were best, the 1990's present a dizzying array of choices. Following is a short review of some of the updates in each generic product line.

Built-up Roofing

The main improvements in built-up roofing have been the shift to fiberglass felts and the use of rubber modified asphalt flashing materials. Fiberglass ply felts now come in two types, the widely used Type IV felt, generally considered the commodity felt, and the newer but stronger Type VI felt. Both have proven to work in well designed applications, and at this point the Type VI felt is positioned as the premium felt, for those inclined to buy upscale. Type VI felt systems generally are required to qualify for longer "system" warranties.

Modified Bituminous Systems

Modified bitumen, sometimes referred to as "mod bits" or modifieds, is a family of asphalt membranes composed of a rubber or plastic additive, combined with asphalt, fillers and felt reinforcement. The modifiers improve the cold flexibility of the membranes over conventional blown asphalt, and are formulated to improve elasticity of the roofing material.

Most typically the mod bit membranes are made in sheets three feet or one meter wide, and resemble rolled roofing. Two primary modifiers are used, SBS or styrene butadiene styrene, a rubber like substance, or APP, atactic polypropylene, a waxy plastic like modifier.

APP modifieds are generally torch applied and SBS membranes are applied in hot asphalt. Cold adhesives for both are also now on the market, which may be helpful in places where torches or hot asphalt cannot be used.

The mod bit systems are usually multiple ply systems, two plies are a recommended minimum. Again, there are numerous choices available to the roof designer, depending on the needs of the application. Hybrid systems, using one, two, or three plies of fiberglass felts in hot asphalt, followed by a finish ply of modified bitumen, has also been a popular development.

If these do not offer enough choices, several roofing manufacturers supply kegs of modified asphalt to allow a modified bitumen application similar to built up roofing, alternating layers of hot modified asphalt with reinforcing felts of fiberglass or polyester.

Modifieds have the same general sensitivity to ponding water as asphalt built up membranes, so sloping to drain is a necessary design feature. They do tend to be fairly durable, and generally have performed well over the past 10 to 15 years here in the U.S.

Single-Ply Systems

This discussion of the composition of single-ply membranes is somewhat fundamental, but is offered for those unfamiliar with the topic. Single-ply systems consist of one layer of an elastic/plastic membrane usually 45 to 60 mils thick and installed in a number of ways, generally ballasted (laid dry, but held in place by gravel or pavers), fully adhered (glued in place) or mechanically fastened (anchored to the roof deck with fasteners). Chemically, these membranes are manufactured from synthetic rubber or plastic, sometimes incorporating a layer of reinforcing fabric or mesh. More commonly they are known by their primary polymer component makeup, EPDM, PVC, CSPE, PIB, EIP, etc.

Single-ply roofing membranes were adapted from other uses of elastomeric membrane materials, such as pond liners Having excellent elongation, they were sold to disgruntled built up roofing owners as a better solution.

I personally know of many, perhaps hundreds of fine installations of these products. In my opinion, here are some things to look for and avoid in the selection of single ply systems.

• Ballasted single-plies have a low initial cost, but are hard to find leaks on and are not well suited to roofs with heavy or frequent traffic. Adding one ton of gravel to the top of a structure for the sole purpose of holding two squares of roof in place seems a bit odd, although I have done just that when my client wanted the least costly roof.
• Fully adhered roof systems are totally dependent on the roof insulation to which they are adhered to for wind uplift resistance. Our experiences have lead us to avoid using fully adhered single-plies on roofs with heavy traffic, not so much because of threat of puncture, but because often the insulation is crushed and damaged. Once the insulation is damaged and the adhesive bond is lost, there is little holding the roof in place. This is especially true with polyisocyanurate insulation in thicknesses less than two inches.
• Mechanically fastened systems have been in the U.S. for nearly 20 years, but became more prominent in the early 80's and continue to see growth within the single-ply arena. These systems rely on attachment to the roof deck by means of fasteners, bars, plates or other clamping devises. Again, as with fully adhered roofs, compression of insulation from heavy roof traffic can cause problems, such as "tenting" of the membrane over fastener heads. These often result in puncture of the membrane.

Mechanically fastened systems must also be carefully designed to accommodate high wind situations, and much study is underway to identify what constitutes sufficient fastener spacings in those high wind exposures.

We have witnessed a peculiar result of wind flutter that occurs in some mechanically attached roof applications. When a roof membrane billows or flutters in winter conditions, warm moist interior air is drawn to the underside of the roof membrane, where it can reach dew point temperature and condense. We have conducted infrared moisture detection scans on roofs that had not leaked, yet we still found wet insulation. Our educated hunch is that the repetitive billowing of the membrane is a contributing factor in this moisture pickup, especially on air permeable roof decks, such as steel decks. An air barrier placed below the roof insulation reduces wind flutter and subsequent moisture infiltration.

Metal Roofing

Metal roofs have come a long way from the leaky metal siding panels that were caulked together and screwed to the structural frame. Today's metal roofs are attached to the structure with concealed clips, which slide to accommodate expansion and contraction. Panel sealants are still used at end laps and some side lap locations, but the sealant is subjected to less movement stresses and is often shielded from U.V. exposure.

Metal roof systems can be used in new and some reroofing situations, but should always require a minimum 1/4" per foot slope. When buildings are too wide to accommodate a single slope from ridge to eave, metal roofing designers must turn to using an interior common gutter, a practice we do not recommend.

We also discourage the use of metal roofing on facilities that expect to add new roof penetrations with some frequency, since the new units must resort to caulk and exposed fasteners, the very items that caused the first generation of metal roofs to leak.

Market Changes

The roofing industry is a dynamic industry, with new innovations, materials, tools and regulations cropping up on a daily basis. For example, in the past two years or so, Owens Corning exited the commercial roofing business, Manville changed their name to Schuller, Goodyear was renamed Versico and was purchased by Carlisle, Cooley Roofing Systems ceased direct marketing of their products, and Trocal roofing systems was sold twice. Over the past 10 years the rubber roofing market went from eight manufacturers of EPDM rubber to two. The number of roofing manufacturers continues to increase while the number of companies leaving the market also increases.

The consequences are predictable. If roofing owners were dissatisfied with built up roofing, the spotty performance single-plies has evoked similar dissatisfaction. I cannot think of another segment of any other industry that has floated so many untried, unproven products on the market, that resulted in so many failures and caused consumers so many problems. To the fortunate owners that bought the right unproven single-ply products and are now enjoying years of watertight service, maybe it was solid investigation and sound decision making, or perhaps it was divine providence. Many others have not enjoyed such success.

Over the past five years there has been a major settling of this market, leaving fewer and more successful companies and membranes to deal with. Perhaps we should be thankful for this small upside.