The construction industry has focused its attention on sustainability and green design. There’s no question that petroleum (and asphalt derived from petroleum) is a finite material and that, eventually, the Earth will have no more to give us.
Pressure is on the roofing industry to increase energy efficiency and durability. On the energy-efficiency side, newly designed low-slope roofs are generally at U-value of 0.05 or lower (R-value of 20 or more), so it will be very difficult to improve much more on that score. Increasing durability and maintaining a high level of performance, however, is still an opportunity, as is recycling the existing inventory.
Coal-Tar Pitch Roofing
In the processing of coal to make coke for steel making, volatile compounds are collected from the coking ovens, condensed, and separated, and become the base of hundreds of raw materials, including dyes, plastics, and a byproduct called coal-tar pitch.
Coal-tar pitch is produced by distillation of the crude coke-oven tar (obtained during the high-temperature treatment of coal to make coke or natural gas). Pitch materials are usually thick, black, or dark brown liquids or semi-solids with a naphthalene-like odor. Coal-tar pitch can typically be recognized by its sharp, burning odor. Coal-tar products are ingredients in medicines used to treat skin diseases, such as psoriasis. They are also used as animal and bird repellants, insecticides, animal dips, and fungicides.
Roofing grade pitch is aromatic in structure as compared to asphalt, leading to a higher degree of resistance to oils, greases, and fats. It has been used on roofs in America’s rust belt for decades, generally as a component of 4- or 5-ply gravel-surfaced built-up roofs. Pitch roofs were about as green as you could get. The pitch itself was a byproduct of the coking ovens, the aggregate was waste slag from steel furnaces, and the felts were recycled organic fibers from waste paper, sawdust, and rags.
With the growth of non-bituminous roofing since the oil embargo of the 1970s, the BUR part of the market is estimated to be down to only 20 percent of the market, and coal-tar pitch just a small fraction of that.
Roofing with hot pitch is not the easiest job in the world. The fumes are pungent and may be carcinogenic if there’s chronic overexposure to the coal-tar pitch volatiles (i.e. exceeding a TLV of 0.2mg/m3 as a time-weighted average over 8 hours). Fumes can burn the eyes and make the skin more sensitive to sunburn, so personal protection is important during application. Tear-offs subject the workers to dust that can burn eye tissue. At first glance, one would wonder why anyone would specify or use such a material in construction.
Durability is without Question
In surveys of roofing experts, coal-tar pitch roofing has always been considered more durable than asphalt, EPDM, PVC, TPO, or anything else. It has a self-leveling property called “self-healing,” and national building codes permit its use at slopes down to dead-level while all other roofing materials are required to be either installed at a minimum slope of 0.25-inches in 12 inches (2 percent), or to have positive slope.
With its resistance to constant immersion in water and its recognized resistance to biodegradation and vegetation root attack, coal-tar pitch appears to be one material of choice for the new vegetated roofs now being specified nationwide.
ASTM D450 Standard Specification for Coal-Tar Pitch Used in Roofing, Dampproofing, and Waterproofing covers the testing and physical requirements of two types of coal-tar pitch:
- Type I, which is generally used in roofing and dampproofing.
- Type II, which has a lower softening point (106 to 126 degrees F.) – too low for exposed roofing, but generally preferred for waterproofing applications.
ASTM D449 Standard Specification for Asphalt Used in Dampproofing and Waterproofing is a similar specification, but the roofing industry is much more familiar with ASTM D312 Standard Specification for Asphalt Used in Roofing for exposed roofing, especially D312 Type III. This is a much harder material and is far less suitable for waterproofing and vegetated applications.
The issues of economics, demand, and health are the reasons generally cited for the decline of pitch roofing. The remaining major providers of roofing pitch are highly respected names in the industry. They actively support the Asphalt Roofing Manufacturers Association (ARMA) and provide excellent guidelines on application and maintenance of their roof systems.
Since pitch roofs can last for many decades, there will be a need for suitable maintenance materials and technical support well beyond the warranty years. Coal-tar roofs are reported to average 25 years of life, and some have been known to last more than 50 years with proper maintenance and surface restoration.
A new company founded in 2004 may fill this supply void. It will provide coal-tar pitch, coal-tar saturated organic and glass fiber felts, and coal-tar maintenance products, among other materials. It claims to have received its needed UL and FM approvals for Class-A roof performance.
Having pitch-based products available for the next several decades is important. If a dead-level roof is to be removed and replaced with something else, you may be required to increase the roof slope, which, in turn, may require tapered insulation, tapered lightweight insulating concrete, raised curbs, and flashings, and perhaps even the addition of more drains to assure positive slope.
The greenest act of all for coal-tar pitch roofs will be to continue to supply appropriate maintenance and repair materials. Pitch may prove to be the most durable material of all for vegetated roofs, and finding problems under a green roof is predicted to be a major concern in the future.