Sustainability Favors the Long Life Cycle of Asphalt Roofing
Long before it was cool to be green, long life cycles were considered desirable. This economic motivation to choose a roof system with a long life cycle aligns well with green aspirations. However, in the rush to save energy by using reflective roofing systems, it is easy to lose sight of the roof life cycle.
Roofing systems have several green aspects, such as energy efficiency, long life cycles (cradle to grave) and recyclability potential. Energy efficiency relates to the way roofing materials affect the heating of and cooling of buildings, which are also affected by insulation and reflectivity. Material life cycles are important because more durable systems are replaced less frequently than systems with short life cycles, resulting in less disposable waste and lower lifetime costs. Recyclability means materials can be reused indefinitely, beyond one product lifetime, conserving natural and manufactured resources.
The purpose of this article is to examine high quality asphalt built-up roofing systems and modified bitumen systems with respect to sustainability. There are several commercial roofing systems that can last for decades when properly installed and well maintained.
Let’s take a closer look at how to maximize life cycle and achieve the goal of sustainability. There are several enemies of a long roof life, some of which are inferior product quality, installation defects, severe weather and thermal oxidative aging.
Defects and Severe Weather
Real standards need to be developed for the performance attributes of roofing systems. Such would encourage manufacturers and installers of all types of roofing systems to continue to seek ways to extend the life cycles of roofing systems. It would inhibit the natural impulse to select a short life cycle roofing system, which is wasteful in terms of materials, manpower and energy.
Installation defects can take their toll on roof life cycle in a number of ways. They can lead to early failures of roofing systems, as when a watertight seal is not achieved from the beginning. They can lead to premature aging of the roofing system, for example, because of poor drainage. Or they can contribute to the catastrophic loss of the roofing system because of severe weather.
To maximize the life of an asphalt BUR or MB roofing system, it is important that installation and manufacturer specifications be followed. In addition, please check your national, state and local building codes for further requirements.
The Hurricane Katrina Wind Investigation Program (WIP) Report released in 2007 by the Roofing Industry Committee on Weather Issues (RICOWI) Inc. provides valuable insights about how to construct asphalt roofing systems to better withstand major windstorms. The complete report titled “Hurricane Katrina Wind Investigation Report” (September 2007) is available from RICOWI, Inc. A similar report generated in the aftermath of previous major hurricanes titled "Hurricanes Charley and Ivan Wind Investigation Report” (March 2006) is also available for comparison. These reports include damage surveys for all major roofing systems and materials. They can be downloaded in PDF format from RICOWI's Web site, www.ricowi.com.
WIP teams surveyed about thirty low-sloped asphalt commercial roofing systems, including 16 modified bitumen (MB) systems and 14 built up roof (BUR) systems. Most of these systems experienced little or no damage, usually limited to edge details and minor scouring. When major damage was noted, it was typically due to a poorly attached system components such as decks or cementitious wood fiber (CWF) panels. The report results stressed that all members of a composite system must be adhered or fastened to resist uplift. The investigators attributed a single case of poor adhesion to an installation defect, i.e., not preparing the concrete with a suitable primer.
The investigations carried out by RICOWI in cooperation with Oak Ridge National Laboratory allow the industry to evaluate the performance of materials and designs in real world constructions subject to extreme conditions created by Nature. These studies identify the types of defects that lead to severe weather damage. Adjustments made to building codes and best practices lead to sustainability in roofing.
Considering the range of installation quality, the wind performance of the asphalt roofing materials at extreme wind speeds was outstanding. The many surviving roofs are a tribute to the quality of the materials and the craftsmanship of the roofers. The lessons learned are that substandard system designs and poor installation practices cannot be tolerated in hurricane zones or any areas prone to extreme windstorms.
Coatings and Aging
Not long ago, the idea of “green” came into direct conflict with the ideal of a long life roof. Oddly enough, the longest life roof available was an asphalt BUR, which tended to have low values of reflectivity and emissivity. As the charge toward green was being led by the cool roof movement, this excellent long life cycle roofing system nearly became a casualty of friendly fire. Fortunately, manufacturers soon realized that the white surface is only skin deep, and it is a small matter to produce a white cap sheet or provide a white coating on a modified bitumen membrane in the field.
Surfacing asphalt BUR and modified bitumen roofing systems with a white coating or highly reflective cap sheet mitigates thermal cycling and can be expected to extend the life cycle of such systems. Whitening of the existing base of a commercial BUR system is important.
Although BUR systems are among the most durable roof systems available, it is possible to extend their life cycles even more with coatings. The technology for extending asphalt BUR and MB roof life cycles has been under development for decades. Much of the old technology is still valid but now much more field experience exists. Many studies have demonstrated that the life of these roofing systems can be significantly extended through the use of appropriate coatings.
Coatings commonly used on BUR systems include solvent- and water-borne asphalt coatings; solvent- and water-borne aluminized asphalt coatings; and water-borne white elastomeric coatings (generally acrylics).
Asphalt coatings, long recognized as effective for prolonging life cycles of aging BUR systems, are applied after a BUR system's initial installation and at regular intervals during the BUR system's life cycle as part of a regular maintenance program.
Aluminum pigments can be used to formulate solvent- and water-borne asphalt coatings to protect against ultra-violet (UV) radiation and provide significant reflectivity. These coatings have small flakes of aluminum pigment dispersed in them. They typically have solar reflectivity values between 0.40 and 0.50 though premium formulations have demonstrated initial solar reflectivities in excess of 70 percent.
Highly reflective white top coats have become more common during the past several years as a means to reduce peak roof surface temperatures. This minimizes peak electrical demand for air conditioning in many buildings and provides ultimate reduction in diurnal temperature cycles, which can stress and fatigue roof systems.
There is nothing wrong with creating incentives to use white coatings so long as you are not discouraging the use of greener roofs and greener practices by doing so. The free market tends to favor long lived, energy efficient roofing systems. If artificial incentives or codes are introduced which tend to substitute cheap reflective roofs for appropriate R values and long roof life cycles then they are disrupting the market and perhaps doing more harm than good.
As Green as it Gets
Asphalt installation methods are becoming cleaner and more reliable. Modified bitumen materials continue to evolve, so today there are excellent materials available whose life cycles are certainly better than many past materials. The technology of coatings today could potentially extend the life cycles of roofing systems indefinitely. Someday a roofing material may appear that will prove as green as asphalt with respect to long life cycles, but for now the smart green money is on asphalt. With reflective cap sheets and coatings now available for those climates requiring white roofs, it appears that asphalt has secured its place as a green material for many years to come.
For more information, please visit the Asphalt Roofing Manufacturers Association (ARMA) web site at: www.asphaltroofing.org.