This article examines the quality

Transcription

1 This article examines the quality of commercial roofing systems in general, and specifically, hot-applied asphalt and modified bitumen (MB). Asphalt built-up roof (BUR) systems continue to set the endurance standard by which other roof products can be measured. Although the traditional, hot-applied asphalt BUR may be the benchmark for quality, modified bitumen products offer other top-quality options. The performance attributes of traditional asphalt BUR are reviewed here with respect to the changing needs of the industry and the introduction of new bituminous roofing products. Quality Standards The word quality often is used simply to refer to a characteristic or attribute. As used by industry today, quality refers to the standard or grade of a product, and the word is often modified by another word or phrase, such as high quality or good enough quality. In a third sense, quality means excellence or superiority. When a company advocates quality as a corporate ideal, it declares that its products or services meet the highest standards, i.e., they are first rate, second to none, or perhaps comparable to the best of the best. Three Durations Now the stage is set for a closer examination of the meaning of quality with respect to commercial roofing. This can be analyzed in the context of three time periods characterized by three qualities. A superior system should receive high marks in all three and be a clear favorite in at least one. Reliability, as it relates to short-term performance immediately after installation. (What are the chances of early failure because of improper installation?) Endurance, or the expected life cycle of a properly installed system. (How long does it last?) Above: The State Capitol building in Frankfort, Kentucky was re-roofed using a 2-ply modified bitumen roofing system from Siplast, an ARMA member. The base layer of modified bitumen was installed in hot asphalt and the modified cap sheet was installed with cold process adhesive. (Photo courtesy of Patrick D. Murphy Co., Inc.) Left A traditional built-up roof (BUR) covers this laboratory building. BUR is one of the longest-lasting roofing systems available. (Photo courtesy of GAF, an ARMA member.) O CTOBER 2006 I NTERFACE 5

2 Graph 1 Graph 2 Sustainability, or the environmental viability of a system. (What resources are consumed or depleted during manufacturing and use? What waste is generated at the end of the life cycle?) Reliability Although the time required to install a roof may be brief compared to its total life cycle, it is a period of great activity. It is also A Asphalt roofing application methods include A) hot-applied, B) coldapplied, and C) torch-applied. (Photos courtesy of ARMA.) a time when quality management by the contractor is a special concern. According to Patrick D. Murphy of Patrick D. Murphy Architects in Louisville, Kentucky, a commercial roofing system is literally manufactured in place on the facility. A well-trained crew encompasses a range of skills, from helpers with experience to journeyman. For that reason, the redundancy of BUR is important. For a built-up roof, where the ply sheets are joined together with the heat of molten asphalt, redundancy is more forgiving than for a single-ply roof, says B C Murphy. When the assembly is complete, the owner has a monolithic, multi-layer roof system to keep the building dry. The Quality Commercial Asphalt Roofing Council (QARC) recently conducted an informal survey of roof consultants and building managers. A somewhat unexpected result was the strong agreement between both consultants and building managers regarding the importance of reliable installation. Of the 24 statements surveyed, the third strongest agreement was received for the statement that Contractor reliability is critical to the installed and long-term costs of a BUR or MB system. (See Graphs 1 and 2.) Fortunately, in North America, a strong infrastructure is in place for the installation of BUR and modified bitumen. Reliable contractors with the proper equipment and training can be found throughout the United States. Consultants often are called upon to serve as quality managers, checking the references of the contractors and monitoring the installation, much as one would monitor the quality of prod- 6 INTERFACE O CTOBER 2006

3 ucts produced in a factory setting. When dealing with reputable contractors and quality materials, the probability of obtaining a reliable BUR is high. Statistics from roof asset management companies indicate that installation errors, if present, are most likely to show up very early in the life cycle. If a system survives for two years without the need for major repairs, it is likely to survive for many more. While this is true for all systems, it is especially true for BUR systems, which can endure for decades if properly installed and maintained. Endurance Endurance is the quality that makes something lasting and resistant to wear and decay. It is longevity. Referring to the period of time between installation and replacement of the roofing system, it is measured as a life cycle or service life of durable goods. In the QARC survey, both roof consultants and building managers agree with the statement, A service life of less than ten years is unacceptable for most commercial roofing applications. In fact, this statement produced the most agreement of the 24 statements, and agreement was stronger among consultants than building managers (See Graph 1). Ironically, today there are many systems that do not offer the long life cycle of asphalt roofing. Fifty years ago, longevity was an essential requirement. Building owners would opt for the longest lasting system that was readily available, and in most cases that meant asphalt BUR. Today, according to Patrick Murphy, Many of our decisions depend on a client s construction budget. The length of time that the owner plans to remain in a facility is very important. For example, the state of Kentucky has used only BUR and two-ply modified bitumen in the reroofing projects on which we have provided consulting. The reason for this is because the state intends to keep the buildings as long-term owners. Sustainability One benefit of a long-lasting system is that because it does not have to be replaced as often, less waste is dumped into the environment. According to the QARC survey, roof consultants and building owners agree with the statement, Preventive maintenance helps maximize the life of a BUR or an MB roof. However, sustainability and environmental concerns take a backseat to reliability and endurance, which are more pressing issues for most building owners and consultants. Fortunately, the goals of sustainability and endurance are mutually compatible. The Original Quality Contest Asphalt BUR and MB systems have excellent credentials. Bitumens won the initial quality contest in the 19th century when asphalt and coal tar pitch were adapted for use on the roofs of commercial buildings. It is estimated that the asphalt BUR originated 170 years ago, during the beginnings of the industrial revolution. Many factories, warehouses, transportation terminals, and tenement buildings that endure today were constructed in the years that followed, and during that time, asphalt in general and BUR systems in particular were established as benchmarks for roofing. To emerge as the winner, bitumens had to possess certain qualities of endurance superior to any other materials available at that time. Asphalt was already known for its applications in shipping, an industry O CTOBER 2006 I NTERFACE 7

4 renowned for its intelligent use of materials. The greatest attributes of asphalt are proven durability and excellent water-leak resistance, both resulting from a redundancy of multiple layers of material. Moisture resistance is an inherent property of asphalt, but it is only one factor of a successful system s ability to resist the elements. The multiple layer construction of BUR and MB assemblies results in membranes thicker than other types of low-slope systems. A four-ply BUR provides about 280 mils of waterproofing thickness, whereas some other systems provide 60 mils and often less. Asphalt remains a superior choice today, just as it was an excellent choice in the past. No material has succeeded in upstaging the performance of hot-applied bitumen as a superior moisture barrier. Even long-lasting metal or tile roofing systems require asphalt-based underlayments for protection against moisture penetration, so it can be argued that asphalt is superior with regard to protection against leaks. Large commercial roofs are especially vulnerable to structural stresses that place great demands on membranes. A welldesigned asphalt system tends to distribute these stresses over a wide area with a thick membrane cross-section. Localized concentrations of high stress can be avoided with a ABOUT ARMA A cold-applied, modified bitumen roofing system. (Photo courtesy of ARMA.) fully adhered asphalt BUR or MB system, which distributes this load over the entire membrane. Asphalt-coated fiberglass felts and modified bitumen sheets provide physical strength, and multiple layers provide unsurpassed moisture protection. The asphalt which imparts the moisture resistance is visco-elastic, i.e., it has a tendency to yield rather than tear or break. Simultaneously, the redundancy of three or more layers of asphalt, felt, or MB sheets The Asphalt Roofing Manufacturers Association (ARMA) is the North American trade association representing the manufacturers and suppliers of bituminous-based residential and commercial fiberglass and organic asphalt shingle roofing products, roll roofing, built-up (BUR) roofing systems, and modified bitumen roofing systems. For additional information, contact ARMA or visit: ABOUT QARC Generally referred to as QARC, the Quality Asphalt Roofing Council is an innovative, built-up/modified bitumen roofing initiative under the auspices of ARMA. The Council is a cooperative effort comprised of asphalt roofing interests, including roll good producers, asphalt suppliers, equipment manufacturers, packaging suppliers, and others. It is also open to current ARMA BUR and modified bitumen manufacturing member companies. The founding members of QARC designated Robert Almon, president of Mid- States Asphalt and Cant Strip, Inc., Tuscaloosa, AL, as its chairman and Todd Ziems, business manager of Low Slope Commercial Roofing for Owens Corning,Toledo, OH, as its vice chairman. The mission of the council, according to ARMA executive vice president Russell K. Snyder, is to promote quality asphalt BUR and modified bitumen to raise the awareness of time-proven quality commercial asphalt roofing systems. 8 INTERFACE further decreases the chances that the moisture barrier will be compromised. For the same reason, asphalt BUR or MB withstands high-velocity winds better than other low-slope systems. Fasteners are designed to hold down a membrane, but high winds produce high stress concentrations that often tear apart membranes that are not fully adhered. Appropriate fasteners, closely spaced, are used successfully in many roofs. Fasteners imitate the adhesion of hotapplied asphalt, but few come close to matching its performance. Liquid asphalt adheres extremely well to a wide range of decking materials. Asphalt binds the membrane together, and in many systems it also adheres the membrane to the deck over a wide area. In these cases, the whole system can withstand extreme uplift forces that are distributed over the entire surface, resulting in relatively low localized forces. Best Membrane in a Supporting Role The asphalt roofing industry is a vibrant, highly competitive industry, which has developed many innovative products over the past century. Most noteworthy are the modified bitumen (MB) membranes. However, none of these new products has made hot-applied asphalt obsolete. Many quality asphalt systems today combine the use of MB sheets with hotapplied asphalt BUR in a hybrid system. These systems can be tailored to the application, giving roof consultants and building owners more design choices for longer lasting roofs. MB base- or cap-sheets can improve the performance of an asphalt BUR system in O CTOBER 2006

5 several respects, but they do not supplant the basic idea of building up a roof with the application of hot asphalt in multiple layers. The mechanical and physical properties of asphalt can be altered in many remarkable ways by blending the asphalt with synthetic polymers in a ratio of approximately five parts asphalt to one part polymer. One of the most remarkable properties of MB is that it allows asphalt to be shaped into integral waterproof membranes. MB sheets are therefore ideal for use as base sheets or cap sheets in a BUR. Alternating expansion and contraction are damaging to many systems. Traditional asphalt with fiberglass felts performs well under such conditions. Newer modified bitumen membranes and hybrid systems (i.e., with mod-bit membranes used as components of asphalt BURs) perform even better in special circumstances. Commercial roofing could be constructed entirely from modified bitumens, omitting the hot mopping of asphalt; however, the many high-quality systems today combine the best attributes of mod bits with the advantages of hot-mopped asphalt. Spotlight on Reflective BUR and MB Roofing The state of California recently passed major legislation relating to energy conservation in commercial buildings. Title 24 has been a topic of great interest to contractors, consultants, building managers, and architects. There are many advantages that can be garnered from MB chemistry, but perhaps none is more timely and appropriate than the recent introduction of highly reflective cap sheets. These cap sheets serve as an outstanding example of the supporting role of MB in enhancing the properties and performance of BURs. While the term reflective BUR may seem like a contradiction of terms, even the stringent reflectivity requirements of Title 24 do not preclude the use of a hybrid BUR system. MB cap sheets with white coatings on the topside offer reflectivity values well above 70 percent. A BUR consists of many layers. Yet reflectance is 100 percent controlled by the almost negligibly thin, topmost coating of the cap sheet. A hybrid system can include a highly reflective cap sheet as the final layer of a hot-applied asphalt BUR. This arrangement combines the longevity of BUR with the energy savings of a cool roof. It is a superb example of how innovative modified O CTOBER 2006 bitumen products play a supporting role in increasing the performance and endurance of traditional built-up roofs. These relatively new products are expected to undergo many improvements and refinements in the years ahead. Cool roofing also encompasses maintenance, cleanability, and the effect of reflectance on life cycles. Interestingly, systems last even longer when surface temperatures are reduced in hot weather. So the use of a reflective MB cap sheet or light-colored gravel can prolong the already long life expectancy of an asphalt system. This new middle school in California has an SBS Title 24 compliant roof. (Photos courtesy of Johns Mannville, an ARMA member.) This important topic merits attention by roof consultants along with further study by product manufacturers and building designers. It has been covered by others 1 [e.g., 1], including papers submitted at the 2005 Cool Roof Symposium, which was hosted in part by the RCI Foundation [2-6]. I NTERFACE 9

6 The Whole Building Approach term performance advan- An ideal commercial tages without compromising asphalt roofing system has on environmental or aesthetmany attributes. When ic benefits. selecting a system, many fac- A professionally installed tors must be evaluated at BUR, hybrid BUR, or MB roof once, assigning different is hard to improve upon. weights to each factor so as Asphalt roofing systems are to achieve a balanced ap favorites of consultants and proach to a particular appli building owners because of cation. In other words, a ply redundancy, versatility, whole building approach is and adaptability. Product necessary, as opposed to manufacturers continually focusing too much on one find new ways to combine the attribute such as reflectivity. moisture resistance with As an example, one would other desirable properties, be ill-advised to install a such as resisting extreme highly reflective roof that winds and hailstone damage. does not provide sufficient This modified bitumen cap sheet has a brilliant white surface, thanks to Quality BUR and MB protection against wind uplift a factory-applied layer of elastomeric coating. (Photo courtesy of GAF, an roofing systems are the workor wind-blown debris; or one ARMA member.) horses of the roofing industhat might survive only a few years of exposure to ultraviolet try. For as long as the roof is considered a critical component radiation. A traditional asphalt built-up roof topped with a moderately reflective modified bitumen cap sheet and moderate amount of insulation could sufficiently reduce heat loads, which would save on air conditioning energy costs during the daytime while still providing outstanding wind resistance and longevity. Real world buildings are not as simple as some cool roof models may suggest. Depending on the area of the roof and the height of the building, heat loads through walls and windows may be more important than the roof. Also, the presence of insulation or a ventilated plenum beneath the roof greatly reduces the heat load on the air conditioning system. Meanwhile, rain showers provide evaporative cooling, reducing surface temperatures to the point where the roof can actually help to cool the building. Shade trees and other sunlight-blocking methods also can be employed to manage the heat load on a building. Moreover, in massive roof construction, heat captured during the daytime can assist heating systems in maintaining when reflectance and other energy or environmental concerns are weighted heavily. Outside California, the value of cool roofs is still under debate. According to the recent QARC survey, reflectance does not rank high in importance for building owners and was even less important for roof consultants, as evidenced by their attitudes toward the statement, Reflectance issues deter me from specifying or installing a BUR or MB system. This statement received on average the strongest level of disagreement of all the statements in the survey (Graph 2). Accolades for Endurance For low-sloped asphalt commercial roofing, the word endurance equates to lasting for decades. The features that made asphalt the leading quality commercial roofing system in the past are still important today. These features include ply redundancy, moisture protection, versatility, low cost, high strength, adaptability to the job, and, most important, its endurance. Today, using a combination of asphalt BUR and of the whole building system, there will be a place for asphalt-based products. References 1. Hutchinson, Tom, Roofing s Dirty Secret, Professional Roofing, April 2005, p Cool Roofing: Cutting through the Glare, symposium hosted by RCI Foundation, Oak Ridge National Laboratory, and the National Research Council Canada, May 12-13, 2005, Atlanta, Georgia. 3. Hoff, James L., The Economics of Cool Roofing: a Local and Regional Approach, ibid. 4. Mellott, Joseph W. and Donald C. Portfolio, The Effect of Reflective Roof Coatings in the Durability of Roofing Systems, ibid. 5. Hutchinson, Thomas W., What the Roof Consultant Needs to Know, ibid. 6. Murphy, Colin, Cool Roof Design Considerations and Case Histories, ibid. comfortable temperatures in the cooler night hours. Environmental issues are of increasing MB roofing, building owners can enjoy long- Robert Almon importance, but a roof s durability and Robert Almon is chairman of the Quality Asphalt Roofing moisture resistance need not be sacrificed Council (QARC) of the Asphalt Roofing Manufacturers for small annual energy savings, even to Association (ARMA). He is one of the principals of Mid States satisfy well-intentioned energy requirements. When the whole building approach Alabama, which markets and manufactures asphalt-based Asphalt, Cant Strip, Inc., and ABH Enterprises, Tuscaloosa, is used to evaluate roofing systems, some products to both the commercial and residential roofing combination of asphalt roofing materials industry. and insulation can be the best choice, even 10 INTERFACE O CTOBER 2006