Pathways to Professionalism Proceedings of the RCI 20th International Convention & Trade Show Miami Beach, Florida March 31 – April 5, 2005 © Roof Consultants Institute 1500 Sunday Drive, Suite 204 • Raleigh, NC 27607 Phone: 919-859-0742 • Fax: 919-859-1328 • http://www.rci-online.org Field Investigation and Laboratory Testing of Exposed Poly(vinyl Chloride) Roof Systems Stanley Graveline, Sarnafil Inc., Canton, MA Hans-Rudolph Beer, Sarnafil International AG, Sarnen, Switzerland Ralph M. Paroli, National Research Council Canada, Ottawa, ON and Ana H. Delgado, National Research Council Canada, Ottawa, ON ABSTRACT A leading supplier of thermoplastic roofing membranes inspected and removed samples from 44 different roofs in America, Austria, Canada, England, Germany, and Switzerland. The roofs ranged in age from 9 to 34 years at the time of sampling. The dual European and North American survey is believed to be the most exhaustive ever conducted for PVC membranes. A variety of physical properties was tested, according to ASTM (USA), DIN (Germany), and SIA (Switzerland) standards. Additionally, glass transition temperature and hail testing were conducted on many of the aged samples. The paper will present the results of the testing. Relevant correlations that may exist between various physical properties will also be looked at. These correlations may be useful in assessing the relevance of some tests in the context of material standards. SPEAKERS STANLEY GRAVELINE is vice president of technical services for Sarnafil Inc. He has lived and worked in the U.S., Canada, and Switzerland in sales and technical management functions. He has participated in various North American and European code, standards, and technical committees over the past 20 years. Stan is an RCI member, a director of the Cool Roof Rating Council, a director of the Northeast Roofing Contractors Association, and a professional engineer in Ontario, Canada. HANS-RUDOLF BEER received his PhD in solid state chemistry from the University of Zurich. He has seven years’ experience in high voltage insulation (plastics and ceramics). In 1988, Beer became head of research and development for Sarnafil, one of the world’s major manufacturers of roofing membranes. He has published numerous articles on roofing membranes, particularly in the fields of ecology, longevity, and hail performance. Beer has served as convenor of the European Standards Committee for plastic roofing membranes (CEN TC 254). Graveline, Beer, Paroli, and Delgado – 55 Graveline, Beer, Paroli, and Delgado – 57 1. INTRODUCTION Poly(vinyl chloride) – also known as vinyl – is one of the most versatile thermoplastics in use today. Vinyl is essentially derived from two simple ingredients: fossil fuel and salt. Petroleum or natural gas is processed to make ethylene, and salt is subjected to electrolysis to separate out the natural element, chlorine. Ethylene and chlorine are combined to produce ethylene dichloride (EDC), which is further processed into a gas called vinyl chloride monomer (VCM). In the next step, known as polymerization, the VCM molecule forms chains, converting the gas into a fine, white powder: vinyl resin. In its basic form, PVC resin is a rigid substance to which plasticizers, stabilizers, and other components must be added to provide the desired properties for the PVC’s intended use. PVC was first used in roof coverings in Europe in the 1950s. It was introduced to the North American roofing market in the 1970s. The basic formula for today’s PVC roof membranes is shown in Table 1.1. There are three types of PVC roofing sheets: unreinforced, unreinforced with fibers or fabrics that act as carriers, and reinforced sheets that contain fiberglass and/or polyester fibers or fabrics. Reinforcement provides tensile and other properties. Reinforcements may be composed of woven polyester or woven or unwoven glass fibers. Polyester reinforcement is used to increase the membrane’s resistance to tearing in the wind. Polyester reinforcement is used mainly for sheets that are going to be fastened mechanically, while fiberglass reinforcements are typically used for adhered and loose-laid systems. The fiberglass carrier facilitates manufacturing and provides dimensional stability to the sheet. Reinforced sheets can be produced by laminating two plies of unreinforced sheet with a layer of reinforcement between them or by a coating process. Generally, unreinforced sheets are produced by calendering or extrusion. Unreinforced sheets have been plagued by numerous performance shortcomings. They have all but disappeared from the market in Europe and in North America. One main advantage of PVC sheets is that adjacent sheets of membrane can be joined by welding the overlaps with air heated to 425°C. The membrane can also be welded to metal flashing that has been factory-coated with PVC. The result is a continuous roofing assembly. Minor damage to the sheet during installation or inservice can be easily repaired by patching using the same hot air welding technique. PVC sheets remain flexible at temperatures as low as -40°C. They are ideal for reroof and repairs because of their high permeability. Moreover, white reflective vinyl membranes contribute to reducing urban heat island effects. They can also be produced in a wide spectrum of colors to meet desired aesthetic features of buildings, have high resistance to puncture and impact, and have excellent resistance to flame exposure and subsequent fire propagation. Loss of plasticizers has been a concern with certain PVC roofing products [1], as it caused embrittlement in the PVC sheets. Significant differences have been noted between different PVC membranes [2]. Products produced with high molecular weight plasticizers that have less of a tendency to volatilize or migrate out of PVC resin have, however, been found to provide very good service. Certain PVC roofing membranes utilizing a very stable formulation have approximately 40 years Field Investigation and Laboratory Testing of Exposed Poly(vinyl Chloride) Roof Systems Table 1.1 – Typical composition of a generic PVC roofing membrane. Ingredients % by Function Mass PVC resin 50 – 55 Basic material (powder or granular) Plasticizers 25 – 35 Impart flexibility Inorganic solids 5 – 10 Increase dimensional stability and mechanical properties Pigments 0.5 – 1.0 Provide color and UV stability to the PVC compound Processing oils 0.5 – 1.0 Improve processing and resistance and biocides to biological attack Stabilizers 2 – 3 Provide resistance to heat and light during manufacture and use Note: Based on technical note and some related specifications. Graveline, Beer, Paroli, and Delgado – 58 experience in Europe and close to 25 years throughout North America. PVC sheets have good resistance to industrial pollutants, bacterial growth, and extreme weather conditions. PVC is incompatible with bitumen and polystyrene, and therefore care must be taken to avoid direct contact with these materials. In Europe, PVC is by far the most commonly used synthetic roofing membrane, accounting for 61.6% [3] of all single-ply membrane sales. In North America, PVC’s growth continues on the strength of ease and safety of application and key properties such as high reflectivity and hot air welded seams. According to SPRI statistics, the volume of PVC sold in 2003 increased about 7% over the previous year. 2. OBJECTIVES All roofs are expected to provide decades of problem-free service. When new products are developed and introduced, there is little knowledge of how they will age beyond data generated in accelerated, artificial weathering tests. Although testing the physical properties of new materials can be useful in trying to compare and even rank them against other similar products, nothing is more useful or informative than actual field experience [4,5]. Physical properties of all roof systems change with age and outdoor exposure. The change in physical properties of a roof membrane may be the result of many factors. A few factors that may affect the physical properties of a vinyl membrane include chemical formulation stability, thickness of the polymer, reinforcement, method of manufacturing, geographic location, heat and ultraviolet radiation exposure, and other products used in conjunction with the membrane and roof slope. These factors cannot adequately be simulated in any test program. The certainty of service life predictions increases with increasing application experience. A major international supplier of PVC membranes with a vast inventory of roofs across Europe and North America decided to survey a large sampling of older roofs to assess how its materials were performing over time. The survey was expected to provide valuable insight on the aging behavior of the products and will serve as a basis for life cycle costing (LCC) and life cycle analysis (LCA) evaluations. 3. METHODOLOGY The manufacturer reviewed its internal project databases and files in the various countries in which it operates to determine the oldest projects in each region. Twenty roofs were selected to be surveyed and sampled in Europe and 25 in North America. The roofs were chosen on the basis of their age, geographic location (reasonable cost to access and to Table 3.1 – Summary of all North American projects studied. Samp le ID Project Location Membrane Typ e* Yea r Ins talled Yea rs Exp osed 1A Canton MA G – 12 1979 22 1D Canton MA S – 12 1979 22 2A Wenh am MA G – 12 1984 17 2D Wenh am MA S – 12 1984 17 3A Woburn MA G – 12 1983 18 4B Dickson TX G – 12 1984 17 5B Tyler TX G – 12 1981 20 5C Tyler TX S – 12 1981 20 6A Euless TX S – 12 1984 17 7A Industry CA G – 12 1979 22 8A El Se gundo CA G – 12 1982 19 9B Mou ntainview CA S – 12 1983 18 10 B Lace y WA G – 12 1982 19 11 B Ft. Steilac oom WA G – 12 1983 18 12 A Atlanta GA S – 12 1986 15 13 A Jac kson vill e FL S – 12 1982 19 14 A Appleton WI S – 12 1985 16 15 B Mt. Prosp ec t IL G – 12 1981 20 15 D Mt. Prosp ec t IL S – 12 1981 20 16 A Park Ridge IL S – 12 1984 17 17 B Hackensack NJ S – 12 1986 15 18 A Englewood NJ G – 12 1985 16 18 C Englewood NJ S – 12 1985 16 19 A Iowa City IA S – 12 1982 19 20 B Davis CA G – 12 1981 20 21 A Haileybury ON G – 12 1981 20 21 C Haileybury ON S – 12 1981 20 22 A Hamil ton ON S – 12 1984 17 23 A Aloue tte QC G – 12 1983 18 25 A Sarn ia ON G – 12 1984 17 26 Calgar y AB G – 12 1982 19 Note: *: G: glass rein force d, S: polyester re info rce d, “- xy”: thickness in mm (31 samples, 25 location s). Graveline, Beer, Paroli, and Delgado – 59 ensure diversity of climate), and owner willingness to allow the company to access their roof and remove samples. Due to accessibility problems, one of the European roofs could not be studied. It should be noted, however, that this roof was still in place and functioning at the time of the survey. A thorough visual inspection was conducted on each roof and samples were taken. In the U.S., local roofing consultants were invited to participate in every investigation. The North American roofs were surveyed in 2001 and the European roofs in 2002. Only roofs with exposed membranes were included in the survey. The manufacturer promotes the use of membranes with a glass (G type) mat carrier in adhered applications, and those with a synthetic (S type) polyester reinforcement in mechanically-attached assemblies. Information on the North American projects is listed in Table 3.1, while the same data for the European roofs is listed in Table 3.2. Unless otherwise specified, the installed thickness of all membranes was 1.2 mm. All samples were sent to the manufacturer’s research and development laboratory in Switzerland for testing. All samples were tested to the requirements of the German standard DIN16726 [6] or the Swiss standard SIA V 280 [7], the relevant standard for single-ply PVC roofing membranes in each country. A second set of samples taken from the North American roofs studied was sent to the National Research Council Canada for testing according to the requirements of ASTM D-4434 [8]. Additional measurements not called for in the standard, such as glass transition and reflectivity, were also conducted on this set of samples. More detailed information on the background of the study and the test methodologies can be found in previous papers by the same authors. [9] [10] A smaller subset of all of the samples was subjected to hail resistance testing at the EMPA in Zurich, Switzerland. 4. ROOF CONDITION SURVEY One of the European roofs that was originally installed in 1980 was replaced in 1993 after the roof was damaged by external influences. The owner replaced the roof with the same material, and therefore the roof was nine years old at the time of the investigation, rather than 22 as expected. All of the roofs were in good condition. The roofs exhibited various degrees of soiling, the level of which depended on their location, surroundings, building occupancy and activity, slope, etc. On some of the adhered roofs, there was evidence of insulation board shrinkage below the membrane. In some instances, this resulted in localized areas of un-adhered membrane. There were patches on a few of the roofs indicating that the membrane had been punctured at some point. Typically when there were patches, they were found at access points and adjacent to mechanical equipment. Although various skill levels were observed, all welds, including field seams, patches, and flashings were watertight. Samples were removed from all roofs. Without exception, new material was welded to the existing, aged membrane. Large weeds were growing in an area where soil had accumulated on one roof. The area was cleared for inspection. The roots had not had any effect on the membrane. On another roof, the skylights had been damaged by hail, although there was no damage to the membrane. Sample ID Location Membrane Type* Year Install ed Years Exposed 135 Per sonico, Switzer lan d G – 12 1968 34 136 Lu ga no, Switzerlan d G – 12 1970 32 104 Vl otho, Germ any S – 12 1975 27 134 Camorin o, Switzer land G – 27 26 133 Kempten, Ge rma ny G – 12 1976 26 105 Fre iburg, G erm any S – 12 1977 25 108 Sch wyz, Switzer lan d S – 12 1978 24 101 Bre genz, Au stria S – 12 1978 24 107 Ni edergösgen, Switzer land S – 12 1978 24 109 Gene va, Switzer lan d S – 12 1978 24 106 Memmin ge n, Ge rman y S – 12 1978 24 13 2 Dortmund, Ge rman y G – 14 1979 23 102 Vill ach, Austria S – 12 1981 21 103 Hau sman nstätten, Austria S – 18 1984 18 112 Canobbio, Switzer land S – 18 1985 17 111 Spre iten bac h, Sw itzer lan d S – 18 1985 17 131 Arnoldstein, Austria G – 14 – Fel t 1986 16 13 7 Rea ding, Uni ted Kingdom G – 12 1987 15 110 Bursins, Switzer land S – 18 1993 9 Note: *: G: glass reinforc ed, S: polyester reinforced, “- xy”: thickness in mm Table 3.2: Summary of all European projects studied. Sample Year Years ID Project Location Type* Installed Exposed 135 Personico, Switzerland G – 12 1968 34 136 Lugano, Switzerland G – 12 1970 32 104 Vlotho, Germany S – 12 27 134 Camorino, Switzerland G – 27 1976 26 133 Kempten, Germany G – 12 1976 26 105 Freiburg, Germany S – 12 1977 25 108 Schwyz, Switzerland S – 12 1978 24 101 Bregenz, Austria S – 12 1978 24 107 Niedergösgen, Switzerland S – 12 1978 24 109 Geneva, Switzerland S – 12 1978 24 106 Memmingen, Germany S – 12 1978 24 132 Dortmund, Germany G – 14 1979 23 102 Villach, Austria S – 12 1981 21 103 Hausmannstätten, Austria S – 18 1984 18 112 Canobbio, Switzerland S – 18 1985 17 111 Spreitenbach, Switzerland S – 18 1985 17 131 Arnoldstein, Austria G – 14 – Felt 1986 16 137 Reading, United Kingdom G – 12 1987 15 110 Bursins, Switzerland S – 18 1993 9 Graveline, Beer, Paroli, and Delgado – 60 5. TEST STANDARDS The DIN and the SIA standards were established in 1976 and 1977 respectively. The ASTM standard was first introduced in 1985. All were the first single-ply standards introduced in their respective countries. It is interesting to note that many of the roofs surveyed were installed before these standards came into existence. 6. TENSILE PROPERTIES Typical force-displacement curves for the tensile testing of the polyester reinforced roofing membranes are displayed in Figure 6.1. The load increased with displacement almost linearly at the beginning as the specimen stretched until the reinforcement broke, which caused an abrupt drop in load. No delamination was observed between the polyester fiber and the PVC matrix. Table 6.1 – Tensile properties, polyester reinforced membranes. Machine Direction Cross Machine Direction Figure 6.1 – Typical force displacement curve for the tensile test of a polyester reinforced roof membrane in the machine (MD) and cross directions (CD). Graveline, Beer, Paroli, and Delgado – 61 Test data for all the polyester reinforced samples, for both machine and cross directions, is shown in Table 6.1. The North American samples were tested according to both the ASTM and DIN test procedures, while the European samples were only subjected to the latter. None of the North American samples met the minimum breaking strength requirement (35 kN/m) as stated in ASTM D-4434, except Sample 13A in the cross direction. The samples retained 70-90% of the minimum breaking strength required for new membranes as specified in ASTM D- 4434 and over 60% of the samples retained more than 80% of that requirement. Note that at the time the membrane was made for most of these projects, the ASTM standard did not exist. All of the samples – European and North American – exceeded the minimum requirements of the DIN standard for new materials (16 kN/m), by 60% to 75%. The German requirement (16 kN/m) is less than half of the American minimum (35 kN/m). It is interesting to note, however, that despite the different test methodologies (see Table 6.2), the tensile results for a given sample correlate remarkably well between the two standards. Additionally, as can be seen in Figure 6.2, there is little variation in tensile strength as the membranes age beyond 15 years. It would appear that the polyester reinforcement is well encapsulated within the PVC matrix and is therefore very effectively protected. As mechanically attached membranes are subjected to countless cycles of wind uplift over their service lives, the maintenance of high tensile strength is a critical factor in the long-term performance of these membranes. All the North American samples exceeded the minimum elongation at break value (15%) specified within ASTM D-4434 for new material. All samples exceeded the minimum requirements of the DIN standard for new membranes (10%). As can be seen in Figure 6.3, however, unlike the tensile data, the elongation values generated by the two test methodologies do not correlate very well. The ASTM method appears to yield consistently higher results than the DIN test. The ASTM procedure not only results in higher values, but also significantly greater data scatter. The DIN data conversely is quite consistent. Although it is beyond the scope of this paper to conduct an in-depth analysis of the test procedures, as can be seen in Table 6.2, there are some notable variations between the two with regards to gauge length and testing speed, which may account for the measured differences. As would be expected, the membranes supported by the light-weight, glass mat behave differently under tensile load than the much stronger polyester reinforced sheets. The glass mat in these membranes is there simply to ensure dimensional stability. These membranes have the lowest level of shrinkage of any single-ply membrane on the market: less than one half of one percent. Figure 6.4 shows a typical forcedisplacement curve for fiberglass reinforced roofing membranes. The load increased linearly with displacement at the beginning. The specimen then started to yield and neck as indicated by the change in slope in the forcedisplacement curve. It stretched Standard ASTM D4434 DIN Type Type II, Grade 1 Tes t method ASTM D638 , Die C Sample Rec tangu lar Rec tangu lar Gauge Leng th (mm) 65 25 Cro sshead speed (mm/min) 50 ±5 100 ± 10 Samples tested 5/ direction 5/ direction Table 6.2 – Tensile test procedures, polyester reinforced membranes. Strength Polyester Reinforced 0 5 10 15 20 25 30 35 40 15 17 19 21 23 25 27 29 Years Exposed kN/m ASTM MD ASTM CD SIA MD SIA CD Figure 6.2 – Tensile strength, polyester reinforced membranes versus age. Standard ASTM D-4434 DIN Type Type II, Grade 1 Test method ASTM D-638, Die C Sample Rectangular Rectangular Gauge Length (mm) 65 25 Crosshead speed 50 ±5 100 ± 10 (mm/min) Samples tested 5/ direction 5/ direction Graveline, Beer, Paroli, and Delgado – 62 to a high degree (over 100% in general) and finally broke with a snap. No delamination was observed between the fiberglass reinforcement and the PVC matrix. Test data for all glass mat supported samples is shown in Table 6.3. Whereas with polyesterreinforced membranes, the strength of the sheet depends almost exclusively on the scrim, in glass-mat-supported membranes, the strength comes from the polymer. To account for the thickness of the sample (i.e., greater strength with increasing membrane thickness), data is reported in MPa. All North American samples exceeded the ASTM minimum requirement for new material (10.4 MPa). The tensile strength of all the samples was greater than the DIN minimum (8 Mpa). As can be seen in Figure 6.5, there is a tendency to increased tensile strength with age in the 15- to roughly 23-year range. This is expected as the sheet loses some flexibility over time. Beyond that range, there are insufficient data points to observe a clear trend. A minimum elongation at break value of 250% is required for new materials in ASTM D- 4434. The measured elongation at break for the North American samples ranged from 45-150%, which corresponded to 18-60% of the minimum value specified for new materials. Samples 4B, 5B, 8A, and 20B had significantly lower elongation at break values (18-40% of ASTM minimum) than the rest (44-60% of ASTM minimum). The reasons for these values are not clear at this time. The DIN standard calls for new membranes to achieve a minimum of 150% elongation at break. As can be seen in Table 6.3, four of the seven European samples achieved this value, one sample was at 95% of this value, and another was at 92% of it (in the machine direction). Overall, 11 of 17 samples (European and North American) surpassed this requirement for new products. Even amongst the samples with the lowest elongation values, all of the roofs were performing at the time of the survey and none showed any signs of any distress. As can be seen in Figure 6.6, there is no correlation between the elongation data generated by the two different test methods. Glass mat supported membranes Strength Elong. Strength Elong. Strength Elong. MD (Mpa) MD (%) MD (Mpa) MD (%) CD (Mpa) CD (%) 1A Canton MA 1979 22 15.2 + 0.4 125 + 5.6 01 A 12.5 212.4 10.2 174.6 2A Wenham MA 1984 17 13.5 + 0.5 119 + 9.7 02 B 12.1 204.4 11.5 198.1 3A Woburn MA 1983 18 14.8 + 0.5 146 + 18.8 03 B 12.1 227.2 11.7 187.8 4B Dickson TX 1984 17 15.2 + 1.1 85.3 + 18.5 04 A 12.9 180.4 12.5 166.4 5B Tyler TX 1981 20 16.0 + 0.6 98.1 + 13.2 05 A 14.5 129.9 14.2 154.9 7A City of Industry CA 1979 22 16.8 + 0.6 124 + 8.2 07 B 13.2 130.8 12.9 128.8 8A EL Segundo CA 1982 19 17.3 + 1.0 44.5 + 14.3 10B Lacey WA 1982 19 13.9 + 0.5 133 + 9.2 10 A 11.1 218.2 11.0 210.9 11B FT. Steilacoom WA 1983 18 14.7 + 0.5 148 + 3.3 11 B 12.6 242.6 11.6 227.8 15B Mt, Prospect IL 1981 20 15.0 + 0.6 139 + 7.0 15 A 12.4 186.1 12.1 183.5 18A Englewood NJ 1985 16 13.1 + 1.7 111 + 36.1 20B Davis CA 1981 20 20.7 + 2.0 56.0 + 18.3 20 A 14.5 109.9 12.8 139.9 21A Haileybury ON 1981 20 13.7 + 0.4 134 + 6.2 23A Alouette QUE 1983 18 11.4 + 0.3 115 + 8.3 25A Sarnia ON 1984 17 15.7 ± 0.4 131 ± 11.8 26 Calgary AB 1982 19 12.4 ± 0.3 151 ± 8.6 131 Arnoldstein, Austria 1986 16 10.5 246.6 10.0 227.2 132 Dortmund, Germany 1979 23 12.8 157.5 13.0 151.5 133 Kempten, Germany 1976 26 9.2 184.5 8.8 160.7 134 Camorino, Switzerland 1976 26 6.9 143.9 6.5 121.0 135 Personico, Switzerland 1968 34 10.2 141.8 9.1 110.4 136 Lugano, Switzerland 1970 32 13.6 92.6 13.4 63.9 137 Reading, United Kingdom 1987 15 11.1 184.9 10.8 175.8 Tensile Data ASTM Tensile Data SIA Project Location Sample ID Year Installed Years Exposed Sample ID Elongation (Polyester Reinforced) 0 5 10 15 20 25 30 35 40 15 17 19 21 23 25 27 29 Years Exposed Elongation (%) ASTM MD ASTM CD SIA MD SIA CD Table 6.3 – Tensile properties, glass mat supported membranes. Figure 6.3 – Elongation at break, polyester reinforced membranes versus age. Graveline, Beer, Paroli, and Delgado – 63 With the glass mat sheets, the DIN procedure results in higher values than the ASTM method, in many cases significantly higher. Once more, the different test parameters (Table 6.4) are assumed to be the reason for the differences. Perhaps not unexpectedly, for both types of membranes, the testing conducted at the lower cross head speed yields the higher elongations at break. 7. PLASTICIZER CONTENT As noted previously, plasticizers are blended with the polymer during the manufacturing of vinyl roofing membranes to make them flexible. This allows the sheets to resist the various loads they are subjected to over their service life such as thermal cycling, substrate (e.g. insulation), and/or structural movement and hail impact. Some plasticizer is lost as vinyl membranes age. The plasticizers that migrate from the sheet are biodegraded. In the formulation of vinyl membranes, the choice of the appropriate types and grades of plasticizers, and their use in sufficient quantities, are critical to the long-term performance of the finished product. For this study, the plasticizer content was determined by weighing each sample before and after it was placed in boiling ethyl ether for one hour. The measured weight difference is the plasticizer that was extracted. The plasticizer content of each sample is reported as a percentage of the original plasticizer content of new material based on production records (see Table 8.1). The residual plasticizer content is plotted against the age of the samples in Figure 7.1. As expected, the plasticizer content decreases with age. As can be seen, the data correlates quite well despite the fact the samples were taken from roofs located in various European and North Figure 6.4 – Typical force displacement curve for tensile test of glass mat supported roof membrane in machine direction (MD). Figure 6.5 – Tensile strength, glass mat supported membranes versus age. Strength (Fibreglass Reinforced) 0 5 10 15 20 25 15 20 25 30 35 Years Exposed Strength (MPa) ASTM MD SIA MD Strength (Fiberglass Reinforced) Standard ASTM D-4434 DIN Type Type III Test method ASTM D-751, B Sample (mm) 25 x 150 Gauge Length (mm) 75 50 Crosshead speed (mm/min) 300 100 ± 10 Samples tested 5/ direction 5/ direction Table 6.4 – Test procedures, glass mat supported membranes. Graveline, Beer, Paroli, and Delgado – 64 American climate zones, and that the roof constructions and building occupancies vary appreciably. Most importantly, with one exception, even the oldest samples (up to 34 years old at the time of testing) still contain approximately 60% or better of their original plasticizer. All of these roofs continue to perform to this day, resisting all the loads imposed upon them in a wide variety of climates. Additionally, all the membranes from these roofs retained sufficient plasticizer to allow them to be hotair welded. Weldability is critical to the long-term performance of any thermoplastic roof as it allows permanent, watertight repairs or modifications to be made to the roof at any time during its useful life. Hot-air weldable membranes that become difficult to weld with age are difficult to maintain and do not allow for modifications to the rooftop (e.g., installation of new mechanical equipment) over time. It should be noted that all of the sampled roofs were light grey in color. It is assumed that the shift to highly reflective white color will result in even lower roof surface temperatures, and will, if anything, slow the aging process even further. Others have looked at plasticizers in vinyl roof membranes. In a study of 87 roofs with vinyl membranes from four different manufacturers, Foley et. al. [2] noted significant differences between the four products. The average plasticizer content of the unexposed portion (within the seam) of the samples, by supplier group, varied from a low of 27.3% (Group ID “B”) to a high of 34.9% (Group ID “D”). For the same products, the mean plasticizer contents of the exposed samples were 23.5% and 33.4% respectively. The mean plasticizer content of the exposed D samples was greater than the plasticizer content of the unexposed samples from Group B. The mean exposed age of the B samples was 4.3 years, while it was 5.8 years for the D samples. Taking the unexposed values as an approximation of the original plasticizer content of the products, the B material lost plasticizer at a rate four times greater than the D samples. The D group of samples are the same products as those upon which this paper is based. In addition to the different quality and quantity of plasticizers used, the lacquer coating applied to this supplier’s membranes impedes plasticizer migration. The authors compared the hail resistance of the aged samples. Perhaps not surprisingly, Elongation (Fiberglass Reinforced) Figure 6.6: – Elongation at break, glass mat supported membranes versus age. Figure 7.1 – Plasticizer content versus age. Residual Plasticizer (% Original) Graveline, Beer, Paroli, and Delgado – 65 according to the authors, “The data comparison of samples from group B and group D reveal dramatic performance differences in the hail simulation testing.” All of the group B samples failed, most with spheres as small as 1″ in diameter, with some of the membranes less than three years of age. The D group of samples demonstrated vastly superior hail resistance. Data on the hail resistance of the samples from this study will be covered in greater detail in Section 10. Clearly, plasticizers are critical to the long-term performance of vinyl roof membranes. It is tempting to try and define minimum plasticizer levels to achieve a desired level of performance. Foley et. al. postulate that on the basis of their testing of aged samples, that an initial minimum plasticizer content of less than 32% may be a cause for concern. As they acknowledge, it is difficult to establish such a base line, as in addition to the quantity of plasticizer, the type, quality, and rate of loss are all critical parameters in assessing long-term performance. Additionally, plasticizer content, like all physical properties, is but one of many that must be looked at in combination with others to assess the quality of a product as produced and its condition at a given point in time. This survey has, however, clearly demonstrated that a properly formulated vinyl membrane with the appropriate type and quantity of plasticizer can provide a service life approaching four decades. 8. LOW TEMPERATURE FLEXIBILITY Flexibility is an important membrane property, particularly during the application phase. The flexibility of all types of roofing membranes decreases with temperature. For this study, the membranes’ low temperature flexibility (LTF) was tested according to the procedure outlined in SIA 280. Five 10 mmwide rectangular specimens are folded with a bending radius of about 15 mm and fixed between two metal plates. The test device is then stored in a chamber and allowed to cool to the desired test temperature. When the samples have reached the required temperature, the device is removed from the freezer and the two metal plates are instantly and quickly pressed together so that the samples are bent to a radius of 5 mm. The lowest temperature at which all five specimens do not break or crack is recorded. The reproducibility of the test method is ± 5°C. The SIA 280 requirement for new material is -20°C. Low temperature flexibility shows a clear dependence on the residual plasticizer content. The linearity is very good, with a correlation coefficient R2 of 0.66. Remarkably, 25 out of 40 samples still fulfill the requirement for new materials, according Age (Years) 1D 22 -35 83.4 9B 18 -30 82.3 6A 17 -30 73.0 5C 20 -30 80.3 3A 18 -30 92.5 2D 17 -30 84.2 2A 17 -30 84.9 14A 16 -30 86.7 13A 19 -30 82.2 7A 22 -25 86.0 5B 20 -25 83.8 4B 17 -25 89.1 16A 17 -25 83.6 15D 20 -25 86.5 1A 22 -20 82.1 18C 16 -20 80.2 17B 15 -20 69.0 11B 18 -20 82.3 10B 19 -20 73.8 106 24 -20 88.1 105 25 -20 92.4 104 27 -20 77.6 103 18 -20 75.7 102 21 -20 82.4 101 24 -20 82.6 109 24 -15 85.8 108 24 -15 73.2 107 24 -15 88.0 20B 20 -10 66.5 15B 20 -10 63.7 131 16 -10 60.2 110 9 -10 76.9 133 26 -5 65.7 132 23 -5 61.6 135 34 0 57.7 134 26 0 66.4 112 17 0 61.1 111 17 0 59.3 137 15 5 45.3 136 32 5 60.4 Table 8.1 – Low temperature flexibility (LTF) and plasticizer content data. Figure 8.1 – Residual plasticizer vs. low temperature flexibility. Graveline, Beer, Paroli, and Delgado – 66 to the SIA requirement of -20°C or lower. Even the two samples with the highest values of 5°C still show considerable flexibility. The testing conditions (rapid 180° bending around a small radius) are obviously severe and do not occur in real roof conditions. Membrane flexibility is an issue mainly during installation and roof maintenance. As can be seen, even the aged installed membranes with a LTF value of 5°C continue to perform. The fact that a majority of all samples are tested with low temperature values above the requirements for virgin material reflects the manufacturers’ efforts to formulate their membranes for longterm behavior. Potential reduction in plasticizer content over long years of roof service is accounted for by the appropriate formulation of the base vinyl material. 9. GLASS TRANSITION TEMPERATURE The glass transition temperature of G and S samples obtained from both E’int and E”max ranges from -54°C to -11°C and from -46°C to -1°C, respectively. The Tg values from E’int shows a similar trend as those from the E”max. Therefore, only the latter will be discussed further. There were no unexposed (control) samples available from any of the roofs at the time of the analysis. Hence, the area under the seam (underlap), when available, was used as a control. To obtain a better representation of the exposed (top) sheet, specimens were cut from at least two different areas. The glass transition temperature of the fiberglass-reinforced samples (unexposed sheets, area under the seam) have a Tg ranging from -46°C to -24°C and that of the exposed (top) sheet ranges from -44°C to -1°C. The glass transition temperature of the polyester-reinforced samples Tg (E”max) of the unexposed specimens ranged from -46°C to -43°C and that of the exposed specimens ranges between -43°C and -39°C. As can be seen in Figures 9.1 and 9.2, the Tg appears to show a trend with aging. Although there is significant scatter and the R2 value is not high, one does see a correlation. The low R2 is due in part to the fact that there is little data between 0 and 15 years of service. More work is required in this area; in particular, the correlation between Tg and plasticizer content as well as with cold bend. This will be part of a future paper. 10. HAIL RESISTANCE Twenty-seven of the samples received at the manufacturer’s lab were large enough after all other analytical procedures (minimum 0.5 m x 0.5 m) to be used for hail testing. The age of these 27 roofs ranged from 15 to 34 years. For the purposes of this investigation, the hail test method developed by the Swiss Federal Laboratories for Materials Testing and Research (EMPA) was chosen for the determination of the hail resistance. It is based on pneumatically propelled spherical projectiles of polyamide (diameter 40 mm, mass 38.8 g). Out of a large number of different projectile sizes, shapes, and materials, the polyamide ball had been proven to provide the best results with regard to reliability and repeata- Figure 9.1 – Glass transition temperature versus age for G membranes. Figure 9.2 – Glass transition temperature versus age for S membranes. Graveline, Beer, Paroli, and Delgado – 67 bility as well as practicability. Polyamide has a similar density as ice; hence, the impact energies of an ice ball or a polyamide sphere of the same size and same terminal velocity are approximately the same. The test method was incorporated in the Swiss standard for polymer waterproofing membranes (SIA280, Ed. 1983). It has recently been adopted as a harmonized European standard. A detailed description of the test procedure is given in the standard (e.g., BS EN 13583:2001). In short, the test procedure is as follows: 1. Place the test specimen on the desired substrate. 2. Cool the test specimen surface with 200g of crushed ice for 3 minutes. 3. After removal of the ice, shoot the test projectiles at the selected velocity level. 4. Test for “watertightness” by applying a soap solution and suction to the impact area. 5. Repeat five times at a given impact velocity at different locations on the specimen (as the test equipment used allowed subsequent shots within a few seconds, the surface was not “re-cooled” between impacts) 6. If no damage occurs, repeat steps 1) – 5) at a higher impact velocity. The highest impact velocity causing no damage is reported. For the purpose of this study the term “damage” is used with reference to leakage as indicated by bubbles in step 4). CEN European standards do not provide minimum (or maximum) requirement values to be met. The Swiss standards SIA280 (polymeric) and 281 (bituminous) require a minimum impact veloci- Fig. 10.1 – Hail resistance of new samples. Table 10.1 – Hail resistance results. Blank fields indicate that no values have been determined. ID Mem brane Type Nominal Thickness Age Hail Re sis tance (m/s) GF Gypsum ISO EPS (mm) (years m/s m/s m/s G 1.2 New 66 39 47 G 1.8 New 96 67 85 S 1.2 New 79 54 61 S 1.8 New 95 68 77 G 1 ) 1.2 New 90 G 2 ) 1.2 New 91 01 A G 1.2 22 39 39 01 C S 1.2 22 37 38 02 B G 1.2 17 39 14 02 C S 1.2 17 52 45 03 B G 1.2 18 40 27 04 A G 1.2 17 12 5 05 A G 1.2 20 30 33 05 D S 1.2 20 19 30 06 B S 1.2 17 32 37 07 B G 1.2 22 17 7 09 A S 1.2 18 46 41 10 A G 1.2 19 29 16 11 B G 1.2 18 43 20 13 A S 1.2 19 14 10 14 B S 1.2 16 58 54 15 A G 1.2 20 37 30 15 C S 1.2 20 34 28 16 B S 1.2 17 51 51 17 A S 1.2 15 52 55 18 D S 1.2 16 59 54 20 A G 1.2 20 18 11 101 S 1.2 24 13 104 S 1.2 27 34 111 S 1.8 17 46 112 S 1.8 17 35 135 G 1.2 34 7 137 G 1.2 15 30 1) membrane fully adh ered to gypsum boar d; 2) fel t bac ked membran e, fully adhere d to gyps um board G 1.2 mm not attached S 1.2 mm not attached G 1.8 mm not attached 1.2 mm felt adhered S 1.8 mm not attached G 1.2 mm adhered 1) membrane fully adhered to gypsum board; 2) felt-backed membrane, fully adhered to gypsum board Graveline, Beer, Paroli, and Delgado – 68 ty of 17 m/s for new roofing membranes. In order to determine how aged material would perform on substrates in use today, the aged membrane was tested over the most commonly used thermal insulations: polyisocyanurate (ISO) for North America, and expanded polystyrene (EPS, density 20 kg/m3) for Europe. Testing was also done on glass fiber reinforced gypsum boards. For comparison purposes, new membranes of the same PVC formulation and different thicknesses were also tested. Test results are summarized in Table 10.1. Testing was only conducted according to the SIA procedure. As can be seen in Table 10.2, there are numerous differences between the ASTM, FM, and SIA hail test methods [11]. Although it is not possible to compare data generated with the SIA methodology to the FM requirements directly, the following equation is useful to relate impact energy (FM) to impact velocity (SIA) : Ekin = 1/2 * m * v2 where Ekin = kinetic energy, m = mass, and v = velocity. On this basis, the SIA minimum requirement of 17 m/s for the 40 mm polyamide sphere corresponds approximately to 25 m/s for FM Class 1-MH and 33 m/s for FM Class 1-SH. [12] Data for new membranes are shown in Figure 10.1. All measured values exceed the three requirements. Not surprisingly, 1.8-mm thick membrane provides greater resistance than 1.2-mm membrane. Results over glassfaced gypsum board are roughly 1.5 times higher than those measured over polyisocyanurate boards for a given set of parameters. Figure 10.2 illustrates the hail resistance values determined on the European samples over EPS insulation. Samples 101 and 135, 25 and 34 years old respectively, have hail resistance values below the requirement for new material. However, despite their age and their locations in regions with high hail risk [13], these roofs exhibited no signs of hail damage. The other four samples, aged from 15 to 27 years, have hail resistance values far above the SIA280 requirement for new membranes. The data for the North American samples, over both polyisocyanurate and the glassfaced gypsum, are presented in Figure 10.3. Although four samples show slightly higher values on ISO, the glass-faced gypsum board generally is found to improve hail resistance. With an average age of 18.6 years, 16 out of the 21 samples still fulfill the requirement FM Class 1-MH for new membranes, while 12 samples meet the requirement FM Class 1-SH on glass faced gypsum board. On ISO, 14 of the samples, aged 17 to 22 years, meet FM Class 1-MH and 11 samples meet FM Class 1-SH. On glass-faced Parameters of Test Projectiles Standard Shape and Material Diameter (mm) Mass (kg) Sample Surface Cooling Kinetic Control of Impact Tool Impact Energy (Nm) ASTM D-3746 steel cyl inder 50 2.27 no h = 1355 mm 30 FM Class 1-SH steel sphere 45 .360 yes h = 5400 mm 19 FM Class 1-MH steel sphere 51 .737 yes h = 1500 mm 10 .8 SIA 280 po lyamide sphere 40 .388 yes v = 17 m/s (minimum ve locity) 5.6 Table 10.2: Test parameters and kinetic energy of ASTM, FM, and SIA hail test methods. Fig. 10.2: Hail resistance of field aged samples Europe, tested on EPS. Graveline, Beer, Paroli, and Delgado – 69 gypsum board, only one sample (13A) had a hail resistance value below the initial requirement of SIA280. All the others meet the requirement for new material. None of the roofs exhibited any signs of hail damage during the inspection. The results are also sorted by r e i n f o rcement type in Figure 10.3: fiberglass (G) and polyester (S). It should be noted that only the reinforcement varies between the two types; the polymer matrix is identical. The S materials appear to have a higher mean hail resistance. However, the data from the four roofs on which both G and S membranes had both been installed is presented in Figure 10.4. As can be seen, the data are inconclusive. Neither the G nor the S type can be said to provide better hail resistance than the other based on these data. In a separate paper [14], one of the authors of this work studied the correlation between hail resistance (impact speed) and other physical properties. Both plasticizer content and low temperature flexibility were found to correlate reasonably well with hail resistance, with correlation coefficients around 0.6 in both cases. This area should be studied in greater depth. No correlation whatsoever was found between hail resistance and impact resistance, confirming that the latter cannot be used as a substitute for assessing the former. 11. REFLECTIVITY The specimens taken from two different areas of the “as received,” top (exposed) sheet were analyzed before and after cleaning. One to two specimens from the bottom sheet (underlap) without cleaning were analyzed. In some cases, two specimens were analyzed before and after cleaning. This was done to check for differences in the H:Sol values between the two areas or between the dirty and clean top surface of the bottom sheet. Weighted average solar reflectance values were obtained using the LBL calculation method. This is based on the ASTM G 159-98, “Standard Tables for References Solar Spectral Irradiance at Air Mass 1.5: Direct Normal and Hemispherical for 37° Tilted Surface.” This standard is a combination of an editorial revision of Tables E-891 and Tables E-892 to make the 0 10 20 30 40 50 60 01 A 02 B 03 B 04 A 05 A 07 B 10 A 11 B 15 A 20 A 01 C 02 C 05 D 06 B 09 A 13 A 14 B 15 C 16 B 17 A 18 D Gypsum Board ISO impact velocity [m/s] FM 1-MH FM 1-SH SIA G-Type S-Type Fig. 10.3 – Hail resistance, aged samples in North America, on GF gypsum and polyisocyanurate. Fig. 10.4 – Aged G & S membranes from the same roof. 0 10 20 30 40 50 60 Canton MA Wenham MA Tyler TX Mt. Prospect IL G-Type on Gypsum Board G-Type on ISO S-Type on Gypsum Board S-Type on ISO impact velocity [m/s] FM 1-MH FM 1-SH SIA Graveline, Beer, Paroli, and Delgado – 70 reference solar spectral energy standard harmonious with ISO 9845-11992. The ASTM G-159 states that the conditions chosen for these tables “are representative of average conditions in the 48 contiguous states of the United States. In real life, a large range of atmospheric conditions can be encountered, resulting in more or less important variations in the atmospheric extinction. Thus, considerable departure from the present reference spectra might be observed depending on time of the day, geographical location, and other fluctuating conditions in the atmosphere.” The weighted average H:Sol values for the unexposed (bottom) and exposed (top) surfaces of these grey-colored membrane samples ranges from 0.29 to 0.55. As expected, surfaces displayed a higher reflectance value after cleaning. The top side of the bottom (unexposed) sheet also showed higher H:Sol values than the exposed side of the top sheet. A detailed analysis will be presented at the RCI/NRC/ORNL Symposium on Reflective Roofing in May 2005 in Atlanta, GA. 12. FUTURE WORK With globalization, the world has become a smaller place. This study has shown that although products are sold globally, originating from many different countries, the standards for products may be very different. For example, it was noticed that the Swiss standard and ASTM International use different speeds for tensile testing. No explanation for this difference is easily available. In other cases, different tests are required. Thickness requirements are not the same for North America and Europe. Seeing that often the same products are used for export, it is important to understand why these differences exist and if the various standardwriting bodies should not attempt to harmonize these requirements. An international committee on roofing exists. The following is taken from the final report of the CIB/RILEM joint committee on roofing (Final Report of the Condition Assessment Task Group RILEM 166-RMS/CIB W.83 Joint Committee on Roofing Materials and Systems, 2001): Historic Committee Activities. In 1983, a Joint Committee was formed under the auspices of RILEM and CIB to undertake studies of importance to the international roofing community. Of particular interest were the emergence of new membrane roof systems and the need for developing standards to aid in the selection and installation of systems that would provide reliable long-term performance. The initial RILEM 75- SLR/CIB W.83 Roofing Committee was entitled Technical Committee on Elastomeric, Thermoplastic, and Modified Bituminous Roofing Systems. It consisted of members from 18 nations from around the world. The Committee’s main objective was to undertake a state-of-the-art review of the properties and performance of these Roofing Systems along with a tabulation of the standards and specifications that had been developed worldwide to support their proper use. In 1988, this Committee issued its final report[15]. This report outlined the needs for development of performance standards for elastomeric, thermoplastic, and modified bituminous roofing systems. A major recommendation was that the international roofing community should investigate the use of thermoanalytical techniques for characterizing roofing membrane materials and evaluating their performance. In 1989, RILEM 120- MRS/CIB W.83 on Membrane Roofing Systems was formed. This Committee was comprised of 40 members representing 22 countries worldwide. The Committee had two objectives: 1. To investigate the applicability of thermoanalytical techniques for evaluating roofing membrane materials, and 2. To review the current codes of practice in countries of the world. Note that the first objective was in response to the recommendation of the initial RILEM/CIB Roofing Committee. To achieve these goals, the 1988 Joint Committee initiated two Task Groups – with each focused on one of the two goals. In 1995, the Thermal Analysis Task Group issued its final report[16]. This report included the results of interlaboratory testing of EPDM, PVC, and APP and SBS modified bitumen membrane materials using three thermoanalytical methods: thermogravimetry (TG), dynamic mechanical analysis (DMA), and torsional pendulum analysis (TPA). Recommendations were made for developing standard procedures for applying these three analytical techniques to roofing membrane materials. The Codes of Practice Task Group of the Joint RILEM 120-MRS/CIB W.83 Committee issued its report in 1996[17]. The term, “Codes of Practice,” refers to written documents, which set forth requirements and/or guidelines for the design, application, and maintenance of Graveline, Beer, Paroli, and Delgado – 71 membrane roof systems. These documents may or may not be mandated by law. The Codes of Practice Index was organized according to two categories: (1) agents and (2) requirements. “Agents” reflect the effects of climate, site, and occupancy on roof performance. “Requirements” reflect the expectations of building owners, occupants, and regulatory authorities, and relate to matters that effect safety, health, energy conservation, and the protection of people in and around buildings. The intent of the Index was to provide to those developing specifications and performance criteria for membrane roof systems an awareness of the design, application, and maintenance criteria that were in place worldwide. It was considered that the Index would be particularly useful to those whose countries had not developed such criteria for their roofing industry. The Current Committee. CIB W.83/RILEM 166-RMS Joint Committee on Roofing Materials and Systems was initiated in 1995, and has a core group of 21 members from 13 countries (Appendix A). This Joint Committee has two objectives: (1) to develop a methodology for assessing the condition of in-place (i.e., existing) flexible roofing membranes, and (2) to determine the state-of-the-art with regard to design, application, and maintenance of sustainable membrane roofing systems. These objectives were developed directly from the results of the previous Committee’s activities. For example, condition assessment of flexible membrane roof systems may involve, among other parameters, the use of thermal analysis techniques to characterize aged membranes. Additionally, a report on the design, application, and maintenance of sustainable membrane roofing systems was a natural extension of the work of the past Codes of Practice Task Group. To meet the two objectives, the Committee initiated two task groups, each of which conducted separate activities to meet the objectives. Task Group 1 focused on, and was entitled, “Condition Assessment of In-Place Membranes.” Task Group 2 examined issues associated with sustainable roofing, and was entitled, “Towards Sustainable Roofing.” This latter title recognizes that the concept and practices of sustainable roofing will be evolving over the life of the Committee, if not well beyond. Based on the above, it would be of interest to the roofing community if this committee initiated a study comparing the various standards available worldwide and recommended an approach for the various standard-writing bodies to harmonize the various material standards. It would also be recommended that the ASTM International task group developing the PVC standard look at differences that exist between different countries and look at harmonizing some of the tests. 13. CONCLUSIONS Forty-four roofs located in six countries in Europe and North America were analyzed, and samples from each were subjected to a variety of physical property tests. Overall, the field performance of these fiberglass and polyesterreinforced vinyl membranes was found to be without problem. The roofing systems averaging 20 years of age were performing well and without leakage. All membranes were capable of being welded to, even after 20 years of weathering. The laboratory testing confirms that although the products tested lost some of their initial physical properties (which is to be expected with any materials as they age), they generally held up very well compared to the standard minimum values for testing new PVC roofing membranes, according to North American and European standards. It is important to note, however, that some of these membranes, which had been tested in the NRC laboratory about 15 years ago, exceeded the minimum requirements of the ASTM D-4434. This is an interesting point because as all roofing materials age/weather, their properties are expected to degrade. Therefore, to ensure that the minimum property values are exceeded after aging/weathering, a new membrane, regardless of the type (i.e., polymeric, elastomeric or asphaltic) must exceed the minimum requirements listed in the standards. As the roofs examined are essentially the oldest in place, it is not possible to predict how much longer they will perform. But considering the age and the condition of the roofs analyzed, these data would indicate that a properly formulated, properly maintained, reinforced PVC roof membrane system could perform in excess of 20 to 30 years in various climates throughout Europe and North America. 14. ACKNOWLEDGEMENTS We would like to thank all the building owners who allowed us access to their roofs and permitted us to remove samples for testing. We would also like to thank all the roof consultants and engineers that helped with site visits and test sampling of the roofs located in the USA. Graveline, Beer, Paroli, and Delgado – 72 REFERENCES 1. R.M. Paroli, T.L. Smith, B. Whelan, “Shattering of Unreinforced PVC Roof Membranes: Problem Phenomenon, Causes and Prevention,” NRCA/NIST Tenth Conference on Roofing Technology, (Gaithersburg, MD, April 22-23, 1993). 2. F.J. Foley, J.D. Koontz, J.K. Valaltis, “Aging and Hail Research of PVC Membranes,” 12th International Roofing and Waterproofing Conference, “Exploring Tomorrow’s Technology Today,” (Orlando, FL, Sept. 25-27, 2002), pp. 1-25. 3. AMI Consulting, Bristol, UK, “The European Market for Polymeric Single Ply Roofing Membranes and Competitive Products,” 2002. 4. Cash, C., “Comparative Testing and Rating of Thirteen Thermoplastic Single Ply Roofing Materials,” Interface, October, 1999. 5. Cash, C., “Thermoplastic Single Ply Roofing Membranes Revisited,” Interface, May, 2000. 6. Deutsches Institut fur Normung DIN16726, 1983-05, Beuth Verlag, Berlin, Germany. 7. Schweizerischer ingenieur und architverein SIA V280, 1986-12, Winterthur, Switzerland. 8. ASTM D-4434-96, Standard Specification for Polyvinyl Chloride Sheet Roofing. 9. Whelan, B., Graveline, S., Delgado, A., Paroli, R., “Field Investigation and Laboratory Testing of Exposed Poly(vinyl Chloride) Roof Systems,” CIB World Building Congress, “Building for the Future,” Toronto, Canada, May 1 – 7, 2004. 10. Beer, H.R., Pfammatter, W., “Durability of PVC Roof Membranes – Field Investigation and Laboratory Testing After Up to 34 Years Exposure,” ICBEST Symposium, Sydney, Australia, 2004. 11. Cullen, W.C., “Hail Damage to Roofing: Assessment and Classification,” Proceedings of the Fourth International Symposium on Roofing Technology, 1997. 12. Factory Mutual Research Corporation, “Susceptibility to Hail Damage, Test Standard for Class 1 Roof Covers,” Class Number 4470, Class 1 Roof Covers, revised August 29, 1992. 13. Schweizerische Hagel- Versicherungs-Gesellschaft, 1999, Zurich, Switzerland. 14. Beer, H.R., Schumann, K., Flueler, P., Hail Resistance of Aged PVC Roofing Membranes – A Field Evaluation of Roofs Ranging Between 15 and 34 Years Carried Out by One of the World’s Major Producers of Thermoplastic Roofing and Waterproofing Membranes,” CIB World Building Congress, “Building for the Future,” Toronto, Canada, May 1 – 7, 2004. 15. “Performance Testing of Roof Membrane Materials,” Recommendations of RILEM 75-SLR/CIB W.83 Joint Committee (November 1988). 16. “Thermal Analysis Testing of Roofing Membrane Materials,” Final Report of the Thermal Analysis Task Group, RILEM 120- MRS/CIB W.83 (December 1995). 17. “International Index of Codes of Practice Related to Membrane Roof Systems,” Report of the Codes of Practice Task Group, RILEM 120-MRS/CIB W.83 (October, 1996.
