Abstract:
This invention relates to an improved fastening technique for single ply roofing membranes comprised of thermoplastic polymer material. In one embodiment, a method of installing a roof on a structure may comprise providing a single-ply roofing membrane comprising thermoplastic polymer material, and periodically securing rigid strips over a roofing deck. In such embodiment, the rigid strips have thermoplastic polymer material on corresponding exterior surfaces thereof. The method may further include laying the roofing membrane over the roofing deck, where the rigid strips are located between the roofing deck and the roofing membrane. Then the method may include heating the roofing membrane and the rigid strips simultaneously, perhaps using a heat induction technique, such that thermoplastic polymer material on the exterior surfaces of the rigid strips fuses directly with the thermoplastic polymer material of the roofing membrane.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application relates and claims priority to provisional patent application 61/077,007, filed Jun. 30, 2008, which is herein incorporated by references for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to roofing products, and more particularly to the use of a fastening system and method for a thermoplastic olefin (TPO) roofing membrane. 
       BACKGROUND 
       [0003]    A single ply building membrane is a membrane typically applied in the field using a one layer membrane material (either homogeneous or composite), rather than multiple layers built-up. These membranes have been widely used on low slope roofing and other applications. The membrane can comprise one or more layers, have a top and bottom surface, and may include a reinforcing scrim or stabilizing material. The scrim is typically of a woven, nonwoven, or knitted fabric composed of continuous strands of material used for reinforcing or strengthening membranes. Such single ply membranes typically comprise base (bottom) and cap (top) polyolefin-based sheets (layers) with a fiber reinforcement scrim (middle) sandwiched between the other two layers. The scrim is generally the strongest layer in the composite. Other materials from which the membranes may be formed include, but are not limited to, polyvinyl chloride (PVC), chlorosulfonated polyethylene (CSPE or CSM), chlorinated polyethylene (CPE), and ethylene propylene diene terpolymer (EPDM). 
         [0004]    A typical method of preparing membranes having scrims comprises unwinding a support sheet, scrim, or stabilizing material, and coating the support material by extrusion of a molten compounded polymers, including one or more fillers, UV and thermal stabilizers, and various pigments and fire retardant agents. Then the process provides for cooling and solidifying the membrane, and winding the membrane into a roll. A novel scrim for use with such single-ply roofing membranes is disclosed in co-pending patent application U.S. 2006/0292945, which is commonly assigned with the present disclosure and incorporated herein by reference in its entirety. 
         [0005]    Single ply heat welded membranes are the fastest growing segment of the low slope roofing materials market. The two main membranes are produced from either thermoplastic olefin (TPO) or polyvinyl chloride (PVC) polymer. In both cases, the membranes consist of two layers of the polymer with a reinforcement scrim laminated in-between, as mentioned above. Such membranes are supplied as wide sheets, typically about 4 to 10 feet wide, in rolls up to 200 feet length. A particular advantage of these membranes is that they can be overlapped and then heat welded together. This results in a monolithic membrane with significantly reduced risk of leakage. 
         [0006]    Roofing systems get tested in a wide variety of ways. In one particular test, the intent is to measure how well a system would stay intact when exposed to high wind loads. Typically, high wind loads result in upward forces that can result in part or all of the roofing system lifting off. To test for this so called “wind uplift” resistance, a deck is built to replicate a roof construction. Typically, these are 10 ft×20 ft or larger assemblies that include a welded seam where the end of one piece of the roofing membrane is connected to the beginning of another membrane sheet. The decks are sealed underneath in such a way that the underside of the roofing system can be pressurized. The pressure is then raised in increments until failure of the roofing system, namely, when the roofing system begins to lift off of the structure. The pressure prior to failure is then the rating of that particular roofing system. 
         [0007]    Single ply membranes in low slope applications are typically installed above a layer of insulation such as polyisocyanurate (polyiso) slab stock foam. Polyiso foam is produced with a facer on either side, typically a cellulosic felt or paper. 
         [0008]    Closely spaced mechanical fasteners used for mechanical attachment of the overlap section of the two membranes to the underlying roofing structure in the conventional method of installation. Such mechanical fasteners typically consist of metal plates and screws that penetrate down through the insulation (polyiso boards) and into the supporting steel or other type of deck material. 
         [0009]    However, such conventional roofing assemblies provide for fastening only along the weld seam via fasteners driven down into the steel deck for the mechanical attachment of just the overlap portion of the membranes. Unfortunately, this means that for wide sheets there can be up to a 10 feet span between attachment points in one direction. System designs attempt to compensate for such a large span between attachment points by increasing the density of fasteners in the other direction, sometimes by moving them as close as 6 inch on center. However, this has a cost impact and has limited benefit. 
         [0010]    An alternative method of securing single ply roofs has been commercialized by O.M.G. Inc located in Massachusetts. O.M.G. sells round metal plates that have been coated with a thermoplastic polymer (or PVC) that acts as a hot melt adhesive. These are currently being sold under the name RhinoBond®. Such plates are distributed evenly using around 6 per 4×8 foot polyiso foam board, and are attached to the roof structure using conventional roofing screws. Such screws hold the plates in place and penetrate through the insulation boards and down into the steel deck, thereby better anchoring the roofing system. Once the membrane is in place over the foam boards having the coated round plates, an induction heater is used to heat each plate in turn, melting the adhesive coating and gluing the plates to the membrane along the locations where the plates have been located. However, even with this approach, installation time is even longer since each coated plate must first be mechanically attached through the insulation board and into the underlying roof structure. 
         [0011]    Accordingly, there is a need for an improved technique for securing single ply roofing membranes to the roofs of structures that does not suffer from the deficiencies found in conventional approaches. For example, simpler installation steps resulting in faster installation times would be especially desirable. The principles disclosed herein provide such a technique. 
       SUMMARY 
       [0012]    This invention relates to an improved fastening technique for heat-weldable single ply roofing membranes comprised of thermoplastic polymer material. In one embodiment, the technique involves strips of rigid material such as metal coated on exterior surfaces with thermoplastic polymer material, incorporated into the upper surface of polyisocyanurate insulating foam boards. In an alternative embodiment, such rigid strips are simply laid out across the entire roof surface. In either approach, once the membrane is laid out over the coated strips, which are laid out over the insulation boards or directly on the roofing deck if boards are not used, the coated strips are heated, for example, with an induction heater, such that the thermoplastic polymer coating on the strips becomes fused on the exterior side to either the insulation boards or the roofing deck and on the interior surface to the thermoplastic polymer-based membrane. In yet another embodiment of the disclosed technique, the coated strips may be incorporated into the surface of an underlayment, such as GAF-Elk&#39;s Versashield®, which functions as an underlying layer for the single ply membrane. In this embodiment, the underlayment having the incorporated coated strips is installed over the roofing deck using mechanical attachments, and then a heating device is used after the membrane is laid over the underlayment to fuse the thermoplastic polymer material on the interior surface of the rigid strips to the membrane. In all embodiments, the overlap portion between adjoining membrane sheets may also be heat welded and/or secured with a mechanical fastener, as found in conventional approaches. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  illustrates a top down view of the installation of a conventional polyiso single ply system; 
           [0014]      FIG. 2  illustrates a partial side cross-sectional view of the installation of a conventional polyiso single ply system; 
           [0015]      FIG. 3  illustrates a top down view of the installation of a polyiso single ply system in accordance with the present disclosure; and 
           [0016]      FIG. 4  illustrates a partial side cross-sectional view of the installation of a polyiso single ply system in accordance with the present disclosure. 
           [0017]      FIG. 5  illustrates a partial side cross-sectional view of the installation of a polyiso single ply system in accordance with the present disclosure. 
           [0018]      FIG. 6  illustrates a partial side cross-sectional view of the installation of a polyiso single ply system in accordance with the present disclosure. 
           [0019]      FIG. 7  illustrates a partial side cross-sectional view of the installation of a polyiso single ply system in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  illustrates a top down view of the conventional installation of a single ply membrane. The membrane sheets are laid down with a section of overlap  103 . Closely spaced mechanical fasteners  105  are used for mechanical attachment of the bottom layer at the overlap section  103  of the two single ply membranes  102  to the roof structure. Such mechanical fasteners  105  typically consist of metal plates and screws that penetrate down through the insulating boards  101 . The overlapping section  103  is then heated creating a heat weld  104 . 
         [0021]      FIG. 2  illustrates the partial cross-sectional view of the installation of a single ply membrane  102  shown in  FIG. 1 . The insulating board  101  is shown layered on top of the steel or other type of deck material  201 . Two sheets of single ply membrane  102  are shown on top of the insulating board  101  aligned so that there is a section of overlap  103  between them. The mechanical fastener  105  is shown penetrating through the bottom one of the single ply membranes  102  and through the insulating board  101  into the decking material  201 . The overlapping section  103  is then heat welded as mentioned above. The mechanical fastener  105  and the heat weld  104  are located within the overlap region  103  of the two single ply membranes  102 . 
         [0022]      FIG. 3  illustrates a plan view of one embodiment of a roof installation technique in accordance with the disclosed principles. This figure also shows the single ply membrane  102  with a section of overlap  103  layered on top of the insulating board  101 . The overlap  103  is heated to form a heat weld  104  that holds the two sheets of single ply membrane  102  together. 
         [0023]    The technique in accordance with the present disclosure avoids the use of individual plate fasteners  105  used in the conventional process described above. Instead, in one embodiment, rigid strips  301  having heat-weldable thermoplastic polymer material on exterior and interior surfaces are used to provide for a more continuous adhesion of the membrane  102  down onto the insulating boards  101 . As used herein, the term “rigid” when referencing the strips  301  means that the strips are resistant to bending or flexing and are sufficiently stiff to maintain their linear shape. However, it does not mean that the strips are not flexible at all, such as with a metal tape measure that is extremely rigid from side-to-side, but somewhat flexible up and down. Moreover, the rigid strips  301  may be formed in lengths from about 3 ft to about 10 ft, and may be about one-half inch to several inches wide and from 1/16 inch to ¼ inch thick. Of course, other sizes may also be employed for the rigid strips  301 . 
         [0024]    The insulating boards  101  are first laid across the roofing deck and secured to the roofing deck. Securing of the insulating boards  101  may be done using mechanical fasteners driven through the boards  101  and down into the roofing deck. Alternatively, an adhesive, such as a urethane adhesive, may be used to adhere the insulating boards  101  onto the roofing deck. Once the insulating boards  101  are secured to the roofing deck, the rigid strips  301  are periodically dispersed on the exterior surface of the insulating boards  101 . Exemplary spacing between each rigid strip  301  may be 36 inches, however, other amounts of spacing may also be selected. The single ply membrane  102  is then laid on top of the rigid strips  301 , and the overlap sections  103  between separate membrane sheets  102  may be heat-welded together. For example, a heated mandrel may be moved along the overlap section  103  between the overlapping membranes pieces  102 . As the mandrel moves along the overlap section  103 , the mating surfaces of the overlapping membrane pieces  102  are heated and then pressed together to complete the heat weld seal between the two. Of course, other techniques for heat-welding or otherwise bonding the overlap section  103  may also be employed. 
         [0025]    After the membrane has been laid out across the roofing deck, the membrane  102  is heated directly above the locations of the strips  301 . Once heated, the thermoplastic material on the exterior or upper surface of the rigid strips  301  fuses directly with the single ply membrane  102 . In this embodiment, the heating also causes the thermoplastic polymer material on the interior or lower surface of the rigid strips  301  to adhere the strips  301  to the polyiso insulating boards  101 , or directly to the roofing deck  201  if no insulating boards  101  are employed. One advantageous technique that may be employed to perform the heating of the thermoplastic material on the rigid strips  301  in the above-described manner is via induction heating. For example, a heated roller may be rolled across the membrane  102  directly over the rigid strips  301 , where the heat from this roller device is transferred through the membrane  102  to the thermoplastic polymer on the rigid strips  301  sufficient to melt the thermoplastic material and adhere the components together as described above. Other techniques to heat the thermoplastic polymer material on the rigid strips  301  sufficiently to adhere to the membrane  102  and to the insulating boards  101  (if employed) may also be employed. For example, hot air may be directed at the areas of the membrane  102  where the rigid strips  301  are located to cause the desired adhesion. Also, a heated iron or similar flat device may be slid across the membrane  102  in the appropriate locations to cause the desired melting and adhering of the components. Of course, other heating techniques may also be employed, however, some heating techniques may not be sufficient as they may melt the membrane  102  before transferring enough heat down to the rigid strips  301  to melt their coating. Accordingly, heating by heat induction is the preferred embodiment. 
         [0026]    An advantage of this novel technique is that adhesion of the membrane  102  to the insulating board  101  or other surface can be improved since any number of rigid strips  301  may be employed at any location across the membrane  102 . As a result, wind uplift performance (related to the system&#39;s ability to withstand severe weather conditions) is improved. In addition, wider sheets of single ply membrane  102  can be installed without compromising roofing performance since the mechanical attachment of the membrane sheets  102  is not only at the overlap between adjoining sheets  102 , as is the case in the conventional installation method described in  FIGS. 1 and 2 , but also along the length of each rigid strip  301 . An additional advantage is that installation of the roofing system would be easier than conventional approaches where the insulating boards  101  are adhered to the roofing deck since the installer does not need to handle washers or mechanically fasten coated plates down to the roofing structure. Accordingly, faster installation times and less installation materials results in overall costs being lowered. 
         [0027]      FIG. 4  illustrates a partial side cross-sectional view of the installation technique described in this disclosure. Again, the figure illustrates the use of the insulating boards  101  layered on top of the roof decking  201 . As discussed above, the insulating boards  101  may be mechanically fastened to the roofing deck  201  or they may be adhered. Rigid strips  301  with thermoplastic polymer material on both exterior and interior (i.e., upper and lower, when mounted) surfaces are located between the polyiso foam insulation board  101  or roofing deck  201  and the single ply membrane sheets  102 . The membrane sheets  102  can be heated to form a heat weld  104  at the location of their overlap  103 , as described above. Also as described above, the thermoplastic material on the exterior and interior surfaces of the rigid strip  301  can also be heated using induction heating, or other appropriate heating technique, to fuse the rigid strip  301  directly to the single ply membrane  102  and either the roofing deck  201  or the polyiso foam boards  101 , depending on what the strips  301  are directly contacting in each particular installation. 
         [0028]      FIG. 5  illustrates an embodiment of the disclosed principles in which insulation foam boards  101  are manufactured with rigid strips  301 , for example, made of metal or other rigid material, incorporated into the exterior surface of the insulating boards  102 . These rigid strips  301  are coated on their exterior surface with a thermoplastic polymer material, such as TPO, and are built into the facer on the top/exterior surface of the foam boards  101 . Once the insulation boards  102  having these strips  301  are installed on the roof structure, the membrane  102  is laid over the boards  101 . A heating device is then used to fuse the coating of thermoplastic polymer material  501  on the strips  301  to the membrane  102  as described above. Since the strips  301  are built into the boards  101 , and the boards  101  have been secured to the roof structure  201  (e.g., mechanically or adhesively), the membrane  102  is secured to the roof structure  201  where the strips  301  have been laid out. In addition, the strips  301  may have holes at periodic positions along their lengths to provide for mechanical attachments that penetrate down to the roofing deck  201 . Moreover, mechanical fasteners used to secure the rigid strips  301  may simultaneously be the means by which the insulating boards  101  are secured to the roofing deck  201 . 
         [0029]      FIG. 6  illustrates another embodiment of the disclosed principles in which the rigid strips  301  may be incorporated into the surface of an underlayment  601 , such as GAF-Elk&#39;s Versashield®. Such an underlayment  601  functions as an underlying sealing layer for single ply membranes. In this embodiment, the underlayment  601  having the incorporated rigid strips  301  is installed on the insulation boards  101  using conventional techniques. The membrane  102  is then laid over the underlayment  601 , and a heating device is used to fuse the coating  501  on the strips  501  to both the membrane  102  and the underlayment  601 . Again, such strips  301  could have holes arranged longitudinally for mechanical attachment down into the roofing deck  201 . Also, insulation boards  101  may or may not be used with this approach. Since the strips  301  are integrated into the underlayment  601 , and the underlayment  601  has been secured to the roof structure  201  or to insulation boards  101  secured to the roof structure  201 , the membrane  102  is now secured to the roof structure  201  where the strips  301  have been laid out by the selected heating and fusing process. 
         [0030]      FIG. 7  illustrates another embodiment in which polyiso foam insulation boards  101  are manufactured with a foil facer  702 . The foil facer  702  would be coated with lines of hot melt adhesive  701 . Again the insulation boards  101  are installed on the roof structure  201 , and the membrane sheets  102  laid over them. A heat device is then used to melt and adhere the adhesive strips  701  to the foil  702  (or other sturdy material) of the insulation boards  101 . Also, the heating of the thermoplastic material  501  on the exterior surface of the rigid strips  301  bonds the strips  301  to the membrane  102 , as in previous embodiments. Since the insulating boards  101  have been secured to the roof structure  201 , and the rigid strips  301  adhered to the boards  101  with the hot-melt adhesive  701  and bonded to the membrane  102 , the membrane  102  is now secured to the roof structure  201  where the rigid strips  301  have been located. 
         [0031]    Yet another approach is the laying out of continuous strips of precoated metal  301  across the entire roof surface. These coated strips  301  would be laid over the insulation boards  101  that have been secured to the roof structure  201 . The coated strips  301  may have holes at periodic positions along their length to provide for standard mechanical attachments that would simply hold the rigid strips  301  from moving around while the membrane  102  is laid on top of the strips  301 . The membrane  102  is then laid over the rigid strips  301 , and a heating device is used to fuse the thermoplastic polymer material on the strips  301  to both the membrane  102  and the underlying roof structure  201  or insulation boards  101 . Thus, the coating is what structurally bonds the strip  301  to the roofing deck  201 , and the strip  301  to the membrane  102 , rather that a large number of roofing screws used to structurally secure the strips to the deck. Not only does this cut the installation time significantly, but it also allows securing the membrane  102  to the roofing deck  201  without making a large number of holes through the deck. 
         [0032]    While various embodiments in accordance with the disclosed principles have been described above, it should be understood that they have been presented by way of example only, and are not limiting. Thus, the breadth and scope of the invention(s) should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the claims and their equivalents issuing from this disclosure. Furthermore, the above advantages and features are provided in described embodiments, but shall not limit the application of such issued claims to processes and structures accomplishing any or all of the above advantages. 
         [0033]    Additionally, the section headings herein are provided for consistency with the suggestions under 37 C.F.R. 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Technical Field,” such claims should not be limited by the language chosen under this heading to describe the so-called technical field. Further, a description of a technology in the “Background” is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Summary” to be considered as a characterization of the invention(s) set forth in issued claims. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of such claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings herein.