Abstract:
A plate employed for securing substrate to a roofing structure employs a recessed central hub through which a fastener is driven. A barrier membrane covers the plate and is bonded in position to the plate. A sidewall of the recessed hub includes at least one vent opening to equalize pressure within the recessed hub during installation and post-installation.

Description:
BACKGROUND 
       [0001]    This application relates generally to roofing plates which secure a substrate to a decking structure by means of a fastener. More particularly, this application relates to roofing plates which bond by means of an adhesive to an overlying barrier membrane. 
         [0002]    In roofing installations to which the present application relates a substrate is secured by a multiplicity of disc-like plates to a decking structure. The substrate is typically a thermal insulation layer such as a board of gypsum, resin foam or other insulating materials. The decking structure is typically a substructure of sheet steel, concrete or wood. Fasteners are driven through a central recessed hub of the plate to secure the substrate. 
         [0003]    For some applications, the plate has a heat activated adhesive on an upper surface of the plate. A barrier membrane, which is typically a single ply waterproof membrane, is installed over the substrate and the grid of metal plates. An induction tool, which generates magnetic eddy currents in the metal plate, heats the metal plate and activates the adhesive. Upon cooling and setting, the adhesive then bonds the underside of the membrane to the plate. 
         [0004]    The membrane covers the plates prior to setting of the adhesive. For some conventional applications, there is a tendency for air to be trapped in the hub recess of the plate. The hub portion is sealed to the substrate at the bottom by the fastener head and at the top by the membrane. During the heating cycle, the trapped air expands. When the plate cools and the adhesive sets, a vacuum forms in the hub recess. The vacuum may draw the membrane into the recess and form concave pockets or indentations across the top of the membrane surface. The consequence of the membrane indentations formed across the membrane surface is that the stretching of the membrane into the indentations results in stress on the membrane, and the membrane may also tend to be susceptible to moisture retention—ultimately jeopardizing the barrier bonding and integrity of the membrane. 
         [0005]    Related phenomena may also occur in other systems that employ various forms of plates and fastening techniques. When a solvent based adhesive is applied to the top of the plates, the solvent vaporizes and may partially become trapped in the hub recess upon covering by the membrane. The trapped solvent may cause the membrane to essentially form a convex-like bubble. Such bubbles tend to cause peeling at the plate/membrane bonding interface and jeopardize the bond. 
       SUMMARY 
       [0006]    A roofing plate comprises a central recessed portion which has a central axial opening. A raised portion surrounds the recessed portion. A wall which may be of a frustoconical form connects the raised portion and the central portion. A vent opening is formed in the wall. A peripheral rim surrounds the raised portion. In one embodiment the recessed portion wall, raised portion and rim are generally symmetric about the axial opening. The plate is preferably metal. A heat activated adhesive may be applied to the raised portion of the plate. The plate may be a one-piece integral member. 
         [0007]    A method for installing a roofing system comprises driving a fastener through a recessed portion of a roofing plate to secure a substrate such as an insulation board to a decking structure. A membrane is placed over the plate and substrate. The membrane is bonded to the substrate to form a cavity between the recessed portion and the membrane. The cavity is vented through a wall of the plate. A heat activated adhesive may be applied to the plate prior to securing the plate into position. Alternatively, an adhesive may be applied to the plate after the plate is secured. A multiplicity of roofing plates are employed for securing the substrate to the deck. The cavities formed in the plates are vented during the installation. 
         [0008]    A roof installation comprises a decking structure. A substrate covers the decking structure. A roofing plate has a fastener driven through the hub and into the structure to secure the substrate to the structure. A member overlies the substrate and is bonded to the substrate by adhesive. A cavity is formed between the hub and the membrane. A vent path through the plate communicates with the cavity. The plate may be metal and the adhesive may be heat activated adhesive, pre-applied to the plate. The vent path is located in a side wall of the recessed hub. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a top plan view of a roofing plate; 
           [0010]      FIG. 2  is a sectional view of the roofing plate of  FIG. 1  taken along the line  2 - 2  thereof; 
           [0011]      FIG. 3  is a sectional view of a roof installation, showing a roofing plate, a fastener, a substrate, a decking structure and an overlying barrier membrane; 
           [0012]      FIG. 4  is a perspective view of an installment stage of a roofing installation showing a plurality of roofing plates secured to a substrate prior to covering by a roofing membrane; and 
           [0013]      FIG. 5  is a sectional view of a prior art roof installation showing a prior art roofing plate, a fastener, a substrate, a decking structure and an overlying barrier membrane. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    With reference to the drawings wherein like numerals represent like parts throughout the several figures, a roofing plate is designated generally by the numeral  10 . The roofing plate  10  preferably has a generally disc-like shape and a sturdy, reinforced construction. The plate is secured to the decking structure  20  by a fastener  12  for retaining the substrate  22  in position to a deck substructure. For a given installation, numerous plates are employed for the substrate and positioned in a grid-like pattern. The substrate  22  is typically a thermal insulation layer such as an insulation board. The deck structure  20  may be a steel sheet or concrete. The roofing plate is configured to properly engage the substrate and facilitate proper orientation of the fastener. 
         [0015]    The roofing plate  10  has a central recessed hub  30  which defines the central opening  32  for the fastener. The bottom surface  34  of the hub provides the plate engagement structure for the underside of the head  14  of the fastener. The peripheral side  36  of the central hub tapers upwardly (preferably a frustoconical surface) to integrally join with an annular raised platform portion  40 . The peripheral portion of the raised platform integrally tapers downwardly to form a circumferential rim  42  which engages the substrate. Surface  34  and rim  42  are generally parallel and have a spacing slightly offset from a co-planar relationship. In some embodiments, the rim  42  is co-planar with the central surface  34  of the recessed hub. In the illustrated embodiment, the plate  10 , rim  42 , raised platform  40  and central hub  30  are generally axially symmetric about a central axis through the fastener opening. The plate may be stamped from metal. Other plate shapes which employ a recessed hub are also possible. 
         [0016]    A vent opening  50  is formed in the tapered recessed wall  36  of the hub. In one embodiment, for a plate having a platform diameter P of 80 mm or 2.66 ins. and a hub surface diameters of 1.16 ins., the diameter of the vent opening  50  is 0.125 ins. and the opening is located at the midpoint of the frustoconical side  36 . The diameter H of the hub is 1.51 ins. and has a depth D of approximately 0.17 ins. In some embodiments more than one such opening may be formed. The opening  50  provides a vent passage which tends to equalize the pressure within the hub and surrounding region during installation and post-installation and throughout the useful life of the installation provided by the roofing plates. 
         [0017]    Roofing plate  10  may be affixed with a heat activated adhesive  44  which is applied to the raised platform  40  of the plate. In typical roof installations, numerous roofing plates are secured to the substrate via a fastener which tightens against the recessed portion. 
         [0018]    With reference to  FIGS. 3 and 4 , a barrier membrane  24  is then installed over the top of the roofing plates  10  and the substrate  20 . The barrier membrane is typically a single-ply moisture resistant or waterproof sheet. The sheet is transported to the roofing structure in roll form and unrolled across the substrate. 
         [0019]    An induction tool (not illustrated) on top of the membrane  24  is brought into the vicinity of the metal plates positioned under the membrane. The induction tool is energized so that magnetically induced eddy currents within the metal plate  10  heat the metal plate to thereby activate the adhesive  44 . The adhesive, which is sandwiched between the membrane  24  and the platform  40  of the plate, is ultimately cooled so that the adhesive sets and bonds the barrier membrane to the plates. In some embodiments, the adhesive may be mixed with metallic particles and the plate may not be metal. 
         [0020]    Because in conventional installations, the barrier membrane essentially hermetically seals across the top of the hub and the bottom surface of the hub is sealingly engaged against the substrate, an air pocket may be typically formed in the hub. Under such conditions, when the prior art plate  11  cools, a seal forms between the underside of the fastener head and the top side of the plate adjacent the hole. A vacuum could be created in the hub thereby forming a depression  27  such as illustrated in  FIG. 5 . 
         [0021]    However, with reference to  FIG. 3  and plate  10 , because of the vent opening  50 , the pressure will rapidly be equalized with the surrounding region and consequently upon cooling and bonding of the plate, the pressure within the hub recess will not be sufficiently different to result in creation of an indentation in the membrane. The membrane will essentially bond in a substantially planar, flat relationship  26  across the entire expanse of the plate (which may-be slightly elevated above the substrate). 
         [0022]    In an installation wherein the induction heat activated process is not employed, the roofing plates are secured against the substrate in a grid-like pattern to anchor the substrate to the decking structure. Solvent based adhesive is then sprayed or otherwise applied across the tops of plates. The barrier membrane is then laid or rolled over the substrate and plates. Any solvent which typically vaporizes off from the adhesive which may become trapped in the recessed hub will be vented via the vent opening  50  to essentially equalize the local pressure and prevent any bubbling effect across the membrane. 
         [0023]    While preferred embodiments of the foregoing have been set forth for purposes of description, the foregoing should not be deemed a limitation. Accordingly, various modifications, adaptations or alternatives may occur to one skilled in the art without departing from the spirit and the scope of the appended claims.