FASTENING SYSTEM

Abstract: In the construction of buildings, multiple superimposed plastic fastening strips (10,12) are employed to affix a building member (8) to a substrate (3). The strips (10,12) are superimposed at least at regions penetrated by mechanical fasteners.

Description: This invention relates to a fastening system useful in building construction. It is well known to use battens in roof construction. Battens are generally metal strips or bars which are used to secure or hold down materials on building roofs. In constructing roofs, one or more flexible cover membranes, such as thermoplastic or elastomeric sheets, are placed over a rigid substrate to form a part of the roof structure. The flexible membranes serve to seal the roof structure against liquid penetration and also may serve to provide an insulating effect. Such membranes are secured in place by use of batten strips or bars which are placed at spaced intervals over the flexible membrane. Headed fasteners, such as screws or nails, are then passed downwardly through the batten strips or pre-punched holes therein and the flexible membranes to secure the battens and membranes to the roof substrate. The batten strips should be of such nature as to permit a pointed mechanical fastener to pass therethrough without destroying the hold-down effectiveness of the batten bar. Under certain conditions wind can uplift the membrane causing it to pull upwardly away causing the batten strip to rip or tear about the fastener with the headed fasteners pulling through the batten strip so as to no longer secure either the batten strip or the membrane to the roof substrate. The batten bars, to be satisfactory, must exhibit high pull-through resistance, i . e ., good tear or split resistance at points where pointed mechanical fasteners penetrate the bars. Batten bars can also be used in accordance with this invention to secure a layer or layers of insulation to a roof substrate or in vertical building walls. They also can be used to secure flashing on buildings and in other fastening applications where strips or bars are employed. For example, "batten strips" can be used as termination bars to secure membranes to the edges of vertical parapet walls to rough structure along the periphery of the roof. Thus, as used herein the term "batten strip" is not limited to roof battens but includes fastening means in building construction applications where strips or bars are useful in fastening building members. Roofing batten bars should not unduly curl, kink or distort when penetrated by a fastener. Metal batten bars made of sheet metal have been used, but such bars are relatively heavy constituting a relatively dead weight on the building roof and can be difficult to penetrate by a threaded mechanical fastener unless pre-drilled openings are provided therein. Metal bars are also known to corrode and diminish the soundness of the roof structure. Aluminum batten bars have also been used, but are more expensive and unless quite thick are subject to curling, kinking or distortion when penetrated by a threaded fastener. Wood battens decay. Plastic batten strips have also been proposed. United States patent No. 4,718,211 discloses batten bars of a particular configuration made of plastic. Likewise, United States patent No. 4,445,306 discloses an elongated fastening bar made of plastic which has a flat batten surface and a convex top surface. The batten strips and fastening bars disclosed in these patents have a thickness at one point of about 1/4 inch (6 mm) and have pre-drilled holes therein to receive fasteners. According to this invention a method of building construction wherein a building member is affixed to a substrate by plastic fastening strip means overlying the building member and mechanical fasteners, penetrating the plastic fastening strip means at intervals throughout its length; is characterised in that the plastic fastening strip means comprise multiple superimposed plastic fastening strips having identical cross-sections at locations where the mechanical fasteners penetrate the fastening strips. Particular examples of methods in accordance with this invention will now be described with reference to the accompanying drawings; in which:- Figure 1 is a fragmentary vertical cross-sectional view of a roof structure in accordance with the invention. Figure 2 is a view similar to Figure 1 illustrating a second embodiment of the invention. Figures 3 through 9 illustrate diagrammatically postulated action of a batten bars employed in accordance with this invention when penetrated by a headed mechanical fastener. Figure 10 is a graph plotting elongation-compression versus load of a single plastic batten strip. Figure 11 is a graph plotting elongation-compression versus load of two superimposed plastic batten strips. Referring to Figure 1, a conventional corrugated metal roof deck 3 is partially shown, over which there is placed a layer of insulating material 5. Covering the insulation is a flexible sheet membrane 8 which can be fabricated of any suitable flexible water-impervious material. Conventional roofing membranes frequently comprise sheets of polyvinyl chloride, chlorosulfonated polyethylene (Hypalon), neoprene, polyisobutylene and ethylene-propylenediene monomer (EPDM). To secure the flexible membrane 8 to the roof substrate in a manner which resists wind uplift, a plurality of superimposed flexible plastic batten strips 10 and 12 are placed at intervals over the membrane. The superimposed batten strips 10 and 12 are penetrated by and fastened to the metal roof deck by headed mechanical fasteners 15. The batten strips 10 and 12 comprise relatively thin strips of plastic. The thickness of the individual batten bars used in accordance with this invention is less than 200 mils (5mm). Typically, the batten strips 10 and 12 each have a thickness of say 20-25 mils (0.5-0.6mm) and are approximately 1 inch (25 mm) in width, although the dimensions can be varied. The batten strips have substantially flat or planar top and bottom surfaces with no longitudinally extending thickened portions or ribs to restrict bending of the strips along a transverse line. The batten strips 10 and 12 can be made from a variety of different corrosion resistant extrudable plastic materials, such as polyvinyl chloride, polyethylene, polypropylene, polycarbonate, nylon and polyesters. A preferred extruded and oriented plastic sheet material from which the batten bars can be cut in desired length and width is described in EP-A-90300108.9. To afford optimum benefits, particularly with respect to preventing the headed fasteners pulling through the battens under strong wind uplift conditions, it is important that the batten strips not be so rigid as to be incapable of bending or flexing in response to forces tending to pull the headed fasteners through the batten. It has been found that a plurality of superimposed thin batten strips afford significantly greater resistance to pull-through than does a single batten strip of the same thickness. For example, it has been found: Pull-through resistance is the force required to cause the batten strip to rip or tear about the fastener with the headed fastener pulling through the batten strip. In practice of the present invention, at least two superimposed batten strips are employed, at least in the area of the fasteners. Figure 1 shows two batten bars 10 and 12 which are co-terminous in length whereas Figure 2 shows another embodiment of the invention in which a multiple layer of batten bars is employed only in the area surrounding the entry of the headed fasteners. A multiple layer of batten bars in accordance with the invention can be formed of unattached separate superimposed batten strips, or a laminate of two or more batten bars can be formed by intimately bonding together two or more batten bars. For example, a plurality of batten strips can be bonded together in superimposed relationship by solvent adhesives, ultrasonic welding, co-extrusion, hot melt adhesives and the like. Due to the unexpected beneficial advantages of the batten system of this invention, the batten strips need not be pre-drilled at specified intervals to receive headed fasteners. This affords greater flexibility in use of the batten bars in building construction, namely that fasteners can be located and spaced as desired. Figures 3 through 9 of the drawings illustrate diagrammatically postulated actions of batten bars employed in accordance with this invention when penetrated by a headed mechanical fastener. Thus, Figures 3 and 4 graphically illustrate that with the use of a plurality of superimposed flexible batten strips, resistance to fastener pull-through is believed to increase because of an increase in the number of edges through which the head of the fastener must pass to pull-out. Thus, as the head of the fastener is pulled downwardly through the superimposed batten strips, bending of the flexible battens occurs with the radius of curvature (R₃) of the lowermost batten 10 being smaller than the radius of the curvature (R₂) of the uppermost batten 12. To compensate for the change in radius upon bending, the lowermost batten strip 10 projects inwardly creating another edge 10A which, along with batten edge 12A, resists pull-through of the headed fastener. Thus, with the multi-ply batten arrangement, the headed fastener meets resistance to pull-through by both edges 10A and 12A. Likewise, it is postulated that the plastic batten strips of the invention, being flexible and bendable unlike rigid materials such as metals or wood, tend to return to their original unbent position as illustrated in Figure 5. Thus, the leading edges 10A and 12A of the batten bars 10 and 12, after being bent downwardly as the fastener penetrates therethrough, tend to return in the direction of the arrows to their previous unbent condition, thereby exerting an upward force against the head of the fastener. Headed fasteners, such as nails or screws, used to secure batten bars to substrate materials generally have a pointed penetrating edge. As can be seen in Figure 6, the flexible multi-ply batten strips used according to this invention are believed to inherently flex or bendably yield to the penetrating point of the fastener rather than abruptly tear as is the case with rigid battens such as metal batten bars. Accordingly, the hole produced in the superimposed batten strips is actually smaller than the external diameter of the penetrating fastener. The flexible plastic batten strips thus exert more clamping force on the fastener, thereby affording greater resistance to back-out of the fastener from the strips. As seen in Figure 7, the superimposed flexible batten strips are thought to bend as the headed fastener 15 penetrates therethrough and the bending edges 10A and 12A follow the contour of the underside of the fastener 15 presenting an increased contact area between the battens and the fastener. Since the pressure required to cause the fasteners to pull through the battens is inversely proportional to the area of contact therebetween, the arrangement of batten strips in accordance with this invention, by providing a greater area of contact, increase the pressure required to cause pull-through or back-out of the fastener. It is believed also from Figure 8 that the multiple layer of batten strips presents greater contractile forces (surface tension) due to a greater number of surfaces 12X, 12Y, 10X and 10Y than is the case with a single batten strip. This again provides greater pull-through resistance to the fastener head during conditions of high wind uplift. Figure 9 illustrates graphically that should one of the superimposed batten strips crack or split, the crack X does not propagate to the next adjacent batten strip due to its own independent surface tension. Figure 10 is a graph showing the elongation-compression/load of a single metal batten strip having a thickness of 0.060 inch (1.5 mm). Figure 11 is a graph showing the elongation-compression/load of two superimposed plastic batten strips each having a thickness of 0.030 inch (0.75 mm). As can be seen, the area under the curve is less for the two-ply batten arrangement indicating greater flexibility than exhibited by the single metal batten strip. The more flexible the batten arrangement, the less tendency to experience fatigue under wind loads.

Claims: A method of building construction wherein a building member (8) is affixed to a substrate (3) by plastic fastening strip means (10,12) overlying the building member (8) and mechanical fasteners (15), penetrating the plastic fastening strip means (10,12) at intervals throughout its length; characterised in that the plastic fastening strip means comprise multiple superimposed plastic fastening strips (10,12) having identical cross-sections at locations where the mechanical fasteners (15) penetrate the fastening strips (10,12). A method in accordance with claim 1 wherein the fastening strips (10,12) have substantially flat planar top and bottom surfaces. A method in accordance with claim 1 or 2, wherein a layer of insulating material (5) is the building member affixed to the substrate (3). A method in accordance with claim 1 or 2, wherein flashing is the building member affixed to a substrate (3). A method in accordance with any preceding claim, wherein the substrate is a roof or a wall. A method in accordance with claim 1 or 2, in which the building construction is a roof construction wherein a flexible roof membrane (8) is affixed to a substrate (3) by means of flexible spaced roof strips (10,12). A method in accordance with any one of the preceding claims, wherein the fastening strips (10,12) comprise strips of an extruded and oriented composition of from about 75 to 96% by weight of polyethylene terephthalate, from about 3 to 20% of polypropylene and from 1 to 5% of a carboxylated polyolefin. A method in accordance with any preceding claim, wherein the thickness of the individual plastic fastening strips is less than 200 mils (5 mm). A method in accordance with claim 8, wherein the thickness of the individual plastic fastening strips is substantially 25 mils (0.6 mm). A method in accordance with claim 1, wherein the fastening strips (10,12) comprise strips of an extruded and oriented composition of from about 80 to 97% by weight of polyethylene terephthalate, from about 3 to 20% of polypropylene and from 1 to 5% of a carboxylated polyolefin.

Inventors: HARRINGTON JENKINS, ROBERT, HASAN, SYED RIAZ-UI, KISH, FREDERICK ANTHONY, RATHGEBER, JUERGEN OSKAR, Rathgeber, Jürgen Oskar
Applicants: ILLINOIS TOOL WORKS INC.
Application year: 1990
Main classification: E04D3
IPC codes: E04D3, F16B43, E04D5