EP0104810A2

EP0104810A2 - Flat roof with cover and hold down devices

Info

Publication number: EP0104810A2
Application number: EP83305193A
Authority: EP
Inventors: Julian H. Otten
Original assignee: Uniroyal Inc
Current assignee: Uniroyal Inc
Priority date: 1982-09-28
Filing date: 1983-09-07
Publication date: 1984-04-04
Also published as: ES284418Y; BR8305219A; NO833513L; JPS5991258A; ZA836651B; EP0104810A3; ES284418U

Abstract

A loosely laid water-proof membrane of elastomeric material (11) covering a flat roof is combined with a series of hold-down devices (14) for securing the membrane to the roof deck (12) against wind-generated uplift forces. Each hold-down device (16) comprises a disc (17) having a domed, downwardly concave, middle portion (17a) and a surrounding, generally flat, transverse peripheral portion (17b) the radial width of which is equal to between about 25% and 50% of the radius of the disc as a whole. The discs, with their concavities facing the membrane, are arranged on the latter at predetermined spacings, being fixed in place by metallic fasteners (18) driven through the domed portions and the membrane deeply into the roof deck. The concavity of each disc is filled with a sealant (20), so that as each disc is pressed down upon tightening of the associated fastener, the sealant is pressed down against the membrane as well as inwardly against the fastener and outwardly against the peripheral portion of the disc. An elastomeric flat ring gasket (19) may also be located between each disc's peripheral portion and the underlying membrane.

Description

This invention relates to flat roofs, and in particular to a roof of this class which includes a water-proof elastomeric sheet or membrane laid loosely flat over a roof deck and secured in place by means of a multiplicity of hold-down devices.
Roofing installations utilizing water-proof elastomeric membranes on flat roofs are known in the art. The term "flat roof" is herein used in its broadest sense, to designate any roof which is perfectly horizontal as well as any roof having a relatively gentle slope or pitch or a dome shape of relatively limited curvature. In any such roof, a prime consideration is that, in addition to being watertight, the installation must be capable of withstanding adverse weather conditions and especially high winds which exert substantial uplift forces and tend to raise and tear the roofing membrane away from the underlying roof deck. To this end, a number of different ways for securing the membrane in place have been heretofore proposed. Among these have been the use of an adhesive to ad- heringly secure the membrane either to the underlying roof deck or to a layer of insulation disposed over such roof deck or (if the insulation does not accept an adhesive) to a series of underlying blocks of a suitable adhesive-accepting material such as fiber board, plywood and the like disposed at various points over the insulation and nailed or screwed to the roof deck. Another arrangement which has been suggested is to lay the membrane loosely over the roof deck and insulation and, apart from securing the membrane in place by means of nails along the perimeter of the roof, to load the membrane with a suitable ballast of stones or the like. Yet another approach which has been suggested is to lay the membrane loosely over the roof deck and insulation and then to secure it in place not by ballast but by means of elongated fastening bars arranged over the membrane and secured to the roof deck by means of fasteners such as screws or bolts driven through the bars and the underlying membrane down into the roof deck.
Although each of these known types of installations has a number of favorable features, each of them is also subject to one or more of a number of drawbacks and disadvantages. Thus, the application of an adhesive to the membrane and/or to its support prior to the laying down of the membrane is in and of itself a messy operation and quite time-consuming and is rendered even more so, as well as expensive and cumbersome, where the requisite adhesive-acceptor blocks must first be installed and then individually coated with the adhesive. In non-adhesive installations where stones are used as ballast, the disposition thereof on the roof is obviously also a time-consuming and laborious task. Moreover, with such a ballast the risk always exists that during adverse weather conditions characterized by high winds some of the ballast may itself be displaced and hurled about, thereby reducing its effectiveness as a hold-down device for the roofing membrane and possibly even causing injuries to persons or property. In non-adhesive installations where screwed-down fastening bars are used, these bars are usually quite long, on the order of about 6 feet (182.88 cm; 1.83 m) to 8 feet (243.84 cm; 2.44 m), and thus are not only heavy but also difficult to manipulate and position accurately. They also require correspondingly long strips of sealing material to be disposed between their undersides and the top surface of the underlying membrane, which requires yet additional expenditures of time, labor and money. Still further, by virtue of the fact that such fastening bars are of necessity fairly thick, when the requisite number of sets of these bars (with the bars of each set in end to end alignment with each other) are installed in place at their designated locations across a roof, they effectively constitute a series of dams which will prevent water from running off freely over the roof to the drains and will cause water to accumulate on the roof, with the attendant adverse consequences that such an accumulation can lead to.
The principal objective of the present invention, therefore, is to provide a flat roof installation which utilizes, in combination with a sheet or membrane that is made of a suitable elastomeric material such as EPDM (ethylene propylene diene monomer) rubber, PVC (polyvinyl chloride) or chlorinated PVC and is loosely laid down onto a roof deck or an associated insulation layer, a plurality of novel hold-down devices which are less expensive to manufacture than the known fastening bars and easier to manipulate as well, and which can be installed with less labor, at less cost and at considerably greater speeds than such bars. A membrane-covered flat roof according to the present invention thus avoids the hereinbefore mentioned drawbacks and disadvantages of the known roofing installations, in that it can be completed more rapidly and with less effort and at less cost per unit area than any of such known installations.
More particularly, the present invention provides, for use in a flat roof installation in which a water-impervious sheet or membrane of elastomeric material is loosely laid flat over a roof deck, a plurality of hold-down devices to secure the membrane to the roof deck, such hold-down devices including membrane-pressing members to be disposed on the membrane and .screw- or bolt-like fasteners to be driven through the members and the membrane down into the roof deck for gripping engagement therewith. In accordance with the present invention, each of the membrane-pressing members comprises a disc which has a domed, downwardly concave, middle portion and a contiguous, surrounding, generally flat, transverse peripheral portion the width of which radially of the disc is equal to between about 25% and about 50% of the radius of the disc as a whole. The shanks of the respective fasteners extend through the middle portions of the associated discs down into the roof deck, and the concave middle portion of each disc is filled with a sealant compatible with the elastomeric material of the membrane. Upon affixation of such a disc by its associated fastener to a roof deck, the sealant confined in the concavity of the disc is pressed into water-tight relation not only against the underlying membrane but both radially inwardly against the fastener and radially outwardly against (and to a certain extent possibly even under) the inner edge region of the peripheral portion of the disc.
The provision of the domed middle portion of the disc, it will be understood, serves a dual function. On the one hand its underside concavity provides the space needed to accommodate the sealant. On the other it enhances the resistance of the disc to flexure and ensures that when the fastener is tightened down, the edge region of the disc does not rise up off the membrane (as it would if the disc were completely flat). Preferably, the maximum height of the domed portion (or alternatively the maximum depth of its concavity) with respect to the plane of the peripheral portion is equal to between about 15% and about 25% of the radius of the domed portion in the plane of the peripheral portion.
In a refinement of the invention, the hold-down devices may (and in the case of devices utilizing metal discs should) include an elastomeric gasket interposed between the peripheral portion of each disc and the underlying region of the membrane, the gasket preferably being in the form of a flat ring having inner and outer diameters approximately equal to those of the peripheral portion of the disc. It is contemplated that the gasket will be installed while the elastomeric material of which it is made is still in an uncured (or only partially cured) state, so that the gasket material will ultimately become cured in situ by the heat of the sun beating down on the roof and will thereby be vulcanized to either or both of the membrane and the disc. Such a gasket, which serves also to prevent water from penetrating in under the disc, leads to yet additional advantages, in that it serves to distribute the pressure of the peripheral disc portion over the underlying region of the membrane and, especially in the case of a metal disc, to prevent heat transfer from the disc to the membrane.
In accordance with the present invention, although the precise configuration of the discs may be polygonal, elliptical or otherwise shaped as desired, it is preferred to use discs which are circular. Moreover, although it is contemplated that discs as small as about 6 inches (15.24 cm) in diameter and as large as about 13 inches (33.02 cm) in diameter can be used (as presently viewed, smaller discs would probably be ineffective and larger discs uneconomical), it is preferred to use discs which have a diameter in the range of from about 9 inches (22.86 cm) to about 12 inches (30.48 cm). Of these, the discs at the lower end of the preferred size range have a peripheral portion with a radial width of about 1.25 inches (3.17 cm), while the discs at the upper end of the size range have a peripheral portion with a radial width of about 2.0 inches (5.08 cm), and in either case the maximum height of the domed middle portion of the disc (or alternatively the maximum depth of the concavity) with respect to the plane of the peripheral portion of the disc is between about 0.5 inch (1.27 cm) and about 0.75 inch (1.91 cm). For a roofing installation using discs of these preferred sizes, it is contemplated that discs at the lower end of the size range will ordinarily be arranged at center-to-center spacings of about 4 feet (121.92 cm; 1.22 m), and that discs at the upper end of the size range will ordinarily be arranged at center-to-center spacings of about 6 feet (182.88 cm; 1.83 m). It will be understood, in this regard, that disc size actually is not the only variable that could be taken into consideration in determining the requisite disc spacing in a particular installation. A second variable that might be factored into the determination is the thickness of the membrane, with a thicker membrane enabling a greater disc spacing to be used for a given disc size than a thinner membrane and vice versa. In the selection of the above-mentioned disc spacings according to the present invention, however, this second variable has been ignored.
In accordance with yet another aspect of the present invention, it is preferred to make the discs of metal, such as galvanized sheet iron, stainless steel, aluminum, and the like, such discs being stamped from starting sheet metal with a thickness between about 22 gauge (0.03125 inch; 0.079 cm) and 26 gauge (0.0187 inch; 0.048 cm). Alternatively, the discs may also be made of synthetic plastics materials such as polycarbonate, ABS, AES, and the like having suitable weathering resistance and strength (for example, a material which it is believed would be highly suitable is currently available commercially under the registered trademark ROVEL), although such discs would probably have to be somewhat thicker than comparable metal discs.
The foregoing and other objects, characteristics and advantages of the present invention will be more clearly understood from the following detailed description of a preferred embodiment thereof when read in conjunction with the accompanying drawings, in which:

Fig. 1 is a fragmentary, partly sectional, perspective illustration of a roofing installation in accordance with the present invention;
Fig. 2 is a top plan view of the structure shown in Fig. 1;
Fig. 3 is a sectional view taken along the line III-III in Fig. 2;
Fig. 4 is a sectional view similar to Fig. 3 but shows the hold-down device secured to the roof deck by means of a different type of fastener;
Fig. 5 is a fragmentary, partly sectional, exploded view, in perspective, of one hold-down device according to the present invention and a membrane-covered roof such as are shown in Figs. 1 to 3; and
Fig. 6 is a transverse section through the structure shown in Fig. 5 but illustrates the same in a more compacted state with the fastener of the hold-down device partially inserted into the roof.

Referring now to the drawings in greater detail, a flat roof 10 having a water-resistant cover 11, constituted by a sheet or membrane of elastomeric material, laid flat over a structural roof deck 12 and an interposed layer of insulation 13, is shown in Fig. 1. The roof deck may be made of any material usually used in such structures, for example, metal, concrete, gypsum, or wood, but the nature of this material has no significance with respect to the present invention except insofar as it dictates the nature of the fasteners to be used in connection with the hold-down devices for the membrane, as more fully described hereinafter. Correspondingly, the nature of the insulation, which may be fibrous, foam, or the like, is of no significance to the present invention; in fact, the principles of the present invention are equally applicable to a roof having no insulation incorporated therein. It will further be understood that the membrane 11, which extends over the entire expanse of the roof deck 12 and is initially laid down loosely, i. e. without being adhered to the underlying insulation (or roof deck, as the case may be), may, in the case of a large roof area, consist of a plurality of sheets laid down side by side with a predetermined degree of overlap and possibly also seamed to each other. Along its perimeter the membrane is secured by nails or like fasteners (not shown) to wooden anchor bars 14, and the junctures of the roof with the building walls are additionally waterproofed by means of flashing 15 (not further illustrated or described in detail herein), as is usual in such installations.
Over the remainder of the roof expanse, the membrane 11 is secured to the roof deck by means of a plurality of hold-down devices 16. In the preferred embodiment of the invention, as shown in Figs. 1 to 3, each hold-down device 16 comprises a membrane-pressing member in the form of a circular disc 17 positioned on the membrane and having a domed, medially apertured, downwardly concave, middle portion 17a and a contiguous, surrounding, generally flat or planar, transverse peripheral portion 17b, and a screw- or bolt-like fastener 18 which extends from the middle portion of the disc down into the roof deck 12, an elastomeric gasket 19 being interposed between the peripheral portion 17b and the underlying region of the membrane 11, and a quantity of sealant 20 being confined in and filling the concavity or underside of the domed portion 17a. As previously mentioned, the width r of the flat peripheral portion 17b of the disc 17 (see Fig. 3), measured radially of the latter, is equal to between about 25% and 50% of the radius R of the disc as a whole, while the height H of the domed middle portion 17a of the disc (see Fig. 6) above the plane of the peripheral portion is equal to between about 15% and 25% of the radius R' of the domed portion in the plane of the disc. In this connection it should be noted that in its starting state the peripheral portion 17b of the disc preferably is not truly located in a plane perpendicular to the axis of the disc; rather, the outer edge of the peripheral portion lies in a plane which is slightly, on the order of magnitude of about 0.025 inch (0.064 cm), lower with respect to the top of the domed portion than the plane in which the inner edge of the peripheral portion lies. This arrangement is intended to ensure that when the fastener 18 is tightened down, the disc will flex sufficiently to bring the peripheral portion into a fully planar state so as to bear fully and evenly on the gasket 19.
Insofar as the fastener is concerned, it will be clear to those skilled in the art that in the case of a wooden roof deck the fastener 18 would be a wood screw, in the case of a metallic roof deck the fastener would be a self-tapping screw, and in the case of a concrete roof deck the fastener would be a screw with a special thread for concrete. In the case of a gypsum or plaster roof deck 12' (see Fig. 4), of course, in which a screw will not hold, the fastener would be in the nature of a toggle bolt 18'. In any event, it is contemplated that the fastener will be a 3/8 inch (0.953 cm) diameter stainless steel screw or bolt having the capacity for withstanding at least 900 lbs. of tensile stress, and that the initial loading on the fastener should not exceed about 360 lbs. in the case of a disc at the lower end of the preferred size range and about 600 lbs. in the case of a disc at the upper end of the preferred size range.
In installing a series of hold-down devices 16 according to the present invention after the membrane 11 has been laid out onto the roof deck (see Figs. 5 and 6), it is necessary merely to deposit the discs 17, each with an associated gasket 19, in the prescribed locations on the roof, with the centers of adjacent discs being spaced from each other a distance D that will depend on the sizes of the discs being used, and then simply to drive the fasteners 18, preferably with the aid of a mechanized screw driver, down through the apertures 17c in the domed portions 17a of the discs, through the membrane 11 and the insulation 13, and into the roof deck 12. Before the fasteners are driven in, a neoprene washer 21 is fitted onto the shank of each fastener above the domed portion of the associated disc. Quite obviously, the installation of the hold-down devices 16 can be carried out very easily and rapidly by even relatively unskilled labor, since the discs are relatively small and light in weight, can be transported in very compact and easy to handle packaging, and can be manipulated with very little effort, and there is only one fastener to be applied per disc. The length of the fasteners must, of course, be sufficient to enable them to be driven sufficiently deeply into the structural roof deck 12 (or through it in the case of the fasteners 18') that they will be securely fastened to the roof deck and hold the discs 17 down against any reasonable upward force that may be exerted thereagainst. In this connection it might also be noted that the sealant 20, which is a tacky non-liquid material, can be deposited in any suitable manner into the domed portions of the discs before the same are deposited onto the roof. By the same token, although the gaskets 19 can be individually laid onto the membrane 11 before the discs 17 are placed thereover with the peripheral portions 17b superposed onto the gaskets, it would also be feasible, especially in view of the fact that the gaskets will initially be of uncured elastomeric material and hence rather tacky and capable of adhering to the material of the discs, to adhere each gasket directly to the underside of the peripheral portion 17b of its associated disc and then to deposit the entire assembly of disc, sealant and gasket in place onto the roof. Ultimately, after the discs have been laid in place and the fasteners have been extended into (or through) the roof deck and tightened to the desired degree, the sealant 20 under each disc will be tightly pressed not only radially inwardly against the shank of the associated fastener but also radially outwardly against the inner edge of the associated gasket 19, while escape of sealant upwardly through the aperture 17c is inhibited by the presence of the washer 21. Entry of water into the spaces under the discs thus is effectively inhibited. Moreover, when, after some passage of time and exposure to the heat of the sun, the gaskets 19 will have become fully cured, they will effectively be vulcanized to the underside of the peripheral disc portions 17b as well as to the upper surface of the underlying regions of the membrane 11, further enhancing the water tightness of the seals.
As will be reaidly apparent from Figs. 1 and 2, with the hold-down devices 16 installed in rows and tiers as shown, the relatively wide spacings therebetween herein envisioned ensure that dams such as are characteristic of the heretofore known fastening bars for a roof membrane will not be formed, and water will thus be able to run off freely into the drains. Moreover, with the discs situated as they are and bearing with flat surfaces on the membrane via the gaskets, not only will there be very little uplift of the membrane in the open areas between the discs but the discs, either during or after the tightening of the fasteners, will not be able to cut into the membrane and destroy its water impermeability. In this regard it should be noted that the term "flat" as herein applied to the peripheral portions of the membrane-pressing discs is to be interpreted not in its strict sense but somewhat more broadly; thus, a peripheral disc portion having a slight degree of curvature or arcuation or terminating in an upwardly curved lip formation at its outer edge is also deemed to fall within the meaning of the term "flat" as used in this context.
In the detailed description of the present invention so far, the membrane 11 has been identified as a sheet of non-porous elastomeric material. Such a membrane, as will be readily appreciated, has substantially no intrinsic insulating value. It is for this reason that it has been described as being laid onto a layer 13 of insulating material. It will be understood, of course, that in a case where insulation is not a requirement, such a membrane could be laid directly onto a structural roof deck without any intervening layer of insulation. However, it is also contemplated by the present invention that in lieu of a sheet or membrane of non-porous elastomeric material a membrane made of expanded or porous elastomeric material may be used. Such a membrane could, if desired, be likewise laid directly onto a structural roof deck devoid of any layer of insulation. This would be acceptable even in a situation where insulation is desired, because the expanded elastomeric material would have an adequate intrinsic insulating capacity (commonly referred to as "R factor" or "R value"); this capacity must, however, then be sufficient to render the use of extraneous insulation unnecessary. In such a case, of course, the porosity of the membrane would have to be of the closed-cell type to ensure that water could not seep or filter through the membrane.
It will be understood that the foregoing description of the present invention is for purposes of illustration only, and that the various structural and operational features herein disclosed are susceptible to a number of modifications and changes none of which entails any departure from the spirit and scope of the present invention as defined in the hereto appended claims.

Claims

1. A hold-down device for use in connection with a flexible elastomeric membrane covering a flat roof deck, comprising, in combination:

(a) a disc having a domed, downwardly concave, middle portion and a contiguous, surrounding, substantially flat, transverse peripheral portion, the width of said peripheral portion radially of said disc being equal to between about 25% and about 50% of the radius of said disc as a whole, and said middle portion on its underside concavity being adapted to receive a quantity of a sealant, and

(b) a screw or bolt-like fastener of a length' sufficient, when said disc is laid onto a membrane on a roof deck, to extend from said middle portion of said disc grippingly into the roof deck.

2. A hold-down device as claimed in claim 1, wherein the height of said domed middle portion of said each disc .above the plane of said peripheral portion is, at the highest part of said middle portion, equal to between about 15% and about 25% of the radius of said middle portion in the plane of said peripheral portion.

3. A hold-down device as claimed in claim 1 or 2, wherein said disc is made of metal, or of plastics material.

4. A hold-down device as claimed in any one of the preceding claims wherein said disc is provided with an aperture in said middle portion adapted to accommodate the shank of said screw- or bolt-like fastener.

5. A hold-down device as claimed in any one of the preceding claims, wherein said peripheral portion has its outer edge located slightly lower, with respect to said middle portion, than its inner edge.

6. A flat roof installation wherein a water-impervious sheet or membrane of elastomeric material is loosely laid flat on a roof deck, and a plurality of hold-down devices secure the membrane to the roof deck, the said hold-down devices including membrane-pressing members disposed on the membrane and screw- or bolt-like fasteners extending through said members and the membrane down into the roof deck; characterised in that:

(a) each of said membrane-pressing members comprises a disc having a domed, downwardly concave, middle portion and a contiguous, surrounding, substantially flat, transverse peripheral portion the width of which radially of said disc is equal to between about 25% and about 50% of the radius of said disc as a whole,

(b) a respective screw- or bolt-like fastener extends through said middle portion of each disc down into the roof deck and is tightened thereto and grippingly engaged therewith for securing said discs and thereby said membrane to said roof deck,

(c) the concave underside of said middle portion of each disc is filled with a sealant compatible with the elastomeric material of said membrane, said sealant under each disc being pressed against said membrane, the respective fastener and the surrounding inner edge of the peripheral portion of that disc, and

(d) said discs are distributed over the expanse of said membrane on said roof deck at predetermined spacings between each two adjacent discs in accordance with the sizes of said discs and the amount of hold-down force to be provided.

7. A flat roof installation as claimed in claim 6 wherein the height of said middle portion of each disc above the plane of the associated peripheral portion is, at the highest part of that middle portion, equal to between about 15% and about 25% of the radius of said middle portion in the plane of said peripheral portion.

8. A flat roof installation as claimed in claim 6 or 7, wherein each disc is made of metal or of plastics material. _N

9. A flat roof installation as claimed in any one of claims 6 to 8, wherein said sheet or membrane is made of either a non-porous or a closed-cell expanded elastomeric material.

10. A flat roof installation as claimed in any one of claims 6 to 9, wherein a respective gasket of elastomeric material is interposed between said peripheral portion of each disc and the underlying region of said membrane.

11. A flat roof installation as claimed in claim 10, wherein the elastomeric material of said gaskets when the same are initially installed is either wholly or partially uncured and thereafter cures in situ to become bonded to said discs and said membrane.

12. A flat roof installation as claimed in any one of claims 6 to 11, wherein said sealant is a urethane-based sealant.

13. A flat roof installation as claimed in any one of claims 6 to 12, wherein each disc is provided with an aperture in said middle portion adapted to accommodate the shank of the associated screw- or bolt-like fastener.

14. A flat roof installation as claimed in any one of claims 6 to 13, wherein said peripheral portion of each disc has its outer edge located slightly lower, with respect to said middle portion of that disc, than said inner edge of the same disc.