Base sheet for roofing assembly

Abstract: An improved base sheet (2) for a roofing assembly wherein the base sheet is perforated with a plurality of apertures (3) characterized by non-cylindrical cutouts in the shape of a closed figure or a polygon having at least two sides or boundaries of unequal length which aperture configuration permits strong attachment of the sheet to a substrate without the aid of auxiliary attachment means and without weakening of the base sheet structure.

Description: BACKGROUND OF THE INVENTION A persistent problem associated with roofing assemblies is wind uplift resulting in separation of a base sheet from a substrate such as the roof deck or a deck surfaced with an insulation layer. In areas of relatively higher wind velocity, has been difficult to achieve the wind uplift resistance required by codes or building designers without using cost-prohibitive construction techniques. In the case of nailable decks, it is often necessary to fasten the roof deck to the surfacing layers at short intervals thus increasing the time and expense of installation. On the other hand, several non-nailable decks have not been able to provide adequate resistance to wind uplift. Accordingly, several alternative methods purporting to avoid attachment failure have been suggested. Foremost is the use in the assembly of a uniformly perforated base sheet having circular perforations which permit flow of an adhesive through the apertures so as to adhere the sheet to the substrate. The adhesive can be applied by hot mopping over the perforated base sheet surface thus permitting follow-through and attachment of the sheet to the deck or an underlying insulation layer in the perforated area. While this method is cost and time saving in that it eliminates the need for securing devices at critical intervals, it has not been found to be effective in environments subject to relatively higher wind velocities since the base sheets currently available do not provide sufficient adhesive force and sheet integrity to resist strong wind uplift forces. In the case of a conventionally perforated base sheet, merely widening the circular perforations or increasing their number is not a viable solution since either approach decreases the strength of the sheet. DE-A-3231372 discloses a sealing sheet comprising a layer of punched foil or film which can be of easily fusible plastic or of a paper or plastic sheet, having voids through which flow of adhesive enables bonding to a substrate. Although the system must be strong enough so that the wind cannot separate the different layers, no mention is made of maximising bonding whilst at the same time maximising wind resistance. Accordingly it is an object of the present invention to provide a roof deck assembly which has superior resistance to wind uplift forces and other damage caused by weathering, without reducing the strength of the sheet. Another object of this invention is to provide a new and improved base sheet for roofing systems having high wind uplift resistance which is economical to produce and install. The objects of the present invention are achieved according to the features of claim 1. Further embodiments of the invention are defined in the dependent claims. This is achieved by providing a base sheet having apertures altered to achieve greater adhesive follow-through per internal area of the aperture. The apertures are non-cylindrical cutouts in the shape of a closed figure or polygon having at least two sides or boundaries of unequal length. For the purposes of this invention, the following terms are defined. An "aperture" allows passage of adhesive. A "void" is a non-cylindrical closed figure or a polygon having at least two sides or boundaries of unequal length, e.g. an oval having a major and minor axis of unequal length and other shapes disclosed herein. A void may be laminar, being a cut-out in the continuum of the base sheet, or three dimensional and include a "void area" in the undercoating below the cut-out. The cut-out and void area need not be of the same shape. The "substrate" is the layer, sheet or deck immediately below the base sheet. The "base sheet" is the sheet suitably apertured to permit attachment to the substrate by having cut-outs in its continuum which are, or form part of, the voids. The "insulation" is a rigid or semi-rigid material which retards heat flow. The "membrane" is a waterproof layer of modified bitumen sheet, roofing felt, asphalt, adhesive, etc. The "roofing assembly" includes the base sheet and all layers or sheets above and below the base sheet. The auxiliary sheet or sheets include one or more layers of roofing felt, modified bitumen, insulation, a capping sheet, a traffic surfacing sheet and the like which are positioned above the base sheet. In a base sheet, an aperture having a circular shape offers the smallest peripheral dimension for a given enclosed area; hence the least area of potential adhesive penetration into a substrate in the region surrounding the aperture site. It is now discovered that by lengthening the perimeter of the aperture relative to its enclosed area, and in fact by any deviation from the configuration of an equilateral, equiangular polygon, one is able to increase the net area of adhesive interaction between the sheet and the substrate and additionally to extend the area for adhesive penetration into the substrate in the region surrounding the extended perimeter of the aperture. This innovation achieves unexpectedly stronger attachment between the substrate and the overlying assembly without concomitant weakening of the base sheet structure normally associated with widening the perforations of the prior art. Thus, the fundamental principal of this invention is that the greater the deviation of instant apertures from a cylindrical shape or the shape of a circle, equilateral triangle or a square, the larger the potential attachment area and the greater the resistance to wind uplift. In the following disclosure it will become apparent that the degree of attachment strength varies directly with the perimeter of the present non-cylindrical apertures and that the resistance to wind uplift forces can be increased at least two fold over circular perforations of the prior art which circumscribe the same internal area. Among the many aperture shapes and configurations contemplated for this invention, there is included ovate, lyrate, channel or slot, T-shape, I-shape, L-shape, Y-shape, star and bladder shapes as being particularly beneficial for increasing adhesion of the base sheet to an underlying substrate. In general, the number of apertures in the base sheet of the present invention is about the same or somewhat less than that conventionally employed and the periphery of apertures herein disclosed is between 7.5 and 15 cm (about 3 and about 6 inches). Instant apertures have a length of from 0.63 to 15 cm (about ¼ to 3 inches) and a width at least 0.37 (⅛ inch) less than the length, e.g. a width of from 0.37 to 0.8 cm (about ⅛ to about 1 / 3 inch) for ovate or slotted shapes. The preferred apertures of this invention are those having rounded edge portions such as for example apertures in the shapes of an oval, bladder, etc. The preferred non-cylindrical apertures of this invention can be defined by the formula: R/R' = >2 where R is radius (a) of a circle circumscribed around a given aperture of the present invention and R' is radius (a') of a circle constructed to have the same internal area of said aperture. The apertures are uniformly spaced on the base sheet and are usuallv inset from the marginal edges of the sheet by from 2.5 to 15 cm (about 1 to about 6 inches) depending in part on the size of the sheet and the type of roofing assembly, e.g. the degree of flexibility, thickness etc. Suffice it to state that they are inset by a margin sufficient to provide good manufacturability and effective adhesion in the construction of the roofing assembly. The apertures are conveniently spaced one from the other by a distance effective to adhere the undersurface of the base sheet to the substrate, e.g. an aperture offset of from 7.5 to 17.8 cm (about 3 to about 7 inches) depending on the size of the sheet commensurate with the shape and size of the aperture; although, when desired, the aperture spacing near the edges of the sheet can be significantly less than that employed in the central portion. Most often, uniform spacing throughout the sheet is preferred. Although any conventional pattern of aperture deployment can be used, it is found that a chevron pattern, an embodiment of which is illustrated in Figure III of the drawings, provides excellent resistance to wind uplift as well as good manufacturability. The apertured base sheet of the present invention can be laid over a conventional roof deck such as one composed of gypsum, cement, wood or metal such as steel in a vented or non-vented system. When desired, a rigid or semi-rigid thermal insulation board of 0.63 to 61 cm (0.25 to 24 inch), preferably 1.2 to 25 cm (0.5 to 10 inch), thickness containing Perlite, polyisocyanurate, polystyrene, polyurethane, fiber board, foam glass and combinations thereof, can be employed between the deck and the base sheet; although insulation can be omitted by option. Alternatively, the insulation layer can be applied in a protected membrane arrangement (e.g. IRMA®) above the base sheet. The width of the base sheet is generally about 30.5, 61, 91.5, 100 or 122 cm (12, 24, 36, 40 or 48 inches) and the sheet is typically supplied in rolls. Although the thickness of the base sheet can vary from about 1 to about 5 mm; a thickness of from about 1.5 to about 3 mm is preferred. The base sheet is composed of an organic or inorganic material, saturated or coated with oxidized or non-oxidized asphalt, a polymer modified asphalt or coal tar, e.g. modified with a polyolefin, SBS, rubber and the like. The top and under surfaces of the present base sheet are coated with an asphaltic material and granules can be embedded in the under surface asphaltic layer. To prevent sticking between layers when shipped in rolls, the base sheet is usually contacted with a release agent, such as sand, talc or a soap. Also, the surface can be covered with a ventilating material, as in granule surfacing or it can be channeled to provide release of accumulated vapor after installation and during the life of the roofing assembly. The apertures of the base sheet can be formed by cut outs in any of the shapes covered herein or they can be formed to include void areas in its undercoating below surface perforations. The sheet can be subjected to surface hot mopping with an adhesive melt. Also the base sheet can be installed and simultaneously bonded to the substrate and other layers of the roofing assembly with adhesives described below. It is also within the scope of this invention to avoid hot mopping by the use of Ruberoid Modified Bitumen Adhesive or other solvent cutback asphaltic adhesive. A torching technique which fuses a torch grade roofing sheet to a substrate through the apertures can also be employed. Conventional types of bonding agent can be employed for attaching the base sheet to the substrate; these include bitumen, such as asphalts and coal tar pitch having softening points of from about 37°C (100°F) to about 500°F. The bonding material can contain from 0 to about 75 wt. % mineral stabilizer, such as that derived from limestone, stone dust, sand or other fine or granulated mineral particles. Before application, the bonding agent is heated to a flowable condition. The base sheets can be laid as panels abutted in side-by-side or overlapping relationship prior to the hot mopping operation or they may be laid and mopped in a single operation, e.g. with a felt laying apparatus. As indicated above, it is also within the scope of this invention to avoid hot mopping in favor of a torching technique which fuses through the base sheet to the substrate. The final roofing assembly includes layers above the base sheet which are conventionally employed in a roof assembly. These additional layers include saturated felt, polymer modified roofing materials, optionally an insulation membrane and other layers desired in the assembly. Generally, the roofing assembly is capped with a weather resistant surface layer. Having generally described the present invention, reference is now had to the accompanying drawings which illustrate certain aspects and preferred embodiments but which are not to be construed as limiting to the scope of the invention as defined in the appended claims. DESCRIPTION OF THE DRAWINGS FIGURE I is a perspective view of base sheet 2 uniformly apertured at sites 3 indicated by X . FIGURE II illustrates preferred shapes of apertures for base sheet 2 in which a through d represent apertures through the base sheet where the cutouts are shown in solid line and where the granulated undercoating of the sheet is absent it the void areas, the edges of which are indicated by dotted line. Apertures e through o indicate other cutout configurations for the apertures in base sheet 2. FIGURE III shows an alternate pattern of aperture deployment on a portion of base hseet 2 employing a chevron placement of slot-like voids. This embodiment employs a 7.5 cm (3 inch) grid (10) and slots (12) of 5 cm (2 inch) length and 1.7 cm (0.5 inch) width having centers offset by about 11 cm (4 inches). Of course it will be understood that other lengths and thicknesses as well as other cutout shapes can be employed for the purposes of this invention. FIGURE IV is a side plan view of an installed and attached base sheet of a roofing assembly 8 including roof deck 5, insulation board 4, base sheet 2 having granules 6 on its undersurface and adhesive layer 7 which permeates apertures 3 of sheet 2 and the surrounding surface areas of insulation layer 4. As indicated above the final assembly optionally includes one or more conventional insulation and/or weather resistant layers over adhesive layer 7; however, the novelty of this invention does not reside in such modifications except in combination with the present base sheet having altered aperture configurations. COMPARATIVE EXAMPLE A A plurality of 61 x 61 cm (24 x 24 inch) non-perforated base sheets, composed of a fiberglass nonwoven core saturated with filled, oxidized asphalt were modified by having 0.47 cm (3/16 inch) wide by 7.5 cm (2.5 inch) long channels on the undersurface of each sheet at 12 cm (4.5 inch) offsets. The area of adhesive penetration through the non-perforated sheet was essentially zero. The internal area of each channel was approximately 3 cm 2 (0.47 square inches) and the perimeter was approximately 13.7 cm (5.4 inches). The base sheets were adhered to a sheet of 1.9 cm (¾ inch) thick plywood by applying a thin layer of BUR mopping asphalt at its equiviscous temperature over the plywood, laying the base sheets in abutment over the mopped asphalt. A similarly thin layer of viscous mopping asphalt was then applied over the base sheet surface and, while hot, another similar piece of plywood was laid over the top of the base sheet assembly. The final assembly was allowed to cool for 3 days, after which a force of 3250 kg/m 2 (665 lbs/ft 2 ), applied in the direction normal to the plane of the sheets, was applied. The assembly failed at a force of 730 kg/m 2 (150 lbs/ft 2 ) which corresponds to 3250 kg/m 2 (665 lbs/ft 2 ) after correction for the weight of the test apparatus. COMPARATIVE EXAMPLE B The assembly in Example A is repeated, except that the base sheets were perforated with conventional 1.6 cm (⅝ inch) circular holes on 7.5 cm (3 inch) centers, and was mopped to a substrate of 2.85 cm (1⅛ inch) thick polyisocyanurate board. The internal area for each aperture is about 1.9 cm 2 (0.3 square inches), and the perimeter of each was approximately 5 cm (2 inches). After cooling, this assembly showed an uplift resistance of only about 3 kN (665 pounds), which corrects to about 730 kg/m 2 (150 lbs/ft 2 ). EXAMPLE C The assembly in Example B is repeateed, except that the perforations were modified to consist of two 1.6 cm ( 6 / 8 inch) wide grooves surrounding and directly communicating with the perforations; which grooves were scraped from undercoating of the base sheet. The apertures were identical to those in Example B, but the associated voids were approximately 3.2 cm 2 (0.5 square inches) in area and 13.7 cm (5.4 inches) in perimeter. After cooling, this assembly showed an uplift resistance of over 4.25 kN (965 pounds of force) which corrects to over 1100 kg/m 2 (225 lbs/ft 2 ) EXAMPLE D The assembly in Example B is repeated, except that the apertures consisted of 0.63 cm (¼ inch) wide by 7.5 cm (3 inch) long slots placed on 12 cm (4.5 inch) centers (chevron style). The internal area of these apertures was 2 cm 2 (0.8 square inches) and the perimeter was approximately 17.3 cm (6.8 inches). After cooling, this assembly showed an uplift resistance of over 4.88 kN (1000 lbs/ft 2 ) of force, which corrects to over 1220 kg/m 2 (250 lbs/ft 2 ). When T-shaped apertures on the base sheet are substituted for the slots in the base sheet of Example D, similar resistance to uplift is attained. Figure V of the drawings is a diagrammatic comparison of base sheet/substrate attachments generally described in Examples A through D above. In this figure, the wind uplift resistance in lbs/ft 2 is plotted along the X axis and the internal area of the aperture in square inches is plotted along the Y axis. Further in this figure, the symbol ▪ represents base sheet apertures of the configuration described in Example A; the symbol  represents the conventional base sheet apertures described in Example B and the symbol ▴ represents the base sheet apertures described in Example D. As the curve illustrates, particularly in the internal area of 0.4-0.45, the configuration of the aperture has a significant affect on the resistance to wind uplift forces. The apertures having an internal area of less than 0.3 are simply to small to provide the desired adhesion between the base sheets and the substrates although the sheet itself retains good strength. An internal area of 0.45 is about the maximum tolerable for base sheet strength when circular apertures are employed; however in the case of ovate or T-shaped apertures, the strength of the base sheet was not noticeably diminished when larger apertures of greater internal areas were employed. Substantially similar improvement is achieved with apertures of the other non-cylindrical configuration described herein.

Claims: A base sheet (2) for a roofing assembly (8), the base sheet adapted to be adhesively bonded to a substrate and having an asphaltic undercoating and spaced voids in the sheet providing apertures (3) to allow flow of adhesive through the voids onto the substrate, the voids being modified to allow increase in the bonding strength between the base sheet (2) and the substrate without diminishing the strength of the sheet, said modified voids being non-cylindrical in the shape of one or more closed figures; characterized in that the base sheet (2) is of thickness of from 1.5 to 3 mm and the asphaltic undercoating thereof has granules (6) embedded therein; in that the voids are non-cylindrical in the shape of polygons having at least two sides or boundaries of unequal length; and in that the voids are defined by the formula R/R' = >2, where R is a radius (a) of a circle circumscribed around a given void and R' is radius (a') of a circle constructed to have the same internal area of said void. A base sheet (2) according to claim 1 wherein the voids are or include cutouts of the said shape in the base sheet (2). A base sheet (2) according to claim 2 wherein the cutouts are non-circular and communicate with non-circular void areas in the granule (6)-embedded undercoating. A base sheet (2) according to claim 3 wherein the cutouts are slot shaped. A base sheet (2) according to claim 1 wherein the base sheet (2) includes a void area in its undercoating which is of said shape. A base sheet (2) according to claim 1 wherein the void area in the undercoating is of larger dimension than a cutout which is directly above and in open communication with said void area, thus providing an aperture through said base sheet and permitting passage of an adhesive through the base sheet and the void area in the said granular (6) embedded undercoating onto the surface of the substrate. A base sheet (2) according to claim 6 wherein the boundaries of the cutout and the void area are circular. A base sheet (2) according to claim 6 wherein channels radiate from a circular cutout to provide a continuous star shaped void area. A base sheet (2) of any one of the preceding claims wherein the voids of the base sheet (2) are uniformly spaced. A base sheet (2) according to claim 9 wherein the voids of the base sheet (2) are in a chevron pattern. A base sheet (2) according to claim 6 wherein said aperture (3) in the shape of a three dimensional figure having a void area in the undercoating has a shape which is an hourglass, a star, a clover leaf or a bladder. A roof assembly (8) comprising a base sheet (2) according to any one of the preceding claims. A roof assembly (8) according to claim 12 wherein the substrate is a roof deck (5). A roof assembly (8) according to claim 12 wherein the substrate is an insulation layer (4). A roof assembly (8) according to claim 12 wherein the substrate is a thermal insulation layer of rigid or semi-rigid fibrous, polymeric or glass foam material interposed between the base sheet (2) and the roof deck (5).

Inventors: GRAZMAN BRENT L, WOODRING WILLIAM J, GRAZMAN, BRENT L., WOODRING, WILLIAM J.
Applicants: GAF BUILDING MATERIALS, BUILDING MATERIALS CORPORATION OF AMERICA
Application year: 1998
Main classification: E04D5
IPC codes: E04D5, E04D11