Abstract:
Building wall panels having lightweight hollow core interiors include embodiments suitable for interior and exterior walls, for industrial, commercial or residential buildings, and for multi-story structures. Various methods for making these wall panels are disclosed, including the formation of cast gypsum firewall layers.

Description:
RELATED APPLICATION 
       [0001]    This is a continuation-in-part of application Ser. No. 11/835,516, filed Aug. 8, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention pertains to lightweight structural wall panels for buildings and, more particularly, to such panels having a hollow core interior construction that may be adapted for use in industrial, commercial and residential building structures. 
         [0003]    The potential for the use of hollow core elements in the construction of buildings and other structures has been known for many years. Hollow cores of corrugated or honeycomb paper or metal sheet material, enclosed by upper and lower skin panels or sheets, have long been used or proposed for use as floor, wall and roof panels for buildings. However, the use of such hollow core panels has been inhibited because of difficulties in fabricating the panels in an efficient and cost effective manner. 
         [0004]    In my co-pending patent application Ser. No. 11/476,474, entitled “Method and Apparatus for Manufacturing Open Core Elements from Web Material”, filed Jun. 28, 2006, and Ser. No. 11/769,879, bearing the same title and filed Jun. 28, 2007, both of which applications are incorporated by reference herein, there are disclosed systems and techniques for manufacturing hollow core panels of widely varying dimensions using corrugating techniques and a unique lay-up process. Those systems and techniques are applied to make building wall panels of diverse constructions. 
         [0005]    In addition, the building wall panels described herein are useful in the construction of buildings utilizing floor and roof constructions described in my co-pending patent application Ser. Nos. 11/485,823, entitled “Hollow Core Floor and Deck Element”, filed Jul. 13, 2006, and Ser. No. 11/777,002, bearing the same title and filed on Jul. 12, 2007, which applications are also incorporated by reference herein. 
       SUMMARY OF THE INVENTION 
       [0006]    In a basic embodiment of the present invention, a building wall panel is provided that includes a rectangular peripheral outer frame having vertical edge frame members and upper and lower horizontal edge frame members joined to the ends of the vertical edge frame members, the frame enclosing an open core element that is defined by a plurality of fluted strips of a web material bonded together by interposed smooth unfluted webs, said open core element having the smooth webs horizontally disposed in use and the flutes oriented perpendicular to the plane of the frame to define with the frame parallel inner and outer panel faces. The frame and at least a portion of the open core element are filled with a closed cell foam. A skin sheet is attached to and covers the inner face of the panel, and an outer layer is attached to and covers the outer face of the panel. The skin sheet preferably comprises a two-layer composite including an inner impervious layer and an outer paper layer. The outer layer may comprise any of several materials used as exterior wall panels, including plywood, oriented strand board, plastic, and steel. In a particularly preferred embodiment, a portion of the open core element is filled, within the frame, with a layer of gypsum. 
         [0007]    In one embodiment of the invention, suited particularly to forming the external wall of a commercial or industrial building, a wall panel comprises a rectangular peripheral outer frame that includes vertical edge frame members and upper and lower horizontal edge frame members that are joined to the ends of the vertical edge frame members. The frame encloses an open core element made from a plurality of fluted strips of a web material that are bonded together and have flutes oriented perpendicular to the plane of the frame to define, with the frame, parallel inner and outer panel faces. Closed cell foam fills at least a portion of the open core element. An inner steel skin sheet is attached to and covers the inner panel face. An intermediate steel skin sheet is disposed between and lies parallel to the inner and outer panel faces. The intermediate steel skin sheet is attached at its peripheral edge to the frame and divides the open core element into inner and outer core elements. An outer layer is attached to and covers the outer panel face. 
         [0008]    The rectangular peripheral frame is preferably made of wood and comprises two-piece vertical edge frame members and two-piece horizontal edge frame members. The intermediate steel skin sheet is sandwiched between and attached to the two-piece vertical and horizontal edge frame members. The wall panel also includes interior wood frame members that extend between and are attached to the vertical edge frame members. The interior frame members lie parallel to the horizontal edge frame members. The interior wood frame members are attached to one piece of the two-piece frame members and positioned on one side of the intermediate skin sheet. Preferably, the interior wood frame members extend laterally and horizontally between the intermediate skin sheet and the inner skin sheet. The outer core element is filled with closed cell foam. 
         [0009]    In a preferred embodiment, the open core element includes smooth webs that are interposed between and bonded to the flute tips of adjacent fluted strips. The core element is oriented with the smooth webs horizontally disposed. The web material preferably comprises paper and the paper web is treated to make it waterproof. The outer panel cover layer could be made of a number of different materials, including steel, wood, plywood, oriented strand board, particle board and plastic. 
         [0010]    The interior wood frame members provide for the attachment of floor and roof supports to the wall panel. The supports are attached to the inner skin sheet with fasteners that extend through the interior skin sheet, the interior wood frame member and the inner or front steel skin sheet. The floor and roof supports typically comprise steel angle sections. 
         [0011]    In another embodiment, suited particularly to residential building construction, the building wall panel has a peripheral frame that encloses an open core element having a plurality of fluted strips of a web material bonded together with the flutes oriented perpendicular to the plane of the frame and defining therewith parallel opposite faces. A continuous layer of gypsum inside the frame fills a portion of the open core element adjacent one panel face. The first skin sheet covers the face adjacent the gypsum layer and a second skin sheet covers the other panel face. The gypsum layer is formed flush with the panel face and the first skin sheet includes a vapor barrier sheet that covers the gypsum layer and a paper sheet covering the vapor barrier sheet. The remainder of the open core element may be filled with a closed cell foam. The second skin sheet comprises a substrate layer that is bonded to the foam filled core element. The substrate layer may be made of plywood, oriented strand board, particle board or the like. 
         [0012]    In an embodiment particularly suited to outer wall construction, a layer of concrete forms a continuous layer inside the frame and fills a portion of the open core element. The layer of concrete is placed flush with the inner face of the panel and is covered by the first skin sheet. A gypsum layer is positioned inside and covers the inside surface of the concrete layer. The remainder of the open core element may be filled with a closed cell foam. Preferably, the open core element includes smooth unfluted webs that are interposed between and are bonded to the flute tips of adjacent fluted strips, and the core element is oriented with the smooth unfluted webs horizontally disposed. 
         [0013]    When used an interior wall panel, the gypsum layer lies flush with the face in which it is formed and is covered by the first skin sheet. The panel includes another gypsum layer inside the frame, flush with the other face and filling another portion of the open core element. 
         [0014]    One method for making a building wall panel, in accordance with the present invention, comprises the steps of (1) forming a hollow core element from strips of a fluted web material and bonding the strips together to form a rectangular core panel having parallel front and rear faces with the flutes oriented perpendicular to the faces, (2) providing an enclosing peripheral frame for the core panel, (3) supporting the frame on a horizontal surface, (4) filling the frame to a selected depth with a liquid gypsum mixture, (5) pressing one face of the core panel into the frame and through the liquid gypsum to the supporting surface and forcing the gypsum into the open core panel to the selected depth, and (6) allowing the liquid gypsum to set sufficiently to form a self-supporting gypsum layer. 
         [0015]    The foregoing method also preferably includes the steps of (1) attaching a paper cover sheet to the face of the frame supported on the horizontal surface before filling, and (2) causing the liquid gypsum to cover the surface of the sheet and to bond thereto after setting. The method may also include the step of providing the inside face of the cover sheet with a barrier layer that is impervious to moisture. 
         [0016]    Another variant of the method of the present invention comprises the steps of (1) filling the frame to a selected depth with a liquid concrete mixture before the liquid gypsum filling step, (2) filling the frame atop the liquid concrete to the selected depth with said liquid gypsum mixture, (3) continuing the pressing step through the liquid gypsum to press the core panel face through the liquid concrete to the supporting surface and (4) allowing the liquid concrete to set sufficiently to form a self-supporting layer joined to the self-supporting gypsum layer. 
         [0017]    Another embodiment of a method of the subject invention for making a building panel comprises the steps of (1) forming a hollow core element from strips of a fluted web material that are bonded together to form a rectangular core panel. The core panel has a front face and a rear face with the flutes of the web material oriented perpendicular to the faces, (2) enclosing the core panel in a peripheral frame, (3) pressing one face of the framed core panel into a liquid gypsum mixture and forcing the liquid gypsum into a portion of the hollow core element on one face of the panel, and (4) allowing the liquid gypsum to set sufficiently to form a self-supporting gypsum layer. 
         [0018]    The method also preferably includes the step of applying a paper cover sheet to the front face of the panel. The front face of the core panel and the gypsum layer are preferably formed coplanar with a front face of the frame and the paper cover sheet covers the front face of the frame. 
         [0019]    The method may also include the steps of (1) inverting the frame, (2) pressing the other face of the frame core panel into the liquid gypsum mixture and forcing the liquid gypsum into a portion of the hollow core element at the other face, and (3) allowing the liquid gypsum in the other face portion of the panel to dry sufficiently to form a self-supporting gypsum layer. 
         [0020]    In certain applications, the basic wall panel of the present invention may have to be modified to add vertical load bearing strength. If the wall panel includes openings for doors, windows and the like, the reduction in load bearing strength can be overcome by the addition of a plurality of reinforcing strips that are attached to the outer panel layer and extend vertically between the upper and lower edge frame members. The strips are placed atop and secured to one another and, preferably, positioned laterally adjacent the openings. In a multi-story panel, the panel is provided with a plurality of reinforcing strips placed over one another with a first of the strips attached directly to the outer layer and extending from a lower end to the upper edge frame member. Each subsequently attached strip has a length less than the strip that precedes it and, preferably, the strips are sequentially shortened in length by about the height of one building story. 
         [0021]    The modified panels may otherwise be constructed generally in accordance with the basic assembly described above. The strips are preferably made of steel sheet material and may have a thickness in the range of about 0.040 to 0.080 inch. The strips may be of the same width or each subsequently attached and incrementally shortened strip may have a width less than the strip that precedes it. 
         [0022]    In a further embodiment of the present invention, the exterior building wall panel is similar to that described above. However, the inner core element, positioned between the interior steel skin sheet and the intermediate steel skin sheet, is filled with a dry sand layer to provide an increased mass and to provide a sound-deadening barrier. Preferably, the entire inner core element is filled with the dry sand, 
         [0023]    The outer core element, between the intermediate skin sheet and the outer layer, may be filled with a closed cell foam, in a manner described with respect to previous embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a perspective view of a two story commercial building utilizing a modular construction including wall panels of the subject invention. 
           [0025]      FIG. 2  is a perspective view of a wall panel of the subject invention used in the construction of the  FIG. 1  building. 
           [0026]      FIG. 3  is a horizontal sectional view taken on line  3 - 3  of  FIG. 2 . 
           [0027]      FIG. 4  is a vertical sectional view taken on line  4 - 4  of  FIG. 2 . 
           [0028]      FIG. 5  is a horizontal sectional detail of the joint between two interconnected wall panels. 
           [0029]      FIG. 6  is a perspective view of an arrangement of two interconnected wall panels made in accordance with another embodiment of the invention. 
           [0030]      FIG. 7  is a horizontal sectional view taken on line  7 - 7  of  FIG. 6 . 
           [0031]      FIG. 8  is a sectional detail of one embodiment of the wall panel of  FIG. 6 . 
           [0032]      FIG. 9  is a sectional detail of another embodiment of the wall panel shown in  FIG. 6 . 
           [0033]      FIG. 10  is a horizontal sectional detail of a further embodiment of the wall panel of  FIG. 6 . 
           [0034]      FIG. 11  is a perspective view of a two story building, similar to  FIG. 1 , but showing the use of vertical load bearing strips applied to the outer panel face. 
           [0035]      FIG. 12  is a perspective view of a wall panel taken from the outside and showing details of the reinforcing strips shown in  FIG. 1   1 . 
           [0036]      FIG. 13  is a horizontal sectional detail similar to  FIG. 5 , but showing a variation in the material filling portion of the open core element. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    In  FIG. 1 , there are shown the components of a two story building  10  utilizing lightweight hollow core elements for the second floor  12  and roof  13 , as described in my above identified co-pending patent applications, and the wall panels  11  which are the subject of the present invention. Each wall panel  1 , for the building shown, is 8 ft. wide and 28 ft. long. As shown in  FIG. 2 , the wall panel  11  may be provided with through openings  14  for windows and/or doors, but the openings are of course optional. The bottom edge of the panel  11  is provided with a series of J-bolts  16  for anchoring in a concrete floor or footing  16  shown in  FIG. 1 . The  FIG. 2  panel also has attached to its inner face  17  a pair of steel angle sections  18 , which provide support for the  FIG. 1  second floor  12  and roof  13 . 
         [0038]    Each wall panel  11  is enclosed by a rectangular wooden frame  20 . The frame includes vertical edge frame members  21  and horizontal upper and lower edge frame members  22 . The ends of the horizontal members  22  may be joined to the ends of the vertical frame members  21  in any suitable manner, including adhesives, mechanical fasteners, or both. Referring particularly to  FIG. 3 , the vertical edge frame members  21  are of two-piece construction, including a front edge portion  23  and a rear edge portion  24 . Similarly, as shown in  FIG. 4 , the horizontal edge frame members  22  are also of two-piece construction and include a front edge portion  25  and a rear edge portion  26 . 
         [0039]    The front inner face  17  of the panel  11  is covered with a thin steel sheet  27  which may be 0.060 in. thick (about 1.5 mm) and covers the entire inner front face including the face of the frame  20 . The steel sheet  27  is bonded to the face of the frame  20  with a suitable adhesive, such as an epoxy. 
         [0040]    The front edge portions  23  and  25  of the two-piece frame may be 3 in.×5 in. in cross section and the corresponding rear edge portions  24  and  26  may be 3 in.×3 in. in cross section. An interior steel skin sheet  28 , of the same size (0.060 in.) and shape as the front steel skin sheet  27 , is sandwiched between the front and rear portions of the two-piece frame members  21  and  22 . The interior skin sheet  28  is secured by bonding with a suitable adhesive as described above. The outer or rear face  30  of the panel  11  is enclosed by an outer layer  31  of any suitable material, including another thin steel skin sheet, plywood, oriented strand board, or the like. 
         [0041]    The interior of the wall panel  11  is filled substantially completely with open core elements  32  of the type made in accordance with the teachings of my above identified co-pending patent applications. Briefly, the open core element  32  is made from a plurality of fluted strips of a web material, such as paper, that are bonded together by interposed smooth unfluted webs. The open core elements  32  which are formed in a rectangular shape are sized to be fully enclosed by the wooden frame  20 . The core elements are oriented such that the flutes are perpendicular to the plane of the frame and the skins sheets  27  and  28 . Preferably, the open core elements  32  are also oriented, in use, with the smooth webs horizontally disposed. 
         [0042]    In the embodiment shown, a thin layer of gypsum  33  fills a portion of the open core element  32  directly against the inside surface of the front skin sheet  27 . The gypsum layer  33  is formed by methods which will be described hereinafter. Between the back face of the gypsum layer  33  and the interior steel skin sheet  28 , the open core element  32  is left open. The open core element  32  between the other face of the interior steel skin sheet  28  and the outer layer  31  is filled with a closed cell foam material  29  for insulating purposes. This helps maintain the front skin sheet  27  and interior skin sheet  28  at roughly the same temperature, thereby limiting distortion of the skins resulting form thermal differential. 
         [0043]    The sectional detail in  FIG. 5  shows how two corner wall panels  11  are connected. A steel angle member  35  is positioned in the open corner and fastened by its flanges  36  to the outside faces of the adjoining vertical edge frame members  21 . The angle member  35  may be suitably bored to receive lag screws  37  driven into the frame members  21 . 
         [0044]    The wall panel  11  also includes interior wood support members  38  to which the wall supporting angle sections  18  are attached. Each wooden support member  38  may conveniently comprise a 3 in.×5 in. piece that extends between and is attached to the front edge portion  23  of the vertical edge frame members  21 . The floor and roof supporting angle sections  18  ( FIG. 1 ) are attached to an interior support member  38  with bolts  40  that extend from the interior of the panel  11 , through the interior steel skin sheet  28 , the support member  38 , the front steel skin sheet  27  and the vertical flange  41  of the angle member  18 . 
         [0045]    The vertical edge frame members  21  of the frame  20  run the full 28 ft. height of the panel. These vertical frame members provide structural column support for the floor and roof members, particularly in the panels away from the building corners. Because of the difficulty in obtaining one-piece 28 ft. members, shorter vertical edge frame members  21 , suitably spliced, are preferable. 
         [0046]    As may be seen in  FIG. 3 , the front edge portion  23  of the vertical edge frame members  21  are provided with corner notches  42 . The front steel skin sheet  27  overlies the notches  42  and suitable sealing strips may be inserted therein as the panels are assembled edge-to-edge. In addition, one of the rear edge portions  24  of a vertical edge frame member  21  may also be provided with a sealing strip  43  that abuts the face of the vertical edge frame member of the next adjacent panel. The panels may be bonded together with a suitable adhesive or by mechanical fasteners. 
         [0047]      FIG. 6  shows a pair of interconnected wall panels in accordance with another embodiment of the invention which are particularly suitable for residential construction. The panels may each be 8 ft. high and 10 ft. long. Each panel is closed on its edges by a frame  45  that includes vertical edge frame members  46  and horizontal top and bottom edge frame members  47 . The vertical edge frame members  46  are provided with complimentary tongue-and-groove profiles  48  to help close and strengthen the glue joint therebetween when assembled edge-to-edge. 
         [0048]    The interior of the frame  45  is filled with an open core element, as described with respect to the preceding embodiments. Thus, the open core element  50  may be made in accordance with the teaching of my above identified pending patent applications. The frame  45  is covered on an inside face with a two-part layer  51  comprising an inner vapor barrier  52  and a paper cover sheet  53 . The open core element  50  just inside the vapor barrier  52  is filled with a gypsum layer  54 . If the overall wall panel thickness is about 4 in., the gypsum layer  54  may be 1 in. thick. The remainder of the open core element  50 , from the inner face of the gypsum layer to an outside cover layer  55 , is filled with a closed cell foam  56 . The outside cover layer may be plywood or oriented strand board to which conventional siding may be applied. 
         [0049]    A variation in the wall panel  44  of  FIG. 8  is shown in  FIG. 9 . The  FIG. 9  construction is identical to the  FIG. 8  panel, except, in the  FIG. 9  construction, a thin concrete layer  57  is formed on the inside face against the two-part cover layer  51 . The concrete layer provides additional load bearing support, particularly in the vertical direction. Abutting the inside face of the concrete layer  57  is a gypsum layer  58  which is essentially the same as the gypsum layer  54  in the  FIG. 8  embodiment, except for its location. In either case, the gypsum layer  54  or  58  provides a protective fire wall, as well as additional structural support, in the same manner as conventional gypsum wallboard. 
         [0050]    In  FIG. 10 , there is shown a sectional detail of a wall panel  60  that is particularly well suited for interior residential construction. The interior wall panel  60  has a wooden frame that comprises vertical edge frame members  61  that may be identical to the edge frame members of the  FIG. 8  and  FIG. 9  embodiments. Horizontal edge frame members, not shown, may also be identical to those previously described. The frame contains an open core element  62  which is filled at opposite panel faces with identical gypsum layers  63 , each of which is covered on the outside face by a paper layer  64 . The paper layer  64  extend over and is bonded to the opposite faces of the panel frame  59 . The open core element  62  between the gypsum layers  63  may be left open or filled with a closed cell foam material. The thickness of the vertical edge frame members  61  may be made just slightly less than the thickness of the open core element  62 , to provide a slight edge relief along the panel edges which would accommodate conventional drywall taping. In addition, plastic wire chase tubes may be run in the interior open core element between the gypsum layers so the fire barrier would not be broken. Junction boxes may be pre-installed and a ground wire or wire pull also put in place. 
         [0051]    A convenient, efficient and effective method of providing a wall panel with one or two gypsum layers, which is applicable to the  FIG. 10  embodiment, as well as other described embodiments, will now be described with respect to  FIG. 10 . First, a hollow core element  62  is made in a rectangular shape sized to fit closely within the frame  59 . As described above, the open core elements  62  are disposed with the flutes extending perpendicular to the panel faces. The frame  59  is covered on one face by a paper layer  64  and supported on a horizontal surface. A liquid gypsum mixture is poured into the frame from the open backside to a selected depth, e.g. ¾ in. (about 19 mm). The rectangular core panel is then pressed into the frame and through the liquid gypsum all the way to the paper layer  64  on the supporting surface. The liquid gypsum is forced into the face portion of the open core panel to the depth selected. The liquid gypsum is then allowed to set sufficiently to form a self-supporting gypsum layer. 
         [0052]    While the panel is intended for exterior building wall construction, the inside of the paper layer  64  is provided with an impervious barrier layer in the manner described previously with respect to other embodiments. To form the gypsum layer  63  in the other face of the panel, a number of alternate methods may be used. Preferably, the open core element, with the set first gypsum layer  63  in place, is removed from the frame, inverted and reinserted into the frame after a second layer of liquid gypsum has been poured therein. The core element is then pressed into the second liquid gypsum layer, in the manner previously described, and the gypsum layer is allowed to set. Alternately, a second layer of liquid gypsum may be filled into the frame after the first gypsum layer has set, the frame immediately inverted with a paper covered supporting layer held on to the back face, and the liquid gypsum permitted to settle into the position of the second layer where it is held until the gypsum sets. It may also be possible to provide the second layer by inverting the entire frame containing the core element and the first set gypsum layer and pressing the entire assembly into a thin pool of liquid gypsum to the selected depth. 
         [0053]    To form the composite two-layer arrangement of  FIG. 9 , the wooden frame  45  would first be filled with a layer of liquid concrete (Portland cement and sand) to a desired depth, e.g. ½ in. (13 mm), and a layer of liquid gypsum poured immediately a top the liquid concrete layer to a selected depth, ¾ in. (19 mm). The open core element  50  is then pressed downwardly through the gypsum layer and then the concrete layer until it reaches the horizontally supported front face of the frame covered with a suitable two-ply vapor barrier/paper cover layer. 
         [0054]    In  FIGS. 11 and 12 , there is shown a modification to the building wall panels shown in  FIGS. 1 and 2  and previously described. The need to provide openings in the wall panels for windows, doors and the like, inherently results in a decrease in panel strength, particularly vertical load bearing strength. In accordance with the embodiment shown in  FIGS. 11 and 12 , the wall panels  11  are reinforced to compensate for the loss in strength resulting from the through openings  14  for windows and doors. 
         [0055]    When the panels  11  are used in the construction of a multi-story building  10 , a plurality of thin steel reinforcing strips  65  are fastened to the outer face  30  of the panels. For a two story building, as shown, two parallel sets of strips  65  are applied to the wall panel  11  between the vertical edge frame members  21  and the openings  14 . Each set of reinforcing strips includes three strips of progressively shortened length fixed atop one another. The first strip  66  of each set runs the full height of the panel between the horizontal upper and lower edge frame members  22 . The second strip  67  is shorter in length than the first and extends from the lower edge of the frame to the second story opening  14 . Similarly, the third strip  68  extends vertically from the lower edge frame member to the first story opening  14 . As shown, the second and third strips  67  and  68  terminate near the lower edges of the respective openings  14 , but they may be extended or reduced somewhat in length as desired or needed. 
         [0056]    The steel strips  65  may have a gauge or thickness the same as the front steel skin sheet  27  or the interior steel skin sheet  28 . However, the gauge of the steel reinforcing strips  65  may be varied considerably, but a thickness range of from 0.040 to 0.080 inch is presently preferred. 
         [0057]    The strips  65  may be secured to the outer rear panel face  30  in any convenient manner. However, adhesive attachment using, preferably, epoxies is preferred. In addition, reinforcing strips of other materials, such as aluminum, may be used. 
         [0058]    Although the reinforcing strips  65 , shown in  FIGS. 11 and 12  are of equal widths, the widths may vary from one strip to another. For example, the longest first strip  66  may have the greatest width and widths of the subsequent second and third strips may be progressively narrowed in width. Preferably, the strips are about  12  inches in width. For buildings having three or more stories, reinforcing strips are applied using the same strategy described for the two story building panels of  FIGS. 11 and 12 . 
         [0059]    Referring to  FIG. 13 , the sectional view of interconnected wall panels  11  is similar to the section shown in  FIG. 5 . However, the gypsum layer  33  in the  FIG. 5  embodiment has been eliminated and that portion of the open core element  32  between the front steel skin sheet  27  and the interior steel skin sheet  28  is filled completely with a dry sand  70 . The sand adds mass and thus stability to the structure. More importantly, however, the sand provides an especially effective sound-deadening layer to the wall panels and to the overall building. 
         [0060]      FIG. 13  wall panels may otherwise be identical to the  FIG. 5  panels. In this regard, the outer open core element  32 , between the interior skin sheet  28  and the outer layer  31 , may be filled with a closed cell foam material.