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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit, pursuant to 35 U.S.C. 119(e), of U.S. Provisional Application No. 60/771,854, filed on Feb. 10, 2006, and said provisional application is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates in general to precast cladding panels, and in particular to precast cladding panels that do not require hangers or other mounting hardware to be cast into the panels. 
       BACKGROUND OF THE INVENTION 
       [0003]    Precast panels of various sizes and shapes are widely used as cladding on building walls, serving as components of building envelope systems intended to prevent infiltration of rain and outside air into the building. Precast cladding panels are commonly made of concrete, but may also be made with other cast materials known in the construction field. Concrete cladding panels are common on large structures such as office buildings, but they are also used on residential housing structures as an alternative to traditional cladding materials such as wood siding and brick. 
         [0004]    Whether installed on large or small buildings, it is desirable for cladding panels to be mounted in such a way that there will be a continuous air space between the rear (i.e., inner) faces of the panels and the supporting structure, while at the same time providing reliable structural support for the panels, both to transfer the vertical weight of the panels to the supporting structure and to provide anchorage against lateral forces (such as wind) that may act on the panels. 
         [0005]    The purpose of the air space is to provide a passage through which any water or moisture vapour that gets behind the cladding can be directed away from the building envelope before it infiltrates other parts of the building. Although caulking or other sealant materials are typically used to seal the spaces between cladding panels, the possibility of moisture infiltration behind the cladding—as a result of vapour migration, direct penetration of rainwater (due to sealant deterioration or other factors), or leakage at roof-to-wall junctures—cannot be entirely eliminated. If such moisture is not removed from the building envelope fairly promptly, it will tend to migrate further into the building, potentially causing a variety of problems that could entail costly maintenance and repairs and could detract from the building&#39;s overall durability and value. Such problems may include drywall damage due to moisture absorption, rot and mold in wooden construction components (e.g., studs and sheathing), corrosion of non-rust-resistant construction hardware, and staining on interior building finishes. 
         [0006]    When an air space is provided behind the cladding, moisture can run downward behind the cladding to exit points such as weepholes built into the cladding system at appropriate locations. The air space also facilitates or enhances air circulation behind the cladding, helping to remove moisture vapour before it can condense inside the wall structure, and helping to dry out any wall structure components that may have become damp due to moisture infiltration. 
         [0007]    The essential problem facing designers of cladding panel support systems is to provide hangers or brackets that can adequately support weight of the panels at a distance away from the face of the supporting structure (i.e., so as to provide the desired air space), without significantly impeding the passage of water or water vapour through the air space. In this regard, it is particularly desirable to avoid or minimize hanger-to-panel connection details where moisture might become trapped or its downward vertical flow impeded. 
         [0008]    It is desirable for concrete cladding panels to be stackable as compactly as possible to minimizing space requirements during storage and shipping. Accordingly, it is desirable to have a precast cladding panel system that reduces or substantially eliminates the space between stacked cladding panels, thus significantly reducing storage space requirements. 
         [0009]    For the foregoing reasons, there is a need for an improved precast cladding panel system that facilitates secure mounting of panels at a uniform distance away from a vertical supporting structure without introducing significant impediments to air flow through the air space thus created between the rear faces of the panels and the supporting structure. In addition, there is a need for a precast cladding panel system that facilitates more compact stacking and storage of panels, with the space between stacked panels reduced or eliminated. The present invention is directed to these needs. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0010]    In general terms, the invention is a precast cladding panel that does not require any brackets, insets, or other mounting hardware or appurtenances to be cast into or affixed to the panel to enable the panel to be mounted on a supporting structure such as a building wall. The panel system of the present invention, in each of its embodiments, inherently provides for the creation of an air space between the rear faces of the panels and the supporting structure. 
         [0011]    In a first aspect, the present invention is a precast panel having a front face, a rear face, an upper edge, and a lower edge, wherein: 
         [0012]    (a) the upper edge of the panel has a continuous notch, forming:
       a.1 a ledge extending rearward from the front face of the panel; and   a.2 a substantially vertical upstand adjacent to the ledge and extending vertically upward from the level of the ledge; and       
 
         [0015]    (b) a plurality of fastener holes extend through the upstand. 
         [0016]    In a second aspect, the invention is a panel assembly comprising a plurality of precast panels mounted to a supporting structure, each cladding panel having a front face, a rear face, an upper edge, and a lower edge, wherein: 
         [0017]    (a) the upper edge of each panel has a continuous notch, forming:
       a.1 a ledge extending rearward from the front face of the panel; and   a.2 a substantially vertical upstand adjacent to the ledge and extending vertically upward from the level of the ledge;       
 
         [0020]    (b) a plurality of fastener holes extend through the upstand; 
         [0021]    (c) each panel is mounted to the supporting structure by means of fasteners passing through said fastener holes; and 
         [0022]    (d) the lower edge of each panel in all but the lowermost courses of the panel assembly is disposed within the notch of the below-adjacent panel or panels. 
         [0023]    The “lowermost course” of a panel assembly will generally be understood as meaning a generally horizontal course near the base of a wall or cladding panel assembly. As used in this patent document, however, the term “lowermost course” may, as the context requires, also mean a course or portion of a course that is not at or near the base of the wall or assembly, but has no panels immediately below it (for example, panels over a window, door, or other opening). 
         [0024]    Although the panel assembly of the present invention might most commonly be constructed in horizontal courses of rectangular panels, persons skilled in the art will readily appreciate that these particular features are not essential to the invention. The principles and concepts of the invention may also be adapted to cladding panels of different shapes, including panels that have one or more curvilinear edges, and panels that are irregularly configured so as to permit construction of panel assemblies with staggered horizontal joints. 
         [0025]    In preferred embodiments of the panel and the panel system, the horizontal ledge of the panel slopes transversely downward toward the front face of the panel, to enhance the efficiency of drainage of moisture down the rear faces of the panels and toward the front faces of the panels in lower edges of the rear faces of the panels. 
         [0026]    Also in preferred embodiments, the thickness of the panel at its lower edge is less than or approximately equal to the transverse width of the horizontal ledge. Accordingly, the lower edges of the panels may be disposed within the notches of below-adjacent panels so as to align the front faces of the panels on either side of a horizontal joint in the panel assembly. This detail facilitates the construction of panel assemblies in which the front faces of all panels lie in substantially the same plane, as will be commonly desirable (for example, when the panels are formed with substantially planar front faces, and it is desired for the panel assembly to provide a substantially flat finished wall surface. 
         [0027]    In other situations, it might be desirable for aesthetic reasons to create an uneven finished wall surface by having the lower edges of some panels project beyond the front faces of below-adjacent panels. Such effects may be achieved by forming the horizontal notches with a width less than the thickness of the lower edges of the panels. Alternatively, the notch width could be approximately the same as the lower edge thickness as previously described, but the panels are installed with their lower edges shifted outward to achieve the desired projection or overhang; in such cases, suitable spacer means could be provided between panel upstands and the rear faces of above-adjacent panels. 
         [0028]    The provision of horizontal notches along the upper edges of the cladding panels facilitates efficient and accurate installation, since the panels can rest on the horizontal ledges of below-adjacent panels while being fastened to the supporting structure. However, it would also be possible (using suitable spacers or other construction techniques) to install the panels with horizontal gaps between the ledges and the lower edges of above-adjacent panels, should that be desired for any reason (e.g., to allow for differential vertical movement, or to enhance drainage of moisture from behind the panels). 
         [0029]    In one embodiment, the panel thickness increase at a substantially uniform rate from the lower edge up to approximately the level of the horizontal ledge. To facilitate air flow behind the panel assembly when panels of this configuration are mounted with their upper edges directly against the supporting structure, horizontally-spaced channels may be formed in the panel&#39;s rear faces, extending downward from the top of the panel&#39;s upstands. Due to the panels&#39; tapering thickness, these channels will typically terminate at a point above the panels&#39; lower edges. Since the panels&#39; lower edges are held away from the face of the supporting structure, there will be airspaces of varying width behind each panel, in fluid communication with each other by virtue of the channels formed in the rear faces of the panels. In this way, the present invention provides for effective air circulation behind the panel assembly even in embodiments where the upper edges of the panels are mounted directly against the supporting structure. 
         [0030]    In a further embodiment of the system, the panel thickness is substantially constant, up to a level below the horizontal ledge, while the rear face of the panel upstand extends down to approximately the same level, such that the upstand protrudes rearwardly from the rear face of the panel. In this embodiment, horizontally-spaced, generally vertical channels may be formed in the rear face of the upstand, for its full height, in order to provide for air circulation behind the panel assembly when the panels are mounted with their upstands directly against the supporting structure. 
         [0031]    However, other embodiments of the invention provide for air circulation behind the panel assembly without need for air channels formed in the rear faces of the panels or upstands. In these alternative embodiments of the panel system, a plurality of upper bumpers are fastened to the supporting structure at appropriate horizontal spacings, such that the rear faces of the panel upstands will abut the upper bumpers, thus effectively spacing the rear faces away from the face of the supporting structure. Air can then freely flow behind the panel assembly, through the spaces between the upper bumpers. In this case, there is not need to provide air channels in the rear faces of the panels or upstands. However, it may be desirable, from a practical standpoint, to provide the panels with air channels so that they can be used with or without upper bumpers, depending on design requirements or preferences for given projects. 
         [0032]    Whether the panels are mounted using upper bumpers or not, the lower edges of the panels in the lowermost course of the panel assembly will typically be spaced away from the supporting structure, using lower spacer means. This detail facilitates the installation of all panels in the assembly with their front faces uniformly aligned, without requiring specially-configured panels for the lowermost course. It also ensures that moisture can drain from behind the wall panels. 
         [0033]    In preferred embodiments of the panel assembly, the lower spacer means comprises one or more J-shaped channel sections, each having a generally vertical inner flange, a generally horizontal lateral web extending outward from the bottom edge of the inner vertical flange, and a generally vertical outer flange extending upward from the outer edge of the lateral web. Typically, the J-channels are fastened to the face of the supporting structure (using screws or other suitable known fastening means) parallel to and slightly above the intended level of the lower edges of the lowermost course of panels, such that a lower portion of the rear faces of the lowermost panels will abut the outer flanges of the J-channels. Preferably, the lateral web of the J-channels will have a mesh, or openings in other suitable forms, to allow for passage of air and/or moisture. Ideally, the mesh or openings will be small enough to prevent insects, rodents, and/or birds from entering the space behind the panels. 
         [0034]    In an alternative embodiment of the panel system, the lower spacer means may be in the form of lower bumpers generally similar to the upper bumpers previously described. The lower bumpers are fastened to the supporting structure at a suitable spacing, such that a lower portion of the rear faces of the lowermost panels abut the lower bumpers, which in turn will maintain the front faces of the lowermost panels in a substantially co-planar relationship (or other desired relationship) with the front faces of the upper panels in the assembly. 
         [0035]    In all of the embodiments described above, the centre of gravity of the panels will be in a position such that the lower edges of the panel will inherently tend to move toward the supporting structure to which they are being mounted. This is a desirable tendency since it helps to maintain the lower panels edges within the notches of the panels below or (as the case may be) against the lower spacer means. This desirable tendency is supplemented for panel embodiments having a tapering thickness (such that the rear face of the upstand is tapered or bevelled), since in these cases the installation of the fasteners mounting the panels to the supporting structure will tend to impart a rotational moment urging the lower panels edges toward the supporting structure. A similar effect may be provided for when using panels having substantially uniform thickness and rearwardly-protruding upstands, by bevelling the rear faces of the upstands. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    Embodiments of the invention will now be described with reference to the accompanying figures, in which numerical references denote like parts, and in which: 
           [0037]      FIG. 1  is a perspective view of a mounted assembly of cladding panels in accordance with a first embodiment of the invention. 
           [0038]      FIG. 2  is cross-section through a typical horizontal joint between cladding panels in the assembly shown in  FIG. 1 . 
           [0039]      FIG. 2A  is a cross-section through the lowermost course of panels in the assembly shown in  FIG. 1 . 
           [0040]      FIG. 3  is a perspective view of the rear face of a cladding panel in accordance with a second embodiment of the invention. 
           [0041]      FIG. 4  is an elevation of the front face of a cladding panel in accordance with one embodiment of the present invention, illustrating a first exemplary fastener hole layout. 
           [0042]      FIG. 5  is an elevation of the rear face of a cladding panel as in  FIG. 4 , having irregularly-formed abutment sections. 
           [0043]      FIGS. 6A and 6B  are top and bottom views, respectively, of a cladding panel in accordance with a preferred embodiment of the invention. 
           [0044]      FIGS. 6C and 6D  are side views of a cladding panel in accordance with the embodiments shown in  FIGS. 6A and 6B . 
           [0045]      FIGS. 6E and 6F  are side views of alternative embodiments of cladding panels in accordance with the present invention, illustrating exemplary optional surface texturing on the front faces of the panels. 
           [0046]      FIG. 7  is a perspective view of a cladding panel in accordance with a third embodiment of the invention. 
           [0047]      FIG. 8  is a cross-section through a typical horizontal joint between cladding panels in the assembly shown in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0048]      FIG. 1  illustrates a mounted assembly of cladding panels  10  in accordance with a preferred embodiment of the invention, and  FIG. 2  illustrates a typical horizontal joint between mounted panels  10 . The panels  10  are shown as being rectangular in shape, but other shapes are also possible without departing from the concept of the invention. Each panel  10  has a front face  20  and rear face  22 . In the embodiment shown in  FIGS. 1 and 2 , the thickness of panel  10  tapers from a top thickness W T  at upper edge  14  of panel  10  to a bottom thickness W L  (which is less than top thickness W T ) at lower edge  16  of panel  10 . Panel  10  is formed with a horizontal notch so as to form a continuous upstand  12  along upper edge  14 . Upstand  12  is inset from front face  20  such that a continuous ledge  15  is formed between upstand  12  and upper edge  14 . Ledge  15  is preferably formed such that when panel  10  is mounted to a support structure  50 , with front face  20  in a substantially vertical orientation, ledge  15  will slope toward front face  20  to facilitate drainage of condensation or other moisture that might run down rear face  22  of the panel  10  above. 
         [0049]    Upstand  12  has a plurality of spaced fastener holes  18 , preferably close to the juncture between upstand  12  and the ledge  15  as shown in  FIG. 2 , for receiving fasteners  32 , which preferably will be threaded fasteners (e.g., wood screws, self-tapping screws, or lag screws as may be appropriate to suit the particular type of supporting structure  50  to which panel  10  is to be mounted), or, alternatively, driven fasteners such as nails or spikes. Fasteners  32  will preferably be of galvanized or stainless steel to prevent or inhibit corrosion. Fastener holes  18  are preferably countersunk, as shown in  FIG. 2 , to accommodate flat-head screws. Fastener holes  18  may be formed in any suitable fashion, and may in fact be formed after panels  10  have cured (e.g., by drilling). Preferably, however, fastener holes  18  will be formed during the casting of panels  10  by means of suitably shaped rubber inserts (such as pieces of tubular rubber) bonded to the panel forms. It has been found that such inserts, due in large part to their flexibility, do not hamper the removal or stripping of cured panels  10  from the forms. 
         [0050]    As shown in  FIGS. 1 and 2 , panels  10  may be mounted to support structure  50  by first fastening a plurality of upper bumpers  30  to support structure  50  in horizontal rows corresponding to the final positions of upstands  12 . Upper bumpers  30  may be made of any reasonably durable material but in preferred embodiments will be made of a firm but resilient material such a rubber, neoprene, or other similar synthetic material. Upper bumpers  30  may be fastened to support structure  50  by any suitable known means, such as nails or screws, which will preferably be of galvanized or stainless steel to prevent or inhibit corrosion. 
         [0051]    It will typically be desirable or necessary to ensure that the front faces of all panels in a finished panel assembly are aligned with each other. For this purpose, lower spacer means will preferably be provided to maintain the lower edges of the panels in the lowermost panel courses at a desired spacing away from the face of the supporting structure. As shown in  FIG. 2A , the lower spacer means may take the form of one or more J-shaped channel sections  70 , each having a generally vertical inner flange  72 , a generally horizontal lateral web  74  extending outward from the bottom edge of inner flange  72 , and a generally vertical outer flange  76  extending upward from the outer edge of lateral web  74 . Typically, J-channels  70  are fastened to supporting structure  50  (using screws or other suitable known fastening means) parallel to and slightly above the intended level of lower edges  16  of the lowermost course of panels  10 , such that rear faces  22  of the lowermost panels will abut outer flanges  76  of J-channels  70 . Preferably, lateral web  72  of J-channels  70  will have a mesh  78 , or openings in other suitable forms, to allow for passage of air and/or moisture. Ideally, the mesh  78  or openings will be small enough to prevent insects, rodents, and/or birds from entering the space behind panels  10 . 
         [0052]    As discussed further on in this specification, lower edges  16  of panels  10  will generally tend to rotate toward supporting structure  50  when fastened thereto, due gravity-induced moment and, in for certain panel configurations, additional moment induced by the installation of fasteners  32 . Accordingly, lower edges  16  of panels  10  in lowermost panel courses will typically have a natural and desirable tendency to press against the lower spaces means. In applications where the lower spacer means comprises J-channels  70 , a continuous or intermittent bead of mastic or other suitable adhesive may be applied to the outer faces of outer flanges  76  prior to installation of the lowermost panel course. Panels  10  of the lowermost panel course will be pressed into the mastic upon installation, thereby creating a positive bond between panels  10  and J-channels  70 , and supplementing the effect of gravity-induced moments to prevent outward movement of lower panel edges  16  of lowermost panels  10  (e.g., due to wind-induced suction pressures acting on the panel assembly). 
         [0053]    A similar beneficial effect may also be achieved at upper horizontal joints between panels  10  by applying mastic to the front faces of panel upstands  12 , prior to installation of above-adjacent panels  10 . In exterior installations in particular, it will typically be preferable for the mastic to be applied as an intermittent bead (i.e., in spaced, short beads) so as not to hamper drainage of moisture through the horizontal joints from behind the panel assembly. 
         [0054]    As an alternative to J-channels  70 , the lower spacer means may be provided in the form of lower bumpers  31  which, although not specifically illustrated in the Figures, may be substantially similar to the previously-described upper bumpers  30 . Lower bumpers  31  may be fastened to support structure  50  slightly above the intended final position of lower edges  16  of the lowermost course of panels  10 . The lateral width or thickness of lower bumpers  31  will typically be greater than that of upper bumpers  30  by an amount corresponding to the difference between top thickness W T  and bottom thickness W L , such that front faces  20  of the lowermost course of panels  10  will be substantially vertical when mounted to a vertical support structure  50 . 
         [0055]    With upper bumpers  30  and lower bumpers  31  in place on support structure  50 , the lowermost course of panels  10  is mounted by positioning each panel  10  with its upstand  12  bearing against two or more upper bumpers  30  and with its lower edge  16  bearing against at least one (and preferably two or more) lower bumpers  31 . Fasteners  32  are inserted through fastener holes  18  in upstands  12 , and securely driven into support structure  50 , thereby anchoring panels  10  in place against support structure  50  and vertically supporting panels  10  therefrom. Due to the use of upper bumpers  30  and lower bumpers  31 , the mounting of panels  10  in the described manner results in the formation of an airspace  60  between rear faces  22  and support structure  50 . Due to the differing thickness of upper bumpers  30  and lower bumpers  31  as previously described, front faces  20  of the lowermost course of panels  10  will be substantially vertical. Due to the tapered configuration of panels  10 , the weight of panels  10  will naturally induce a moment that tends to urge lower edges  16  against their corresponding lower bumpers  31 . Due to the fastener holes  18  being lower than their corresponding upper bumpers  30 , the driving of fasteners  32  into support structure  50  will exert an additional moment that further acts to hold lower edges  16  of the lowermost course of panels  10  against their corresponding lower bumpers  31 . 
         [0056]    Once the lowermost course of panels  10  has been mounted, with their ledges  15  in generally horizontal alignment, the mounting of upper courses of panels  10  is straightforward. As may be appreciated from  FIG. 2 , upper course panels  10  may be set on the ledges  15  of the panels  10  in the course beneath them, thus automatically aligning the upper course while at the same time covering up the heads of fasteners  32  of panels  10  in the course below. Lower edges  16  of the upper course panels  10  are held in position against upstands  12  of the lower course panels  10  by the moments induced by gravity and by the fasteners  32  used to mount the upper course panels  10 , in the same fashion as previously discussed in connection with the lowermost course of panels  10 . The width of ledge  15  is selected to ensure that the front faces  20  of all panels  10  will be substantially vertical, and substantially flush with each other, when their lower edges  16  are positioned against the upstands  12  of the panels  10  beneath them. 
         [0057]    As conceptually illustrated by the water droplets shown in  FIG. 2 , any moisture that accumulates on rear face  22  of a given panel  10  will flow down to the juncture between upstand  12  and ledge  15  of the panel  10  below, and then will be directed toward front face  20  of the lower panel  10 , preferably assisted by a built-in drainage slope on ledge  15  as previously discussed. This drainage toward the front face  20  of the lower panel  10  may be further assisted by forming intermittent notches  19  at the lower edges of rear faces  22 , as shown in  FIGS. 6C-6F . 
         [0058]    It sill be readily appreciated that it is unnecessary to apply caulking or mortar to the horizontal joints between panels  10 , because of the way the panels overlap the panels below. Although not illustrated, alternative variants of the cladding panels of the present invention may be readily devised which also do not require caulking or mortar in vertical joints either, by forming the vertical or side edges of the panels such that they can overlap or interlock with adjacent panels (i.e., in a fashion analogous to shiplap or tongue-and-groove lumber products). This construction detail will prevent or inhibit the entry of moisture (such as from wind-driven precipitation) through the vertical joints and into the space between the cladding panels and the supporting structure. Alternatively, the same effect could be achieved by providing suitably configured flashings associated with the vertical panel joints (e.g., flashing could be installed behind the panels and extending across the vertical joints). 
         [0059]      FIG. 3  illustrates a cladding panel  110  in accordance with an alternative embodiment of the invention, which can be mounted to a support structure  50  without the need for upper bumpers  30  but while still providing for a continuous airspace behind the mounted panel assembly. This is accomplished by forming generally vertical air channels  24  into the upper portion of rear face  22  of panel  110  (and at the same time forming abutment sections  25  between the air channels  24 ). The thickness of panel  110  tapers as previously described in connection with panel  10 , and due to this taper, each air channel  24  intercepts rear face  22  at a point X above lower edge  16  of panel  110 . Accordingly, panels  110  may be mounted to a support structure  50  in much the same fashion as described in connection with the embodiment shown in  FIGS. 1 and 2 , but with the top rear edges  26  of panels  110  bearing directly against the face of support structure  50 . It will still be necessary or desirable in most cases to use lower spacers means when installing the lowermost course of panels  110  (to keep the front faces  20  of lower course panels  110  in desired alignment with upper panels  110 ), but otherwise the system is “bumperless”, further reducing field labour and material costs. Despite the fact that the top rear edges  26  of mounted panels  110  will be in contact with the face of support structure  50 , air channels  24  will ensure that air can circulate behind the mounted panel assembly. 
         [0060]    Persons skilled in the art will readily appreciate that numerous variants may be devised without departing from the basic concept of the invention. For example, while panel  110  shown in  FIG. 3  has equally-spaced fastener holes  18 , this is not essential; as indicated in  FIGS. 4 and 5 , the spacing of fastener holes  18  may be varied as necessary or desirable (subject to minimum structural requirements).  FIG. 5  also illustrates that air channels  24  of “bumperless” embodiments do not have to be regularly-shaped (like the air channels  24  shown in  FIG. 3 ). It has been found that forming air channels  24  in irregular patterns (such as shown in  FIG. 5 ) can produce interesting visual effects on the front faces  20  of the panels, while not affecting the function of air channels  24 . 
         [0061]      FIGS. 6A through 6F  illustrates optional features and designs that may be applied to cladding panels in accordance with the present invention.  FIGS. 6A and 6B  are top and bottom views, respectively, of an alternative embodiment of “bumperless” panels  110 , with air channels of trapezoidal cross-section. As shown, the rearward portion  17 A of side edges  17  may have a 45-degree bevel to facilitate mounting the panels around building corners (i.e., forming what are known in the art as “quirk” joints). Although the side edge bevel is illustrated in the specific context of a “bumperless” panel, this feature would be optionally applicable to other panel embodiments as well. 
         [0062]      FIGS. 6A and 6B  also illustrate how the frontward portion  17 B of side edges  17  may also be bevelled, for visual effect and also to facilitate panel forming and stripping. A 5-degree bevel is shown in  FIGS. 6A and 6B  for exemplary purposes. However, other bevel angles (and indeed other edge treatments) could be used without departing from the present invention; such bevelling or other edge treatments are not essential to the invention. 
         [0063]      FIGS. 6C and 6D  are side views of the panel shown in  FIGS. 6A and 6B . 
         [0064]      FIGS. 6E and 6F  are side views of further alternative embodiments of the cladding panel of the present invention, having different front face profiles,  FIG. 6E  illustrates a panel with an irregular front face profile  20 A (built out from the basic structural thickness of the panel), while  FIG. 6F  shows a panel with a built-out section  20 B of more regular geometric configuration (which could be in the form of spaced vertical ribs or projecting panel sections, or any of many other conceivable designs). Front surface treatments such as illustrated in  FIGS. 6E and 6F  are purely aesthetic considerations, and are not in any way essential to the present invention. 
         [0065]      FIGS. 7 and 8  illustrate a further embodiment  210  of a “bumperless” cladding panel in accordance with the invention. As shown, panel  210  is basically of constant thickness, rather than tapered. Spaced abutment sections  25  are formed along the upper portion of panel  210 , projecting rearward from rear face  22 , with air channels  24  being formed between abutment sections  25 . Fastener holes  18  are located in some or all of the abutment sections  25 , to facilitate mounting of panels  210  to a support structure  50  as shown in  FIG. 8  and generally as previously described, using fasteners  32  driven through fastener holes  18  and into support structure  50 . Abutment sections  25  are preferably formed with a slight taper on their rear faces, as may best be seen in  FIG. 8 . Due to this taper, the driving of fasteners  32  into support structure  50  will exert an additional moment that helps to hold lower edges  16  of panels  210  against the upstands  12  of the panels below. Desirable as this tape may be, though, it is not essential to the present invention, and the rear faces of abutment sections  25  of panel  210  may be unbeveled without departing from the scope of the invention. 
         [0066]    Although the embodiment shown in  FIGS. 7 and 8  is described herein as being “bumperless”, it will be appreciated that lower spacer means will typically be required along the lower edges of the lowermost course of panels  210 , in order to keep their front faces  20  in a desired alignment relative to other panels in the assembly. 
         [0067]    It will be readily appreciated by those skilled in the art that various modifications of the present invention may be devised without departing from the essential concept of the invention, and all such modifications are intended to be included in the scope of the claims appended hereto. It is to be especially understood that the invention is not intended to be limited to illustrated embodiments, and that the substitution of a variant of a claimed element or feature, without any substantial resultant change in the working of the invention, will not constitute a departure from the scope of the invention. 
         [0068]    In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following that word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element may be present, unless the context clearly requires that there be one and only one such element.

Summary:
In a precast cladding panel system requiring no cast-in mounting hardware, each panel has a continuous notch along its upper edge, forming a ledge adjacent the panel&#39;s front face, and an upstand adjacent the panel&#39;s rear face. Each panel is mounted to a supporting structure using fasteners installed through openings formed in the upstand. The panels are configured such that their lower edges fit into the notches of underlying panels, with the front faces of all panels being substantially co-planar, aided by spacer means fastened to the supporting structure adjacent to the lowermost panel course. Air circulation behind the installed panel assembly is facilitated by spaced bumpers fastened to the supporting structure so as to space the panel upstands away therefrom. Alternatively, the panels may be mounted with the upstands directly against the supporting structure, with the panels having vertical air channels formed into the upstands and rear panels faces as appropriate.