A transparent or translucent modular upstanding seam flange panel unit comprising opposed seam flange panels mounted in metal male and female locking engagement members designed to interlock and provide an internal gutter for collecting infiltrating water and for accommodating lateral expansion and contraction of the panels as well as a method for erecting an architectural structure for passing sunlight into an interior region of a building using such panel units.

CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This patent application claims the benefit of U.S. Provisional Patent Application No. 61/045,818, filed Apr. 17, 2008. 
    
    
     FIELD OF THE INVENTION 
     This invention pertains to modular upstanding seam flange glazing panels for architectural structures and, more particularly, to systems for assembling such modular upstanding seam flange panels into unique paired glazing panel units and for installing the units in sloped glazing, skylights, roofs, walls, and other architectural structures in ways not heretofore imagined. 
     BACKGROUND OF THE INVENTION 
     Extruded modular panels with upstanding seam flanges made of polycarbonate and other resins are widely used in the design of various architectural structures because they are a strong, lightweight alternative to traditional materials, like glass, which they often replace. For example, such modular glazing panels joined along abutting upstanding seam flanges that extend along their edges can be used either alone or with a supporting framework of, e.g., purlins or rafters, to form overhead or roofing structures. The ability of such panels to transmit light has made them particularly useful where it is desired to allow sunlight to pass into a structure such as to illuminate the interior region of a building. An additional advantage of these panels is that they have good energy conservation and sound insulation characteristics. Indeed, it has been found that when such glazing panels are paired one over the other into a unit with an enclosed airspace between the panel pair, improved energy conservation and sound insulation properties can be achieved. Paired extruded modular panels also have greater structural strength making them useful in applications where single panel units could not be used or would require additional supporting elements. 
     Each modular upstanding seam flange glazing panel is typically up to 40 feet in length, 2-4 feet wide and flexible. It therefore requires substantial skill and is time-consuming to assemble and install panel pairs on-site. The challenge to assembling and installing the panel pairs faced by such skilled workers can be appreciated, for example, by examining  FIG. 1  which illustrates a current representative panel pair assembly system. More particularly,  FIG. 1  shows a purlin  1  and one of a series of myriad metal retaining clips  2  affixed along the purlin. The retaining clips include horizontal flanges  3 . Once the series of spaced retaining clips are in place on the purlin (or other supporting member), polycarbonate (or other resin) bottom modular panels  4 A and  4 B are manipulated into position and slid horizontally under the flanges of the retaining clips. Then, an elongated resilient batten joint connector  5  with a downwardly facing elongated bottom cavity  6 A is forced down over the upstanding seam flanges  7 A and  7 B of modular panels  4 A and  4 B to lock them onto the retaining clips by way of sawteeth in the bottom cavity that mate with sawteeth on the flanges of the bottom panels. Finally, top modular panels  8 A and  8 B are manipulated into position with their seam flanges  9 A and  9 B aligned with the upwardly facing elongated top cavity  6 B in the batten joining connector and pressed into place with the sawteeth of flanges  9 A and  9 B of modular panels  8 A and  8 B held in place by corresponding sawteeth within cavity  6 B. 
     While there are many typically inferior variations on the paired modular panel unit system of  FIG. 1 , it is indicative of the relative complexity of assembling and installing sloped glazing, skylights, roofs, walls and other architectural structures having paired modular panel units on-site. The system of  FIG. 1  also illustrates the conventional metal (retaining clip) to polycarbonate skin (flange of panel) contact employed in current modular upstanding seam panel retention systems. Because those skilled in this art have been wed to fixing the panels in place through such direct engagement of an unforgiving hard or high ultimate tensile strength metal retention clip against the resilient low ultimate tensile strength skin of the polycarbonate modular panel, it has been necessary to take extra steps to ensure that load specifications are met. For example, skin weight of the panel flanges is greater than it otherwise would need to be in order to prevent cracking of the polycarbonate skin of the flanges under load. This excess weight results in unnecessary material usage/cost and less than optimal light transmission. Also, large numbers of closely spaced retention clips are often required to meet wind load and other load specifications by spreading out the load across more clips also to prevent cracking of the polycarbonate skin of the flanges under load. 
     There is therefore a great need for a system that makes it easier and less time-consuming to assemble and install or erect paired modular panel units. If such a system also provided a completed architectural glazing structure comprised of modular upstanding seam flange panels which is safe, secure, surprisingly strong and able to withstand substantially increased wind loads, a particularly unexpected and useful contribution to the art would be at hand. If such a system further eliminated the inherent limitations of conventional metal-to-polycarbonate engagement, required fewer retention clips, and made it possible to reduce panel flange skin thickness an extremely important and unexpected advance in the art would be in the offing. 
     The present invention provides such a system for readily assembling together pairs of such modular glazing panels either on-site (but in convenient ground level work areas) or off-site and then readily installing the pre-assembled modular panel units on-site to erect the sloped glazing, skylights, roofs, walls, and other architectural structures. This new system is particularly elegant in that it armors the standing seams of the modular panels to thereby provide a unique new metal-to-metal retention that withstands increased wind and snow loads while making it possible to reduce the weight of the polycarbonate skin of the flanges and optionally to use bottom or inner panels with lighter skins across the entire panel. It is also surprisingly economical in terms of materials (e.g., reduced number of retention clips and thinner polycarbonate skins) and in terms of construction costs since it can be erected quickly and generally without special skills, and produces architectural structures that can accommodate wider spans, are surprisingly effective in limiting air, water and sound infiltration, and have outstanding energy conservation characteristics. Indeed, the present system makes it possible to readily insert infill into the airspace between the panels off-site (or on-site) in the form of translucent insulation (e.g., glass fiber), or to add metal screening for improving the fire resistance of the panel unit and for resisting severe localized impacts on the outer panel. It is extremely difficult and expensive to add infill to prior art panel units which must be assembled on-site. 
     Finally, it is important to accommodate horizontal expansion and contraction of the modular panels. While prior systems for assembling and installing panel pairs have a limited ability to accommodate such expansion and contraction, the use of the interlocking male and female locking engagement members of the present invention accommodates such horizontal expansion and contraction far better than any earlier design and in a way not remotely contemplated by those skilled in this art. 
     SUMMARY 
     In one embodiment, the present invention comprises a modular upstanding seam flange panel unit. The unit has opposed transparent or translucent elongated top and bottom upstanding seam flange panels with corresponding elongated upwardly and downwardly directed flanges and an airspace disposed between the panels. The seam flanges are disposed at opposite lateral edges of the panels. Finally, interlocking metal male and female locking engagement members are provided each having upwardly and downwardly disposed cavities attached respectively to the corresponding upwardly and downwardly directed flanges of the panels. The panel flanges each have sawteeth and the cavities of the interlocking metal male and female locking engagement members have corresponding sawteeth that engage the panel flanges. 
     When two panel units are interlocked, the metal male and female locking engagement members of the two adjoining laterally disposed panel units form an internal gutter for collecting any water that infiltrates past the opposed lateral edges of the top modular panels of adjoining modular panels. The bottom of the internal gutter is defined by a guide member that projects from the male locking engagement member in cooperation with a walled cavity in the female locking engagement member that receives the guide member. Also, preferably the walled cavity in the female member includes a resilient member disposed to sealingly engage the guide member when the male and female locking engagement members are interlocked. 
     In another preferred embodiment, the male locking engagement member includes a guide member having a generally downwardly directed nub and the female locking engagement member includes a walled cavity for receiving the guide member with a corresponding generally upwardly directed nub on a wall of the cavity. The upwardly directed nub on the wall of the cavity is positioned to engage the nub on the guide member as the male and female locking engagement members are moved into interlocking position. 
     In another embodiment the invention comprises an architectural structure for passing sunlight into an interior region of a building having supporting structure while limiting the infiltration of water, air and sound. At least two transparent or translucent modular panel units are provided having opposed elongated top and bottom modular panels with corresponding elongated upwardly and downwardly directed flanges and an airspace disposed between the panels. The seam flanges are disposed on opposite lateral edges of the panels. Interlocking metal male and female locking engagement members are disposed respectively at the opposite lateral edges of the panels, with each of the locking engagement members having upwardly and downwardly disposed cavities attached respectively to the corresponding upwardly and downwardly directed flanges. 
     The panel skins have substantially lower ultimate tensile strength than the ultimate tensile strength of the interlocking metal male and female locking engagement members. Finally, a second panel unit a having a locking engagement member is disposed opposite the corresponding locking engagement member of a second one of the units and interlocked therewith. Preferably at least one of the corresponding locking engagement members is affixed to a supporting structure by metal retaining clips. 
     In a preferred embodiment the modular panels of the architectural structure include resilient areas along their lateral edges. These resilient areas accommodate lateral expansion and contraction of the modular panels in conjunction with the interlocking locking engagement members to help control air, water and sound infiltration when the panel units are interlocked and to avoid buckling of the panels as a result of lateral panel expansion. 
     In another embodiment the invention comprises a method of erecting an architectural structure for passing sunlight into an interior region of a building having supporting structure while limiting the infiltration of water, air and sound. The method includes assembling at least two transparent or translucent modular upstanding seam flange panel units having opposed elongated top and bottom modular panels with corresponding elongated upwardly and downwardly directed flanges and an airspace disposed between the panels. The seam flanges are disposed at or near opposite lateral edges of the panels, with interlocking metal male and female locking engagement members each having upwardly and downwardly disposed cavities attached respectively to the corresponding upwardly and downwardly directed flanges at the opposite lateral edges of the modular panels. Finally, the corresponding male and female locking engagement members are interconnected to complete the architectural structure. In a preferred embodiment, at least one of the corresponding male and female locking engagement members is affixed to the supporting structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to aid in understanding the invention, it will now be described in connection with exemplary embodiments thereof with reference to the accompanying drawings in which like numerical designations will be given to like features with reference to the accompanying drawings wherein: 
         FIG. 1  is a partial exploded perspective view of a prior art modular panel pair assembly and installation system; 
         FIG. 2  is a sectional view of a portion of a modular upstanding seam flange panel that may be used in the practice of this invention; 
         FIGS. 3A and 3B  are elevation views taken respectively at ends of male and female locking engagement members of an embodiment of the invention before and after interconnection; 
         FIGS. 4A and 4B  respectively correspond with  FIGS. 3A and 3B  but modular panels are shown installed in the male and female locking engagement members of adjoining panel units; 
         FIGS. 5A and 5B  correspond generally to  FIGS. 4A and 4B  except that alternative male and female locking engagement members are depicted in panel units with an enlarged airspace between the top and bottom panels; 
         FIG. 6  corresponds to  FIG. 5B  except that yet another interlocking male and female locking engagement member design is used in which the locking engagement members are provided with side stiffener bars; 
         FIG. 7  is a partial exploded perspective view of another modular panel design which may be used in the practice of the invention; 
         FIGS. 8A and 8B  are, respectively, partial elevation views of panel units using still other locking engagement member designs with the modular panels of  FIG. 7 , before and after interconnection of the panel units; and 
         FIG. 9  is a partial elevation view of the tops of adjacent panel units assembled in accordance with the present invention in which a gasket is disposed in the gap between the adjacent top panels and held in place by a pin affixed to one of the locking engagement members of the units. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning now to  FIG. 2 , a single modular upstanding seam flange panel  10  is shown in cross-section, with a seam flange  12  at its distal end  14 . The seam flange extends along the entire length or lateral edge of the panel which may be, for example, up to 40 feet in length and from 2 to 4 feet in width. A second flange will be located along the opposite edge of the modular panel parallel to flange  12 . Of course, the panels may be provided in other sizes if desired. 
     Modular panel  10  may be extruded from polycarbonate (or other resin) and may have a plurality of internal cells in a honeycomb configuration  17  (or other configuration) disposed in the interior of the panel between its outer surface  16  and its inner surface  18 . Modular panels  10  with this upstanding seam flange design are known in the art and described for example in U.S. Pat. No. 6,164,024, which is incorporated by reference for purposes of describing the panels and installations in which they may be used. Modular panels with upstanding seam flanges of the design shown in  FIG. 2  and modified versions thereof that function generally in the same fashion, made of polycarbonate or other resins, will be referred to herein as “modular panels,” “modular upstanding seam flange panels,” etc. 
     The preferred honeycomb cell configuration  17  of modular glazing panels  10  helps control the panel thermal expansion in all directions and gives it resistance to impact and wind and snow loading while maintaining superior light-difusion capabilities. Particularly desirable modular panels  10  are available from CPI Daylighting, Inc., 28662 Ballard Drive, Lake Forest, Ill. 60045 as PENTAGLAS®NANO-CELL® architectural panels. 
     Upstanding seam flanges  12  have a series of sawteeth  20  along their inner surface  22  and will generally be flat along their outer surface  24  optionally with the protruding open bubble corner area  146  discussed below. The surface  26  of the flanges (at the top or bottom of the flanges depending on how it is oriented in the panel unit) may also be flat. Additionally, it should be noted that preferably the flanges also include internal cells to give them enhanced strength, resilience, and expansion/contraction properties. Other modular panel designs appear in  FIGS. 6 ,  7  and  8  and will be addressed below. In all cases the modular panels have a thin low ultimate tensile strength skin. 
     In accordance with one embodiment of the invention,  FIG. 3A  shows a metal female locking engagement member  30  and its corresponding metal male locking engagement member  32  with a metal retention clip  34  juxtaposed between the two. Members  30  and  32  are designed to interlock as illustrated in  FIG. 3B . Both locking engagement members may be made, for example, as aluminum extrusions and are each configured for attachment to upstanding seam flanges  12  of corresponding pairs of panels to construct a panel unit while armoring the standing seam flange to thereby provide a panel surface for metal-to-metal engagement with retention clip  34 . The metal construction of the clips means that they have high ultimate tensile strength. 
     The armoring of the skin of the flanges by the metal of the locking engagement members protects the flanges (and panels) from damage at the points of contact by the retention clip and elsewhere that might otherwise occur due to wind or snow loads. It also makes the entire panel unit substantially stronger making it possible to reduce the weight of the skin of the panel flanges and to use the panel unit across spans and in other applications in which conventional panel units could not be used without additional retention clips and structural support. Indeed, unlike conventional systems where the bearing load is sustained primarily by the bottom or inner panel, in the present invention the load is sustained primarily by the male and female locking engagement members and the top or outer panel so an overall lighter skinned inner panel can be used. 
     In  FIG. 3A , female locking engagement member  30  is disposed vertically (as it would be, e.g., at rest in a horizontal roof or skylight installation) and male locking engagement member  32  is angled with respect to the female locking engagement member to correspond to the orientation of the locking engagement members during the course of final on-site or erection process which concludes with the panel units installed in the juxtaposed arrangement of, e.g.,  FIG. 4B . Alternatively, the panel units may be installed by aligning them vertically and sliding them together until the locking engagement members interlock. 
     Female locking engagement member  30  includes a base  36  which is oriented vertically in the figure and generally U-shaped upwardly and downwardly directed arms  38  and  40  which depend from the back surface  42  of the base. Arm  38  includes a generally flat horizontal portion  44  and a generally flat vertical portion  46 . Horizontal portion  44  includes an optional angled outer corner portion  45  to enhance the resilience and resistance to breakage of arm  38  at this corner. The back surface of the base and the U-shaped arm together define an upwardly directed cavity  48  for receiving the flange of the top modular panel of panel unit  142  as illustrated in  FIGS. 4A and 4B . Finally, at least one sawtooth and preferably at least two sawteeth  50  (as shown) project from back surface  42  into cavity  48  to engage sawteeth  20  on upstanding flange  12  of panel  10  in the assembly of the modular panel unit on locking engagement member  38 . Sawteeth  50  include horizontal portions  52  and angled portions  54  which are angled and dimensioned to engage sawteeth  20  of the panel flange. 
     In a like manner, downwardly directed U-shaped arm  40  includes a generally horizontal portion  56  and a vertical portion  58 . The horizontal and vertical portions define a downwardly directed cavity  60  which will engage the upstanding flange of a second panel of the modular panel unit assembled on locking engagement member  38 . Horizontal portion  56  may be stepped downwardly, as shown, to produce a slot  62  having an upwardly directed lip  64  for receiving engagement hook  74  of retention clip  34  and achieving a metal-to-metal retention of the panel unit flange. Other alternative structural arrangements for engagement between the retention clip and the locking engagement member may, of course, be used so long as metal-to-metal engagement is ensured. 
     Retention clip  34  includes a base  66  with a hole  68  for receiving a fastener  70  which will be driven or screwed into a purlin, rafter or other support (not shown) to hold adjoining juxtaposed modular panel units (e.g., units  142  and  144  of  FIG. 4B ) in place. Base  66  supports an upstanding wall  72  and an engagement hook  74 . The hook includes a ledge  75  and a downwardly directed lip  76  dimensioned to fit within slot  62  and engage the inner surface of locking engagement member lip  64  to retain female locking engagement member  30  and (after it is interlocked with the corresponding female locking engagement member) adjoining male locking engagement member  32  in place during the on-site erection of the desired sloped glazing, skylights, roofs, walls, and other architectural structures from series of juxtaposed panel units. As noted elsewhere, however, in short span applications the panel units may be interconnected and erected in place without the use of retention clips. 
     Horizontal portions  44  and  56  of upwardly and downwardly directed arms  38  and  40  are spaced from each other to define or wall in a horizontally directed inner cavity  80 . Inner cavity  80  receives a guide member  82  of male locking engagement member  32  and in doing so helps form an inner gutter  81  ( FIG. 3B ) in the final interconnected locking engagement member pair  83 , which will be discussed in more detail below. The guide member is responsible for resisting loads on the interconnected locking engagement members and so must be strong and long enough to accommodate the maximum expected load on the interconnected locking engagement members. 
     Preferably a resilient sealing strip  84  will be positioned in cavity  80  along the back surface  42  of base  36  in horizontally directed inner cavity  80  to engage guide member  82  establishing a gutter seal  90  to help achieve and maintain a water-and air-tight condition in inner gutter  81  while also enhancing the soundproofing properties of the final interconnected locking engagement member pair  83  as illustrated in ( FIG. 3B ) Inner gutter  81  in turn carries the water to an open end of the interconnected locking engagement members where a still and appropriate flashing will be provided to collect escaping water and to carry it away from the slopped glazing, skylight, roof, wall or other architectural structure. 
     Also, top corner  85  of step portion  62  preferably will have a nub  86  with front and back inclined surfaces  87  and  88  which facilitate the interlocking process as will be described below. Finally, an optional water rail  90  projects away from the outer surface  92  of vertical portion  46 . As will be discussed further below, this rail directs any water that infiltrates or is drawn down between the adjacent top panels of juxtaposed panel units and will move down surface  92  due to surface tension effects or through the gap  96  between vertical portions  46  and  108  away from gutter seal  91  to minimize the likelihood that the water will find its way to the gutter seal. 
     Turning now to male locking engagement member  32  in  FIG. 3A , it is seen that this locking engagement member has a base  100  and U-shaped upwardly and downwardly directed arms  102  and  104  which depend from the back surface  106  of the base. Arm  102  includes a generally flat vertical portion  108 , and a bottom  110  made up of a first flat portion  112  generally perpendicular to base  100  and second upwardly angled flat portion  114 . This bottom configuration is chosen to enhance the resilience and resistance to breakage like the corner on arm  38  described above and is, of course, optional. Back surface  106  of base  100  and U-shaped arm  102  together define a generally upwardly directed cavity  116  for receiving the downwardly directed flange of the top modular glazing panel of the panel unit, as will be described below. Finally, sawteeth  50  project from back surface  106  into cavity  116  to engage sawteeth  20  on upstanding flange  12  of a modular panel  10 . Sawteeth  50  include horizontal and angled portions that are dimensioned to engage sawteeth  20  of the modular panel flange. 
     Downwardly directed U-shaped arm  104  of the male locking engagement member includes a generally horizontal portion  120  and a vertical portion  122 . Arm  104  and base back surface  106  define a downwardly directed cavity  124  which will engage the upstanding flange of the second panel of modular panel unit  142  ( FIG. 4B ). 
     As in the case female locking engagement member  30 , horizontal portion  120  may be stepped downwardly, as shown, to produce a slot  126  having an upwardly directed lip  128  for receiving engagement hook  74  of retention clip  34  and armoring the panel flange to achieve a metal-to-metal engagement. Other alternative structural arrangements for engagement between the retention clip and the locking engagement member may, of course, be used. Also, as can be readily understood from  FIG. 3A , retention clip  34  may be rotated 180 degrees to engage slot  126  and lip  128  of the male locking engagement member rather than step  62  and upwardly directed lip  64  of the female portion, depending on construction requirements and the desire of the installer erecting the modular glazing panel units in place. Of course, as noted earlier, in less preferred embodiments other locking configurations could be used and, indeed, only one of the male and female locking engagement members may be provided with the slot and lip for accommodating the retention clip. In all cases, the resulting metal-to-metal interconnection represents a significant advance over prior systems, providing greatly enhanced resistance to wind load and other advantages as discussed earlier. 
     Guide member  82  includes a spine  83  that projects generally perpendicularly relative to surface  106  of base  100  and in this embodiment extends from portion  120  of downwardly directed U-shaped aim  104 . Member  82  has a nub  130  adjacent its distal end  132  which projects downwardly from its bottom surface  134  to cooperate with nub  85  on portion  56  of the female locking engagement member during the interconnection of the male and female locking engagement members as will be explained below. Nub  130  has front and back inclined surfaces  136  and  138  which facilitate the interlocking process and help keep the corresponding locking engagement members together as installation of the panel units proceeds. 
     An end flange  140  is located at the distal end of spine  83  of guide member  82 . Flange  140  has a generally flat outer surface  142  and an optional hook portion  145  which is dimensioned to rest below horizontal portion  44  of the female locking engagement member when the male and female locking engagement members are interconnected as in  FIG. 3B  to help limit water entering the inner gutter from reaching gutter seal  90  and to limit upward movement due to loading on the guide member. Finally, spine  82  and end flange  140  are dimensioned to ensure that when the male and female locking engagement members are interlocked as in  FIG. 3B , flat outer surface  141  will abut (and preferably compress) resilient insulating strip  84  in cavity  80  of the female locking engagement member. 
     Turning now to  FIGS. 4A and 4B  (which correspond to  FIGS. 3A and 3B ), female and male locking engagement members  30  and  32  are shown with modular glazing panel units  10  locked into respective upwardly and downwardly directed cavities  48 ,  60 ,  106 , and  124  by the engagement between sawteeth  20  of the panel units and sawteeth  50  of the locking engagement members. This forms modular panel units  142  and  144 . Such units may be assembled either on-site in a convenient ground level area or off-site and transported to the work site. Once at the worksite the panel units will be erected into sloped glazing, skylights, roofs, walls or other architectural structures. 
     The modular panels in panel units  142  and  144  also include optional resilient areas in the form of, e.g., protruding open bubble areas  146  at the lateral edges of the panels. These open bubble areas substantially increase the resilience of the panel edges so that they can deform when the corresponding lateral edges of the panels move in and out due to lateral panel expansion and contraction. The adjacent resilient panel areas cooperate with the male and female locking engagement members which also accommodate lateral movement. Thus, unlike prior art systems where the lateral panel expansion cause the panels to bow, the present panels remain flat. At the same time, these resilient edges close the gap between adjacent panels to help in limiting or preventing air, water and sound infiltration. Other gap sealing approaches can of course be used. 
     Referring to  FIGS. 4A and 4B , the installation method of the invention may proceed as follows:
         A. First, examplary  40  foot panel units  142  and  144  of  FIG. 4A  are assembled, transported to the work site if necessary, and then preferably oriented and pre-positioned conveniently to the location where they will be installed. It should be noted that panel unit  142  has a male locking engagement member at its opposite (hidden) lateral edge whereas panel unit  144  has a female locking engagement member at its opposite (hidden) lateral edge.   B. Next, unit  142  may be positioned on the appropriate purlin or rafter (not shown) and locked in place by a series of retention clips  34  spaced, e.g., about 4 to 10 feet apart with their engagement hooks engaging slots  62  and lips  64  of the female locking engagement member which in turn engages armor the 40 foot modular panel flanges. As noted earlier, attachment to the male locking engagement members may proceed from the other side by rotating the retention clip 180 degrees and first installing panel unit  144  by way of attachment slots  126  and lips  128  of the male locking engagement members. Also, for shorter spans the assembly may not require intermediate support making it possible to dispense with the use of retention clips.   C. Assuming that unit  142  is already affixed in position, modular glazing panel unit assembly  144  is then juxtaposed against unit  142  with its lateral edge  160  opposite the lateral edge  162  of the already affixed panel unit  142 . In this orientation, guide member  82  will be located opposite inner cavity  80  of female locking engagement member  30 .   D. Then, panel unit  144  will be pivoted about adjoining lateral edges  160  and  162  as inclined surface  136  of nub  130  on the guide member first engages inclined surface  87  on nub  85  of the female member and the nub  130  rides over numb  85  causing an audible “click” and providing the installer with a tactile indication that the male and female locking engagement members are properly interconnected with flat outer surface  141  of flange  140  abutting and preferably compressing resilient insulating strip  84  as depicted in  FIG. 3B  and the lower lateral panel edges  164  and  166  abutting as well. When the locking engagement members are interconnected in this way abutting inclined surfaces  88  and  138  will maintain units  142  and  144  together so that the installer can move to the next lateral adjacent position to begin installing the next panel unit.   E. In an alternative installation approach, panel unit  144  may be vertically aligned and slid horizontally into place until the locking engagement members are interconnected.   F. This process continues until the outer panel units are reached. The outer panels are affixed by conventional perimeter framing. Thus a series of units held in place by retention clips as illustrated in  FIG. 4B  and confined by outer panels or separate conventional structural members to ensure that the entire installation will withstand substantial loads even up to hurricane levels while providing outstanding resistance to air, water and sound infiltration as well as outstanding energy conservation characteristics and the ability to accommodate lateral expansion and contraction of the modular panels to a degree not heretofore thought possible.       

       FIGS. 5A and 5B  illustrate an alternative embodiment of the invention in which female and male locking engagement members  202  are used to assemble panel units  204  and  206 . As is apparent in these figures, locking engagement members  200  and  202  are taller than locking engagement members  30  and  32  thus establishing a taller and larger airspace between the module panel pairs. For example, the airspace of the units of  FIGS. 4A and 4B  may be, for example, about 2.5 inches in height whereas the airspace of the units of FIGS.  5 A and  5 B may be, for example, about 4.0 inches in height. This height difference is achieved by incorporating a second inner cavity  80 A and corresponding second guide member  82 A spaced a distance “x” from the first inner cavity. Smaller and larger inner cavities and guide members as well as more than two pairs of these features may be used. These additional features further enhance the installation process by, e.g., improving the signaling and interlocking operation of the male and female locking engagement members. The greater height airspace panel units are also stiffer, further enhancing their ability to withstand loads and the added lower inner gutter  81 A (which may optionally be fitted with a gasket strip) further limits water and sound infiltration. 
       FIG. 6  illustrates yet another alternative embodiment of the invention in which male and female locking engagement members  250  and  252  are used. These locking engagement members generally correspond to locking engagement members  200  and  202  of  FIGS. 5A and 5B  except that the locking engagement members are provided with outer brackets  254  and  256  for holding side stiffener bars. The side stiffener bars run along the locking engagement member improving the section moment of inertia of the locking engagement members, thereby enhancing the load capacity characteristics of the overall panel unit and its ability to handle longer spans. The side stiffener bars are preferably made of solid aluminum or steel although they may be hollow if desired. 
       FIG. 7  depicts a modular panel  300  having a double connector design comprising an outer connector  302  and an inner standing seam flange  304 . Such panels are shown installed in male and female locking engagement members  306  and  308  in  FIGS. 8A and 8B  forming panel units  310  and  312 . The locking engagement members use the pivoting or sliding interlocking motion of the earlier-described locking engagement members and form an inner gutter  324  in the same way using like structural features. Upstanding lip  314  onto which a hook  74  of a retention clip  34  is fit again achieves the metal-to-metal engagement discussed earlier. Additionally, the female locking engagement member includes a ledge  316  on which outer panel connector  302  rests to provide enhanced load bearing capability and a downwardly directed shoulder  318 . Male locking engagement member  306  has a corresponding first shelf  320  for supporting the outer connector  302  of the adjacent panel  300  of panel unit  310 . Finally, shelf  320  jogs downwardly to provide a second lower shelf  322  which engages downwardly directed shoulder  318  of the female locking engagement member when the panel units are interconnected as depicted in  FIG. 8B . The engagement of shoulder  318  and shelf  322  is the first line of defense against the infiltration of water into the inner gutter  324  in the interconnected units and also provides enhanced load bearing capabilities ( FIG. 8B ). 
     Finally,  FIG. 9  is a partial view of the top modular panels of two panel units interconnected using male and female locking engagement members  300  and  302 . This Figure is included to illustrate an alternative embodiment in which the lateral edges  304  and  306  of the panels are spaced from each other. In this arrangement, a resilient gasket  308  is fitted into the gap between the panel edges and held in place by a pin  310  affixed to locking engagement member  300 . 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.