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CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit under 35 U.S.C. 119(a) of Canadian Patent Application No. 2,907,245, filed Oct. 5, 2015, the entirety of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates generally to building construction, and more particularly to the use of corrugated furring strips that are particularly useful in steel-framed cladded wall construction with a rainscreen, where potential benefits include reduced thermal bridging and improved ease of installation. 
     BACKGROUND 
     In commercial grade building construction, it is common to employ a multi-layered wall construction in which vertical steel studs are covered with an external sheathing layer, over which a series of metal Z-channels are installed with rigid insulation panels between them to define an external insulation layer, over which another series of metal channels (e.g. hat-channels) are then installed as furring to support the final exterior cladding layer at a spaced distance from the underlying insulation layer in order to create a rainscreen, whereby the resulting air space between the cladding and the insulation space allows drainage and evaporation to occur. This construction method is material and time intensive, requiring installation of the sheathing, addition of the Z-channels thereto, insertion of the insulation between the Z-channels, subsequent mounting of the hat-channels, and finally installation of the exterior cladding. In addition, each Z-channel creates a thermal bridge across the insulation layer over the full length of the channel, thereby reducing the effectiveness of the insulation layer. 
     Applicant has developed a new furring product and new resulting steel wall construction that addresses the forgoing shortcomings of the forgoing conventional steel wall construction technique. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, there is provided, in combination, an upright wall structure, an exterior cladding for said upright wall structure, and a furring strip comprising an elongated strip of material that is corrugated with alternating lands and grooves in a longitudinal direction of said elongated strip, wherein the elongated strip is mounted to an exterior side of the upright wall structure in abutment therewith at the grooves of the elongated strip, and an interior side of the exterior cladding is mounted to the elongated strip at the lands thereof on an opposite side of an air space that is maintained between said exterior cladding and said upright wall structure by the elongated strip, whereby the elongated strip situates the exterior cladding across the air space from the upright wall structure to create a rainscreen that enables drainage and evaporation from behind the exterior cladding. 
     According to a second aspect of the invention, there is provided a finished exterior wall comprising: 
     a wall structure comprising:
         a plurality of framing members;   sheathing supported on the plurality of framing members;   an insulation layer situated on an exterior side of the sheathing opposite to the framing members;       

     furring strips disposed externally of the insulation layer on an outer side thereof opposite the sheathing; each furring strip being corrugated with alternating lands and grooves in a longitudinal direction of said furring strip, the furring strips being oriented with the lands held outwardly away from the insulation layer and the grooves being recessed toward the insulation layer from said lands, and the furring strips being fastened to the framing members at the grooves in said corrugated furring strips; and 
     exterior cladding placed over, and fastened to, the lands of the corrugated furring strips, whereby the corrugated furring strips space the exterior cladding outwardly away from the insulation layer to create a rainscreen; 
     wherein the corrugated furring strips are abutted directly against the insulation layer with no intermediate disposed therebetween. 
     According to a third aspect of the invention, there is provided a method of assembling a finished exterior wall, the method comprising: 
     on a wall structure having a plurality of framing members, sheathing supported on the plurality of framing members, and an insulation space situated on an exterior side of the sheathing opposite to the framing members: 
     (a) installing corrugated furring strips externally of the insulation space on an outer side thereof opposite the sheathing with lands of the corrugated furring strips held outwardly away from the insulation space and grooves of the corrugated furring strips recessed toward the insulation space from said lands, including fastening the furring strips to the framing members at the grooves in said corrugated furring strips; and
         (b) installing exterior cladding over the lands of the corrugated furring strips, whereby the corrugated furring strips space the exterior cladding outwardly away from the insulation space;       

     wherein step (a) comprises starting at one end of the wall structure, and in a single pass moving toward an opposing second end of the wall structure, inserting insulation material into the insulation space and periodically fastening the corrugated furring strips in place through inserted pieces of said insulation material prior to insertion of subsequent pieces of said insulation material into the insulation space. 
     According to a fourth aspect of the invention, there is provided a furring strip comprising an elongated strip of material that is corrugated with alternating lands and grooves in a longitudinal direction of said elongated strip, and has at least one longitudinal rib formed in said elongated strip. 
     According to a fifth aspect of the invention, there is provided a furring strip in combination with an upright wall structure, a plurality of fasteners by which the furring strip is mounted to said upright wall structure, and a plurality of washers respectively installed between the elongated strip and heads of said plurality of fasteners, wherein the furring strip comprises an elongated strip of material that is corrugated with alternating lands and grooves in a longitudinal direction of said elongated strip and the washers are less thermally conductive than the fasteners. 
     According to a sixth aspect of the invention, there is provided a furring strip in combination with a land-covering bridging member, the furring strip comprising an elongated strip of material that is corrugated with alternating lands and grooves in a longitudinal direction of said elongated strip, and the land-covering bridging member being arranged for mating with the furring strip in a position lying perpendicularly thereto with a cross-sectional profile of the land-covering bridging member conformingly overlying a respective land of the elongated strip and reaching downwardly into adjacent grooves on opposite sides of said respective land. 
     According to a seventh aspect of the invention, there is provided a furring strip in combination with a groove-occupying bridging member, the furring strip comprising an elongated strip of material that is corrugated with alternating lands and grooves in a longitudinal direction of said elongated strip, and the groove-occupying bridging member being arranged for mating with the furring strip in a position lying perpendicularly thereto with a cross-sectional profile of the groove-occupying bridging member received in a respective groove of the elongated strip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One embodiment of the invention will now be described in conjunction with the accompanying drawings in which: 
         FIG. 1  is an elevational view illustrating horizontal installation of corrugated metal furring strips to exterior sheathing during erection of a steel construction exterior wall. 
         FIG. 2  is an elevational view illustrating vertical installation of corrugated metal furring strips to exterior sheathing during erection of a steel construction exterior wall. 
         FIG. 3A  is a plan view of an outside corner of the steel construction exterior wall of  FIG. 1 . 
         FIG. 3B  is a plan view of an inside corner of the steel construction exterior wall of  FIG. 1 . 
         FIG. 4A  is a plan view of an outside corner of the steel construction exterior wall of  FIG. 2 . 
         FIG. 4B  is a plan view of an insider corner of the steel construction exterior wall of  FIG. 2 . 
         FIG. 5A  is an isolated view of a bridging member that spans between the corrugated furring strips of  FIGS. 1 and 2  in a position overlying matching lands of the two corrugated furring strips. 
         FIG. 5B  is a cross-sectional view of the bridging member of  FIG. 5A  as taken along line B-B thereof. 
         FIG. 5C  is a cross-sectional view of the bridging member of  FIG. 5A  as taken along line C-C thereof. 
         FIG. 6A  is an isolated view of a support brace for providing auxiliary support to the bridging member of  FIG. 5A  at an intermediate location between the corrugated furring strips. 
         FIG. 6B  is a cross-sectional view of the support brace of  FIG. 6A  as viewed along line B-B thereof. 
         FIG. 6C  is a cross-sectional view illustrating the bridging member and support brace of  FIGS. 5C and 6B  in cooperative assembly with one another. 
         FIG. 7A  is an isolated view of another bridging member that spans between the corrugated furring strips of  FIGS. 1 and 2  in a position occupying matching grooves of the two furring strips. 
         FIG. 7B  is a side view of the bridging member of  FIG. 7A . 
         FIG. 7C  is a cross-sectional view of the bridging member of  FIG. 7A , as viewed along line C-C thereof, in combination with fasteners for attaching the bridging member to the corrugated furring strips. 
         FIG. 7D  is a cross-sectional view similar to  FIG. 7C , but showing the bridging member thereof in cooperative assembly with one of the corrugated furring strips. 
     
    
    
     In the drawings like characters of reference indicate corresponding parts in the different figures. 
     DETAILED DESCRIPTION 
       FIGS. 3A and 3B  illustrate a construction of a steel framed externally insulated exterior wall using corrugated metal furring strips  10  to support the final exterior cladding layer  18  of the finished wall. The wall features a series of vertically upright steel studs  12  horizontally spaced apart from one another at regular intervals to form a structural framework of the wall, and a layer of exterior sheathing  14  fastened to the studs  12  at outwardly facing edges thereof. A layer of insulation  16  resides opposite the studs on the external side of the sheathing  14 , and may feature semi-rigid mineral wool, rigid insulation, insulation panels, structural insulated panels (SIP), or other thermal insulation. Each furring strip  10  is mounted opposite the sheathing  14  on the outer side of the insulation layer  16 , and is fastened to the studs  12  through the insulation layer  16  and underlying sheathing  14 . The finished wall is completed by the installation of cladding  18  over the furring strips  10 , which act to space the cladding  18  outwardly away from the underlying insulation layer  16  in order to create a rainscreen having an open airspace behind the cladding  18  for drainage and evaporation purposes. 
     Each corrugated furring strip  10  has a longitudinal direction in which its corrugated shape alternates between lands  20  and grooves  22 . In longitudinal planes parallel to the longitudinal direction of the furring strip  10 , the lands  20  are flat or linear in shape, and the grooves are trapezoidal. A floor or bottom  22   a  of each groove  22  lies coplanar with the floors or bottoms of the other grooves, and parallel to the lands  20 , which are likewise coplanar with one another. The floor or bottom  22   a  of each groove is obliquely joined to the two neighbouring lands  20  by angled side walls  22   b  of the groove&#39;s trapezoidal shape. The furring strips  10  are installed in an orientation placing the floor or bottom  22   a  of each groove against the outer side of the insulation layer  16  (i.e. the side thereof facing outwardly away from the interior space of the building). The lands  20  are thus held outwardly away from the insulation layer  16  by the angled side walls  22   b  of the grooves, while the bottom  22   a  of each groove is recessed toward the insulation layer from the lands  20 . To support the furring strips  10 , threaded fasteners  24  are driven through the furring strips  10  at select grooves  22  that align with the studs  12  of the wall&#39;s structural framework. 
       FIGS. 1 and 3  illustrate horizontal installation of the furring strips, in which case the longitudinal direction of each corrugated furring strips spans horizontally across multiple studs  12  and is accordingly fastened to more than one such stud. While the bottoms of the fastened grooves are held against the insulation by the fasteners, drainage and airflow vertically across the horizontal furring strip is allowed by the open space between the insulation and the lands  20  on both sides of each fastened groove. 
       FIGS. 2 and 4A -B illustrate vertical installation of the furring strips, in which case the longitudinal direction of each corrugated furring strip spans vertically along a singular studs  12  at a position aligned therewith across the insulation and sheathing layers, and so each furring strip is fastened only to a respective single stud at vertically spaced positions therealong. If the framework of the wall features bridges or blocks spanning horizontally between adjacent studs, furring strips may additionally be fastened to such components of the framework at grooves of the furring strips that align therewith. The open space between the insulation layer and each land enables airflow across the vertical furring strip to communicate the airspaces or cavities on opposite sides of each furring strip with one another. 
     To minimize thermal bridging between the interior and exterior of the finished wall, each threaded fastener  24  is fitted with a washer ( 26 ) of thermally insulative material that has lower thermal conductivity than the threaded fastener  24  and the corrugated furring strip, whereby the head of the fastener  24  is separated from the floor or bottom  22   a  of the groove  22  by the washer  26  in order to thermally isolate the furring strip  10  from the fastener  24 . The fasteners  24  are the only members traversing the insulation layer  16 , thus reducing the amount of thermal bridging compared to conventional steel wall construction techniques in which Z-channels traverse the external insulation layer. Together with the insulative washers  26  that reduce conductive heat transfer from the fasteners  24  to the corrugated metal furring strips  10 , the insulation layer of the finished wall structure is particularly effective. 
     As shown in  FIGS. 1 and 2 , the floor or bottom  22   a  of each groove  22  in each furring strip  10  features a predefined fastener opening  28  having an oblong shape that is elongated in the longitudinal direction of the furring strip  10 . The width of the oblong shape (measured perpendicularly of the longitudinal direction along the minor axis of the oblong shape) slightly exceeds to the diameter of the threaded fasteners  24  to accommodate passage of the respective fastener  24  through the fastener opening without requiring drilling of the metal furring strip during installation. The length dimension of the fattener opening  28  measured in the longitudinal direction on the major axis of the oblong shape exceeds the width of the fastener opening in order to accommodate a degree of longitudinal adjustment of the fastener position along the floor or bottom of the groove to enable proper alignment of the fastener with a respective stud  12  of the wall framework in the case of horizontal installation of the furring strip  10 . 
     Each furring strip  10  features a pair of longitudinal ribs  30  at each land  20 , and a matching pair of longitudinal ribs at the floor or bottom  22   a  of each groove  22 . The two ribs of each pair lie parallel to the central longitudinal axis of the furring strip  10  at symmetric positions on opposite sides thereof, and so each rib thus resides adjacent a respective side edge of the furring strip. The longitudinal ribs  30  are of radiused curvature in cross-sectional planes lying normal to the longitudinal direction, and serve to reinforce the strength of the corrugated strip. During manufacture, each strip may be pressed into its corrugated form from an initially flat strip-shaped blank, which for example may have been punched or cut from a larger metal sheet, and then punched in one or more operations to create the oblong fastener openings  28  and the longitudinal reinforcement ribs  30 . While the drawings show separation of the ribs on the floor of each groove from the ribs on the adjacent lands, i.e. a lack of illustrated connecting ribs on the side walls of the groove that join up with the ribs on the lands and the groove floors, the furring strip may alternatively feature full-length ribs continuously spanning the entirety of the strip from one end to the other. In such instance, the continuous full-length ribs may be pressed into the sheet or blank prior to forming thereof into the final corrugated shape. 
       FIG. 1  illustrates horizontal installation of the corrugated furring strips  10  during erection of a steel-framed, externally insulated wall. Here, the insulation layer  16  is formed by elongated rectangular insulation panels  32  that are mated together side-by-side in upright orientations over the underlying stud framework of the wall. Each furring strip  10  spans across a plurality of the insulation panels  32  and is fastened to the regularly spaced framework studs  12  through the insulation panels. To accomplish this, the insulation panels and furring strips  10  may be installed together during a single pass along the sheathed wall framework from one end to the other. Starting at one end, a first insulating panel, or first set of two or more insulating panels, are placed up over the sheathing, and then one of the furring strips is held up at a selected height and a first threaded fastener  24  is driven into a stud at this starting end of the sheathed wall structure through the underlying first insulation panel. At any subsequent studs likewise already covered by the initially placed insulation panel(s), a respective fastener  24  (accompanied by a thermally insulative washer  26 ) is driven into the stud  12  through insulation layer  16  at the respective groove  22  of the corrugated furring strip  10 . This placement and fastening of a corrugated furring strip is repeated at another height on the same wall at a positioned spaced from and parallel to the first strip, for example to accomplish the illustrated two-strip furring configuration of  FIG. 1 . The next insulation panel (or next group of panels) is then inserted behind the furring strips and shifted back toward the first end of the wall framework in order to mate with the last inserted insulation panel at the upright side edge thereof, at which point the furring strips can be fastened into the next stud  12  through this latest insulation panel. These steps are repeated until the installer reaches the second end of the wall framework, where this same process can be repeated along the next side of the building until the full perimeter of the building has been furred. 
       FIG. 2  illustrates vertical installation of corrugated furring strips  10 . Here, the insulation layer  16  is again formed by elongated rectangular insulation panels  32 , but this time mated together in horizontal orientations stacked one atop the other over the underlying stud framework of the wall. Each furring strip  10  spans vertically across a plurality of the insulation panels  32  and is fastened to a respective singular stud  12  of the wall framework. Again, the insulation panels and furring strips  10  may be installed together during a single pass along the sheathed wall framework from one end to the other. Starting at one end, a first set of two or more insulating panels are stacked atop one another over the sheathing, and then one of the furring strips is aligned over the first stud at this first end of the sheathed wall framework and fastened into place using a series of threaded fasteners  24  driven into the first stud through the insulation panels at grooves of this first furring strip, again using the insulative washers  26 . At any subsequent studs likewise already covered by the first stack of insulation panel(s), an additional respective furring strip is likewise fastened in place in alignment with the respective wall stud  12 . The next set of insulation panels are then stacked up and mated side-to-side with the previous stack, with corresponding furring strips then respectively fastened to the studs residing behind this latest stack of insulation panels. These steps are repeated until the installer reaches the second end of the wall framework, where this same process can be repeated along the next side of the building until the full perimeter of the building has been furred. 
     In the forgoing installation processes, the insulation and furring strip are installed in conjunction and do not require two separate steps, substantial additional fasteners, adhesives or supplementary layers of additional metal framing or furring, as is traditionally required. Cladding is subsequently installed over the lands of the furring strips, whereupon the corrugated strips provide for a complete separation of cladding and substrate, and a full thermally-broken rain screen system is achieved. 
     As different types of cladding will vary in weight and required structural support, the fastening of the furring strips to the studs may alone be sufficient for some types of cladding, but not others. Accordingly, bridging members  40 ,  42  may be used to perpendicularly interconnect two or more corrugated furring strips  10  as shown in  FIGS. 1 and 2  to form a more rigid support grid for carrying the final cladding layer of the finished wall assembly. Use of the bridging members can also serve other purposes, for example to provide for additional fastening locations at areas other than the furring strips themselves, for example at panel joints or at locations of wall penetrations where mechanical, electrical or other protuberances are present or required. 
       FIG. 5  shows a first type of bridging member  40  configured to mate with the corrugated furring strips in positions overlying the lands  20  thereof, and is therefore referred to herein as a land-covering bridging member  40 . The land-covering bridging member  40  is an elongated metal channel of trapezoidal cross-sectional profile, which has a central span  44  and two side walls  46  extending obliquely downward from opposing sides of the central span. As best shown in  FIGS. 5B and 5C , the thickness of each side wall  46  may be doubled up by bending of the channel back over itself at the lower end of the side wall  46  to increase the strength of the channel profile. The angle of divergence between the side walls  46  of the land-covering bridging member  40  matches the angle of divergence between the angled sides  22   b  of the trapezoidal grooves  22  in the furring strips  10 , and the width of the central span  44  between the two side walls  46  of the land-covering bridging member  40  matches or slightly exceeds the width of each land  20  of the corrugated furring strips  10 . As a result, each land-covering bridging member  40  is matable with each furring strip  10  in a position embracing over a respective one of the lands and reaching downwardly into the two adjacent grooves  22 . In width, the side walls  46  of the land-covering bridging member  40  are equal to or slightly shorter than the side walls of the grooves  22  so that the land-covering bridging member  40  conforms to the underlying furring strip  10 , with the central span  44  of the land-covering bridging member  40  sitting flush atop the respective land  20  of the furring strip and the side walls  46  of the land-covering bridging member  40  likewise sitting generally flush atop the adjacent sides  22   b  of the two neighbouring grooves  22 . 
     Placement of the land-covering bridging member  40  over a set of matching lands on the installed furring strips  10  places the land-covering bridging member  40  in a position spanning perpendicularly across the furring strips  10 . Each side wall  46  of the land-covering bridging member  40  features a series of vent holes  48  therein that are uniformly spaced apart in relatively close proximity over the full length of the land-covering bridging member  40 . Where these vented side walls of the land-covering bridging member  40  overlie the corrugated furring strips, the land-covering bridging member  40  can be attached to each of the furring strips by driving a respective self-tapping screw fastener  50  through the vent hole  48  in one or both of the bridging member&#39;s side walls into the angled side wall  22   b  of the respective groove  22  of the furring strip  10 . Accordingly, the head of the screw fastener  50  resides within the groove  22 , and therefore does not project beyond the plane of the lands  20  and interfere with flush mounting of the cladding  18  against the gridwork of furring strips and bridging members. Other means of securing the land-covering bridging member  40  to the furring strips may be employed, for example using mating features built-into these components to provide a snap-lock fit or other self-locking attachment therebetween, for example similar that mentioned below for the groove-occupying bridging member. 
     While the described flush-mounted conformance of the land-covering bridging member  40  to the furring strips means that the land-covering bridging member  40  will be spaced from the underlying insulation layer  16  by at least the thickness of the furring strips  10  at the bottom of floor of the grooves, thereby allowing airflow across land-covering bridging member  40  from one side thereof to the other in the finished wall structure, the vent holes  48  in the side walls  46  improve this allowable airflow, while also allowing drainage. For strengthening purposes, the central span  44  of the land-covering bridging member  40  features a pair of symmetrically disposed longitudinal ribs  30  on opposite sides of the central longitudinal axis of the bridging member  40 , for example, just like those of the corrugated furring strips  10 . 
     The attachment of each land-covering bridging member  40  to the furring strips reinforces the mounting of the furring strips to the studs  12  in order to provide a substantially rigid support grid on which to the carry the cladding. Further reinforcement of the support grid can be provided by installation of the support brace  52  shown in  FIG. 6 , which cooperates with the bridging member  40  at an intermediate position therealong between the furring strips  10 . The support brace  52  is similar to a short length of hat-shaped channel with short upturned retention tabs  54  on opposite sides of the channel-profile. The support brace  52  thus has a three-sided central rectangular channel  56  that opens downwardly, a pair of legs  58  that extend laterally outward from opposite sides of the open side of the channel  56 , and a respective upturned retention tab  54  at the distal end of each leg  58 . The coplanar legs  58  lying perpendicular the side walls of the central channel  56  define a base plane of the support brace  52 . In the installed position of the brace  52 , this base resides against a support surface defined by the outer side of the insulation layer  16 . The three-sided central channel  56  of the support brace  52  stands off from the base plane to one side thereof in order to abut against an underside of the central span  44  of the land-covering bridging member  40 , and thereby provide support to same. 
     The central span  44  of the land-covering bridging member  40  has recessed areas  60  therein at spaced apart positions along the member&#39;s longitudinal direction. These recessed areas  60  reside between the furring strips  10  in the final assembled state of the support grid. Each support brace  52  is placed beneath a respective one of these recessed areas  60 , and the height of the support brace  52  measured from the underside of the base legs  58  to the topside of the central rectangular channel  56  is generally equal to the distance from the plane of the outside surface of the insulation layer to the underside of the recessed area  60  of the land-covering bridging member  40 . Accordingly, the topside of the support brace&#39;s central channel  56  abuts against the recessed area  60  of the land-covering bridging member  40 . Each recessed area  60  features a predefined fastener hole  62  at a central location of the recess to enable driving of threaded fastener  64  through a corresponding aperture  63  in the central channel  56  of the support brace  52  and onward through the insulation layer  16  to a suitable anchor point in the wall framework (e.g. in a stud, or bridge/block thereof). The fastener  64 , shown in  FIG. 6C , thereby couples the support brace  52  and overlying bridging member  40  together, and secures the same to the rigid wall framework. A thermally insulative washer  65  is again used with this insulation-piercing fastener  64  to minimize thermal bridging by thermally isolating the fastener  64  from the underlying bridging member  40 . 
     The upturned tabs  54  at opposing sides of the support brace  52  angle inwardly toward one another at an angle of convergence generally matching the angle at which the two side walls  46  of the land-covering bridging member  40  converge toward the central span  44  thereof, and the width of the support brace&#39;s base between the two tabs  54  generally matches the width of the open side of the land-covering bridging member  40 , as measured across the distal ends of the angled side walls  46  thereof. As shown in  FIG. 6C , the land-covering bridging member  40  is placed over the support brace  52  into a position in which the recessed area  60  of the bridge member&#39;s central span  44  abuts flush against the topside of the support brace&#39;s central channel  56 , and the tabs  54  of the support brace clip externally over the bottom ends of the side walls  46  of the land-covering bridging member  40  below the vent holes  48  therein. Accordingly, the support brace engages to the underside of the land-covering bridging member in a snap-fit therewith that maintains the support brace in proper alignment beneath the recessed area  60  of the land-covering bridging member until the fastener  64  is driven through the aligned fastener hole  62  and aperture  63  in the two snapped-together components  40 ,  52 . 
       FIG. 7  shows the other type of bridging member  42  which is also used to perpendicularly join two or more corrugated furring strips  10  together, as shown in  FIGS. 1 and 2 , but does so at matching grooves  22  of the furring strips  10 , rather than at matching lands  20  thereof. This second bridging member  42 , therefore referred to as a groove-occupying bridging member  42 , is an elongated metal channel having a somewhat W-shaped cross-sectional profile. The cross-sectional shape features a downwardly opening three-sided rectangular channel  66  at its center, much like the support brace  52  of  FIG. 6 , but instead of two flat legs extending perpendicularly outward from the sides of the central three-sided rectangular channel  66 , the groove-occupying bridging member  42  features two angled wings  68  extending obliquely upwardly and outwardly from the open lower side of the central three-sided rectangular channel  66  at acute angles from the two opposing side walls thereof. The angle at which the wings  68  diverge from one another is generally equal to the angle at which the two side walls  22   b  of each groove  22  in the corrugated furring strips diverge from one another, and the width of the central three-sided rectangular channel  66  measured between the two angled wings  68  is generally equal to the floor-width of each such groove  22 . 
     Accordingly, as shown in  FIG. 7D , insertion of the groove-occupying bridging member  42  into one of the grooves  22  with the central three-sided rectangular channel  66  opening downwardly acts to seat the groove-occupying bridging member  42  within the groove in a conforming manner, in which the two angled wings  68  of the groove-occupying bridging member  42  reside flush against the two side walls  22   b  of the respective groove  22 . Each angled wing  68  features a respective set of apertures  70  therein near each end of the groove-occupying bridging member  42 . The distance between the two sets of apertures  70  in each angled wing  68  matches the distance by which two corrugated furring strips  10  are spaced apart from one another in the assembled support grid. Accordingly, a respective self-tapping fastener  72  can be driven through one or more of the apertures  70  in each set in order to fasten the groove-occupying bridging member  42  to the side walls  22   b  of the grooves  22  in the furring strips. In addition to anchoring of each groove-occupying bridging member  42  to the respective corrugated furring strips with threaded fasteners, the bridging member  44  and furring strips may be arranged to self-couple to one another by way of a clip-like connection, for example through use of small tabs pressed into the bridging during manufacture, which can then be snapped into receiving openings on the furring members. This clipped snap fit connection would temporarily secure the two components together while the fasteners  72  are installed to form a more robust attachment between them. 
     Fastening of both types of bridging members  40 ,  42  to the side walls of the grooves places all the fastener heads inside the grooves  22 , where they won&#39;t project beyond the plane of the lands  20  of the furring strip in the finished support grid. This prevents the fasteners from interfering with flush mounting of the cladding layer  18  atop the support grid in the final step of the wall construction. To enable driving of the self-tapping fasteners  72  perpendicularly through the angled wings  68  of the groove-occupying bridging member  42  and underlying angled side of the furring strip groove  22  without interference from the central rectangular channel  66  of the bridging member  42 , a respective fastener depression  73  is provided at the topside of the channel  66  at a position aligned with each fastener hole  70  in the wing  68 . The depression  73  slopes downwardly and outwardly away from the center of the rectangular channel&#39;s topside  66   a  to the respective side wall  66   b  of the rectangular channel, thus defining a recessed area at the corner of the three-sided central channel  66 . The depression or recess is sloped at an angle of ninety degrees to the plane of the respective wing  68 . Accordingly, each depression  73  defines a sloped pathway along which the respective fastener  72  can be driven through the wing  68  of the groove-occupying bridging member  42  at a proper ninety degree angle thereto. Each predefined fastener aperture  70  and its respective fastener depression  73  thus collectively define a fastening guide for driving the respective fastener  72  into the side of the furring strip groove  22  at the appropriate angle. 
     With reference to  FIG. 7B , a series of notches or cut-outs  74  are provided at regularly spaced intervals over the length of the groove-occupying bridging member  42  at the bent corner between each angled wing  68  and the respective side wall of the central three-sided rectangular channel  66 . These act similar to the vent holes  48  of the land-covering bridging members  40  to improve the allowed airflow across the groove-occupying bridging member  42  within the assembled support grid. These notches or cut-outs  74  may be formed by punching holes into a flat metal blank along the intended bend lines on which the blank is subsequently folded during a pressing operation to create the cross-sectional profile of the groove-occupying bridging member  42 . This way, a single linear array of holes produces openings in both the angled wing  68  and the adjacent side wall of the central three-sided rectangular channel  66 . 
     A height of the central channel  66  of the groove-occupying bridging member  42  is equal to a height of depth of each groove  22  in the corrugated furring strips  10  such that the topside of the channel  66  resides flush with the coplanar lands  20  of the corrugated furring strip  10  in the installed position of the groove-occupying bridging member  42 , in which the open bottom side of the central channel  66  is seated against the bottom or floor  22   a  of the respective groove  22 . This way, placement of a cladding layer  18  in abutment against the lands  20  of the furring strips  10  will likewise place the cladding layer  18  in abutment against the central channel  66  of the groove-occupying bridging member  42  for robust support of the cladding layer. 
     When reinforcement of the furring strips by bridging members is required, for example to ensure adequate support for the cladding layer that is to be installed over the corrugated furring strips, either the land-covering bridging members or the groove-occupying bridging members  42 , or a combination thereof, may be used to cooperatively form a more rigid support grid with the corrugated furring strips.  FIGS. 1 and 2  illustrate use of both types of bridging members to span between parallel corrugated furring strips.  FIG. 2  additionally shows the use of support braces  52  to further reinforce the land-covering bridging members  40  at intermediate points thereon between each parallel pair of corrugated furring strips  10 . Once the furring strips, and any optional bridging members, are installed over the insulation layer  16 , the cladding  18  can be placed up over the furring strips or support grid, and fastened thereto through the lands  20  of the corrugated furring strips  10 . Some of these lands  20  may be overlaid with the optional land-covering bridging members  40 , in which case a threaded fastener driven through the cladding  18  and into the corrugated furring strips is driven through the overlying bridging member  40  in the process, thereby further strengthening the fastened connection between the bridging member and the furring strip, and giving the cladding fastener more material to bite into to better support the cladding layer  18 . 
     In one example, the furring strips may be pre-formed light gauge, galvanized metal strip, 50 mm wide, 25 mm in height, and of any length limited only by ease of use and fabrication. The fasteners  24  by which the furring strips are mounted to the wall framework through the simulation may, for example, be full depth screws, c/w, 30 mm diameter phenolic washers to provide the described thermal break. Use of stainless or non-conductive fasteners will significantly reduce or eliminate thermal bridging at the exterior wall. 
     The land-covering bridging members  40  may be pre-formed 18-gauge galvanized metal strip, reinforced with rolled edges and the aforementioned radiused channels or ribs along its length. The recessed areas or localized depressions  60  may be spaced apart from one another at 406 mm or 610 mm intervals to match typical wall framing intervals at which the studs are spaced apart from one another, and the furring strips are preferably spaced apart by the same interval during installation so that each support braces reside centrally between two furring strips. The braces allow optional standalone installation of the land-covering bridging members in matching orientation to wall framing members (e.g. studs) behind the insulation layer. The land-covering bridging members may also be used to provide closures at corners of the building where different walls meet, for example by folding a land-covering bridging member around an outside corner of the building. This is shown in  FIG. 1 , where broken line  100  denotes the interior side of the insulation layer of an “out-of-plane wall” that lies perpendicularly from the “in-plane” wall (i.e. the wall that features the solid-line insulation layer  16  residing “in the plane” of the drawing sheet). A folded land-covering bridging member  44 ′ overlies a half-land on each of the two illustrated corrugated furring strips  10  on the “in-plane” side of the building, and folds around a corner of the building to the “out-of-plane” side of the building, where the remainder of the folded bridging member  44 ′ overlies a half-land on each of another two corrugated furring strips. The half lands of the furring strips on the two sides of the building meet up with one another at the corner, and each side wall  46  of the folded bridging member  44 ′ resides on a side wall  22   b  of the furring strip groove  22  that is nearest the building corner on each of the two furring strips on a respective one of the two adjacent sides of the building. 
     The groove-occupying bridging members may be pre-formed 18-gauge galvanized metal strip, with folds arranged to reinforce its cross-sectional profile, and may be configured to clip into the grooves of the corrugated furring members, and optionally further fastened with self-tapping fasteners. Even if the cut-outs or notches  74  were omitted from the groove-occupying bridging member, a drainage space is provided therebeneath by the thickness of the main furring strips in order to provide a complete rain screen regardless of the horizontal or vertical installation direction. Both types of bridging members are used for bridging or blocking of the furring strips to create an overall support grid, which provides additional strength, backing and/or blocking for variations in cladding orientation and sizes. 
     The support brace  52  may be pre-formed 18-gauge galvanized metal piece, 50 mm wide, with a folded profile to clip into the land-covering bridging members. The brace&#39;s profile allows for solid bearing of the base of the brace against the insulation/sheathing, and provides support directly under the top of the bridging member&#39;s central channel for fastening into the wall framing, similar to fastening of conventional strapping installations. 
     Although not detailed in the drawings, stretcher clamps may be provided, for example in the form of pre-formed light-gauge galvanized metal strip, 38 mm wide and 203 mm in length, and reinforced with radiused ribs or channels along its length. Three fastener locations are punched to allow for use in localized reinforcement of the corrugated metal furring strips  10 . These can be used in vertical orientations to match wall framing, or in horizontal applications, but only where blocking has been installed in wall framing to suit. Although not shown, adjustable clips may be provided for hidden fastener cladding installation. Such clips may be supported off of the lands of the primary furring strips, and off of one or both types of bridging members  40 ,  42  in the horizontal furring installation format. 
     It will be appreciated that the specific material and dimensional details presented above are for exemplary purposes only, and may be varied without effect on the functionality of the present invention. 
     Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the scope of the claims without departure from such scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.

Summary:
Corrugated furring strips are used on the outer side of an exterior insulation layer in an exterior wall construction. The corrugated furring strips support a final cladding layer at an offstanding position from the insulation, thereby providing a rainscreen. The corrugated furring strips are fastened to the framework of the wall through the exterior insulation layer. Optional bridging members shaped to conformingly mate with lands and grooves of the corrugated furring straps cooperate therewith to define a support grid with improved load capacity for heavier cladding materials and more fastening location options. The insulation layer is free of any thermal bridges other than the insulation-penetrating fasteners used to support the furring and optional bridges. Thermally insulative washers isolate the furring and optional bridges from the fasteners to further improve the insulating effect of the wall.