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RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 11/200,026 filed 10 Aug. 2005 which itself is a continuation of Patent Cooperation Treaty application No. PCT/CA03/001975 filed 24 Dec. 2003 and a continuation-in-part of U.S. application Ser. No. 10/360,740 filed 10 Feb. 2003. 
    
    
     TECHNICAL FIELD 
     The invention relates to mounting prefabricated construction units in apertures in building envelopes. Particular embodiments of the invention have application to a system for mounting windows in apertures in a building envelope. 
     BACKGROUND 
     Today most windows are provided in the form of a unit which includes one or more glass panes mounted in a frame. The glass panes typically comprise sealed double-or triple-glazed panels. The frame is typically made of vinyl or another plastic material which does not conduct heat well although some aluminum-framed window units are still sold. The frame of each window unit typically includes a broad flange which projects in a lateral direction and extends around the periphery of the window unit. Other types of prefabricated construction units such as doors, vents and sunlights may have similar flanges. 
     A typical wood frame building has a frame of wooden members which includes apertures for prefabricated construction units such as windows, doors, vents, sunlights and the like. An appropriately-sized construction unit is received in each of the apertures with the flange overlapping with and abutting the outside of the building frame. The construction units are typically secured in place by placing a few screws or nails through the flange into the building frame on each side of the construction units. 
     One disadvantage of the way that construction units are currently installed is that a person must be outside of the building to install the construction units. This is especially problematic for window units, since window apertures may be located well above ground level. Windows in such locations are often installed by a person standing on a ladder. This can be dangerous, especially if the weather is windy or during winter conditions. 
     Another disadvantage of the way that construction units are currently installed is that many buildings have a waterproofing membrane applied to their exterior. Puncturing the membrane with screws or nails reduces the effectiveness of the membrane. 
     There is a need for more efficient ways to install construction units. 
     SUMMARY OF THE INVENTION 
     This invention provides prefabricated construction units with tabs which can be used to affix the construction units in place in the apertures of a building wall from inside the building. One aspect of the invention provides a clip for use in affixing a construction unit to a building structure. The clip comprises a thin tab having a transverse groove at an exterior end thereof for receiving a flange of a frame of the construction unit and at least one attachment point at an interior end thereof. The attachment point may comprise, for example, an aperture and/or a projection which projects from the tab. The clip can be affixed to a frame by inserting a flange of the frame into the groove. The attachment point can be used to affix the clip to a building structure. 
     Another aspect of the invention provides a clip for affixing a construction unit to a building structure. The clip comprises an exterior end and an interior end. The exterior end of the clip has means for affixing the clip to a frame of a construction unit. The interior end of the clip comprises means for affixing the interior end of the clip to a building structure. Various means for performing these functions are described below. 
     A still further embodiment of the invention provides a construction unit comprising a frame; a flange projecting laterally from the frame around a periphery of the frame; and, a plurality of tabs projecting from the frame in an interior direction. Each of the tabs is attached to the frame at an exterior end thereof and comprises at least one attachment point at an interior end thereof. The attachment point comprises an aperture and/or a projection which projects from the tab. 
     Yet another aspect of the invention provides methods for installing a construction unit in an aperture in a wall of a building structure. One such method comprises affixing a plurality of tabs to a frame of a construction unit with the tabs projecting interiorly from the frame; placing the construction unit into the aperture; and, affixing an interior end of the tabs to the building structure. 
     Further aspects of the invention and features of specific embodiments of the invention are described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In drawings which illustrate non-limiting embodiments of the invention, 
         FIG. 1  is a partially cut-away isometric view of a window being installed in a building structure with the use of mounting clips according to the invention; 
         FIG. 2  is an isometric view of a window mounting clip according to a particular embodiment of the invention; 
         FIG. 3  is a cross-section through a portion of a window installed in an aperture in a building frame using window mounting clips of the type shown in  FIG. 2 ; 
         FIGS. 4A ,  4 B and  4 C are isometric views of end portions of window mounting clips according to alternative embodiments of the invention. 
         FIG. 5A  is an isometric view of a window mounting clip according to another embodiment of the invention; 
         FIG. 5B  is a cross-section through a portion of a window installed in an aperture in a building frame using window mounting clips of the type shown in  FIG. 5A ; 
         FIGS. 6A and 6B  are respectively cross-sectional and isometric views of a window mounting clip according to another alternative embodiment of the invention; and 
         FIGS. 7A and 7B  are cross-sectional views of window mounting clips according to still further embodiments of the invention. 
     
    
    
     DESCRIPTION 
     Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
       FIG. 1  shows a portion of the frame  10  of a typical wood-framed structure. Frame  10  comprises wooden studs  11  covered on the exterior by sheathing  12 . Frame  10  includes an aperture  13  surrounded by wooden framing members  14  for receiving a window unit  15 . Window unit  15  includes a window frame  16 , which may be made from any suitable material, and a glass panel  18 . 
     Window unit  15  is illustrated as being four-sided. The invention may also be used with construction units having other shapes such as triangular, round, semi-circular, polygonal etc. 
     Window frame  16  includes a flange  20  which projects in a lateral direction around the periphery of window frame  16 . Aperture  13  is smaller than the outer dimension of flange  20  and is dimensioned to receive window frame  16  while flange  20  bears against the exterior surface of sheathing  12 . 
     This invention provides clips  30 . Each clip  30  has an exterior end  32  adapted to engage window frame  16  and an interior end  34  adapted to be fastened to building frame  10  from the inside of building frame  10 . Clips  30  are used by affixing one or more clips  30  to each side of window frame  16 . In the example shown in  FIG. 1 , two clips  30  are affixed to each side of window frame  16 . For larger window units, three or more clips  30  might be affixed to each side of window frame  16 . In most cases, two or more clips  30  will be affixed to each side of window frame  16 . 
     In the illustrated embodiment of the invention clips  30  attach to flange  20 .  FIG. 2  shows a clip  30  in greater detail. Clip  30  is formed from a strip of any suitable material, such as steel, strong plastic, or the like. The material of clip  30  is preferably resilient. In some embodiments, clip  30  may be coated with a coating layer (not shown) which is thermally non-conductive relative to the material of clip  30 . For example, such a coating layer may comprise rubber, plastic, vinyl, fiberglass or the like. Such a coating layer may help to reduce or prevent condensation on the surface(s) of clip  30 . In some embodiments, a coating layer may be provided on the contact surface(s) of clip  30 . Interior end  34  of clip  30  comprises one or more apertures  36  which can receive fasteners, such as screws or nails, to affix interior end  34  to building structure  10 . Apertures  36  constitute one possible means for affixing interior end  34  to a building structure. 
     Exterior end  32  of clip  30  is bent to define a deep groove  38 . As shown in  FIG. 3 , groove  38  is deep enough to receive flange  20  of window frame  16 . The portions  39 A and  39 B of clip  30  on either side of groove  38  are preferably (but not necessarily) resiliently biased toward one another, so that clip  30  tends to grip flange  20 . Inwardly-angled teeth  40  ( FIG. 2 ) may optionally be provided on one or both sides of groove  38 . After flange  20  is received in groove  38 , teeth  40  bite into flange  20  and resist any forces which might tend to pull flange  20  out of groove  38 . 
     An outer side  42  of groove  38  may be tapered so that it is easy to guide flange  20  into groove  38 . As flange  20  is introduced into side  42  of groove  38 , it tends to wedge portions  39 A and  39 B apart so that flange  20  is held securely in groove  38 . 
     Clip  30  is preferably (but not necessarily) bent at a location intermediate ends  32  and  34 . The bend defines a fulcrum  44 . As shown in  FIG. 3 , when end  34  is fastened to structure  10 , clip tends to pivot about fulcrum  44  so that end  32  is biased into even firmer engagement with flange  20 . Clip  30  is preferably resiliently flexible. As end  34  is fastened to building structure  10  by fasteners, such as nails  46 , clip  30  is straightened. 
     Providing a bend in clip  30  also facilitates affixing clip  30  to building structure  10  with fasteners (for example nails or screws) which are angled in an inward direction. When such fasteners are tightened, clips  30  are drawn inwardly and pull window frame  16  firmly into the aperture. 
       FIGS. 4A ,  4 B and  4 C illustrate a number of alternative configurations for interior end  34 . In each of  FIGS. 4A ,  4 B and  4 C, end  34  includes a number of projections  48  which project from clip  30  and which may be driven into framing members  14  ( FIG. 1 ) when clip  30  is affixed to a window frame  16 . In the illustrated embodiments, projections  48  are integral with the material of the body of clip  30  and are formed by bending flaps of the material of clip  30 . Projections  48  may be triangular, as shown in  FIGS. 4A and 4B , or may have more elongated shapes, as shown in  FIG. 4C , or may have other shapes. The embodiments of  FIGS. 4A and 4C  comprise both apertures  36  and projections  48 . Projections  48  may project at right angles to end  34  of clip  30 . In alternative embodiments, projections  48  capable of use for affixing end  34  to building structure  10  could comprise separate elements affixed to end  34  in any suitable manner. For example, suitable projections  48  could be spot-welded to end  34 . Projections affixed to end  34  provide an alternative means for affixing end  34  to a building structure  10 . 
     In the embodiment of  FIG. 4C , projections  48  are located near the ends of flexible fingers  49 . 
     Projections  48  are not necessarily large enough to permanently affix ends  34  to a building structure  10 . In some embodiments, projections  48  may be used to temporarily hold ends  34  to the building structure until screws or nails are inserted through apertures  36 . 
       FIGS. 5A and 5B  illustrate a clip  30  according to another embodiment of the invention. In the embodiment of  FIGS. 5A and 5B , clip  30  comprises a protuberance  33  which projects upwardly from a surface of middle portion  31 . When window unit  15  is mounted in a building aperture  23  using clips  30  of the type shown in  FIGS. 5A and 5B , protuberances  33  create a gap  37  between the uppermost edge  14 A of framing members  14  and a lower edge  16 A of window frame  16 . Gap  37  extends between adjacent clips  30  on the same side of window unit  15 . Gap  37  may be used to facilitate the exchange of gas and/or moisture between the exterior and interior of a building, and to facilitate the escape of gas and/or moisture from between the layers of a building wall. 
     Although  FIG. 5B  depicts clip  30  in use on a lower side of window unit  15 , it will be appreciated that clips incorporating protuberance  33  may be used to create gaps  37  on other sides of window unit  15 . Protuberance  33  depicted in  FIGS. 5A and 5B  represents one possible embodiment of a protuberance that will create a gap  37  between window frame  16  and framing members  14 . Some alternative embodiments comprise a plurality of protuberances on each clip  30 . Some alternative embodiments comprise one or more protuberances that project in the opposing direction from an opposite surface of middle portion  31  (i.e. towards framing members  14 ). In other alternative embodiments, clip  30  comprises one or more protuberances which project in an interior direction from a surface of portion  39 B to provide a gap between window flange  20  (and portion  39 B of clip  30 ) and the exterior surface of sheathing  12 . Such a gap may communicate with gap  37  to facilitate the exchange of gas and/or moisture. In still other alternative embodiments, the relative thickness of middle portion  31  (and/or portion  39 B) of clip  30  are increased, so that clip  30  can act as a spacer to provide gaps between a window frame and adjacent structures. 
       FIGS. 6A and 6B  are respectively cross-sectional and isometric views of a clip  130  according to a further alternative embodiment of the invention. Clip  130  comprises a plurality of pieces, which include exterior piece  130 A, interior piece  130 B and thermal isolation coupling  137 . As shown in  FIGS. 6A and 6B , exterior piece  130 A preferably comprises exterior end  132 , including portions  139 A,  139 B which define deep groove  138 . Interior piece  130 B preferably comprises interior end  134  and middle portion  131 . Thermal isolation coupling  137  couples interior piece  130 B to exterior piece  130 A and provides thermal insulation therebetween. Thermal isolation coupling  137  is fabricated from a material (or materials) that are thermally insulating relative to the material of exterior and interior pieces  130 A,  130 B. For example, exterior and interior pieces  130 A,  130 B may comprise steel or some other metallic alloy., while thermal isolation coupling  137  may comprise rubber, plastic, vinyl, fiberglass or the like. Thermal isolation of interior piece  130 B from exterior piece  130 A reduces the possibility of moisture condensing on interior piece  130 B due to cold temperatures experienced by exterior piece  130 A. 
     In the illustrated embodiment; thermal isolation coupling  137  comprises grooves  141 A,  141 B for respectively receiving the ends of exterior and interior pieces  130 A,  130 B. Preferably, thermal isolation coupling  137  is fabricated from a resilient material, such that when exterior and interior pieces  130 A,  130 B are inserted into grooves  141 A,  141 B, the deformation of grooves  141 A,  141 B acts to hold the ends of exterior and interior pieces  130 A,  130 B in-place (i.e. to couple the ends of exterior and interior pieces  130 A,  130 B to thermal isolation coupling  137 ). In alternative embodiments, adhesive, rivets and/or other suitable fasteners may be used to help couple the ends of exterior and interior pieces  130 A,  130 B to thermal isolation coupling  137 . Thermal isolation coupling  137  may be molded in place around the ends of pieces  130 A,  130 B. Exterior and interior pieces  130 A,  130 B may be coated with a coating layer (not shown) which is thermally non-conductive relative to the material of exterior and interior pieces  130 A,  130 B. Such a coating layer may also help reduce or prevent condensation on the surface(s) of exterior and interior pieces  130 A,  130 B. 
     It can be appreciated that the use of this invention can significantly simplify the installation of prefabricated construction units in a building, especially where one would need a ladder, scaffold, man lift or the like to reach the locations where-the construction units will be installed from the exterior of the building. A worker can affix clips  30  according to the invention to a construction unit and then, from inside the structure, orient the construction unit at an angle to the aperture in which the construction unit will be installed and pass the construction unit through the aperture to the outside of the structure. Still working from inside the structure, the worker can then draw the construction unit into place in the aperture and fasten the construction unit in place by affixing interior ends  34  of clips  30  to the structure. If necessary, shims may be installed around the frame of the construction unit to properly align the construction unit in the aperture. 
     A further advantage of the invention is realized in situations where a waterproofing membrane or the like is applied to the exterior of building frame  10 . Prior art systems for securing construction units to building structures typically require the membrane to be punctured by nails or screws in the area adjacent to aperture  13 . In some cases building codes prohibit fastening the lower sides of construction units in ways which result in the membrane being punctured. Sometimes windows are installed with no fasteners on their lower sides for this reason. The result can be that the lower sides of the windows can move, especially in windy weather. The use of clips  30  according to the invention allows the membrane to remain intact and still permits securing the lower side of window units and other construction units by way of one or more clips  30 . 
     It can be appreciated that clips  30  having an exterior end  32  as described above can be affixed to a construction unit frame with minimal tools and without the need to drill holes in the frame or to modify the window or door frame in other respects. 
     Where a component (e.g. a member, tab, fastener etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention. 
     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example:
         While the above detailed description relates primarily to window units, it is to be understood that clips according to the invention may equally be used to secure other types of construction units, such as door units, vent units, sunlight units and the like, into appropriately sized apertures in a building frame.   In some embodiments, a layer of deformable, elastomeric material (not shown) may be attached to one (or both) of the surfaces of middle portion  31  of clip  30 . Such deformable, elastomeric layer(s) may make clip  30  more malleable, thereby facilitating installation of clip  30  and preventing clip  30  from accidentally damaging window unit  15  or frame  10 . Such deformable, elastomeric layer(s) may also help to accommodate warpage in the shape of the edges of window unit  15  and/or framing members  14 . Similar deformable, elastomeric layer(s) may be used with all of the above-discussed clip embodiments.   In some embodiments, thermal isolation coupling  137  may have a different shape than the one depicted in  FIGS. 6A and 6B  and may be coupled to exterior and interior pieces  130 A,  130 B in a different manner than that depicted in  FIGS. 6A and 6B .  FIGS. 7A and 7B  respectively depict cross-sectional views of window mounting clips according to still further embodiments of the invention. Clip  130  of  FIG. 7A  comprises an exterior piece  130 A and an interior piece  130 B. Pieces  130 A,  130 B are coupled to one another by a thermal isolation coupling  137 ′ that is T-shaped in cross section, with flanges  150 A,  150 B that extend over pieces  130 A,  130 B. Thermal isolation coupling  137 ′ may be coupled to exterior and interior pieces  130 A,  130 B using adhesive, rivets and/or other suitable fasteners (not shown). Those skilled in the art will appreciate that T-shaped thermal isolation coupling  137 ′ may be inverted (relative to pieces  130 A,  130 B) such that flanges  150 A,  150 B extend under pieces  130 A,  130 B. In the embodiment of  FIG. 7B , exterior and interior pieces  130 A,  130 B are coupled together by a relatively flat-shaped thermal isolation coupling  137 ″. Thermal isolation coupling  137 ″ comprises exterior and interior ends  152 A,  152 B, which extend respectively over pieces  130 A,  130 B. Thermal isolation coupling  137 ″ may be coupled to pieces  130 A,  130 B using adhesive, rivets and/or other suitable fasteners (not shown). Those skilled in the art will appreciate that flanges  152 A,  152 B of thermal isolation coupling  137 ″ may alternatively extend below pieces  130 A,  130 B or both above and below pieces  130 A,  130 B. Thermal isolation couplings  137 ′,  137 ″ are preferably thermally non-conductive relative to the material of exterior and interior pieces  130 A,  130 B.
 
Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.

Summary:
A clip is provided for affixing a construction unit to a building structure. The clip comprises: a generally planar middle portion, an exterior portion located on an exterior side of the middle portion and an interior portion located on an interior side of the middle portion; the exterior portion comprising a groove at an exterior end of the clip for receiving a construction unit flange, the groove having a generally U-shaped cross-section, the groove defined at least in part by a pair of generally parallel groove portions and a base portion connecting the groove portions at a base of the groove, the base of the groove spaced apart from an opening of the groove; the middle portion extending from an interior side of groove toward the interior portion; and the interior portion at an interior end of the clip, the interior portion extending from the middle portion at an obtuse angle to define a fulcrum at a junction between the middle portion and the interior portion.