Patent Publication Number: US-7707778-B2

Title: Frame assembly for windows or doors with removable sash

Description:
This application claims the benefit of U.S. Provisional Application No. 60/457,593, filed Mar. 27, 2003, the entirety of which is hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   This invention relates to an improved frame assembly for windows or doors. 
   BACKGROUND OF THE INVENTION 
   A common style of window construction has a first framed pane of glass (the sash) mounted within a larger frame (herein referred to for convenience as the master frame) in such a way that the sash is slidable between open and closed positions within the master frame. Typically, adjacent horizontal members of the sash frame and master frame are provided with slidably engaging tongue-and-groove style projections and recesses to define and support the sliding movement of the sash within the master frame. By adjusting the dimensions of the sash frame and master frame, this construction can also be used to provide doors, such as sliding patio doors. 
   A known technique for constructing frame assemblies for windows or doors is to extrude sections of aluminum or vinyl having a desired cross-sectional profile for the various vertical and horizontal members of the frames. The extrusions are then cut to length, and the sash frame is fully assembled, while the master frame is only partially assembled. The sash frame can then be slid into the partially assembled master frame, after which assembly of the master frame can be completed. An example of known extrusion profiles for constructing window frames can be seen in U.S. Pat. No. 4,621,478 (Phillips et al.). 
   Another frame construction for a sliding window is disclosed in U.S. patent application Ser. No. 09/735,498, having Publication No. US 2002/0124494 (Zen). This frame construction has a two-piece master frame, between which a sash frame is sandwiched. The sash comprises two injection molded halves which are secured together with fasteners. The assembled sash is positioned between two halves of the master frame, each of which are also separate, injection molded elements, secured together with fasteners. 
   The construction techniques described above can be relatively time-consuming and costly. Also, if the assembly is improperly performed, problems with the function or appearance of the product may result. Accordingly, it may be advantageous to provide a frame assembly for a window or door wherein the master frame and sash frame are each integrally molded, one-piece structures. 
   SUMMARY OF THE INVENTION 
   The present invention provides a frame assembly for a sliding window or patio door, in which the frame assembly includes an integrally moulded unitary master frame having upper and lower horizontal members, and opposed first and second vertical jamb members extending between the horizontal members. An integrally moulded unitary sash frame is slidably mounted within the master frame. 
   In one embodiment, the frame assembly includes a mullion integrally moulded with the master frame, the mullion extending contiguously from, and vertically between, the upper and lower horizontal members, at a position between the first and second vertical jamb members. The master frame and the sash frame have inter-engaging channels and projections for supporting the sash frame within the master frame. The projections and channels are integrally moulded with the respective sash frame and master frame. More particularly, the upper and lower horizontal members of the master frame are provided with vertically projecting tongues, and the upper and lower horizontal members of the sash frame are provided with grooves shaped to receive the tongues in sliding engagement. 
   The present invention also provides an injection moulded frame assembly for a sliding window or door that is reversible. The frame assembly has a master frame and sash frame slidably supported within the master frame. At least the master frame can be installed in either one of a first position or a second position that is generally inverted (rotated 180 degrees in a vertical place) relative to the first position. In another embodiment, both the master frame and sash frame are inverted to provide the first and second positions. An interlacing configuration can be provided on two opposite horizontal or vertical frame elements to provide a gap between the sash frame and master frame for installation and removal of the sash frame within the master frame. Duplicate attachment elements can be provided for attaching gliders or other space-taking support elements for selectively filling the gap along one of the opposing frame elements. 
   In another aspect of the invention, a frame assembly for a window or patio door is provided with a weather buffering chamber across one or more flow paths between interior and exterior sides of the frame assembly and through which water or air may try to penetrate from the exterior to the interior side of the assembly. The weather buffering chamber can have an exterior seal with a first pressure gradient, and an interior seal with a second pressure gradient, the first and second pressure gradients being portions of the total pressure gradient across the two sides or faces of the assembly. The weather buffering chamber can be independently drained relative to any drains for water that may penetrate to the interior face of the assembly. 
   In another aspect of the invention, a sealed valve element is provided for draining water that may have penetrated to the interior face of the assembly. The sealed valve element can inhibit the suction of air from the exterior face to the interior face of the assembly. 
   In another aspect, the present invention provides a frame assembly for a window or door that has integrally moulded attachment elements for attaching gliders, locks, handles, seal elements including weatherstripping, in press fit or snap fit arrangements. A break-away panel can be provided to seal off duplicate attachment elements that may be provided for a reversible frame assembly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention and to show more clearly how it would be carried into effect, reference will now be made by way of example, to the accompanying drawings that show a preferred embodiment of the present invention, and in which: 
       FIG. 1  is a perspective view of a frame assembly according to one embodiment of the present invention, looking at the exterior face; 
       FIG. 2  is a perspective view of a sash frame shown in  FIG. 1 ; 
       FIG. 3  is a front view of the frame assembly shown in  FIG. 1 , with the sash frame positioned between open and closed positions; 
       FIG. 4  is a front view of the frame assembly shown in  FIG. 1 , with the sash frame in the closed position; 
       FIG. 5  is a vertical section of the frame assembly shown in  FIG. 3  taken along the line  5 - 5 ; 
       FIG. 6  is a vertical section of the frame assembly shown in  FIG. 3  taken along the line  6 - 6 ; 
       FIG. 7  shows the frame assembly of  FIG. 1  viewed from a different, lower angle; 
       FIG. 7   a  is an enlarged view of a portion of the frame assembly shown in  FIG. 7 ; 
       FIG. 7   b  is an enlarged view of another portion of the frame assembly shown in  FIG. 7 ; 
       FIG. 8  is a perspective view of the frame assembly shown in  FIG. 1 , but viewed from below, and looking towards the opposite (interior) face of the frame assembly; 
       FIG. 8   a  is an enlarged portion of the frame assembly shown in  FIG. 8 ; 
       FIGS. 9   a ,  9   b , and  9   c  are vertical section views of the frame assembly of  FIG. 1  showing first second, and third positions, respectively, of the sash frame during installation into the master frame; 
       FIG. 10  is a horizontal section of the frame assembly shown in  FIG. 4  taken along the line  10 - 10 ; 
       FIG. 11  is a horizontal section of the frame assembly shown in  FIG. 4  taken along the line  11 - 11 ; 
       FIG. 11   a  is an enlarged view of the check rail shown in  FIG. 11 ; 
       FIG. 11   b  shows an alternate embodiment of the check rail of  FIG. 11   a;    
       FIG. 12  is a horizontal section of the frame assembly shown in  FIG. 4  taken along the line  12 - 12 ; 
       FIG. 13   a  is a front exterior view of a modified, reversible assembly in accordance with another embodiment of the present invention; 
       FIG. 13   b  is a front exterior view of the frame assembly of  FIG. 13   a , shown in a reversed position; 
       FIG. 14  is a section of the frame assembly shown in  FIG. 13   a , taken along the line  14 - 14 . 
       FIG. 15  is a perspective view of a portion of the frame assembly shown in  FIG. 13   a;    
       FIGS. 16   a ,  16   b , and  16   c  are perspective views of alternate embodiments of gliders provided in the sash frame of  FIG. 2 ; 
       FIG. 17  is a perspective view of a frame assembly according to another embodiment of the present invention, looking at the exterior face; 
       FIG. 18  is a perspective view of a sash frame shown in  FIG. 17 ; 
       FIG. 19  is a front elevation view of the frame assembly shown in  FIG. 17 , with the sash frame positioned between open and closed positions; 
       FIG. 20  is a front elevation view of the frame assembly shown in  FIG. 17  with the sash frame in the closed position; 
       FIG. 21  is a vertical section of the frame assembly shown in  FIG. 19  taken along the line  21 - 21 ; 
       FIG. 21   a  is an enlarged end view of a carrier strip portion shown in  FIG. 21 ; 
       FIG. 21   b  is a perspective view of a lower portion of the sash frame shown in  FIG. 18 . 
       FIG. 21   c  is a front sectional view of the portion of the sash shown in  FIG. 21   b;    
       FIG. 22  is a vertical section of the frame assembly shown in  FIG. 19  taken along the line  22 - 22 ; 
       FIG. 23  shows the frame assembly of  FIG. 17  viewed from a different, lower angle; 
       FIG. 23   a  is an enlarged view of a portion of the frame assembly shown in  FIG. 23 ; 
       FIG. 23   b  is an enlarged view of another portion of the frame assembly shown in  FIG. 23 ; 
       FIG. 23   c  is a sectional view of the assembly of  FIG. 23 , taken along the line  23   c - 23   c;    
       FIG. 24  is a perspective view of the frame assembly shown in  FIG. 17 , but viewed from below, and looking towards the opposite (interior) face of the frame assembly; 
       FIG. 24   a  is an enlarged portion of the frame assembly shown in  FIG. 24 ; 
       FIG. 24   b  is a sectional view of a portion of the frame assembly shown in  FIG. 20 , taken along the line  24   b - 24   b;    
       FIG. 24   c  is a perspective view of sectioned portion of the portion of the frame assembly shown in  FIG. 24   b;    
       FIGS. 25   a ,  25   b , and  25   c  are vertical section views of the frame assembly of  FIG. 17  showing first, second, and third positions, respectively, of the sash frame during installation into (or removal from) the master frame; 
       FIGS. 26   a ,  26   b ,  27   a ,  27   b ,  28   a , and  28   b  are horizontal section views of the frame assembly shown in  FIG. 20  taken through the lines  26   a - 26   a ,  26   b - 26   b ,  27   a - 27   a ,  27   b - 27   b ,  28   a - 28   a , and  28   b - 28   b , respectively; 
       FIG. 29  is a perspective view of a portion of the frame assembly shown in  FIG. 17 , looking towards the interior face of the frame assembly; 
       FIG. 30  is an exploded perspective view of the portion of the frame assembly shown in  FIG. 29 ; 
       FIG. 31  is front elevation view of a sectioned portion of the portion of the frame assembly shown in  FIG. 30 ; 
       FIG. 31   a  is a perspective view of the sectioned portion of the frame assembly shown in  FIG. 31 ; 
       FIG. 32  is a perspective view of the portion of the frame assembly shown in  FIG. 29  but looking at the exterior face of the frame assembly, and showing spaced-apart sections to better illustrate some inner features; 
       FIG. 33  is an enlarged perspective view of a portion of the frame assembly shown in  FIG. 32 ; 
       FIG. 34  is a vertical section view of a portion of the frame assembly shown in  FIG. 32 ; 
       FIG. 34   a  is an enlarged view of a portion of  FIG. 34  showing a sealed valve element in greater detail; 
       FIG. 35  is an enlarged perspective view of a portion of the frame assembly shown in  FIG. 32 ; 
       FIG. 36  is a further enlarged perspective view of a portion of the frame assembly shown in  FIG. 35 ; and 
       FIG. 37  is a front sectional view of the portion of the frame assembly shown in  FIG. 35 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A frame assembly for a window or door according to the present invention is shown generally at  110  in  FIG. 1 . The frame assembly  110  has a master frame  112  and a sash frame  114 , which is slidably mounted within the master frame  112 . 
   The master frame  112  is generally rectangular, having upper and lower horizontal members  116  and  118 , respectively. Vertical side members  120   a  and  122   a  extend between the upper and lower horizontal members  116  and  118 , at either side of the master frame  112 . The upper and lower horizontal members of the master frame  112  are commonly referred to as the header  116  and sill  118 , respectively. 
   Aspects of the present invention generally provide a frame assembly having a slidable sash mounted in a master frame. Embodiments of the invention can provide horizontally or vertically slidable sash frames within respective master frames. For the purposes of illustration, in the embodiment illustrated in  FIG. 1 , the frame assembly  110  is a horizontal slider in which the sash frame  114  slides horizontally between the vertical side members  120   a  and  122   a . The master frame  112  has a third vertical member defined as a mullion  124 , which extends between the header  116  and sill  118 , at a point approximately midway between the vertical side members  120   a  and  122   a . The mullion  124  divides the master frame  112  into a vent side  126 , extending between the vertical side member  120   a  and the mullion  124 , and a fixed side  128 , extending between the vertical side member  122   a  and the mullion  124  (see also  FIG. 4 ). The vertical side members  120   a ,  122   a  are conveniently referred to as the vent side jamb  120  and the fixed side jamb  122 , respectively. 
   The sash frame  114  is slidable within the master frame  112  between fully open and fully closed positions. In the fully open position, the vertical member  136  of the sash frame  114  is generally positioned behind the mullion  124 , and the check rail  138  generally abuts (or nearly abuts) the fixed side jamb  122 . In the fully closed position ( FIG. 4 ), the vertical member  136  abuts (and generally sealingly engages) the vent side jamb  120 , and the check rail  138  abuts (and generally sealingly engages) the mullion  124 . The sash frame  114  can also be moved to any one of an infinite number of partially open positions between the fully closed and fully open positions. In any of the partially open positions, the vertical member  136  of the sash frame is generally spaced apart from the vent side jamb  120 , between the vent side jamb  120  and the mullion  124  of the master frame  112  ( FIG. 3 ). When in an open position (partially open or fully open), air can flow through the vent side  126  of the master frame  112 , between the exterior and interior faces  121  and  123  of the assembly  110 . Air flow between the exterior and interior faces  121  and  123  is generally prevented when the sash frame  114  is in the fully closed position. 
   In the frame assembly  110 , glazing  130  can be set directly into the fixed side  128  of the master frame  112 . A screen element  129  can be provided in the vent side  126  of the master frame  112 . Details of how the glazing  130  and screen element  129  may be mounted in the frame assembly  110  are provided hereinafter. 
   The frame assembly  110  has an exterior face  121  which would typically be exposed to the elements, and an interior face  123  opposite the exterior face  121 . The glazing  130  and screen element  129  are positioned towards the exterior face  121  of the frame assembly  110 , and the sash frame  114  is mounted interiorly of the glazing  130  and screen  129 . 
   The master frame  112  of the frame assembly  110  is of one-piece, integrally moulded construction, devoid of any seams or joint lines between contiguous vertical and horizontal members  116 ,  118 ,  120 ,  122 , and  124 . In the embodiment illustrated, the members of the master frame  112  are advantageously provided with geometrical configurations which can facilitate manufacturing the master frame by a moulding process, such as, for example, but not limited to, injection moulding. More particularly, the geometrical configurations of the vertical and horizontal members of the master frame  112  have, in cross-section, a generally uniform wall thickness, and an orientation which permits ejection of the master frame  112  from a mould. The master frame  112  can be constructed of a suitable plastic material. 
   Referring to  FIG. 2 , the sash frame  114  is also of one-piece, integrally moulded construction. The sash frame  114  is rectangular in shape, having upper and lower horizontal members  132  and  134 , respectively. Vertical side members  136  and  138   a  extend between the horizontal members  132  and  134  at either side of the sash  114 . The vertical side member  138   a  is also called the check rail  138 . Like the master frame  112 , the geometrical configurations of the vertical and horizontal members of the sash frame  114  have, in cross-section, a generally uniform wall thickness, and an orientation which permits ejection of the master frame  114  from a mould, and the master frame  114  can be constructed of a suitable plastic material. In the frame assembly  110 , glazing  131  can be set into the sash frame  114 , in a manner described in further detail hereinafter. 
   Front views of the exterior face  121  of the frame assembly  110  can be seen in  FIGS. 3 and 4 . In  FIG. 3 , the sash frame  114  is shown in an intermediate position, between the vent side jamb  120  and fixed side jamb  122 . In  FIG. 4 , the sash frame  114  is shown in the closed position, in which the vertical member  136  of the sash frame  114  generally abuts the vent side jamb  120  of the master frame  112 . 
   As best seen in  FIG. 3 , in the embodiment illustrated, the sill  118  has a first portion  118   a  generally provided along the vent side  126  of the master frame  112 , and a second portion  118   b  generally provided along the fixed side  128  of the master frame  112 . As well, the header  116  has first and second portions  116   a ,  116   b  generally provided along the vent and fixed sides  126 ,  128  of the master frame  112 , respectively. The first portions  116   a ,  118   a  are contiguous with the respective second portions  116   b ,  118   b  but have some differences in cross-sectional profile, as described below. 
   As best seen in  FIGS. 5 and 6 , in the illustrated embodiment of the frame assembly  110  the first and second portions of the horizontal members of the master frame  112  and sash frame  114  are provided with channels and projections to slidably retain the sash frame  114  within the master frame  112 . 
   Referring to  FIG. 5 , which shows a cross-section of the frame assembly  110  taken along the line  5 - 5  of  FIG. 3 , the first portion  118   a  of the sill  118  has a generally upwardly directed projection or tongue  140 , which is received within a downwardly directed channel or groove  142  provided in the lower horizontal member  134  of the sash frame  114 . The tongue  140  has a generally flat upper surface or runner  144  along which the sash frame  114  glides. A vertically projecting strip mount  146  extends along the runner  144 , along the edge nearest the exterior face  121  of the master frame  112 , for supporting a length of weather-stripping  148  in a snap-on arrangement. Opposite the strip mount  146 , the runner  144  of the tongue  140  has a step  150  which is undercut, providing a horizontally projecting nub  152  for laterally stabilizing the sash frame  114 , as further described hereinafter. 
   The groove  142  of the lower horizontal member  134  of the sash frame  114  is disposed between interior and exterior sidewall portions  154  and  156  of the lower horizontal member  134  of the sash frame  114 . The sidewall portions  154  and  156  extend downward past the nub  152  and weather-stripping  148 , respectively, to support the sash  114  above the sill  118  in a lateral direction. 
   A glider  157 , comprising a glider housing  158  and gliding element  160 , is provided within the groove  142  at either end of the lower horizontal member  134  (see also  FIG. 2 ). In the embodiment illustrated, the glider housing  158  is advantageously integrally moulded with the sash frame  114 , and positioned adjacent the interior sidewall portion  154  of the lower horizontal member  134 . The glider housing  154  has recesses  155  which are shaped to receive attachment fingers  159  extending from the gliding element. When assembled, the gliding element  160  bears against the runner  144  of the tongue  140  to slidably support the sash frame  114  above the sill  118  of the master frame  112 . 
   Referring to  FIGS. 16   a ,  16   b , and  16   c , details of alternative gliders  157   a ,  157   b , and  157   c , respectively, can be seen. In each case, the glider housing  158   a ,  158   b ,  158   c  projects generally vertically from the inner surface of the groove, between the sidewalls  154  and  156 . Each housing  158   a ,  158   b ,  158   c  is adapted to receive the corresponding glider element  160   a ,  160   b ,  160   c , generally by having a recess  155   a ,  155   b ,  155   c  which is shaped to receive attachment fingers  159   a ,  159   b ,  159   c  extending from the glider element  160   a ,  160   b ,  160   c . The attachment between fingers  159  and recesses  155  may be secured by a snap-fit arrangement ( 157   a ,  157   b ) or by a separate fastener ( 157   c ). 
   As seen in  FIG. 5 , the lower horizontal member  134  of the sash frame  114  may also be advantageously provided with integrally moulded glazing support features  161  to support the glazing  131  set in the sash frame  114 . The glazing support features  161  can include a backstop surface  162  for supporting the interior surface of the glazing  131 . The backstop surface  162  can be formed along a portion of the interior sidewall  154  extending vertically away from the groove  142 . Furthermore, a generally planar support surface  164  is provided to extend adjacent an edge of the glazing  131  (below the lower edge of the glazing  131  in  FIG. 5 ). The planar support surface can be used to frictionally support the glazing  131  within the sash frame  114 , by means of setting block housings  240  and setting blocks  242  (as seen in  FIG. 15  with respect to the glazing  130 ), described further hereinafter. 
   As well, the integrally moulded glazing support features can include an attachment recess  166  provided opposite the glazing support surface  164  and directed towards the exterior face  121  of the frame assembly  110 . The attachment recess  166  is shaped to receive a length of glass stop  168 , which bears against an exterior surface of the glazing  131 . Further details of the glazing support features  161  are described hereinafter. 
   In the first portion  118   a  of the sill  118 , screen-mounting details  170   a  can also be provided. In the embodiment illustrated, the screen mounting details  170   a  include a screen support step  170 , providing in a generally vertical plane an abutment surface  171  against which the frame  174  of a screen  129  can be positioned. The screen mounting details  170   a  further include horizontal support surfaces  172  provided adjacent the vertical face  171 , to support the screen  129  vertically. 
   Referring again to  FIG. 5 , details of the upper horizontal members  116  and  132  of the master frame  112  and sash frame  114  will now be described. The first portion  116   a  of the header  116  has a generally downwardly directed tongue  180  having a generally flat lower surface  182 . In a similar arrangement as for the tongue  140 , a strip mount  146  (to which a length of weather-stripping  148  may be attached) projects vertically from the surface  182 , adjacent the end nearest the exterior face  121  of the frame assembly  110 . A nub  152  extends horizontally from the surface  182 , opposite the strip mount  146 . 
   The upper horizontal member  132  of the sash frame  114  is provided with a channel or groove  186  which is directed upwardly and extends between generally vertical interior and exterior sidewall portions  188 ,  190 , respectively, of the upper horizontal member  132 . The interior sidewall portion  188  extends upwardly beyond the nub  152  of the tongue  180 , and the exterior sidewall portion  190  extends upwardly beyond the strip mount  146  and the weather-stripping  148 . Accordingly, the sidewalls  188 ,  190  of the groove straddle the horizontally outermost elements  152 ,  148 , respectively, of the tongue  180 , thereby providing lateral support for the sash frame  114 . 
   Furthermore, the upper horizontal member  132  of the sash frame  114  can be advantageously provided with glazing support features  161  to support glazing  131  set within the sash frame  114 . This includes the backstop surface  162 , planar support surface  164 , attachment recess  166 , and glass stop  168 , similar to those provided for the lower horizontal member  134 . 
   Referring to  FIG. 6 , showing a section along the lines  6 - 6  of the  FIG. 3 , the second portion  118   b  and  116   b  of the sill  118  and header  116  will now be described. The second portion  118   b  of the sill  118  also comprises the tongue  140 , having the runner  144 , as provided in the first portion  118   a . In other words, the runner  144  extends generally continuously across the master frame  112 , from the vent side jamb  120  to the fixed side jamb  122 . The width of the runner  144  of the sill profile  118   b  extends between nubs  152  provided at its edges facing both the interior face  123  and exterior face  121  of the frame assembly  110 . 
   Towards the exterior face  121  of the frame assembly  110 , the sill second portion  118   b  of the sill  118  is provided with integrally moulded glazing support features  161 . The support features  161  again include the back stop surface  162 , planar support surface  164 , and attachment recess  166  for receiving a length of glass stop  168 . 
   The second portion  116   b  of the header  116  includes the tongue  180 , projecting downwardly from the header  116 . The strip mount  146  and the weather-stripping  148  are generally not required along the header second portion  116   b , and can be replaced by a second nub  152 , extending towards the exterior face  121 . The opposed nubs  152  are positioned between the interior and exterior sidewall portions  188  and  190  of the upper horizontal member  132  of the sash frame  114 , providing lateral support for the sash frame  114 . 
   Above the sidewall portions  188  and  190  of the horizontal member  132 , and extending outwardly from the tongue  180 , are interior and exterior shoulders  196 ,  198 , respectively. The shoulders  196 ,  198  prevent the sash frame  114  from being lifted up, thereby ensuring that the groove  142  of the lower horizontal member  134  of the sash frame  114  remains properly engaged with the tongue  140  of the sill  118 . Further details concerning lift-up of the sash frame  114  will be provided hereinafter. 
   Adjacent the exterior shoulder  198  and towards the exterior face  121 , the header second portion  116   b  is provided with glazing support details  161  for supporting the fixed glazing  130 . The glazing support details  161  again comprise the backstop surface  162 , planar support surface  164 , and the attachment recess  166  for receiving a length of glass stop  168 . 
   Referring again to  FIG. 5 , vertical clearance  200  is provided between staggered surfaces of the header first portion  116   a  and the upper horizontal member  132  of the sash frame  114 . More specifically, the vertical clearance  200  is provided between the surface of the header  116  and the adjacent upper ends of the interior and exterior sidewall portions  188 ,  190  of the upper horizontal member  132 . As well, the vertical clearance  200  is provided between the base of the groove  186  and the lower-most extending portion (in this embodiment the weather-stripping  148 ) of the tongue  180 . The vertical clearance  200  is provided to permit lift-up of the sash frame  114  within the master frame  112 , thereby facilitating installation and removal of the sash frame  114 . 
   To provide the vertical clearance  200 , in the illustrated embodiment of the frame assembly  110  the profile of the header  116  of the master frame  112  has a sash frame interlacing configuration  202  along at least a portion of the length of the header  116 . The sash frame interlacing configuration  202  has a longitudinal extent along the length of the header  116  that is at least as long as the length of the upper horizontal member of the sash frame  114 . The sash frame interlacing configuration  202  comprises channels and projections in the header  116  that match with corresponding projections and channels in the upper horizontal member  132  of the sash frame  114  to laterally support the sash frame  114  slidably within the master frame  112 , while also providing the vertical clearance  200  for lift-out of the sash frame  114 . 
   In the embodiment illustrated, the sash frame interlacing configuration  202  of the header  116 , includes the tongue  180  having downwardly projecting exterior and interior sidewalls  181 ,  183 , respectively, which are spaced sufficiently narrowly apart to fit within the sidewalls  188 ,  190  of the groove  186 . No shoulders or other surfaces extend outward from the tongue sidewalls  181 ,  183  to interfere with lift-up of the upper edges of the groove sidewalls  188 ,  190 . Furthermore, the extent to which the tongue  180  projects vertically from the header  116  is sufficiently short to fit substantially within the hollow depth of the groove  186 . 
   The sash frame interlacing configuration  202  need not be provided along the entire length of the header  116 , but may advantageously be provided along only a portion thereof. In the embodiment illustrated, the sash frame interlacing configuration  202  is provided along only a portion of the header  116  that extends a length which is just slightly longer than the length of the upper horizontal member  132  of the sash frame  114 . The portion of the header  116  along which the sash frame interlacing configuration  202  (and hence, vertical clearance  200 ) is provided defines a lift position  204  (see  FIG. 7 ) with which the sash frame  114  must be aligned in order for lifting of the sash frame  114  to be possible ( FIGS. 7 and 8 ). In the embodiment illustrated, the sash frame interlacing configuration  202  extends from a first end  203   a  on the header  116  adjacent the vent side jam  120  of the master frame  112 , to a second end  203   b  along the header  116  which is above the fixed side  128  of the master frame  112 . In particular, the sash frame interlacing configuration  202  of the header  116  extends behind (when viewed from the exterior face  121  of the frame assembly  110 ) the mullion  124 , crossing from the vent side  126  to the fixed side  128  of the master frame  112 . 
   To extend the sash frame interlacing configuration  202  behind the mullion  124 , a recess or cavity  205  can be provided in the header  116  between the mullion  124  and the tongue  180  ( FIGS. 7   a  and  8   a ). The present invention comprehends that providing the cavity  205  may not be in the line-of-draw with respect to a traditional moulding process. Accordingly, a slide or lift detail may be required in the die to mould this feature. 
   Between the second end  203   b  of the sash frame interlacing configuration  202  and the fixed side jamb  122  of the master frame  112 , the header  116  is generally provided with the header profile  116   b  (as best seen in  FIG. 6 ). Accordingly, the sash frame interlacing configuration  202  (and vertical clearance  200 ) is not provided along this portion of the header  116 , since the shoulders  196  and  198  extend outwardly from the tongue  180  at a position directly above the upper ends of the sidewalls  188  and  190  of the upper horizontal member  132  of the sash frame  114 . 
   Between the first end  203   a  of the sash frame interlacing configuration  202  and the vent side jamb  120  of the master frame  112 , integrally moulded interior and exterior shoulders  206 ,  208  can be provided (as best seen in  FIG. 7   b ). Accordingly, the sash frame  114  cannot be lifted when any portion of the upper horizontal member  132  of the sash frame is in vertical alignment with the shoulders  206 ,  208 . This can provide enhanced protection or security of the frame assembly  110 , particularly when closed, and can also facilitate alignment of the sash frame  114  with the vent side jam  120  when sliding the sash frame  114  to the closed position. 
   In use, to install the sash frame  114  in the master frame  112 , the sash frame  114  is positioned adjacent the interior surface  123  of the frame assembly  110 , and the upper horizontal member  132  of the sash frame  114  is aligned with the lift position  204 , between the ends  203   a  and  203   b  of the interlacing configuration  202 . The lower horizontal member  134  of the sash frame  114  is tilted away from the master frame  112 , and the groove  186  can then be aligned with the tongue  180  of the header  116  ( FIG. 9   a ). 
   The sash frame  114  can then be lifted up, so that the vertical clearance  200  is occupied by the various elements of the tongue  180  and groove  186 , and the lower horizontal member  134  of the sash frame  114  may then be swung over the tongue  140  of the sill  118 , so that the groove  142  of the lower horizontal member  134  is aligned with the tongue  140  ( FIG. 9   b ). 
   The sash frame  114  may then be lowered, until the glider  157  engages the runner  144  of the tongue  140  ( FIG. 9   c ). At this point the sash frame  114  is in its operating position, and is free to slide back and forth along the sill  118 . 
   Removal of the sash frame  114  from the master frame  112  is substantially the reverse operation. It will be understood that, to initiate the procedure, the sash frame  114  must first be aligned with the lift position  204 , between the ends  203   a  and  203   b  of the interlacing configuration  202 . 
   Additional members of the master frame  112  and sash frame  114  will now be described. Referring to  FIG. 10  (section  10 - 10  of  FIG. 4 ), the profiles of the vent side jam  120  of the master frame  112  and the vertical member  136  of the sash frame  114  are provided with vertically elongate channels and projections which co-operate to provide a generally weather-proof seal when the sash frame  114  is slid to the closed position. In particular, the vent side jam  120  has a projection or tongue  210  which is directed towards the mullion  124  and is shaped to be received in a channel or groove  212  provided in the vertical member  136  of the sash frame  114 . 
   Between the tongue  210  and the exterior face  121  of the frame assembly  110 , the vent side jam  120  may advantageously be provided with screen support details. In the embodiment illustrated, a step is positioned along the profile  120 , providing a vertical surface  216  against which the frame  174  of a screen element  129  can bear. Furthermore, an aperture  218  is provided adjacent the step, for receiving a plunger or clip for retaining the screen  129  in the master frame  112 . 
   Opposite the groove  212 , the vertical member  136  of the sash frame  114  may be advantageously provided with integrally moulded glazing support features  161 , for supporting the sash glazing  131 . In the embodiment illustrated, the glazing support details  161  comprise the back stop surface  162 , planar support surface  164 , and the attachment recess  166  for receiving a length of glass stop  168 . 
   The cross-sectional profiles of the mullion  124  and check rail  138  can best be seen in  FIG. 11 , which shows a section of the frame assembly  110  taken along the line  11 - 11  of  FIG. 4 . Towards the exterior face  121  of the frame assembly  110 , and adjacent the vent side  126 , the mullion  124  can be advantageously provided with integrally moulded screen support features. These features can include a vertical abutment surface  220 , and a series of retaining lugs  222  extending parallel to but spaced away from the vertical plane of the abutment surface  220  (see also  FIG. 7   a ). 
   Also adjacent the front face  121  of the frame assembly  110 , but directed towards the fixed side  128  of the master frame  112 , the mullion  124  may be provided with integrally moulded glazing support features  161  for supporting the fixed glazing  130 . The glazing support features  161  comprise the back stop surface  162 , planar support surface  164 , and the attachment recess  166  for receiving a length of glass stop  168  (not illustrated). 
   The mullion  124  further comprises an engagement flange  226 . The engagement flange  226  extends from the mullion  124  opposite the back stop surface  162 , and parallel to the direction along which the sash frame  114  can slide within the master frame  112 . 
   A reinforcement recess  228  may optionally be provided in the mullion  124 , for receiving metal reinforcement bars  229  or the like, which may be desired to limit the maximum deflection of the mullion  124 . In the embodiment illustrated, a reinforcement recess  228  is provided in the mullion  124 , opposite the attachment recess  166 . 
   The cross-sectional profile of the check rail  138  of the sash frame  114  can also best be seen in  FIG. 11  and in  FIG. 11   a . The check rail  138  is adapted to provide secure, sealed engagement with the mullion  124  when the sash frame  114  is slid to the closed position. In the embodiment illustrated, the check rail  138  is provided with a seal surface  230  which is aligned opposite to, and spaced slightly away from the engagement flange  226  of the mullion  124 . The seal surface  230  is provided with a seal recess  232 , which is shaped to receive a length of weather-stripping (not shown) in a press-fit arrangement. The weather-stripping can bear against the engaged flange  226  to provide a generally weather tight seal between the check rail  138  and the mullion  124  when the sash  114  is in the closed position. 
   A return bracket  234  extends from the seal surface  230  so as to engage the engagement flange  226  of the mullion  124 . In particular, in the embodiment illustrated, the return bracket  234  has an offset portion  236  which extends from the seal surface  230  in a direction towards the exterior face  121  of the frame assembly  110 , and at a position spaced slightly away from the terminal vertical edge  227  of the engagement flange  226  when the sash frame  114  is in the closed position. A catch portion  238  extends from the offset portion  236  in a direction towards the mullion  124 , and, for the embodiment illustrated, in generally parallel alignment with the engagement flange  226 . 
   Accordingly, when the sash  114  is in the closed position, the return bracket  234  provides a mechanical coupling between the check rail  138  and the mullion  124  in a direction perpendicular to the sliding operation of the sash frame  114 . Forces such as, for example, wind loads that may tend to push the sash frame  114  laterally towards the interior face  123  of the assembly  110  are counteracted by the overlap of the catch portion  238  of the check rail  138  and the engagement flange  226  of the mullion  124 . The overlap can increase the lateral stability of the sash frame  114  within the master frame  112 , and can ensure that the weather-stripping provided in the check rail  138  remains satisfactorily engaged with the engagement flange  226  of the mullion  124 . 
   To facilitate the integral injection moulding of the return bracket  234  of the check rail  138  when moulding the sash frame  114 , the offset and catch portions  236 ,  238  of the return bracket  234  may advantageously be provided in a staggered arrangement. Such an arrangement can facilitate moulding by reducing the requirements for additional slides in the die, and can improve the flow characteristics of the plastic when filling the mould by reducing the overall die cavity volume. 
   The portion of the check rail  138  facing the opposite vertical member  136  of the sash frame  114  may be provided with integrally moulded glazing support details  161  for supporting the sash glazing  131 . The glazing support details  161  comprise the backstop surface  162 , planar support surface  164 , and the attachment recess  166  for receiving a length of glass stop  168 . 
   As best seen in  FIG. 11   a , the check rail  138  may be provided with a elongate cap  250  extending along the height of the return bracket  234 . The cap  250  may advantageously be shaped to snap fit over the return bracket  234 , and may be of vinyl, metal, or other suitable material. The cap  250  can serve to provide a smooth, finished appearance for the return bracket  234  of the check rail  138 , and can also strengthen and reinforce the return bracket  234 . 
   As best seen in  FIG. 11   b , a modified check rail  138 ′ has a return bracket  234 ′ separately attachable to the check rail  138 ′, rather than being integrally moulded with the master frame  12 . The return bracket  234 ′ includes perpendicular portions  236 ′ and parallel portion  238 ′, and can be secured to the modified check rail  138 ′ by means of a fastener  252  tightened into a fastener  256  recess  254  provided in a lug extending from the modified check rail  138 ′. Since the return bracket  234 ′ can be separately manufactured from the check rail  138 ′, the perpendicular and parallel portions  236 ′,  238 ′, need not be provided in a staggered arrangement, but can extend continuously along the height of the return bracket  234 ′. 
   The cross-sectional profile of the fixed side jam  122  of the master frame  112  can be best seen in  FIG. 12 , which shows a section along the lines  12 - 12  of  FIG. 4 . The fixed side jamb  122  may also advantageously be provided with glazing support details for supporting the fixed glazing  130 . The glazing support details comprise the back stop surface  162 , planar support surface  164 , and the attachment recess  166  for receiving a length of glass stop  168 . 
   In accordance with the present invention, the frame assembly  110  may also be provided in a modified form, referred to as a reversible frame assembly  110 ′. The reversible frame assembly  110 ′ is similar to the frame assembly  110 , but is configured to be selectably installed in either a slide-right or slide-left configuration for opening the window, as best seen in  FIGS. 13   a  and  13   b , respectively. In other words, the frame assembly  110 ′ can be inverted to reverse the relative positions of the vent side  126  and fixed side  128 . 
   The reversible frame assembly  110 ′ has a modified master frame  112 ′ and a modified sash frame  114 ′. The modified master frame  112 ′ has a modified sill  118 ′ which is substantially a mirror image of the header  116 . In particular, the sill  18 ′ is provided with the same interlacing configuration  202  as provided in the header  116 , thereby defining a second lift position  204 ′ along the adjacent horizontal elements  118 ′ and  134 ′ of the master frame  112 ′ and sash frame  114 ′, respectively. 
   Details of the modified sill  118 ′ and horizontal member  134 ′ of the modified frame  110 ′ can best be seen in  FIG. 14 , showing a cross-section of  FIG. 13   a  taken along the line  14 - 14 . The first portion  118   a ′ of the sill  118 ′ has a modified tongue  140 ′ which corresponds in mirror image to the tongue  180  provided in the header  116 . Accordingly, the sash frame interlacing configuration  202 ′ is provided along the modified sill  118 ′, including the provision of the cavity  205 ′ behind the mullion  124  (see  FIG. 15 ). 
   Referring again to  FIG. 14 , the sash frame  114 ′ has a modified lower horizontal member  134 ′ which corresponds in mirror image to the upper horizontal member  132  of the sash  114 . In particular, the modified lower horizontal member  134 ′ has a deeper groove  142 ′ (as compared to the groove  142  of the horizontal member  134  shown in  FIG. 5 ), providing vertical clearance  200 ′ between the modified sill  118 ′ and the upper ends of the interior and exterior sidewalls  154 ′,  156 ′ of the lower horizontal member  134 ′. 
   To account for the vertical clearance  200 ′ provided by the interlacing configuration  202 ′ of the modified lower horizontal member  134 ′, a modified glider  157 ′ is provided within the groove  140 ′ of the horizontal member  134 ′ to operably support the sash frame  114 ′ above the sill  118 ′ of the master frame  112 ′. The modified glider  157 ′ includes the glider housing  158  and a modified glider element  160 ′. The modified glider element  160 ′ has a greater vertical height than the glider element  160 , to compensate for the increased depth of the groove  142 ′ provided in the lower horizontal member  135 ′, as compared to the groove  142  provided in the lower horizontal member  134  ( FIG. 5 ). When installed, the glider  157 ′ engages the runner  144  of the tongue  140 ′, and thereby supports the sash frame  114 ′ above the sill  118 ′. 
   When the reversible frame  110 ′ is installed as shown in  FIG. 13   a , a window having a vent side  126  to the left, and a fixed side  128  to the right, (when viewed from the exterior) is provided, similar to that described in the original frame assembly  110 . To install the reversible window frame assembly  110 ′ with the vent side  126  and fixed side  128  in reverse positions ( FIG. 13   b ), the frame assembly  110 ′ need merely be rotated 180 degrees in a vertical plane, and the glider element  160 ′ attached to the glider housing  158 ′ provided in the horizontal member  132 , rather than in the horizontal member  134 ′, of the sash frame  114 ′. 
   Referring now to  FIGS. 11 and 15 , further details of the integrally moulded glazing support features  161  will be described. The glazing support features  161  include a planar surface  164  which extends around the perimeter of the glazing (not shown) to be installed. At various locations along the planar surface  164 , integrally moulded setting block housings  240  for holding setting blocks  242  are provided. The housings  240  can be a series of ribs on which the setting blocks  242  are placed, having taller outermost ribs for providing a press fit seat for the setting blocks  242 . The setting blocks  242  may be constructed of a resilient material, providing a snug fit around the edge of the glazing and, offering a degree of compressibility to accommodate thermal expansion and contraction. 
   Furthermore, the glazing support features  161  include elongate recesses  166  extending generally parallel to and adjacent to the planar surfaces  164 . The recesses  166  are shaped to receive a length of glass stop  168  ( FIG. 15 ). In particular, the glass stop  168  has a nose portion  243  shaped to snugly fit in the recess  166 . The glass stop  168  may also be provided with tabs  244 , shaped to snap fit in corresponding recesses  246  provided along an inner surface of the recesses  166 . 
   Once the length of glass stop  168  has been inserted, the glazing is securely fixed in the master frame  112  or sash frame  114  by being squeezed between the backstop surface  162  of the respective frame, and an opposed contact surface  248  provided on the length of glass stop  168 . Furthermore, the glazing is constrained from moving in a direction parallel to the glazing by the setting blocks  242 . It is again noted that according to the present invention, the backstop surface  162 , planar support surface  164 , recesses  166 , setting block housing  240 , and the recesses  246 , can be advantageously integrally moulded with the respective frame elements  112  and  114 . 
   An alternate embodiment of a frame assembly  310  according to the present invention can be seen in  FIG. 17 . The frame assembly  310  is similar to the frame assembly  110 , but has some features and modifications that can provide advantages such as, for example, but not limited to, improved performance ratings, better wind and water resistance, and improved ease of manufacture. Features of the frame assembly  310  corresponding to those of the frame assembly  110  have been identified by the same reference numerals, incremented by 200. 
   Referring to  FIGS. 17-20 , the general construction of the window frame assembly  310  with its master frame  312  and sash frame  314  can be seen. The master frame  312  is of one-piece, integrally moulded construction, devoid of any seams or joint lines between contiguous vertical and horizontal members  316 ,  318 ,  320 , and  322 , and the mullion  324 . 
   The members of the master frame  312  are shaped and sized to facilitate manufacturing the master frame  312  by a moulding process, such as, for example, injection moulding. The master frame  312  can be constructed of a suitable plastic material, such as polypropylene or a recycled plastics material. 
   The sash  314  is similarly of one piece, integrally moulded construction, having contiguous horizontal and vertical members  332 ,  334 ,  336 , and  338 . The sash  314  can be constructed of the same material as the master frame  312 . 
   In the embodiment illustrated, the frame assembly  310  is reversible, similar to the frame assembly  110 ′. In other words, the frame assembly  310  can provide a sliding window or door with the fixed side  328  on either the left or the right side when looking at the exterior face  321 . In the embodiment illustrated, the fixed side  328  is on the right side of the frame assembly  310  when viewed from the exterior. 
   Referring to  FIGS. 17 and 19 , the frame assembly  310  is provided with track or carrier strips  502  that line a portion of the perimeter of the vent side  326  of the master frame  312 . In the illustrated embodiment, the portion of the perimeter provided with the carrier strips  502  includes a portion of the header  316 , the sill  318 , and the vent side jamb  320  of the master frame  312 . 
   As best seen in  FIG. 21 , regarding the header and sill portions  316  and  318 , the carrier strips  502  are provided along upper and lower surfaces, respectively, of the tongues  340  and  380  extending from the first portions  318   a  and  316   a  of the sill  318  and header  316 . As best seen in  FIGS. 26   a  and  26   b , regarding the vent side jamb  320 , the carrier strip  502  is provided along the surface of the tongue  440  extending from the vent side jamb  320 . The fixed side jamb  322  is without the carrier strips  502  ( FIGS. 28   a  and  28   b ), as are the second portions  318   b  and  316   a  of the sill and header  318  and  316 . 
   Details of the carrier strips  502  and their attachment to the tongues  340 ,  380 ,  440  will be described by way of example with respect to the strip  502  mounted to the tongue  340  and referring to  FIGS. 21 and 21   a . The carrier strip  502  has a facing surface  504  that extends between two support legs  506   a ,  506   b . The facing surface has across its width a generally orthogonal portion  504   a  and an inclined portion  504   b . The opposed support legs  506   a ,  506   b  have inwardly directed clips  508   a ,  508   b , respectively, to engage the underside of outwardly projecting tabs  510  that extend from the tongue  340 . 
   The carrier strip  502  is adapted to support weatherstripping  348  that extends along the length of the carrier strip  502 , providing a seal between the tongue  340  and the lower horizontal member  334  (Shown in  FIG. 21 ) of the sash frame  314 . In the embodiment illustrated, the opposed support legs  506  of the carrier strips  502  each have outwardly directed T-slots  512  extending along the length of the carrier strips  502 . A length of weatherstripping  348  can be inserted in each T-slot, to provide seals between the tongue  340  and the lower horizontal member  334  of the sash frame  314  along both sides of the carrier strip  502 . The weatherstripping  348  can be of a synthetic pile construction. 
   To install the carrier strip  502  onto the tongue  340 , the support legs  506  can be pressed over the tabs  510  so that the clips  508  are spread apart and then snap back into place as the clips  508  are pressed past the tabs  510 . The carrier strip can be constructed of a durable plastic material and can be manufactured by an extrusion process. The carrier strips  502  can be provided with rubber-like fins  514  extending downward from the ends of the support legs  506 . The fins  514  can provide a seal between the tongue  340  and the strips  502 , and can be coextruded with the strips  502 . The seal provided by the fins  514  can inhibit penetration of weather elements underneath the carrier strips  502 , so working their way from the exterior face  321  of the assembly  310  to the interior face  323 . 
   In use, the orthogonal portion  504   a  of the facing surface  504  of the strip  502  attached to the tongue  340  provides the runner  344  against which the roller/glider  357  of the sash  314  can bear ( FIG. 21 ). The inclined portion  504   b , which is disposed between the orthogonal portion  504   a  and the exterior face  321  of the frame assembly  310 , can facilitate drainage of any water that may have worked its way between the groove  342  of the sash  314  and the tongue  340  (with the carrier strip  502 ) of the master frame  312 . 
   Referring again to  FIG. 21 , the first portion  316   a  of the header  316  is, in the embodiment illustrated, provided with a skirt attachment recess  520  to which a skirt  522  is attached. The skirt  522  extends alongside the tongue  380  of the header  316 , towards the exterior face  323  of the frame assembly  310 . The skirt  522  extends generally vertically from the header  316 , a sufficient distance to at least partially overlap the upper horizontal member  332  of the sash  314 . The skirt  522  provides added protection against intrusion of water and wind past the weatherstripping  348  between the sash  314  and the tongue  380  of the header  316 . 
   Any water that does make its way past the skirt  522  and exterior weatherstripping  348  is channeled to remain on the exterior side of the sash glazing  331 , within the groove  386 . In particular, the upper horizontal member  332  of the sash  314  has a protruding dam  526  that extends along the inside lower surface of the groove  386 , and forms a drainage channel  527  between the dam  526  and the exterior sidewall  383  of the tongue  380 . The channel  527  is positioned laterally between the exterior weatherstripping  348  and the position of the glazing  331 . Water that does pass the weatherstripping  348  into the groove  386  is conveyed along the channel  527  to the vertical members  336  and  338  of the sash  314 , where it is again channeled along the exterior side of the glazing  331 . The water is then directed onto the inclined portion  504   b  of the carrier strip  502  on the tongue  340 , and drains towards the exterior facing surfaces of the sill  318 . The water may temporarily rest on top of the exterior weatherstripping  348   b , but generally eventually works it sway through the piles of the weatherstripping and drains down the exterior sloped portion of the sill  318 . Between the tongue  340  and the exterior edge of the sill  318 , an attachment recess  520 ′ can be provided, to receive the skirt  522  when the frame assembly  310  is in the inverted position, for reversing the vent and fixed sides  326 ,  328 , respectively. 
   The inventors have found that in some cases, water that penetrates the exterior weatherstripping  348  along the tongue  380  could migrate, by capillary action, across the facing surface  504  of the carrier strip  502 . Such water could thereby cross from the exterior side to the interior side of the glazing, and pose a risk of water intrusion. To eliminate such water migration, the carrier strip  502  is provided with a drip groove  528  positioned laterally between the exterior weather stripping  348  and the drainage channel  526 . Any water traveling across the surface  504  beads up and falls down upon encountering the groove  528 , landing in the channel  527 . The drip groove  528  can also be seen in  FIG. 21   a.    
   Referring now to  FIG. 22 , the second portions  318   b  and  316   b  of the sill  318  and header  316  do not, in the embodiment illustrated, have carrier strips  502  attached to the tongues  340  and  380 . The tongue  340  has an upper surface  530 , which in the embodiment illustrated, has a generally orthogonal portion  530   a  and an inclined portion  530   b.    
   The portions  530   a  and  530   b  are laterally adjacent each other, as best seen in  FIG. 22 , with the orthogonal portion  530   a  positioned nearer to the interior face  323  and the inclined portion  530   b  positioned nearer to the exterior face  321  of the frame assembly  310 . The orthogonal portion  530   a  of the upper surface  530  of the tongue  340  provides the runner  344  along the fixed side  328  of the assembly  310  against which the roller/glider  357  of the sash  314  can bear. 
   As best seen in  FIGS. 21   b  and  21   c , in the embodiment illustrated, the roller/glider  357  comprises a wheel  360  that can be snapped into one of three slots  355   a ,  355   b , and  355   c  provided in a housing  358 . The three slots  355   a - c  are of differing depths to provide for height adjustment of the sash  314  within the master frame  312 . The housing  358  can be press fit into a pocket  353  provided in the underside of the lower horizontal member  334  of the sash  314 . In the embodiment illustrated, the pocket  353  for receiving the glider/roller housing  358  is also provided in the upper horizontal member  332  of the sash  314 , to permit inverted installation of the frame assembly  310 , for reversing of the vent and fixed sides  326 ,  328  of the frame assembly  310 . 
   The glazing support details  361  of the frame assembly  310  will now be described referring to  FIG. 22 . The glazing support details  361  include a planar support surface  364  that extends laterally beyond the width of the glazing  330  in the embodiment illustrated. This extra width can accommodate a wider glazing unit if desired, by providing adequate support beneath the entire width of glazing units that may range in width. Typical glazing unit width dimensions include ¾ and 1 inch widths. Glass stops  368  with shorter or longer arms can be used in combination with the wider or narrower glazing  330 , to clamp the glazing  330  securely between the glass stops  368  and backstop surfaces  362 . Also shown in the embodiment illustrated is the provision of double-sided glazing tape  532  that can be used to mount the glazing  330  against the backstop surface  362  of the glazing support features  361 . 
   Referring now to  FIGS. 21 and 25   a - 25   c , the frame assembly  310  is also provided with vertical clearance  400  between the upper horizontal member  332  of the sash  314  and the header  316  of the master frame  312 . More specifically, in the embodiment illustrated, the profile of the header  316  has a sash frame interlacing configuration  402  along a portion of the length of the header  316 , that portion defining the lift position  404 . When the sash  314  is aligned along its path of travel so that the upper horizontal member  332  is within the lift position  404 , the sash frame  314  can be lifted upward relative to the master frame  312 , so that the sash  314  can be installed in, and removed, from the master frame  312  ( FIGS. 25   a  and  25   b ). The skirt  522  is spaced apart from the tongue  380  to accommodate the exterior sidewall  390  ( FIG. 25   a ), when lifting the sash frame  314  for installation or removal. 
   As best seen in  FIGS. 23 ,  23   a , and  23   b , in the embodiment illustrated, the interlacing configuration  402  extends from a first end  403   a  adjacent the vent side jamb  320  to a second end  403   b  which is above the fixed side  328  of the master frame  312 . Between the first end  403   a  of the interlacing configuration  402  and the vent jamb  320 , the tongue  380  extending from the header  316  is provided with an integrally moulded interior shoulder  406  ( FIG. 23   b ). The shoulder  406  generally occupies the space above the interior sidewall  388  of the groove  386  of the upper horizontal member  332  of the sash  314  (see  FIG. 21 ). As a result, the vertical clearance  400  is no longer provided and lift out of the sash  314  is prevented when any portion of the sash  314  is positioned below the shoulder  406  (i.e., when the sash  314  is in or near the closed position). 
   Between the second end  403   b  of the lift position  404  and the fixed side jamb  322  of the master frame  312 , the header  316  is generally provided with the second header portion profile  316   b . The second portion  316   b  includes the exterior shoulder  398  above the exterior sidewall  390  of the groove  386  of the upper horizontal member  332  (see  FIG. 22 ). As a result, the vertical clearance  400  is not provided between the sash  314  and the second portion  316   b  of the header  316 . 
   Referring now to  FIGS. 23   a  and  24 , a recess or cavity  405  is provided in the header  316  between the mullion  324  and the tongue  380 , for extending the sash frame interlacing configuration  402  behind the mullion  324 . 
   As best seen in  FIGS. 23   c  and  24   a , the recess  405  has two portions, namely, a primary recess  536  and a secondary recess  538  that are separated from each other by a dividing wall  539 . The primary recess  536  has a length  540  that extends from a first end  542  generally even with the edge of the mullion  324  nearest the vent jamb  322 , to a second end  544  positioned along the second portion  316   b  of the header  316  and defined by the dividing wall  539 . The second end  544  of the primary recess  536  is positioned to provide a space between the leading edge of the shoulder  406  and the second end  544  that corresponds to the lift-out position  404 . 
   Referring now to  FIG. 24   b , the primary recess  536  has a depth  546  that extends generally from the exterior shoulder  398  to a generally horizontal base surface  548 . The depth  546  of the primary recess  536  is sufficient to provide the vertical clearance  400  between the base surface  548  and the exterior sidewall  390  of the groove  386  of the sash  314 . 
   Referring now to  FIGS. 27   a  and  27   b , the frame assembly  310  is further provided with an optional weather buffering chamber  550  positioned in the pathway of air and water that may try to work its way from the exterior face  321  to the interior face  323  of the frame assembly  310  when in the closed position. Under certain weather conditions, relatively high pressure conditions caused by, for example, wind loads, can be applied to the exterior face  321  of the frame assembly  310 , while the interior face  323  remains exposed to relatively low pressure conditions. This pressure differential across the frame assembly  310  can generate a suction-like effect, drawing the outside air, along with any water, to the interior side of the frame assembly  310 , through any gaps or weaknesses in the seams between the sash frame  314  and the master frame  312 . 
   The inventors have observed that one pathway along which air and water can be drawn through the frame assembly is between the mullion  324  and the sash checkrail  338 . This pathway can be seen at arrows  448  in  FIGS. 27   a  and  27   b . To provide the weather buffering chamber  550 , two spaced-apart strips of weatherstripping  552   a ,  552   b  are provided between the mullion  324  and the check rail  338 . 
   The first strip of weatherstripping  552   a  extends along the height of the mullion  324 , adjacent an edge of the mullion  324  near the vent side  326  of the frame assembly  310 . The second strip of weatherstripping  552   b  extends generally parallel to the first strip, but is positioned nearer to the fixed side  328  of the frame assembly  310 . In the embodiment illustrated, the strips of weatherstripping  552   a  and  552   b  can be press-fit into corresponding attachment slots  554   a  and  554   b  that extend along the height of the mullion  324 . The slots  554   a  and  554   b  can be integrally moulded with the master frame  312 . The space between the weatherstripping  552   a  and  552   b , and between the mullion  324  and the checkrail  338  generally defines the weather buffering chamber  550 . 
   The first strip of weatherstripping  552   a  has its upstream side (relative to the flow path  448 ) exposed directly to the exterior elements. The downstream side of the first strip  552   a  is exposed to the weather buffering chamber  550 . The strip  552   a  acts as an exterior seal, serving as an initial wind and rain barrier, through which some penetration of wind or water can be tolerated. The first strip (exterior seal)  552   a  can be constructed of, for example, but not limited to, densely packed synthetic pile. 
   Any wind or rain that penetrates the external seal  552   a  ends up in the weather buffering chamber  550 . The invading wind can elevate the air pressure in the chamber  550 , so that the pressure is higher than interior conditions but lower than the exterior conditions. To manage the invading water, the chamber  550  can be provided with an exterior drain  555   a  for draining the invading water from the chamber  550  to the exterior  321  of the frame assembly  310 . Further details of the exterior drain  555   a  are provided hereinafter. 
   The upstream side (relative to the flow path  448 ) of the second strip of weatherstripping  552   b  is not exposed directly to the exterior elements, but rather, is exposed to the weather buffering chamber  550 . The downstream side of the second strip  552   b  is generally exposed to the interior  323  of the frame assembly  310 . The second strip  552   b  acts as an “interior” seal. It is generally undesirable to have significant amounts of wind or water penetrate the interior seal. 
   In use, the weather buffering chamber  550  reduces the air pressure and amount of water to which the interior seal  552   b  is exposed. This reduces the amount of air and water that ultimately penetrates from the exterior  321  to the interior  323  of the frame assembly  310 . The inventors have found that in one aspect the buffering chamber divides the total pressure gradient across the assembly  310  into a first, exterior gradient across the exterior seal  552   a , and a second, interior gradient across the interior seal  552   b . By having two separate, discrete pressure gradients across each of the exterior and interior seals  552   a ,  552   b , each of which is lower than the total pressure gradient across the frame assembly  310 , the forces tending to draw air and water across these seals are reduced. 
   The inventors have observed that tuning or balancing the pressure gradients across the seals  552   a ,  552   b  can further enhance the overall wind and water resistance of the frame assembly  310 . Having a very high pressure drop across one of the seals  552   a ,  552   b  relative to the other can reduce the effectiveness of the weather buffering chamber  550 . 
   Referring now to  FIGS. 27   b  and  29 , to facilitate tuning the external and internal pressure gradients, the weather buffering chamber  550  can be vented by providing ventilation apertures  560  between the chamber  550  and an adjacent air reservoir. This venting can, for example, reduce the pressure gradient across the exterior seal  552   a  by drawing air into the chamber  550  through the apertures  560 , rather than through the exterior seal  552   a . Preferably, the apertures  560  would draw on a supply of dry air (rather than a mixture of air and rain, for example), so that the amount of water to which the interior seal  552   b  is exposed is kept to a minimum. 
   In the embodiment illustrated, the mullion  324  has a generally hollow mullion cavity  556 , which can serve as an air reservoir for supplying air to the chamber  550 . The slots  554   a ,  554   b  for the seals  552   a ,  552   b  can be provided on opposite sides of the mullion cavity  556 , so that the cavity  556  is in fluid communication with the chamber  550 . 
   The mullion  324  can have a cover plate  558  that generally covers the cavity  556  and separates the mullion cavity  556  from the weather buffering chamber  550 . The cover plate  558  can be assembled by means of a snap fit or press fit between the walls of the cavity  556 . 
   To provide fluid communication between the cavity (or reservoir)  556  and the chamber  550  for venting the chamber  550 , the cover plate  558  can have ventilation apertures  560  in the form of notches  561  along one edge. Alternatively, the notches  561  can be positioned along the walls of the mullion  324  adjacent the cover  558 , to provide a gap between the mullion  324  and the cover  558 . The cover  558  can also have cut-outs  562  at the upper and lower ends of the cover  558 . The cut-out  562  at the upper end of the cover  558  can serve as an additional ventilation aperture  560 . The cut-out  562  at the lower end of the cover  558  adjacent the sill  318  (see  FIG. 29 ) can also act as a ventilation aperture  560 , and can also allow any water that may be in the mullion cavity  556  to drain into the weather buffering chamber  550 . 
   The mullion cavity  556  can be in fluid communication with the exterior atmosphere by means of external apertures  564  provided in the sidewalls of the mullion  324 , on the opposite side of the cover  558  as the chamber  550 . In the embodiment illustrated, the external apertures  564  are integrally moulded in the mullion  324  at a position behind the lugs  422  for retaining the window screen  329  ( FIG. 27   b ). Although the screen, when installed, partially obstructs the external aperture  564 , air can still easily flow through the gaps between the screen  329  and the adjacent surfaces of the mullion  324 . This positioning of the external apertures  324  can help to keep rain from entering into the mullion cavity  556 . 
   Details concerning the drainage of any water that may penetrate the exterior and interior seals  552   a ,  552   b  will now be described with reference to  FIGS. 30 and 31 . In accordance with the present invention, independent exterior and interior drains shown generally at  555   a  and  555   b  are provided for draining any water that makes its way to the downstream side of the exterior and the interior seals  502   a  and  502   b , respectively. The exterior and interior drains  555   a  and  555   b  are formed from the cooperation of various surfaces of the master frame  312  and the sash frame  314  when the sash frame  314  is in the closed position, and provide separate exterior and interior water drainage flow paths  553   a  and  553   b , respectively, as will hereinafter be described in greater detail. 
   The separate drains  555   a  and  555   b  can cooperate with, and enhance the function of, the weather buffering chamber  550 . For example, the exterior drain  555   a  and interior drain  555   b  each drain water between environments having distinct pressure differentials between them. The pressure differential across the drains can be a significant factor in keeping water from penetrating to the interior face  323 , since, particularly under high load conditions, the suction effect can draw water in through the drain, rather than discharging water to the exterior. 
   In the embodiment illustrated, the exterior drain  555   a  drains water from the weather buffering chamber  550  to the exterior face  321  of the frame assembly  310 . The pressure differential across the chamber  550  and the exterior face  321  (and hence across the exterior drain  555   a ) is generally equal to the exterior pressure gradient across the exterior seal  552   a , which is less than the total pressure gradient between the exterior and interior faces  321 ,  323 . The interior drain  555   b , however, drains water from the interior face  323  to the exterior face  321  of the frame assembly  310 . The pressure differential across the interior drain is therefore equal to the total or maximum air pressure across the exterior and interior faces of the frame assembly  310 , which will generally be equal to the sum of the pressure differentials across the exterior seal  552   a  and the interior seal  552   b.    
   The exterior drain  555   a  discharges water from the chamber  550  directly to the exterior along the flow path  553   a . The reduced pressure differential across the exterior drain  555   a  (i.e. from inlet end to outlet end of the drain  555   a ) permits direct discharge to the exterior face  321  without significant suction problems than inhibit drainage. The interior drain  555   b  discharges water from the interior to the exterior via a valve element  557  which is placed between upstream and downstream portions of the flow path  553   b . The valve element is movable between an open position  557   a , in which the interior and exterior environments are in fluid communication, and a closed position  557   b , in which fluid communication through the interior drain  555   b  is sealed off. 
   In the embodiment illustrated, to provide the exterior and interior drains  555   a  and  555   b , the inventors have made clever use of the recess  405  that is located in the sill  318 . The recess  405  in the sill  318  is the same as the recess  405  in the header  316 , and is provided in the sill  318  so that the frame assembly  310  can be inverted to reverse the relative positions of the vent and fixed sides  326  and  328 . 
   The recess  405  in the sill  318  is generally covered by a diverter cap  570  ( FIG. 30 ). The diverter cap  570  has an exterior portion  572  and an interior portion  574  connected to each other by a web  576 . The exterior and interior portions  572 ,  574  each have dust plug supports  578   a ,  578   b  for supporting exterior and interior dust plugs  580   a ,  580   b , respectively ( FIG. 31 ). 
   The exterior and interior dust plug supports  578   a ,  578   b  (and dust plugs  580   a ,  580   b ) are spaced apart so that they are generally aligned with the exterior and interior seals  552   a  and  552   b  extending along the mullion  324 . The supports  578   a ,  578   b  and dust plugs  580   a ,  580   b  generally fill the width of the recess  405 , and form a continuous seal with exterior and interior seals  552   a  and  552   b , respectively. The dust plugs  580   a  and  580   b  engage the underside of the sash  314 . The supports  578   a ,  578   b  resiliently urge the dust plugs upwards into contact with the sash  314 . 
   The space between the exterior and interior supports  578   a ,  578   b  and dust plugs  580   a ,  580   b  and around the narrow web  576  provides an opening  581 , forming part of the exterior drain  555   a  and through which the flow path  553   a  extends. The diverter cap  570  further has a seal plate portion  582  ( FIG. 31 ) extending from the exterior portion  574 , to a length that reaches and extends beyond the divider wall  539 , such that the seal plate portion  582  slightly overhangs above the secondary recess  538 . 
   The diverter cap  570  can be secured in the recess  405  in the sill  318  by means of dual sided adhesive sealant tape  584  provided between the underside of the seal plate portion  582  of the diverter cap  570  and the upper periphery of the primary recess  536  and positioned towards the interior side  323  of the interior dust plug  580   b . The interior portion  572  of the diverter cap  570  is supported by a leg  585  extending downward from the exterior dust plug support  578   a  and generally abutting the first end  542  of the primary recess  536 . 
   As best seen in  FIG. 31  and  FIGS. 35-37 , the diverter cap  570  with the exterior and interior dust plugs  580   a  and  580   b  provides a further part of the sealed exterior drain  555   a  that forms flow path  553   a . The flow path  553   a , for draining water from the weather buffering chamber  550 , is sealed on the exterior side by the exterior seal  552   a  (see  FIGS. 27   a  and  b ) and exterior dust plug  580   a . The flow path  553   a  is sealed on the interior side by the interior seal  552   b , interior dust plug  580   b , and the seal plate portion  582  of the diverter cap  570 . The drain  555   a  is in fluid communication with the chamber  550  at the upstream side, and with the exterior atmosphere on the downstream side. 
   Most of the water that makes its way into the buffering chamber  550  will generally be drained through the exterior drain  555   a . Accordingly, the pressure differential across the interior seal  502   a  will generally draw only air to the interior face  323  of the frame assembly  310 , rather than water and air. However, under high loads, some water may work its way to the downstream side of the interior seal  502   a . Although this may be undesirable, such water penetration is acceptable provided it is contained along the sill  318 . Typical rating standards generally require that interior water be contained to the extent that it can eventually drain back to the exterior side  321  of the frame assembly  310 . Wind loads are typically cyclical, so that periods of high load and highly increased water penetration are punctuated by periods of lower loads in which little or no water penetrates, and any contained water can drain. Tests to determine window ratings initiate these fluctuations by cycling applied loads between higher and lower pressure ratings. 
   One method for containing water that penetrates to the interior of a window is to provide the frame with a vertical barrier along the inside of the sill  318 , forming a well in which a volume of water can collect or build-up during the higher-load periods. To achieve high ratings, however, such barriers must be of significant size so that a well of sufficient volume is created. Large vertical barriers can increase the raw material cost of the window, and can be unsightly and reduce the proportion of viewing area of the window relative to the frame dimensions. Furthermore, having a substantial pool of water along the interior of a window can be undesirable. 
   In the present invention, the weather buffering chamber  550  greatly reduces the amount of water that penetrates the interior seal for a given load. Water that does penetrate the interior seal is drained by means of the interior drain  555   b . The interior drain  555   b  comprises the secondary recess  538  in the sill  318 , along with an intake channel  586  and an outlet channel  588 . The intake channel  586  is provided along the upper surface of the seal plate portion  582  of the diverter cap  570 , between upper portions of the vertical sidewalls of the recess  405  that extend along either side of the seal plate portion  582  ( FIG. 34 ). The intake channel extends between the interior dust plug  580   b  and the secondary recess  538 . 
   The outlet channel  588 , as best seen in  FIGS. 32-34 , extends from the secondary recess  538  to the exterior face  321  of the frame assembly  310 . An aperture  589  is provided between the recess  538  and the channel  588  ( FIG. 34 ). The aperture  589  can be provided by removing a break at panel  589 ′, which is left in tact in the header  316  (see  FIG. 24   b ). In the embodiment illustrated, the outlet channel  588  is provided with the valve element  557  in the form of a sealed weep  590 . The weep  590  has a frame  591  and a hinged flap  592  supported in the frame  591 . The flap  592  has a gasketed upstream surface  594 . During periods of high loads, the suction pulls the flap  592  tightly closed, so that the gasketed surface  594  is tightly sealed against the periphery of the frame  591 . During low load conditions, the force of upstream water can push the flap  592  open to allow collected water to drain. 
   The valve element  557  can comprise a single sealed weep  590  ( FIGS. 29 and 30 ), or alternatively, can comprise a regulator drain valve assembly  600  ( FIGS. 32-34 ). The valve assembly  600  has a housing  602  with one sealed weep  590  positioned at an upstream end, and a second weep  590 ′ positioned at a downstream end of the assembly  600 . The second weep  590 ′ can be the same as the sealed weep  590 , or alternatively, can be unsealed devoid of the gasketing  594 . Apertures  604  can be provided between the weeps  590  and  590 ′ to permit some ventilation and entry of dry air into the space  606  between the weeps  590  and  590 ′. 
   While preferred embodiments of the invention have been described herein in detail, it is to be understood that this description is by way of example only, and is not intended to be limiting. The full scope of the invention is to determine from reference to the appended claims.