PRIORITY 
     Benefit of the Mar. 15, 2013 filing date of the U.S. Provisional Application Ser. No. 61/787,411 is claimed; and that application is expressly incorporated herein by reference as if fully set out herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to shower floors and more particularly apparatus for building shower floors to meet compliance with the Americans with Disabilities Act. The invention more specifically relates to the construction of shower floors without lips, curbs, sills or other obstructions at transitions of shower floors to surrounding floors. 
     BACKGROUND OF THE INVENTION 
     Typically, shower floors or areas are set off or separated from surrounding floor surfaces such as bathroom floors by a curb or lip defining edges of the shower area and preventing water deposits, overflow, spray or the like on the adjacent or surrounding floor of a bathroom, for example. While of traditional construction, any such raised curb, lip, sill or the like constitutes an upstanding barrier between the shower floor and the surrounding or adjacent floor area such as the other floor surface in a bathroom. 
     While these barriers work well to contain water within the shower floor area, they constitute barriers to ingress and egress from the shower area, particularly for disabled persons. For example, if a person is confined to or must rely on a wheeled device for transfer into a shower area from an adjacent bathroom floor, that device must transit any upstanding lip, curb or sill. Frequently, these elements do not permit transfer of or block the wheeled device such as a chair or other support into or from a shower area. 
     In order to overcome this inherent difficulty, architects and builders attempt to install a shower floor with no lip, curb or sill. Typically, this is accomplished by “notching” or cutting out portions of the shower-underlying floor joists so a shower floor can be installed at a lower level, even with the surrounding floor and without an upstanding lip, curb or sill. Such a process entails the lowering of the subfloor to the notched-out joist tops and the provision of drain, tile and the like thereon. This permits a wheeled support device such as a wheelchair to be easily wheeled into and from the shower floor and to the surrounding bathroom floor. 
     Nevertheless, such process involves inherent disadvantages, severely limiting the possibility of such construction. First, “notching” the underlying floor joists by cutting away upper portions thereof can substantially weaken the underlying joists. Additional weight of any mud bed (mortar) further weakens such a floor. 
     Such a prior art construction is shown in elevational cross-section in  FIG. 1  herein. 
     Such constructions are limited since builders use minimal dimension joists which cannot be notched without structural weakening and costly structural engineering involvement. Moreover, some builders are using engineered joists or joists of synthetic material which cannot be notched or cut out at the site. 
     Accordingly, it is one objective of the invention to provide apparatus and process for installing a shower floor without lip, curb, sill or other upstanding element between the shower floor and surrounding floor and without notching or weakening underlying support joists. 
     A further objective has been to provide a sloped water-draining shower floor extending from a surrounding floor without break or obstruction and without modifying underlying support joists. 
     A further objective has been to provide a sloped, water-draining shower floor extending from a surrounding floor without any raised obstruction and over supporting joists having upper edges at the same height as supporting joists underlying the surrounding floor. 
     A further objective has been to provide improved shower floor components and combinations thereof providing continuous smooth interfacing with surrounding floor areas without intervening lip, curb or sills and supported with standard, non-modified joists. 
     SUMMARY OF THE INVENTION 
     These and other objectives and advantages are obtained in a preferred embodiment of the invention by use of a unique drain plate combined with a rigid underlayment supported on the top edges of non-modified original joists. 
     That underlayment also rests on the tops of in-place floor joists, not modified in any way. A relatively thin mortar bed is sloped from the upper surface of the drain plate up to the upper surfaces of the tile underlayment of an adjacent floor. A membrane covers the underlayment, mortar bed and drain plate and a layer of thin set adhesive is applied to secure tile thereover. 
     Accordingly, there is no lip, curb or sill across the adjacent edges of the shower floor or adjacent bathroom floor, water-tightness across both is assured, weight is reduced and no changes are required in any joists. Drain placement is virtually unlimited between joists. The drain plate edge itself functions as a screed pivot point to produce the desired slope from there to the upper surface of surrounding or adjacent backer board. 
     These and other aspects of the invention will become readily apparent from the following written description and from the attached drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a prior art form of a shower floor built over notched-out floor joists; 
         FIG. 2  is a cross-sectional view of one embodiment of the invention; 
         FIG. 3  is a top, plan view of the drain plate of the invention; 
         FIG. 4  is a cross-sectional view taken along lines  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a plan view of the top of the drain plate of  FIGS. 2-4  showing a drain fitting therein; 
         FIG. 6  is a view similar to  FIG. 5  but showing the drain fitting removed and inverted for clarity; 
         FIG. 7  is a view similar to  FIG. 5  but showing the drain fitting in upright orientation spaced from the drain plate but not inverted; 
         FIG. 8  is a view similar to  FIG. 5  but illustrating the various components of the structural underlayment and the interface thereof with the drain plate; and 
         FIG. 9  is an isometric view of the underlayment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates the prior art construction of a shower floor adjacent a bathroom floor. This bathroom floor comprises a plywood subfloor, tile underlayment and tile finish surface. 
     The prior shower floor components of  FIG. 1  include, from bottom up, a plywood subfloor, a pre-sloped material, a pvc membrane, a thick mortar bed and tile, with a drain fixture. 
     Note in this construction the two notched joists with 2×4 blocking as additional support. The upper edges of the notched joists have been cut out in the overlying subfloor lowered thereon and lie below the level of the top edges of the joists of the adjacent floor. The tile on the shower floor is sloped to the drain and extends smoothly from the tile over the surrounding, or adjacent floor. 
     As noted, upper edges of the two notched floor joists are oriented below the upper edges of the joists which are not notched or modified under the surrounding floor. The left side of the drain illustrates a studded shower wall over a traditional subfloor. 
     Thus, traditional construction to avoid transitional breaks or obstacles across the adjacent floors requires joist modification. 
     Turning now to  FIGS. 2-9 , the drain plate of the invention will be described. Construction of a shower floor according to the invention, with the drain plate, is further described with reference to these FIGS. 
       FIG. 3  is a top plan view of a drain plate  10  according to the invention. Plate  10  is preferably made of any suitable synthetic material and comprises four panels on surfaces  11 - 14  sloped downwardly ( FIG. 4 ) from an edge  15  along each panel  11 - 14  to a center aperture  16 . 
       FIG. 4  illustrates a slight downward slope in panel surfaces  11 - 14  to aperture  16  but it will be appreciated that the plate  10  is preferably of integral one-piece or monolithic construction, such as pivoted by molding or any other suitable process. The slope of the panels  11 - 14  to aperture  16  is indicated by angle alpha @ in  FIG. 4 , and is preferably less than 180 degrees (i.e. the slope declining preferable 1 to 2 degrees from horizontal). 
     Plate  10  has an outer surrounding flange or upwardly facing ledge surface  17  along the panels  11 - 14  and terminating in an outer edge  18 . 
     Plate  10  is provided with a drain fixture  25 , having a flange  26  fitting on the shoulder  27  surrounding aperture  16 . Preferably, fixture  25  is glued onto shoulder  27  ( FIG. 7 ) and extends downwardly for connection to any suitable drain or waste line (not shown). 
     Turning now to  FIG. 2 , the integration of plate  10  in a shower floor area  30  is illustrated. 
     According to the invention as shown, shower floor area  30  is set over a plurality of joists  45 ,  46  having the same spatial orientation as joist  47  under an adjacent floor  40 . 
     Floor  40 , such as an adjacent bathroom floor, is comprised of a plywood subfloor  41 , a suitable tile underlayment  42 , a covering or tileable membrane such as chlorinated polyethylene (CPE) for example, and is tiled (as at  43 ). 
     Drain plate  10  is oriented preferably between joists  45 ,  46  as in  FIG. 2  and is supported by cross-blocking  48  between joists  45 ,  46 . 
     A rigid structural underlayment  50 , such as the product disclosed in U.S. Pat. No. 7,735,279, incorporated herein by reference, extends from engagement on flange surface  17  of plate  10  over to the top edge of joist  47 , for example, where underlayment  50  abuts subfloor  41 . Underlayment  50  also extends around plate  10  preferably on all sides, resting on surrounding flanges or ledge surfaces  17  of plate  10  ( FIG. 4 ). 
     A mortar bed  52  slopes from a level of the upper surface of tile underlayment  42  downwardly to the inner edge  15  of plate  10 , thus providing a desirable drain slope. Edge  15  may act as a screed pivot during installation. 
     The tileable membrane ( FIG. 2 ) is preferably continued over mortar bed  52  to the area proximate aperture  16  in plate  10 . 
     Drain fixture  25  is extended through aperture  16  in plate  10  to an appropriate drain/waste connection as illustrated in  FIG. 2 . 
     It will be appreciated that underlayment  50  is preferably a structural underlayment which is further described for other applications at the website www.tileyourdeck.com, incorporated herein by reference as well as in U.S. Pat. No. 7,735,279. 
     Consistent with these disclosures, underlayment  50  is a composite construction provided with a series of parallel, dove-tail shaped stiffening ribs  60  (see  FIGS. 8 and 9 ), upstanding from a flat undersurface as shown. 
     More particularly, the interface between the underlayment  50  on flange surface  17  of plate  10 , is illustrated in  FIG. 8  with only a portion of underlayment  50  being shown. Underlayment  50  includes a flat undersurface with a plurality of parallel upstanding stiffening ridges  60  extending upwardly ( FIG. 9 ). A mortar fill  61  ( FIG. 8 ) is provided between these ridges  60 , making for a very stiff, rigid underlayment with a mechanical bond to mortar bed  52 . Tileable membrane  63  preferably defined as sheet or liquid is disposed on mortar bed  52  and a thin-set adhesive  64  is disposed thereon to secure tile  43  thereto. Only portions of these elements are illustrated in  FIG. 8  for clarity. 
     Underlayment  50 , mortar bed  52 , membrane  63  and tile are oriented around and over plate  10  to complete shower floor  30  ( FIG. 2 ). 
     It will be appreciated that, as illustrated in  FIG. 2 , there are no lips, curbs, sills or other breaks or obstructions between adjacent floors  30  and  40 , so access therebetween by wheeled assistance devices is not impeded. At the same time, joists  45 ,  46  under floor  30  are not modified, notched or otherwise designed, placed or oriented any differently than other regular floor joists  47 ; the shower floor is well-supported and lighter than the prior floor ( FIG. 1 ) and the shower floor is watertight and may be tiled while providing adequate drain slope.
A shower pan provides a shower floor adjoining a surrounding bathroom floor with no raised lip, curb or other obstruction between the two. This allows easy wheeled access for the disabled and comprises a drain plate in combination with an underlayment, which provide a gradual slope from a surrounding floor to a drain and supported on unmodified joists with upper surfaces in the same plane as surrounding bathroom floor joists.