Patent Publication Number: US-8117789-B2

Title: Door and window sill pan flashing with drain

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 10/730,414, filed Dec. 8, 2003, now abandoned which is related to and claims priority from U.S. Provisional patent application No. 60/497,078 filed Aug. 22, 2003, and U.S. Provisional patent application No. 60/507,915 filed Oct. 1, 2003. 
    
    
     FIELD OF INVENTION 
     This invention relates to a sill pan flashing for a rough opening of a door or window, where the sill pan flashing drains accumulated moisture from the entire rough opening. 
     BACKGROUND 
     In this specification and claims, the term “sill” refers to the horizontal bottom part of a window or door as defined by ASTM E 2112-07 Standard Practice for Installation of Exterior Windows, Doors, and Skylights, section 3.2.121. 
     In this specification and claims, the term “pan flashing” or “sill pan flashing” refers to “a type of flashing used at the base of rough opening to divert incidental water to the exterior or to the exterior surface of concealed WRB (weather-resistive barrier),” as defined by ASTM E 2112-07 section 3.2.91. As further described in Note 3 to ASTM E 2112-07:
         “sill pan flashing have upturned legs at the interior edge and ends of the rough opening to from a three-sided pan. They are intended to collect and drain water toward the exterior including water that may enter through the window unit (for example, between the jambs and sill) or around the window (between the rough opening and the fenestration). The pan flashing [or sill pan flashing] must be integrated with other flashings and the window assembly to capture water that may otherwise penetrate to the sill framing and allow it to freely drain to the exterior. The window, flashings, and pan are to be sealed in a manner that reliably inhibits air and moisture flow to the interior.”       

     A “sill pan flashing” is different structurally and functionally from a “sill”. The sill is a structural part of a window or door assembly that connects bottom of the frame (jamb) members and does not extend to the full width of a rough opening, and does not collect or drain the water that enters around the door or window unit (between the jamb and the rough opening). A sill is not integrated with the Water Resistive Barrier (WRB). 
       FIG. 24  is a front perspective view provided in ASTM E 2112-07 as an illustration of the sill pan flashing. 
     It is desirable to provide a relatively low cost sill pan flashing for the entire rough opening to be installed underneath window and door sills for directional drainage of water and moisture which can be used for construction in all price ranges of housing, and for any door or window width. In one embodiment of the current invention, a base unit is provided which can be manufactured by extrusion and either cut to a desired length to fit the door or window width opening, or used with other similar elements and connectors to establish a desired final length. End pieces and optional center joining elements are provided for field assembly. 
     The prior art includes U.S. Pat. No. 5,921,038 to Burroughs which describes a window sill pan with an inclined plate and ribs perpendicular to the front edge. The patent includes a front cover, but does not disclose end members. 
     U.S. Pat. No. 6,385,925 B1 to Wark teaches an inclined plate with ribs perpendicular to the front edge. The Wark patent does not include a cover, but does have end members. Wark also describes the possible use of other window support means such as truncated cones. Wark describes the supports as being on the apparently solid inclined base. 
     It is desirable to provide a sill pan flashing that can be used for doors or windows of any length. It is desirable to provide an economical sill pan flashing that can be used in most construction. One way to provide a relatively low cost device is to extrude the base. It is desirable in such applications to provide window or door supports which can be extruded in relatively long lengths suitable to be cut in the field in order to accommodate different size windows and doors. It is desirable to extrude a unit which includes door or window supports in order to avoid attaching separate support elements to a base unit. 
     It is desirable to manufacture window and door sill pan flashing elements in an efficient and economical extrusion process, to supply the elements in relatively long lengths, and to cut the elements to a desired length at a construction site. This manufacturing and installation method may provide sill pan flashing units that are more readily available to builders and which are more economical that purchasing prefabricated sizes from a supplier who is required to stock a large number of possible widths. This manufacturing and installation method eliminates the need for special ordering of sill pan flashings for different field dimensions. 
     Also, if an injection molding tool were required for each size, then relatively high volumes of each size would be required to pay for the tool. It is difficult to order and store many different sizes of sill pan flashing for the variety of window and door dimensions which are used in construction. By designing the sill pan flashing for manufacture by extrusion, a single extrusion tool and a single injection molding tool for end pieces can provide sill pan flashing of a variety of lengths. In some embodiments, sections of base may be connected to establish a desired length. In other embodiments, the base may be cut to a desired length. 
     SUMMARY 
     The current invention is for a window sill pan flashing or door sill pan flashing. In some embodiments of the current invention, the device can be made in a low cost manufacturing operation by extrusion. In one embodiment, SureSill™ is made by combining extrusion and injection molding processes. The sill pan flashing typically includes an inclined base, window or door supports which can be extruded as part of the base unit, and corner elements which can be snapped or otherwise attached to the base. 
     In some embodiments, the base may be solid. In other embodiments, the base may be hollow with window or door supports extending vertically through the base. In the case of fiberglass construction, the base may include a slanted upper face, but no lower face. 
     In one embodiment, the sill pan flashing has offsets provided in both a rear sill pan wall and in a front flange. These offsets create a flow path for water to drain from the rough opening. 
     In one embodiment, the sill pan flashing includes corner side flanges that are preferably provided without openings, and the sill pan flashing is secured in a window or door opening by stapling across a corner of the side flange, by bending a nail over the flange, or by nailing through the flange. 
     In some embodiments, the window support means is provided in a horizontal orientation so that the base can be extruded. In other embodiments, the base may be fabricated from fiberglass, metal, or molded plastic, and may not have a horizontal orientation. 
     In other metal or plastic embodiments, the sill pan flashing is provided as a center piece that can be cut to a desired length, and as end elements that can be snapped or glued to the center piece. 
     In one embodiment, an extruded base unit is cut to a desired length, and an installation tolerance is provided in corner units which slide onto the base unit. 
     In another embodiment, a base unit is provided in two or more sections which slidably overlap in a manner that compensates for rough framing tolerances, so that the sill pan flashing can be adjusted to cover the entire rough opening width. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and advantages of the present invention are set forth below and further made clear by reference to the drawings, wherein: 
         FIG. 1  is a top view of an embodiment of the invention 
         FIG. 2  is a side cross section view of the embodiment of  FIG. 1 . 
         FIG. 3  is a front view of the embodiment of  FIG. 1 . 
         FIG. 4  is an exploded view of an embodiment with a base element and corner elements. 
         FIG. 5  is an enlarged detail perspective view of the right end element of the embodiment of  FIG. 4 . 
         FIG. 6  is a metal embodiment of the invention with a lateral additional central ridge. 
         FIG. 7A  is a top view of a fiberglass embodiment of the invention. 
         FIG. 7B  is a cross section view of the fiberglass embodiment of  FIG. 7A . 
         FIG. 7C  is a front view of a fiberglass embodiment of  FIG. 7A . 
         FIG. 8  is an exploded view of an alternate embodiment with a base element and end elements. 
         FIG. 9  is an enlarged detail view of a right end element for the embodiment of  FIG. 8 . 
         FIG. 10  is a perspective view of a lock in channel base plate for the embodiment of  FIG. 8 . 
         FIG. 11  is a cross sectional view of the base element for the embodiment of  FIG. 8 . 
         FIG. 12A  is a perspective view of a fiberglass sill pan flashing embodiment. 
         FIG. 12B  is a perspective view of a fiberglass sill pan flashing embodiment. 
         FIG. 13A  is a top perspective view of an extruded sill pan flashing section. 
         FIG. 13B  is a perspective view of the extruded sill pan flashing section of  FIG. 13A  with material removed in order to create a drain path. 
         FIG. 14A  is a top perspective views of another embodiment of an extruded sill pan flashing section. 
         FIG. 14B  is a top perspective view of the extruded sill pan flashing section of  FIG. 14A  with a drain slot. 
         FIG. 15A  is an exploded top perspective view of a sill pan flashing base and corner units. 
         FIG. 15B  is a top perspective view of the assembled base and corner units of the sill pan flashing of the embodiment of  FIG. 15A . 
         FIG. 15C  is a top perspective view of an alternate embodiment of a right end element. 
         FIG. 16  is a detailed cross section view of the base of the embodiment of  FIG. 15A . 
         FIG. 17A  is a front perspective view of the right corner unit of the embodiment of  FIG. 15A . 
         FIG. 17B  is a rear perspective view of the right corner unit of the embodiment of  FIG. 15A . 
         FIG. 17C  is a bottom perspective view of the right corner unit of the embodiment of  FIG. 15A . 
         FIG. 18A  is a top perspective view of an assembled two-part sliding joint sill pan flashing. 
         FIG. 18B  is an exploded top perspective view of the two-part sliding joint sill pan flashing of  FIG. 18A . 
         FIG. 18C  is a bottom perspective view of the two-part sliding joint sill pan flashing of  FIG. 18A . 
         FIG. 18D  is a top perspective view of the second section of the two-part sliding joint sill pan flashing of  FIG. 18A   
         FIG. 18E  is a bottom perspective view of the second section of the two-part sliding joint sill pan flashing of  FIG. 18A   
         FIG. 18F  is a top perspective view of the first section of the two-part sliding joint sill pan flashing of  FIG. 18A   
         FIG. 18G  is a bottom perspective view of the first section of the two-part sliding joint sill pan flashing of  FIG. 18A   
         FIG. 19A  is a top perspective view of an assembled two-part sliding joint sill pan flashing where the sections have been cut to a desired length. 
         FIG. 19B  is an exploded top perspective view of the two-part sliding joint sill pan flashing of  FIG. 19A . 
         FIG. 19C  is a bottom perspective view of the two-part sliding joint sill pan flashing of  FIG. 19A . 
         FIG. 20A  is a top perspective view of an assembled two-part sliding joint sill pan flashing with a cap section. 
         FIG. 20B  is an exploded top perspective view of the two-part sliding joint sill pan flashing of  FIG. 20A   
         FIG. 20C  is a bottom perspective view of the two-part sliding joint sill pan flashing of  FIG. 20A   
         FIG. 21A  is a top perspective view of an assembled two-part sliding joint sill pan flashing with a middle extension. 
         FIG. 21B  is an exploded top perspective view of the sill pan flashing of  FIG. 21A . 
         FIG. 21C  is a bottom perspective view of the sill pan flashing of  FIG. 21A . 
         FIG. 22A  is a top perspective view of an alternate embodiment of the sill pan flashing. 
         FIG. 22B  is a bottom perspective view of the sill pan flashing of  FIG. 22A . 
         FIG. 23A  is a top perspective view of an assembled adjustable sill pan flashing. 
         FIG. 23B  is an exploded top perspective view of the sill pan flashing of  FIG. 23A . 
         FIG. 23C  is a bottom perspective view of the sill pan flashing of  FIG. 23A . 
         FIG. 23D  is a top perspective view of a left corner element for the sill pan flashing of  FIG. 23A . 
         FIG. 23E  is a bottom perspective view of the left corner element of  FIG. 23D . 
         FIG. 23F  is a top perspective view of a right corner element for the sill pan flashing of  FIG. 23A . 
         FIG. 23G  is a bottom perspective view of the right corner element of  FIG. 23F . 
         FIG. 23H  is a top perspective view of a bottom element for the sill pan flashing of  FIG. 23A . 
         FIG. 23I  is a bottom perspective view of the bottom element of  FIG. 23H . 
         FIG. 23J  is a bottom perspective view of a cap element for the sill pan flashing of  FIG. 23A . 
         FIG. 23K  is a bottom perspective view of the cap element of  FIG. 23J . 
         FIG. 24  is a prior art perspective view of a sill pan flashing as illustrated in ASTM E 2112-07. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT 
     Plastic Sill Pan Flashing with Extruded Base Cut to Desired Length 
     Referring now to  FIG. 1 , which is a top view of a single sill pan flashing, the sill pan flashing includes a base  30  with a downwardly sloping top surface. The sill pan flashing has a front support ridge  31  and a rear support ridge  32  for supporting a window or door. The window or door typically includes a horizontal sill which is supported by the sill pan flashing of the current invention. In this embodiment, the sill pan flashing includes an extruded middle piece  16 , or lock-in channel plate, and end pieces  15 , or, lock-in corners, which may be molded or provided by other manufacturing processes. Pieces are typically joined with cement such as PVC glue or with a snap together feature. 
     Referring now to  FIG. 2  which is a side view of the sill pan flashing embodiment of  FIG. 1 , the base  30  has a slope from the rear portion of the sill pan flashing to the front portion The front support ridge  31  is solid through the base so that it rests on the bottom and the rear support ridge  32  is also solid, thereby transmitting the weight of the window or door to the support area for the sill. Wall thickness for the walls can be approximately ⅛ of an inch thick. In one embodiment the front support pedestal has a width of approximately ¾ of an inch, and the rear support pedestal has a width of approximately 1 inch. 
     As shown in the  FIGS. 1 and 2 , this embodiment includes a rear wall  25  and a downward extending lip  23 . The rear wall may include offsets (not shown) to provide a drain path between the rear wall and the window or door. The downward extending lip  23  may include an offset to provide a drain path between the sill pan flashing and the siding or other materials installed around the window or door. These offsets create a drain path for moisture which might become present in the rough opening. 
     In this embodiment the front ridge may further include a gap  34  between the support ridge and the sides and may further include a drain channel  33  to permit the drainage of moisture. The corner pieces include a side upward lip  24  and a downward lip  23 . 
     Referring now to  FIG. 3  which is a front view of the embodiment of  FIG. 1 , the front support ridge  31  includes gaps  33  and  34  for drainage. 
       FIG. 4  is an exploded view of an embodiment with a base element and end elements. In this case the extruded middle piece  16  includes a first channel  44  and a second channel  45 . The right corner element  15 A includes a first tab  46  which fits into the first channel  44 , and a second tab  47  which fits into the second channel  45 . The left corner element  15 B also includes a first tab  46  which fits into the first channel  44 , and a second tab  47  which fits into the second channel  45 . The tabs and channels create an interlocking between the middle piece and the corner elements. 
       FIG. 5  is an enlarged detail view of the right end element  15 A of the embodiment of  FIG. 4 . In this embodiment, the corner element includes a first tab  46  or alignment extension which may be inserted into the first channel  44  in the base portion; a second tab or alignment extension  47  may be inserted into the second channel  45  in the base portion; and an overlapping lip  42 . 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Method of Manufacturing Extruded Base 
     It is desirable to provide a relatively low cost product which can be used for construction in all price ranges of housing. In one embodiment of the current invention, a base unit is provided which can be manufactured by extrusion to a common long length, such as 16 feet, and cut to a desired length. 
     In this embodiment the base has longitudinal features, such as illustrated in  FIGS. 1 and 2 , that can be extruded. For instance, the cross section of the base is consistent throughout the length so that the rear support is the same height throughout the length of the base, and the front support is the same height throughout the length of the base. 
     A drill or cut operation may be included to provide one or more drain slots in the support member front support so that water may drain from the sill pan flashing. 
     End segments which are molded or otherwise produced may be attached to a desired length of base in order to provide a completed sill pan flashing unit. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Metal Sill Pan Flashing 
     A metal sill pan flashing or a plastic sill pan flashing may be manufactured by extrusion as described above. 
     Referring now to  FIG. 6 , which is another metal embodiment of the invention, the sill pan flashing may include a center support ridge  39  which includes drain-hole areas. In this example the sill pan flashing is fabricated from a metal such as stainless steel. Other metals such as copper, lead, or aluminum may also be used. 
     The metal sill pan flashing may also be produced by welding or otherwise securing the metal members. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Sill Pan Flashing with Extruded Base Sections Joined by Connectors to Form a Desired Length 
     In this embodiment the middle base may be constructed from two or more relatively short pieces which are joined by connector segments on one or both ends to achieve a desired length. In one connector embodiment, each end of the connector includes tabs such as  46  and  47  shown in  FIGS. 4 and 5 . These tabs fit into channels  44  and  45  on the base unit segments. The sill pan flashing also comprises end pieces which may be snapped onto or glued to the ends of the base unit. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Fiberglass 
     In this embodiment, the door or window is supported by a rear support element and a front support element of a fiberglass sill pan flashing. 
       FIG. 7A  is a top view of a fiberglass sill pan flashing which includes a rear support  32  and a front support  51  which tapers in plan toward drainage openings  52 . This taper directs water to the drainage openings. The drainage openings such as gaps, holes, or slots are typically provided at the ends of the front support, and may also be provided at one or more locations along the length of the support. Alternatively, weep holes may be provided in the front support. The weep holes may be formed as part of a molding operation in fiberglass or as a post extrusion process step for metal or plastic sill pan flashing. 
       FIG. 7B  is a cross section view of the fiberglass sill pan flashing of  FIG. 7A , and  FIG. 7C  is a front view of the sill pan flashing. The rear wall may include a lip  53 , The front edge of the rear support  32  may be tapered for ease of manufacture. In this embodiment, the sill pan flashing includes a sloping drain surface  54 . In this example, the fiberglass base does not have a solid surface on the bottom, and the front and rear support ridges extend to the bottom of the sill pan flashing, and no additional supports are required for the sloping drain surface  54 . If the sloping drain surface were load-bearing, then additional supports may be provided. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Alternate Fiberglass Sill Pan Flashing 
       FIGS. 12A and 12B  are front perspective views of an alternate fiberglass sill pan flashing. In this embodiment, the window or door is supported by a rear support  32  and a front support  31 . In this embodiment, the front support is not tapered as in the previous example. Drain slots  33  and  34  are provided in the front support in order to remove water from the sill pan flashing. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Extruded Base with Alternate Interlocking End Pieces 
       FIG. 8  is an exploded view of an alternate embodiment with a base element  16  and corner end elements  15 A and  15 B. In this embodiment, the end pieces are designed to fit over cut down portions to the front support  31  and rear support  32  and rear wall  25  so that the front and rear supports are essentially constant height across the assembled sill pan flashing. In this embodiment, the base element  16  is typically produced by extrusion, and right and left end pieces  15 A and  15 B are typically molded, such as by injection molding. 
     Referring now to  FIG. 9  which is an enlarged detail view of a right end element  15 A for the embodiment of  FIG. 8 , the end element includes a an overlapping lip  35  which fits over a portion of the right end of the base. The overlapping lip includes a rear portion which fits over a portion of the rear wall of the right end of the base, a rear support portion which fits over a portion of the rear support of the right end of the base, a middle portion which fits over a portion of the right end of the base between the rear support and the front support, a front support portion which fits over a portion of the front support of the right end of the base, and a front lip portion which fits over a portion of the front lip of the right end of the base. Preferably, the overlapping lip overlaps the right end of the base in a manner that keeps the rear support and the front support substantially level across the sill pan flashing. This end piece, also described as a lock-in corner, is preferably molded such as by injection molding, or vacuum forming. 
     Referring now to  FIG. 10  which is a perspective view of a lock-in channel base plate  16  for the embodiment of  FIG. 8 , the right end of the base plate or lock in channel plate is preferably provided with incisions  61  on the front support plate  31 , on the rear ridge  32 , and on the rear upward lip  25 . In one embodiment, these incisions are prepared after cutting a standard length of extruded sill pan flashing base, such as a  16  foot length, to a desired length. The incisions remove a portion of the right end of the front support plate  31 , the rear ridge  32 , and the rear upward lip  25  as shown in  FIG. 10 . This removal may be accomplished by cutting a plastic or metal piece to the desired depth with a hacksaw or other cutting tool. In some cases, the cut material may be removed by a chisel. In other cases a special cutting tool may be provided. 
     Referring now to  FIG. 11  which is a cross sectional view of the base element for the embodiment of  FIG. 8 , the base plate includes a keyed channel  50  for receiving a keyed profile  36  from the corner element. In some embodiments, the rear upward lip  25  may be extended downward or back and downward, to provide a surface that can be nailed or screwed into the window or door framing elements. The base preferably includes a plurality of channels that can be used to accept an excess of a sealant or adhesive that may be used to set the window or door sill. Although it is desirable to provide a level window or door opening, in practice it is often difficult to achieve a level framing. In such cases, the sill pan flashing may be set on an adhesive, such as PL 400 or PL Premium, by Osi Sealants, Inc.; or on a sealant such as NP1 by Sonneborn, by Chemrex. 
     In one embodiment, a window may be set into the sill pan flashing and attached to the front ridge, by an adhesive. Drainage holes or slots in the front ridge are open, or will open, to direct the moisture to the outside. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Extruded Plastic Base with UV Resistance 
     In this embodiment, the base is extruded from a plastic such as PVC, polyvinyl chloride. The plastic includes ultraviolet light (UV) inhibitors that prevent the UV light from breaking down the plastic. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Extrusion and Cutting Process 
     It is desirable to develop an extrusion process for plastic or metal sill pan flashings. In some embodiments, door or window supports may be provided in a lateral orientation to permit the supports to be extruded. In an alternate embodiment, the base unit may be extruded as a solid piece and then post-processed with a cutting operation to remove material. 
     For example, the base plate can be extruded with no slope on the top surface  60  as illustrated in  FIG. 13A , so that the top surface is parallel with the bottom surface. After extrusion, the base plate can be inserted in a tool, such as punch press, saw, or combination, or device to make incisions in the top surface. In one embodiment, incisions  62 , as shown in  FIG. 13B , have a downward slope towards the front of the sill pan flashing, and may be perpendicular to the sill pan flashing or at an angle with respect to the sill pan flashing. For example, incisions can be 3″ wide, and ½″ apart. Incisions create drainage channels, and spaces between incisions create offsets to permit a drain path. Offsets typically have a coplanar surface and are used as support for installation of windows and doors. 
     In another post-extrusion processing example, an extrusion creates the middle piece or lock-in channel plate  16  as described in embodiments above. The top surface of the sill pan flashing  30  is sloped toward the front of the sill pan flashing. The extruded section has a front support ridge  31  and a rear support ridge  32  which are typically coplanar. One or more intermediate ridges may be provided between the front ad rear support ridge. After extrusion, this middle section  16  can be inserted in a tool, such as punch press or saw, or other device that makes cuts in the front and intermediate ridges in order for water to drain downwardly and outwardly through the ridges. The bottom of the incisions  63  as shown in  FIG. 14B  would have coplanar surface with the sloping top surface  30  of the lock-in channel plate. For example, incisions can be ½″ wide, 12″ apart. This embodiment shows example with perpendicular incisions on the front ridge, and other incision orientations are possible. In another embodiment, the auxiliary ridges may drain to the ends of the ridge, without additional drain slots in the middle of the ridges. This embodiment shows example with perpendicular incisions on the front ridge, and other incision orientations are possible. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Extruded Base with Alternate Interlocking End Pieces 
       FIG. 15A  is an exploded top perspective view of a base  300  which may be extruded and corner units  400  and  450  which are typically molded. The base includes a rear wall  310 , a rear support  320 , a base top surface  331  which may be sloped, a front support  330  with drain gaps  340 , and a front face  350 . In this embodiment, the drain gaps are preferably provided on 6″ centers.  FIG. 15B  is a top perspective view of the assembled base  300  and corner units  400  and  450  of  FIG. 15A .  FIG. 15C  is a top perspective view of an alternate embodiment of a right end element  450  which includes a nail slot  451  in the side flange  452 . In this embodiment, the nail slot has a height of about 0.13 inches. 
       FIG. 16  is a detailed cross section view of the base  300  of  FIG. 15A . In this example, the front support  330  overlaps the front face  350 , and includes an inset rear face  332 . The rear support  320  includes recesses  322 ,  323 , and  324  for engaging tabs from a corner element. In one example, the base has a depth of about 4.688″, a front support width of about 0.722″, a rear support width of about 0.989″, and rear wall and front face thicknesses of about 0.94″. In this embodiment the base top surface has a slope of about 1.7 degrees. 
       FIGS. 17A and 17B  are front and rear perspective views of a right corner unit  400  which includes a front face  440  and a side face  442 . In this example, the corner unit has several overlap features to snap or press fit with a base unit so that the sill pan flashing can be assembled without glue or adhesive if desired. An overlap tab  410  is provided with a width selected to form a press fit between the front edge of the rear support  320  and the inset rear face  332  of the front support  330 . In this example, the tab has a convex front face  411  to fit with the inset rear face  332  of the front support. The width of tab  410  is preferably slightly tapered on the end so that the fit becomes tighter as the corner is inserted on the base  300 . This tab has a top surface  412  that aligns with the top surfaces of the rear and front supports. In this example, the corner unit also includes a rear wall  430  and a lip  432  which overlap the base rear wall  310 , and a front inset portion  436  which overlaps the front face  350  and front end of the front support  330 . 
       FIG. 17C  is a bottom perspective view of the right corner unit  400  which shows rear tabs  422 ,  423 , and  424  which mate in the base section recesses  322 ,  323 , and  324  respectively. These tabs are also preferably slightly tapered on the ends. 
     In this example, the left corner unit  450  is symmetrical to the right corner unit and includes similar tabs and overlap features. 
     This embodiment permits a sill pan flashing base section to be cut to a desired length in the field for fitting a particular opening. The corner piece elements are then installed on the base section, and the assembled sill pan flashing is placed on the bottom of the rough opening, so that the assembled sill pan flashing provides directional drainage for the entire rough opening. The window or door is then installed on top of the sill pan flashing and inside the rough opening. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Adjustable Sliding Joint 
     In this embodiment, the sill pan flashing comprises a first section which includes a first corner and a portion of the base, and a second section which includes a second corner and a portion of the base. These sections are designed to slide together without adhesive in a manner that provides for a framing tolerance of several inches. For wider openings a third center section is provided. 
     Each portion of base includes a lower part offset from an upper part. In one section, the upper part extends past the lower part, and in the other section the lower part extends past the upper part. These extensions provide an installation tolerance. For instance, a typical 3′ door requires a framed rough opening of 36½″ to 39″. It is desirable to provide a sill pan flashing which will fit into the opening and cover the entire rough opening width regardless of the actual dimension of the rough framing. 
       FIG. 18A  is a top perspective view of an assembled two-part sliding joint sill pan flashing having a first section  100  which overlaps a portion of a second section  200 . In this example, the first section  100  includes a rear wall  110 , a rear support  120 , a sloped base top surface  130 , a front support  140  with drain gaps  142 , and a front face  150 . The first section also includes dams  170 ,  171 , and  172 . The second section  200  includes a rear wall  210 , a rear support  220 , a front face  250 , and an end dam  270 . In this example, the first section includes a right corner, and the second section includes a left corner. The second section end dam  270  is snapped or glued between the rear support and the front support of the second section so that it retains accumulated water over the sloped base top surface  230  and directs that water to drain forward rather than toward the first section  100 . 
       FIG. 18B  is an exploded top perspective view of the two-part sliding joint sill pan flashing of  FIG. 18A . In this embodiment, the second section  200  includes an end portion with ribs  260  which support the overlapping end of the first section. The support ridges  260  preferably have a downward slope toward the front of the sill pan flashing. The support ridges  260  define base drain channels  262  for draining any moisture toward the front of the sill pan flashing. The base channels  262  are preferably also sloped toward the front of the sill pan flashing. The front end of the support ridges  260  overlap the front face  250  so that there is a drainage area provided between the front faces of the top part an bottom part. The end portion also includes channels  264  and  265  for aligning with ribs  164  and  165  of the first section as shown in  FIG. 18C  which is a bottom perspective view of the assembled sill pan flashing. The ribbed end portion of the second section extends 3″ beyond the end dam  270 . 
       FIG. 18D  is a top perspective view of the second section  200  showing details of the end dam  270 , the ribs  260 , drain channels  262 , and alignment channels  264  and  265 . 
       FIG. 18E  is a bottom perspective view of the second section  200  showing a flat bottom surface  270 . 
       FIG. 18F  is a top perspective view of the first section  100  showing details of dams  170 ,  171 , and  172  which are preferably molded with the section. 
       FIG. 18G  is a bottom perspective view of the first section  100  showing details of aligning ribs  164  and  165 . 
       FIG. 19A  is a top perspective view of an assembled two-part sliding joint sill pan flashing where the sections  100  and  200  have been cut to a desired length. 
       FIG. 19B  is an exploded top perspective view of the two-part sliding joint sill pan flashing of  FIG. 19A  which shows the first section  100  cut at a point past the dam  171  and the dam  170  (not shown). In this example, the end portion of the second section  200  has also been shortened. The shortened first section and the shortened second section are assembled as shown  FIG. 19C  which is a bottom perspective view of the assembled sill pan flashing. In some cases it may not be necessary to cut either side, because the sliding joint feature will accommodate a range of lengths. In other cases, it is only necessary to cut one of the sections in order to create a sill pan flashing with the desired length. 
     In this example, the top part extends 5″ beyond the top part. A typical minimum overlap between the first section and the second section is about 1½″, so that the working range of this embodiment has a range of about 6½″ in width. This working range may be utilized by increasing the overlap of the sections. 
     The top surfaces  130  and  230  of the first section and the second section may be continuously sloping. In other embodiments, the profile of the top surfaces of the sill pan flashing may be flat in the rear and front and sloping in the middle. This variable profile may enhance the interlocking between the top part and the bottom part. 
     The top part and bottom part sections are typically fabricated separately, and the first section is inserted over the second section. The assembly may be glued in the factory, but is designed to be snapped together without adhesive in the field. 
     This embodiment may be fabricated from a plastic such as PVC or a metal such as aluminum. Parts can be made by injection molding, or blow-molding plastic/PVC, or aluminum casting, or with other materials and manufacturing methods. 
     This embodiment provides sliding joints to accommodate variations within a range of window or door size, and in rough opening size without cutting the sill pan flashing. Alternately, the sill pan flashing can be shortened in the field by cutting a portion from the mating end of each section. 
     Referring now to  FIGS. 20A and 20B  which are top perspective assembled and exploded views of a sill pan flashing, an optional cap section  280  may be installed over the exposed rib extensions of the second section. 
     In this embodiment, sill pan flashing may include one or more additional middle sections such as shown in  FIGS. 21A-21C . In this embodiment, each middle extension  180  has a first end, like the end of the first section, that slides over a ribbed extension; and a second end, like the end of the second section, which is a ribbed extension. Thus the sliding joints in the middle section are like the sliding joint of the two-section embodiment. The sections are preferably joined by overlapping the ends without adhesive. 
     In this embodiment, the adjustable sill pan flashing provides a drainable, sloped sill pan flashing for windows and doors, with a recessed slope for easy drainage and a horizontal mounting surface for windows and doors. The sliding joint design concept has a first one-piece left corner section, and a second one-piece right corner section. The first and second pieces partially slide into each other to provide an adjustable length sill pan flashing. Additional middle extensions may be inserted to allow the sill pan flashing to accommodate larger rough openings. The sliding joint design can accommodate a range of dimensions in window/door size, and in rough opening size, without cutting the pan. A further range of rough openings and standard sizes for windows and doors can be accommodated by cutting the portion of the sliding joint in the field. The sill pan flashing can be assembled quickly without glue joints or adhesives, so that the installation can be performed regardless of temperature, under any weather conditions. The parts can be made out of injection molding, or blow-molding plastic/PVC, or aluminum casting, or other materials and manufacturing methods. The preferred minimum overlap is 1.5″. In this embodiment, a portion of the second section is designed to slide underneath a portion of the first section, and has a recessed slope with perpendicular ribs, to channel any water that may accumulate in the joint, or on the lower section, to the exterior of the wall cavity. There are built-in dams on the upper surfaces of all sections to prevent water from upper surfaces from spilling to a lower portion. The upper portion of all sections has a recessed slope and longitudinal ridges for installation of windows and doors, with cuts in the front ridge for drainage. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Slidable Corner Elements 
       FIGS. 23A-B  are top perspective view of another embodiment of a slidably adjustable sill pan flashing base. In this embodiment, a left corner element  630  and a right corner element  635  fit adjustably over a base element  600 . A cap element  640  may be inserted over the exposed base unit between the corner elements.  FIG. 23C  is a bottom perspective view of the assembled pan. 
       FIGS. 23D-E  are top and perspective views of a left corner element for the sill pan flashing of  FIG. 23A . The corner element includes front and rear supports and a dam element as discussed in embodiments above. The corner element includes ribs  633  and  634  for aligning with corresponding channels in the base unit. 
       FIGS. 23F-G  are top and perspective views of a right corner element for the sill pan flashing of  FIG. 23A . The corner element includes front and rear supports and a dam element as discussed in embodiments above. The corner element includes ribs  633  and  634  for aligning with corresponding channels in the base unit. 
       FIGS. 23H-I  are top and perspective views of a base unit for the sill pan flashing of  FIG. 23A . The base unit includes a plurality of support ridges  610 . The support ridges define base drain channels  620  which are preferably sloped toward the front of the base unit in order to draining any moisture toward the front of the sill pan flashing. The recessed surface between the support ridges may slope towards the front. In some embodiments, the support ridges may also slope to the front of the sill pan flashing. The base unit also includes channels  631  and  632  for aligning with ribs  633  and  634  of the corner sections  630  and  635 . 
     In one embodiment, the base element is cut to a desired rough opening width after allowing for the corner sections. The base can be cut to rough opening size or slightly less. 
     In one embodiment, corner sections fit on top of the base unit, and no adjustment in the length of the base unit is needed due to corners. Corners should overlap the base sufficiently for the weight of windows and doors to be transferred to the structure. This assembly is easily accommodates thermal expansion or contraction of windows and doors and the wall structure, due to sliding joint design. The corner sections are then assembled on the base unit, and may be adjusted by sliding the corner sections along the ends of the base unit. The corners are preferably placed on ends of the base unit with the slide-in joint and without glue. 
       FIGS. 23J-K  are top and perspective views of a cap element  640  for the sill pan flashing of  FIG. 23A . The corner element includes front and rear supports and dam elements as discussed in embodiments above. The cap element may be cut to length to fit between the corner pieces. The cap element may include ribs  633  and  634  to snap into the channels  631  and  632  of the base unit. In some embodiments, there may be more than one base section and more then one top plate assembling the unit. For example, base section and top plate could be manufactured in 38″ lengths, and then either cut to smaller size to fit the opening or multiple pieces used for wider openings. The top plate should generally be the length of the base plate minus two corners that are installed on the base plate. 
     DETAILED DESCRIPTION OF EMBODIMENT 
     Plastic Sill Pan Flashing with Rear and Front Drainage Channels 
       FIG. 22A  which is a top perspective view of an alternate embodiment of the invention. In this embodiment, the sill pan flashing has a base  500  which may have a downwardly sloping top surface or a relatively flat top surface. In the case of a relatively flat top surface, a portion of the moisture that collects on the base is dissipated by evaporation. In this embodiment, the sill pan flashing has a plurality of ridge supports  510  that may be provided with a regular or an irregular spacing. Irregular spacing of the ridge supports permits more supports to be placed closer to the ends of the sill pan flashing in areas that typically bear more of a door or window load than the central portions. 
     The sill pan flashing includes a rear wall  520  which preferably includes offsets  522 . These offsets provide rear drainage channels  524  which permit moisture to drain from the rear of the window or door through the rear drainage channels into base drainage channels  514  formed between the support ridges  510 . The sill pan flashing includes a front plate  530  which extends downward from the front edge of the base. The front plate preferably includes offsets  532 , which provide front drainage channels  534  for the base drainage channels  514 . The combination of the rear drainage channels, the base drainage channels, and the front drainage channels provides a continuous drain path for moisture which may accumulate on the sill pan flashing. 
     Each end of the sill pan flashing base  500  includes a side plate  550  which may include offsets  552  (not shown) to provide side drainage channels  554  (not shown) to the base. The offsets may be angled in order to provide bracing to a molded corner section. The end pieces preferably include a front plate  505  which extends above and below the base. The sill pan flashing is typically secured to the framing by staples across the corners of the front plate  505 , or by bending a nail over the front plate  505 . 
       FIG. 22B  which is a bottom perspective view of an alternate embodiment of the invention illustrates a flat base  560  for the sill pan flashing.