You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION  
       [0001]    The present invention relates generally to building structure and in particular, to a structural insulating panel and flat roof structure employing the same. 
       BACKGROUND  
       [0002]    Historically, flat or horizontal roofs on commercial and residential buildings have been common in warmer, drier climates where water accumulation as a result of precipitation is not a problem. More recently, flat roofs have become popular in cooler, wetter climates. Unlike sloped roofs, flat roofs have ineffective drainage characteristics making them prone to leakage problems. In wetter climates, to deal with this drainage issue, complex water proofing is typically required in flat roofs. In commercial buildings, drains are sometimes provided in the flat roofs to collect rainwater and melting snow and direct the water off of the roofs. 
         [0003]    For example, U.S. Pat. No. 5,144,782 to Paquette et al. discloses a draining system for water which may collect between the upper and lower membranes of a flat insulated roof. Insulating panels located between the upper and lower membranes are provided at both their upper and lower faces with a network of intersecting grooves. The networks of grooves communicate with each other through passages made through the insulating panels or constituted at the insulating panel joints. The grooves and passages provide drainage channels for any water that has seeped under the upper membrane as a result of perforations in the upper membrane. A lower drain is sealed to and opens above the lower membrane to drain water collected by the drainage channels. Drainage of the water helps to prevent deterioration of the insulating panels and water accumulation which may provoke overload problems. 
         [0004]    Although such drainage structures are effective in removing water from flat roofs, they add significant complexity to the building structures and hence, increase costs making them unsuitable in many environments. As will be appreciated, alternative techniques to improve drainage in flat roofs are desired. 
         [0005]    It is therefore an object of the present invention at least to provide a novel structural insulating panel and roof structure employing the same. 
       SUMMARY  
       [0006]    Accordingly, in one aspect there is provided a structural insulating panel for use in a flat roof structure comprising upper and lower structural layers and an intermediate layer between said upper and lower structural layers, the intermediate layer being shaped such that said upper structural layer is sloped relative to a horizontal plane when said structural insulating panel is installed in a flat roof structure. 
         [0007]    In one embodiment, the intermediate layer is shaped such that the upper structural layer is sloped in multiple dimensions relative to the horizontal plane. The upper structural layer may slope generally linearly downwardly in generally orthogonal directions or may curve downwardly in different directions. In another embodiment, the intermediate layer is shaped such that the upper structural layer slopes generally linearly downwardly in a single direction. 
         [0008]    In one form, the intermediate layer is sandwiched directly between the upper and lower structural layers. The thicknesses of the upper and lower structural layers are selected to give the structural insulating panel a desired fire rating. Each of the upper and lower structural layers may have a thickness in the range from about ⅛″ to about 1⅛″. The intermediate layer may have a minimum thickness of about 1″ and a maximum thickness of about 16″. 
         [0009]    According to another aspect there is provided a flat roof structure comprising a plurality of abutting structural insulating panels, each structural insulating panel spanning at least a pair of adjacent rafters of the flat roof structure and defining an upper decking surface on which roofing is applied, the structural insulating panels being configured such that the upper decking surface is non-horizontal thereby to promote drainage. 
         [0010]    The structural insulating panels in one form are arranged at least one of end-to-end and side-to-side with adjacent structural panels carrying mating formations. Sealant seals seams between the adjacent structural insulating panels. 
         [0011]    According to yet another aspect there is provided a structural insulating panel comprising an intermediate layer sandwiched between and adhered to first and second structural layers, the intermediate layer varying in thickness such that the first and second structural layers are non-parallel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    Embodiments will now be described more fully with reference to the accompanying drawings in which: 
           [0013]      FIG. 1  is a top plan view of a flat roof structure employing structural insulating panels; 
           [0014]      FIG. 2  is a side elevational view of the roof structure of  FIG. 1 ; 
           [0015]      FIG. 3  is an enlarged portion of  FIG. 2 ; 
           [0016]      FIG. 4  is a perspective view of a structural insulating panel forming part of the flat roof structures of  FIG. 1 ; 
           [0017]      FIG. 5  is a cross-sectional view of  FIG. 4  taken along line  5 - 5 ; 
           [0018]      FIG. 6  is a cross-sectional view of  FIG. 4  taken along line  6 - 6 ; 
           [0019]      FIG. 7  is a top plan view of an alternative structural insulating panel for use in a flat roof structure; 
           [0020]      FIG. 8  is a cross-sectional view of  FIG. 7  taken along line  8 - 8 ; 
           [0021]      FIG. 9  is a cross-sectional view of  FIG. 7  taken along line  9 - 9 ; 
           [0022]      FIG. 10  is a top plan view of yet another structural insulating panel for use in a flat roof structure; 
           [0023]      FIG. 11  is a cross-sectional view of  FIG. 10  taken along line  11 - 11 ; 
           [0024]      FIG. 12  is a cross-sectional view of  FIG. 10  taken along line  12 - 12 ; 
           [0025]      FIG. 13  is an enlarged side elevational view of a portion of adjacent structural insulating panels showing an alternative joint; and 
           [0026]      FIG. 14  is an enlarged side elevational view of a portion of adjacent structural insulating panels showing yet another joint. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0027]    Turning now to  FIGS. 1 to 3 , a flat roof structure is shown and is generally identified by reference numeral  30 . The flat roof structure  30  comprises a plurality of abutting structural insulating panels  32  arranged in an array. In this embodiment, the array comprises six (6) rows and three (3) columns of panels  32 . Those of skill in the art will appreciate that the 6×3 array of panels  32  is shown for illustrative purposes only. The dimensions of the panel array can vary significantly depending on the overall size of the flat roof structure  30  and the dimensions of the individual panels  32  in the array. The longitudinal dimension of each panel  32  is selected so that each structural insulating panel  32  spans at least one pair of adjacent rafters  34 . Typically, each structural insulating panel  32  will have a lengthwise dimension in the range of from about eight (8) feet to about twenty (20) feet and a widthwise dimension equal to about four (4) feet. Suitable fasteners (not shown) such as screws or nails are used to secure the structural insulating panels  32  to the rafters  34 . 
         [0028]    The upper surfaces  36  of the structural insulating panels  32  define the decking  38  of the flat roof structure  30  on which roofing (not shown) is applied. The structural insulating panels  32  are configured so that the decking  38  is pitched in multiple dimensions thereby to promote drainage towards the outer peripheral edges of the flat roof structure  30 . The pitch in each dimension is typically selected so that it does not exceed 1/12″. In the embodiment of  FIG. 1 , the structural insulating panels  32  in column C 1 , rows R 1  to R 3  and in column C 3 , rows R 1  to R 3  are configured so that the flat roof structure  30  slopes linearly downwardly to the right as indicated by arrows  40  and slopes linearly downwardly from its central longitudinal axis  42  towards its peripheral side edge  44  as indicated by arrows  46 . The structural insulating panels  32  in column C 1 , rows R 4  to R 6  and in column C 3 , rows R 4  to R 6  are configured so that the flat roof structure  30  slopes linearly downwardly to the right as indicated by arrows  40  and slopes linearly downwardly from its longitudinal axis  42  towards its peripheral side edge  48  as indicated by arrows  50 . The structural insulating panels  32  in column C 2 , rows R 1  to R 3  are configured so that the flat roof structure  30  slopes linearly downwardly to the left as indicated by arrow  52  and slopes linearly downwardly from its longitudinal axis  42  towards its peripheral side edge  44  as indicated by arrow  46 . The structural insulating panels  32  in column C 2 , rows R 4  to R 6  are configured so that the flat roof structure  30  slopes linearly downwardly to the left as indicated by arrow  52  and slopes linearly downwardly from its longitudinal axis  42  towards its peripheral side edge  48  as indicated by arrow  50 . 
         [0029]    Turning now to  FIGS. 4 to 6 , one of structural insulating panels  32  is better illustrated. As can be seen, structural insulating panel  32  comprises an intermediate layer  60  sandwiched between and bonded to upper and lower structural layers  62  and  64  respectively by suitable adhesive. In this embodiment, the intermediate layer  60  is formed of expanded polystyrene (EPS) foam and comprises a core  70  typically having a thickness in the range of from about 1″ to about 16″, a top skin  72  on the core  70  having a thickness of about 7/16″ and a bottom skin  74  on the core  70  having a thickness of about ⅝″. The upper and lower structural layers  62  and  64  are formed of a suitable structural material such as for example plywood and have a thickness generally in the range of from about ⅛″ to about 1⅛″. The thicknesses of upper and lower structural layers  62  and  64  are selected to give the flat roof structure  30  its desired fire rating. 
         [0030]    The core  70  varies in thickness to give the structural insulating panel  32  its desired pitch. As a result, the upper structural layer  62  which overlies the top skin  72  of the intermediate layer  60  conforms to the orientation of the intermediate layer and thus, provides the sloped upper decking surface onto which the roofing is applied. One side edge of the lower structural layer  64  has a groove  80  formed therein and the opposite side edge of the lower structural layer  64  has a tongue  82  formed thereon. The groove  80  is shaped to receive a tongue formed on an adjacent structural insulating panel  32  and the tongue  82  is shaped to be inserted into the groove formed in another adjacent structural insulating panel  32 . 
         [0031]    Looking back to  FIG. 3 , one of the seams  90  between two adjacent structural insulating panels  32  is shown. As can be seen, the tongue  82  on the lower structural layer  64  of one structural insulating panel is received in the groove  80  formed in the lower structural layer  64  of the other structural insulating panel. Adhesive caulking  92  is applied to the tongue  82  and/or groove  80  prior to insertion of the tongue into the groove to secure the lower structural layers of the adjacent structural insulating panels  32  together. A sealant  94  such as for example, a foam seal or sill seal gasket, is used to fill any gaps between the intermediate layers  60  and upper structural layers  62  of the adjacent structural insulating panels at the seam  90 . 
         [0032]    In the above embodiment, the structural insulating panels  32  of the flat roof structure  30  are configured so that the flat roof structure  30  slopes linearly downward in two different directions. Those of skill in the art will appreciate however, that other structural insulating panel configurations can be used in flat roof structures  30  to promote drainage. For example, turning now to  FIGS. 7 to 9 , another embodiment of a structural insulating panel for use in a flat roof structure is shown and is generally identified by reference numeral  132 . Similar to the structural insulating panel  32 , structural insulating panel  132  also comprises an intermediate EPS layer  160  sandwiched between upper and lower structural layers  162  and  164  respectively. In this embodiment, rather than sloping linearly downwardly in two different directions, the core  170  of the intermediate layer  160  has a parabolic shape and thus, curves downwardly from its center in all directions towards the edges of the intermediate layer. 
         [0033]      FIGS. 10 to 12  show yet another embodiment of a structural insulating panel  232  for use in a flat roof structure. Similar to the structural insulating panels  32  and  132 , structural insulating panel  232  comprises an intermediate EPS layer  260  sandwiched between upper and lower structural layers  262  and  264  respectively. In this embodiment, the core  270  of the intermediate layer  260  slopes linearly downwardly in only one direction. 
         [0034]    Although the embodiments described and shown above show adjacent structural insulating panels  32  as comprising mating formations in the form of tongues and grooves, those of skill in the art will appreciate that alternative joints between adjacent structural insulating panels can be used. For example,  FIG. 13  shows adjacent structural insulating panels  32  interconnected via an overlap joint and  FIG. 14  shows adjacent structural insulting panels interconnected via a butt spline joint. 
         [0035]    Although dimensions for the structural insulating panels and components therefor, are provided above, those of skill in the art will appreciate that the dimensional information is exemplary. Depending on the environment in which the structural insulating panels are being deployed, the overall dimensions of the structural insulating panels and the dimensions of the panel components may vary from those discussed above. 
         [0036]    In the embodiments described above, the upper and lower structural layers  62  and  64  are described as being formed of plywood. Those of skill in the art will appreciate that the upper and lower structural layers may be formed of other suitable structural material such as for example OSB, metal sheet, fire resistant board etc. Also, the intermediate layer  60  need not be formed of EPS. Other foam material such as for example urethane foam, polyurethane foam, isocyanurate foam etc. or other suitable non-foam material such as for example honeycomb board may be used. 
         [0037]    While particular examples of structural insulating panels that provide pitched upper decking surfaces are described and illustrated above, those of skill in the art will appreciate that the structural insulating panels may take on other orientations to promote drainage. Of course, if desired the structural insulating panels can be used on wall structures for structural and/or decorative purposes. 
         [0038]    Although embodiments have been described above with reference to the drawings, those of skill in the art will appreciate that variations and modifications may be made without departing from the spirit and scope thereof as defined by the appended claims.

Summary:
A structural insulating panel for use in a flat roof structure comprises upper and lower structural layers and an intermediate layer between the upper and lower structural layers. The intermediate layer is shaped such that the upper structural layer is sloped relative to a generally horizontal plane when the structural insulating panel is installed in a flat roof structure.