Abstract:
The present invention is a modular roof covering made up of a plurality of interlocking modular trays having moisture or water absorbing component or medium in the tray to absorb moisture and allow it to evaporate or otherwise dissipate over time. The trays interlock with each other and are held down by weights or other ballast to secure the trays to the roof without having to create a physical connection between the trays and the roof structure. The modular roof covering can be made up of different types of tray assemblies, where some have vegetation growing in the tray, others have merely water absorption and dissipation capability, while others have photovoltaic cells for the collection and use of solar energy. The present invention provides a light weight, low cost roof covering system for extending the life of current roof structures, and to restore and protect the environment, moderate and aid in controlling building temperature, manage stormwater runoff and collect and utilize solar energy.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of roof coverings, in particular a modular roof covering system which extends longevity of traditional roofing membranes, restores and protects the environment, moderates and helps control building temperature, manages stormwater runoff and collects and utilizes solar energy. 
     To maintain a comfortable interior space at a low cost, many advances have been made in roofing and insulation technology. Most developments have been made in the materials which are placed in the attic space such as slurried or rolled insulation. There has been relatively little development in materials applied to the exterior surfaces of roofs. As costs for energy and concerns over the environment increase, there is an increasing demand for low cost, energy efficient methods to reduce the amount of energy needed to maintain a comfortable living and work space, particularly in existing buildings where the costs of most modem solutions can be prohibitive. 
     To address these concerns, additional roofing coverage has been placed over the standard or existing roofing materials for added thermal insulation. One example of additional roofing coverage is vegetation. A covering of vegetation on a roof structure provides a layer of insulation that helps keep the building interior cool in the summer and warm in the winter. Most modem turf covering methods or systems use a layer of soil and a complex system of multi-layered materials to protect the underlying structure from damage. This type of construction is expensive, can add a significant amount of weight to the roof, and may require significant modification to the roof or physical attachment to the roof structure. Because of the high costs and undesirable weight additions of most current systems, many existing buildings cannot utilize these systems. 
     SUMMARY OF THE INVENTION 
     The present invention provides a light weight and low cost alternative for roof coverings to extend longevity of traditional roofing membranes, restore and protect the environment, moderate and help control building temperature, manage stormwater runoff and collect and utilize solar energy. 
     The present invention uses a series of modular interlocking trays or containers which hold several functional layers, which vary from embodiment to embodiment depending on the design requirement for the particular application. The trays are interlocked with each other, or otherwise connected to each other to cover a large area on a roof or other surface. Additionally, the trays are ballasted or weighted down without being physically connected to the roof surface on which they are positioned. 
     In the first embodiment, the top layer in the modular trays is a layer which consists of vegetation, such as grass or sedum species, which is selected to accommodate the climate in which the system is used and address any aesthetic intentions or requirements. Under the top layer is a lightweight soil matrix layer to support the plant growth, by providing support for the roots. Below the soil matrix layer is a filter layer to prevent erosion of the soil matrix layer and to remove particulate and other matter from the water runoff, and a water-capture area (in the tray) to mitigate storm water runoff. 
     The trays are ballasted or weighted down by any commonly known or used method, but preferably by paving stones which are laid in spaces created by the interconnection of the trays. In addition to providing ballast, the paving stones also provide a means to move about the roof without stepping into or otherwise disturbing the vegetation growing in the trays. Optionally, in this embodiment, an irrigation or sprinkler system can be installed to provide water irrigation for the vegetation or additional cooling for the building. This is particularly applicable to hotter and dryer climates. In this embodiment the modules may be pre-assembled, requiring only installation of the modules on the roof or other surface, or the vegetation may be added after the modules are placed in position through the use of seeds, cuttings, or root formed plugs. 
     In the second embodiment, there is also a series of functional layers. In this embodiment, the top layer consists of a permeable membrane rather than vegetaion that allows water to flow through. Below the top membrane is a reservoir designed to capture, hold and slowly release precipitation and moisture through evaporation and/or drainage (when the membrane becomes saturated). In an alternative embodiment, the reservoir contains an absorbent or super absorbent polymer (“SAP”) to further increase the water absorption and/or reduce runoff. Below the reservoir layer is a roof drainage layer, that holds the layers positioned above it above the roofing membrane. The roof drainage layer allows excess precipitation to flow off of the roof, without compromising the integrity of the modules or the layers positioned therein. It is noted that although this embodiment includes the interlocking modular trays previously discussed, the functional layers may be enclosed in moisture absorbent bags which are secured together, without the use of the trays. A sprinkler system may be installed to provide moisture to the functional layers of this system depending on the climate and system requirements. Further, any suitable ballast or weighting system can be used to provide support and security for this embodiment. 
     The third embodiment of the present invention uses modular trays to support a top layer consisting of a housing or structure holding an array of (or single) photovoltaic cells or panels and drainage holes. The housing allows the cells or array to pivot and/or rotate thereby tracking the sun for optimum performance of the cells or array. Below the array or cell housing is a reservoir designed to capture, hold and slowly release moisture or precipitation through drainage and/or evaporation. This reservoir function is similar to, and can be, the same structure and method described above in the second embodiment. 
     Because the underlying modules or trays for each of the above embodiments can be the same, a roofing system can be installed which utilizes a combination of any of the above embodiments. The present invention is not limited to the use of a single embodiment in any one roofing system. 
     The present invention provides a low-cost, low-weight system for moderating building temperature and increasing the useful life of roof coverings and structure while at the same time reducing energy use and environmental impact. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages, nature and various additional features of the invention appear more fully upon consideration of the illustrative embodiments of the invention which are set forth in the drawings, in which: 
     FIG. 1 is a diagrammatical representation of a modular tray according to the present invention which can be used with any of the embodiments of the present invention; 
     FIG. 2 is a diagrammatical representation of a cross-section of a modular tray according to the first embodiment of the present invention; 
     FIG. 3 is a diagrammatical representation of the cross-section of a preferred modular tray configuration according to the first embodiment of the present invention; 
     FIG. 4 is a diagrammatical representation of a modular tray according to the first embodiment of the present invention; 
     FIG. 5 is a diagrammatical representation of a preferred sprinkler head and system used with the present invention; 
     FIG. 6 is a diagrammatical representation of modular trays according to the first embodiment of the present invention shown secured to each other and placed on a roof structure; 
     FIG. 7 is a diagrammatical representation of an alternative method of securing the modular trays of the present invention to each other; 
     FIG. 8 is a diagrammatical representation of the preferred embodiment of the modular tray according to the first embodiment of the present invention shown installed on a roof structure; 
     FIG. 9 is a diagrammatical representation of a second embodiment of the present invention shown secured on a roof structure; 
     FIG. 10 is a diagrammatical representation of a cross-section of the modular tray according to the second embodiment of the present invention; 
     FIG. 11 is a diagrammatical representation of a modular tray according to the third embodiment of the present invention shown secured to other trays and placed on a roof structure; and 
     FIG. 12 is a diagrammatical representation of the roof of a building having a plurality of trays of the present invention, where a representation of each of the embodiments is shown in position on the roof structure. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is now explained in further detail with reference to the accompanying drawings, which do not limit the scope of the invention in any way. 
     Turning now to FIG. 1, this Figure shows a typical modular tray  10  that can be used with any of the various embodiments of the present invention. The tray  10  can be made from any known commonly available material, limited only by manufacturing limitations and cost restraints, and can be made in any practical size or shape as design parameters permit. In a preferred embodiment, the trays  10  are shaped to allow ballast or weights  23  placed in cavities formed between the assembled trays as shown in FIG.  1 . Such a shape allows easy installation of ballast to aid in keeping the trays  10  secure to a roof under adverse conditions. Although the tray  10  shown in FIG. 1 is an eight-sided rectangle with beveled corners to create the space for the ballast weight, the present invention is not limited to this shape configuration. For example, the trays  10  can be configured in a rectangular shape having mid-span indentations in each of the sidewalls in which the ballast is placed upon installation. 
     Materials that can be used for the modular trays include any polymer or plastic type material or any metal material including aluminum. In the preferred embodiment the material used is aluminum (for example 3003 H14 aluminum) as it is relatively strong, light and easy to manufacture. Because of its relative strength, the thickness of a metal tray can be thinner than other materials. The tray  10  can be manufactured by any known method, and the method of manufacture is generally selected for the material used. For example, if a plastic is used then injection molding may be used, while if the tray is made from a metal then stamping may be the most appropriate manufacturing technique. 
     A preferred embodiment of a polymer material is a co-polymer which contains approximately a 50% polypropylene and 50% polyethylene mix. The wall thickness of a polymer tray is generally thicker than that of an aluminum tray. 
     As shown in FIG. 1, the tray module  10  has a series of troughs  11  and ridges  12  to provide structural stability and precipitation or water storage capability, surrounded by walls  13 . Water is stored in the troughs  11  to allow slow evaporation over time, instead of allowing the water to runoff immediately after it passes through the layers (discussed below). The walls  13  have a height determined by the design for the particular application and vary depending on the specific application. Further, in a preferred embodiment the walls  13  of the tray  10  are substantially perpendicular to the surface of the roof when the trays are installed in the roof system. This is not necessary, and the angle at which the walls  13  project from the tray  10  can be optimized for each particular application of the present invention. Additionally, in a preferred embodiment, the ridges  12  may have slight depressions  18  with holes  14  to allow excess water to drain out of the tray  10 , when the tray  10  becomes full. These holes prevent the trays  10  from becoming over-filled with precipitation, thus regulating the weight on the roof and preventing saturation damage to the various layers or structure placed on the trays  10 . The drain holes  14  may alternatively be located within the troughs  11 , and be placed some distance from the bottom of the troughs. The placement of the drain holes  14  are determined by the design of the roof system and weight limitations of the roof structure. The higher the holes within the tray  10 , the greater total weight that the roof is required to hold. 
     Further, in an alternate embodiment of the present invention, at least some of the trays  10  installed on a roof have sprinkler line attachments or connections  15  which allow plumbing for a sprinkler system secured to the trays  10  to prevent unnecessary damage to the sprinkler system. Although in FIG. 1 the tray  10  is shown with these connections  15  on the outside perimeter of the tray  10 , these connections  15  can also be made at the bottom of the tray  10 , to allow the plumbing network for the sprinkler system placed under the trays, instead of between them. This allows the trays placed closer together to optimize roof space. When this configuration is used, the trays  10  access slots  35 , as shown in FIG. 6, to allow the sprinkler network placed under the trays  10 . The use of the sprinkler connections  15  is not necessary, but is preferred when a sprinkler system is used as exhibited in FIGS. 1-4. However, the preferred irrigation method for the present invention is that shown in FIG.  5 . 
     Finally, the tray  10  has protrusions  16 ,  17  for mechanically connecting the tray  10  to another adjacent tray (not shown). The mechanical connection between trays can be made by any known or commonly used method such as by the interlocking the trays or any known mechanical fastening method (i.e. screws, bolts, rivets, adhesive, chemical bonding, spot welding, etc.), or a combination of any of these. The present invention does not limit, in any way, the method by which trays  10  are secured to each other. In FIG. 1, a keystone interlock  16  and connection flange  17  are shown as a method to attach trays to each other. FIGS. 6 and 7 show alternative methods of securing the trays  10  to each other. FIG. 6 shows the trays  10  secured to each other with a separate bracket  21 , which is essentially U-shaped (although the shape may vary depending on the design of the tray  10 ) and secures the walls  13  of two adjacent trays to each other, while also providing a barrier to substantially prevent moisture or precipitation from flowing between adjacent trays  10 . FIG. 7 shows yet another alternative for securing the trays  10  to each other, through the use of braces  20  which cross an open area  22  formed between adjacent trays  10 , where the braces  20  secure the trays  10  to each other and provide a platform for a ballast weight  23  to aid in keeping the trays  10  secured to the roof structure. If either brackets  21  or braces  20  are used to secure trays  10  to each other, additional fastening can be provided for additional joint security. This can be accomplished by any mechanical fastening method, such as the use of screws, bolts, rivets, adhesive, chemical bonding, spot welding, etc. 
     FIG. 2 shows a cross-section of a tray  10  according to the first embodiment of the present invention. As shown, the tray  10  can have interlocking ridges  24  around its perimeter which allow the tray  10  to interlock with any adjacent tray  10 . This method of locking the trays  10  may be used to secure adjacent trays to each other. Additional mechanical fasteners could be used in this embodiment if desired. In this Figure, the bottoms of the troughs  11  make contact with the roof structure  9 , and although this is preferred it is not necessary as the troughs  11  can be raised off of the roof structure  9 . FIG. 3 depicts a preferred cross-section of the tray  10  of the present invention. As shown, the tray  10  is manufactured relatively simply, thus keeping cost and materials to minimum, particularly if the tray  10  is made from a stamped metal, where the creation of the ridges  24  is difficult. With this configuration the trays  10  are secured to each other by any known or commonly used mechanical means, such as rivets, screws, bolts, bonding, adhesive, etc. 
     FIGS. 2 and 3 also depict the layers of the first embodiment. The top layer  25  is the layer which retains the vegetation  28  used in the first embodiment. The vegetation  28  used is selected based on the climate of the region in which the system is installed, and any required or desired aesthetic conditions. It is desirable that the species of vegetation used be native to the region of the installation and have a high tolerance to drought conditions and sustained sunlight exposure. Alternatively, a sedum type species can be used, which has a high drought and sunlight tolerance. 
     The top layer  25  sits on a growing medium layer  26  which includes a substantially uniform and consistent mixture of a combination of four main components, aggregate, sand, peat and compost, and a fifth sub-component of SAP (super absorbent polymer). A suitable SAP typically comprises about 95% to about 98% crossed linked polyacrylamide copolymer and about 2% to about 5% moisture, and is commercially available from companies such as Aquatrols, 5 North Oinley, Cherryhill, N.J. 08003, and Hydrosource, Castle International Resources, 2370 West Highway 89A #11-300, Sedona, Ariz. 86339-5344. It is noted that the SAP component is not essential, but adds additional absorption capability, and is preferably used in the present invention. Although the exact mixture and composition of this layer  26  varies depending on many conditions, such as the vegetation used, the climate and weather conditions, the density of the growing medium in this layer  26  in the preferred embodiment is approximately 78 lbs./cubic foot. Further, the depth of this layer  26  also varies depending on the various application and design criteria, but is preferably about 2″ thick. The growing medium layer  26  is the layer in which the majority of water absorption occurs. The combination of the capillary action in the aggregate used in this layer, along with absorption in the compost and the super absorbent polymer (if used) provides the layer&#39;s absorbence. 
     In a preferred embodiment, the aggregate used in the growing medium layer  26  is a lightweight aggregate consisting of expanded slate or any other lightweight aggregate products such as Permatil®, available from Carolina Stalite Company, P.O. Box 1037, Salisbury, N.C. 28145-1037. An additional example is Minergy LWA®, available from Minergy LWA, 231 W. Michigan St., Milwaukee, Wis. 53205. A preferred composition of the growing medium layer  26  in this embodiment is described below: 
     Aggregate 
     ASTM C29 Dry Weight Loose - 48-55 lbs./ft 3   
     ASTM C127 Specific Gravity - 1.45-1.60, SSD 
     ASTM C330: ASTM Gradation as follows: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Sieve Size 
                 % Passing 
               
               
                   
                   
               
             
             
               
                   
                 ½ inch 
                 100 
               
               
                   
                 ⅜ inch 
                 80-100 
               
               
                   
                  #4 
                 5-40 
               
               
                   
                  #8 
                 0-20 
               
               
                   
                 #16 
                 0-10 
               
               
                   
                   
               
             
          
         
       
     
     Aggregate is approximately 60% by volume of the total growing medium. 
     Sand 
     USGA coarse sand consisting of the following grain size distribution (ASTM C136-95A): 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Sieve Size 
                 % Passing 
               
               
                   
                   
               
             
             
               
                   
                 ⅜ inch 
                 100 
               
               
                   
                  #4 
                  95-100 
               
               
                   
                  #8 
                 85-97 
               
               
                   
                  #16 
                 60-80 
               
               
                   
                  #30 
                 10-20 
               
               
                   
                  #50 
                  5-15 
               
               
                   
                 #100 
                 0-5 
               
               
                   
                   
               
             
          
         
       
     
     Sand is approximately 25% by volume of the total growing medium. 
     Peat 
     Partial Decay and carbonized vegetation consisting mostly of mosses, having a pH between 3.5 and 7.0. 
     Peat is approximately 10% by volume of the total growing medium. 
     Compost 
     Compost consists of about 66% of organic yard waste, such as composted leaves, and about 34% of aged poultry litter. 
     Compost has the following approximate upper limits: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Magnesium (Mg) 
                 70 
                 PPM 
               
               
                   
                 Iron (Fe) 
                 3.8 
                 PPM 
               
               
                   
                 Manganese (Mn) 
                 1.0 
                 PPM 
               
               
                   
                 Copper (Cn) 
                 0.10 
                 PPM 
               
               
                   
                 Zinc (Zn) 
                 0.15 
                 PPM 
               
               
                   
                 Soluble salts 
                 5.50 
                 mmho/cm 
               
               
                   
                   
               
             
          
         
       
     
     pH falls between 6.0 and 7.0. 
     Compost is approximately 4-5% by volume of the total growing medium. 
     Super Absorbent Polymer (SAP) 
     SAP is used to supplement the moisture retention of the growing medium for applications in periodically dry or arid climates. 
     SAP is applied to the growing medium in granular or powdered form. 
     SAP need not be more than approximately 1% by volume of the growing medium. 
     Although the composition above is a preferred growing medium for layer  26 , the present invention is not limited to this composition and any known combination of the above materials, and/or their equivalents, can be used. The SAP in the preferred embodiment is capable of absorbing a weight of water or moisture at least 15 times its own weight (although this absorbence not required). This absorption ratio is preferred in the present invention. 
     As shown in FIG. 2, below the growing matrix layer  26  is a filter layer  27  to prevent the erosion of the growing matrix  26  and to remove particulate from the water runoff to prevent the particulate from blocking the drain holes  14  or otherwise compromising the integrity of the trays  10 . In preferred embodiment, filtering of water is performed by a woven polymer geo-textile. The geo-textile can be connected to the tray  10  by any known or commonly used method. In the preferred embodiments, if the tray is made from aluminum the geo-textile can be connected to the tray  10  with pop-rivets (or any similar method) around the perimeter. If the tray  10  is made from plastic or an injection molded polymer, the geo-textile can be connected to the tray  10  with heat stakes, such that the filter fabric is placed over polymer stakes secured to the tray along the perimeter. The heat stakes (not shown) are molded into the tray  10  and the stakes pretrude through the geo-textile to hold it in place. Heat is then used to melt the polymer of the heat stakes to the geo-textile. It is preferred that the stake melting process be accomplished by a sonic welding process, but any commonly known or used method of attaching the geo-textile to the tray  10  can be. The geo-textile used is preferably composed of high-tenacity mono and multifilament polypropylene yarns, which are woven into a stable network in which the yarns retain their relative position. An example of a yarn used in a preferred embodiment of the present invention is Mirafi FW500®, available from TC Mirafi, 365 South Holland Drive, Pendergrass, Ga. 30567. It is also preferred that the yarn material be inert to biological degradation and resistant to environmental chemicals, such as alkalis and acids. The preferred material has a thickness of approximately 24 mils, with a tensile strength of about 2100 to 2400 lbs./ft, and a puncture strength of at least about 135 lbs. The permeability rate, in the preferred embodiment, is at most about 0.027 cm/sec, with a flow rate of at most about 35 gal/min/ft 2 . 
     FIG. 5 shows a preferred configuration of the sprinkler system in which a sprinkler head  30   a  is positioned in the open area  22  between trays  10 . Although this sprinkler system is depicted in FIG. 5 in combination with the first embodiment of the present invention, it may be used with any of the embodiments disclosed herein. 
     FIG. 4 shows a single tray  10 , with vegetation  28  growing, according to the first embodiment of the present invention, with optional sprinkler heads  30  and an alternative sprinkler system plumbing  31 . The use of a sprinkler system  30 ,  31  depends on the climate and desired performance of the roof covering system. The sprinkler system can be used both to provide additional cooling for the roof of the building and to support the vegetation  28  growth in arid and hot climates. Any standard or commonly known sprinkler or irrigation system can be used in the present invention. 
     In FIGS. 6 and 8, the installation of the present invention according to the first embodiment is shown. The installation consists of a plurality of individual trays  10  connected to each other by any of the previously discussed methods, although the use of the channel  21  is shown. A plurality of paving stones  23  and  23   a  are used as ballast to ensure the structural integrity of the system under adverse weather conditions. The ballast used can be any structure which provides sufficient weight to keep the installed system on the roof surface. In a preferred embodiment, the ballast material supports the weight of a person walking on the ballast without damage, for example, monolithic concrete. This prevents unnecessary damage to the tray modules  10 , and the tray contents. It is preferred that the ballast or paving stones be shaped to fit the openings  22  created by the trays  10  when the trays are assembled on the roof, and that the ballast fill substantially all of the space within the open area  22 . 
     Also shown in FIG. 6 is a tray protector  37  which is made of extruded aluminum which engages with the tray wall, and is locked into place by any type of common mechanical connection. The tray protector  37  is optional and provides added protection of the tray edges  13  from damage and fire. Further, FIG. 6 shows a perimeter flashing  32  that may be used on the outside perimeter of the tray installation area, to protect the tray area perimeter from damage and fire. The flashing  32  can be fastened to the tray  10  by any commonly used or known mechanical attachments and can be made as part of the tray  10  during manufacture. In the preferred embodiment, perimeter drainage  33  is provided in the trays  10  to allow water draining from the trays  10  to flow freely under the trays  10 . 
     Additionally, the trays  10  are shown with an access slot  35  and tray alignment tab  36  which are also preferred. The access slot  35  allows installation of the sprinkler system, if used, and the tab  36  allows for the easy alignment of trays  10  during installation, while also providing added structural integrity to the tray array under adverse conditions. Finally, as shown in FIG. 6, ballast or paving stones  23  and  23   a  may be supported by a ballast shelf  34  which extends from the trays  10 . In a preferred embodiment the shelves  34  are integral with the tray  10 . Alternatively, separately formed shelves can be attached to the trays  10 . 
     In a preferred embodiment, the ballast or paving stones  23 ,  23   a  are suspended some distance above the roof. This allows the maximum weight of the ballast applied to the trays to maximize the efficiency of the ballast. 
     FIG. 8 depicts trays  10  made in accordance with the preferred embodiment of the present invention shown cross-section in FIG.  3 . 
     In FIGS. 9 and 10 a second embodiment of the present invention is shown, in which vegetation is not used, but instead an absorbent bag  40  is employed, which is made to fit inside the tray  10 . The bag  40  is made up a series of layers to absorb water and retard runoff. The top layer  44  is made of any known water-permeable material which allows water to pass through to the layers beneath. In a preferred embodiment, the top layer is made of a material which also protects the contents of the bag  40  from UV radiation. Under the water permeable layer  44  is a water absorption layer  45  which captures, stores and slowly releases water, moisture and precipitation through either drainage or evaporation. This layer may also include an SAP to further increase the water absorption of this layer. The water absorption layer  45  can be made of any known material which has the above characteristics (including, for example, newspaper, cardboard, cellulose or carpet). The material does not degrade significantly over time, to ensure maximum performance of the system. In a preferred embodiment, this layer  45  is also protected from UV radiation to extend the operational life of this layer. The thickness and other dimensions of this layer are easily selected for a desired application. In a preferred embodiment, the dry thickness of this layer is about ½ inch in thickness, and its saturated thickness is about 2 inches. A thicker and larger layer retains more water thus increasing weight loads. Below the water absorption layer  45  is a filter layer  46  similar in construction to the filter layer in the first embodiment of the present invention, which can also have a non-woven geo-textile layer  47 . Layer  47  functions as a drainage layer for the water absorption layer  45 , and for water that drains from the roof in overflow conditions or from areas that are not covered by the modular system. A suitable material for the bag  40  is commercially available from National Sorbents, Inc., 10139 Commerce Park Drive, Cincinnati, Ohio 45246. 
     This layer  47  allows water to flow underneath the modular system, when it is installed on a roof. In a preferred embodiment, the non-woven structure of this layer  47  has a high compression strength (up to 20,000 psi). An example of the material that can be used is Miradrain G100W®, available from TC Mirafi, 365 South Holland Drive, Pendergrass, Ga. 30567. This product has a three-dimensional, non-woven matrix that is adhered to a filter fabric, similar to Mirafi FW500® or Mirafi 140NC®. Other similar materials can be used. For example, a nylon non-woven geo-textile, such as Mirafi Enkamat 7018®, 7020®, or 7920® can be used and adhered to a layer of Mirafi FW500® to form layer  47 . 
     Although the bag  40  of this embodiment can be manufactured in a number of commonly known ways, preferably the bag  40  is constructed as a sewn bag, where all of the layers are sewn together, and the sides of the bag are the same material as the top of the bag. In a preferred embodiment, reservoirs  43  are formed in the top surface of the bag  40  which capture water and hold it while it is slowly absorbed into the water absorption layer  45 . The exact configuration, number and depth of the reservoirs vary with the design of the bag  40  and the system. 
     The bag  40  may also include connection flaps  42 , sewn or made integrally with the bag  40 , which allow bags  40  connected to each other by bag connector  41 . This connection provides added system integrity over the use of the tray connectors  21  alone. It is also possible to use mechanical fasteners such as screws, bolts, rivets, adhesive, chemical bonding, spot welding, etc. in addition to the bag connector  41 , to increase joint integrity. Bag  40  can also be used in another embodiment of the present invention in which a plurality of the sewn bags  40  are secured to each other and placed on the roof structure, without trays  10 . The flaps  42  then allow the bags  40  adequately secured to each other. In the embodiment, the bottom layer of the bags is a filter layer designed to permit water which is not absorbed to flow freely off the roof surface. 
     The sprinkler system previously described may be used to optimize the performance of the roof system when using the bags  40 . Additionally, the paving stones  23 ,  23   a  previously described can be used as ballast to secure the bag system on the roof. 
     The third embodiment of the present invention is shown in FIG.  11 . In this embodiment, the top layer consists of a formed housing  50  formed to hold photovoltaic cells  51  and drainage holes  53 , which allow water to pass through the housing  50  into layers underneath the housing  50 . This embodiment also uses the standard modular tray  10 , thus allowing the components present in the trays varied while using the same trays. The housing  50  is made of a material which provides adequate protection from the elements for the cells  51 , but is also substantially transparent to allow sunlight to pass through to allow optimum performance of the cells  51 . Preferably injected molded clear plastic is used for the housing. Because some plastics and polymers have relatively poor longevity when exposed to UV radiation for extended periods of time, in a preferred embodiment the housing  50  is made from glass, or a similar material, or stamped aluminum with glass windows. Further, in a preferred embodiment, the housing  50  has a mechanism allowing the housing to pivot and rotate to allow the photovoltaic cells  51  to track the sun. The cells  51  used can be any known or commercially available cells and are suitably chosen to meet system requirements. The cells are electrically connected to each other through a standard connection  52 . In a preferred embodiment the trays  10  have access holes allowing electrical connections  52  without interfering with a sprinkler system or the ballast weights  23 ,  23   a.    
     Although the shape and design of the housing  50  vary with the particular design of the system and cells used, in a preferred embodiment, the housing  50  has at least two major faces, and each face is inclined at an angle to the floor of the tray  10 . The housing  50  also has at least one drainage channel adjacent to at least one of the inclined faces so that precipitation and water coming from the face(s) can flow into the channel. Preferably the channel is formed integrally in the housing. The drainage channel has at least one drainage hole to allow water in the channel to flow into the reservoir  54  below the housing  50 . 
     Below the housing  50  is a reservoir  54 , which captures and slowly releases water and precipitation via drainage and/or evaporation, either through drain holes in the reservoir  54  or through the holes  53  in the housing  50 . The drain holes in the reservoir are positioned to prevent overfilling of the reservoir. Optionally, the water absorption layer of the second embodiment is used in the reservoir to provide additional absorption and stability. 
     A combination of any or all of the modular embodiments described herein may be used in a single system. FIG. 12 shows a combination of these embodiments. FIG. 12 shows a roof system in accordance with the present invention, having a plurality of tray assemblies made in accordance with the first embodiment  100 , second embodiment  200 , and third embodiment  300 . Further, in order to provide roof access and mobility, paths of trays  400  are shown, which are empty or have paving stones configured to fit in the tray. Any known type of pathway material can be used and placed in the pathway trays  400 . 
     It is of course understood that departures can be made from the preferred embodiments of the invention by those of ordinary skill in the art without departing from the spirit and scope of the invention that is limited only by the following claims.