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: 
CLAIM OF PRIORITY TO PRIOR APPLICATION 
       [0001]    This application claims priority to provisional patent application Ser. No. 61/952,532, filed Mar. 13, 2014, and entitled  Roofing System with Sensors . 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to roofing systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Rain, heavy snow and roof gardens can place a great strain on many roofing structures. Over time, even a small leak can lead to catastrophic failure if not discovered and fixed. A roofing failure cannot only lead to damage and loss of property, it can also be very dangerous. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention comprises a roofing method and system in which sensors are placed on the roof substrate, and a water impermeable membrane is placed over the sensors. This can be accomplished by applying the sensors and membrane separately, or by applying a membrane which incorporates the sensors. The sensors may be selected so as to provide strain and temperature information. A system monitoring this information may provide an alert if a roof leak or excessive strain is detected. 
         [0005]    These and other objects, advantages, purposes and features of the present invention will become more apparent upon review of the following specification in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    FIG,  1  is a perspective view of a building showing roofing membrane in accordance with a preferred embodiment of the present invention; 
           [0007]      FIG. 2  is a perspective view of a building for which sensors have been placed on the roof substrate, and membrane is being applied over the sensors; 
           [0008]      FIG. 3  is a plan view of a scrim incorporating sensors; 
           [0009]      FIG. 4  is a sectional view of the roofing membrane of  FIG. 1 ; 
           [0010]      FIG. 5  is an exploded view of the roofing membrane of  FIGS. 1 and 4 ; 
           [0011]      FIG. 6  is a sectional view of an alternative embodiment sensor membrane; 
           [0012]    FIG,  7  is a sectional view of a second alternative embodiment sensor membrane.; 
           [0013]      FIG. 8  is a sectional view of a third alternative embodiment sensor membrane; 
           [0014]      FIG. 9  is a sectional view of a fourth alternative embodiment sensor membrane: and 
           [0015]      FIG. 10  is a schematic of a roof monitoring and reporting system of the preferred embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    In the preferred embodiments, the roofing system of the present invention may comprise a roofing membrane  20  incorporating sensors as shown in  FIGS. 1 ,  3 ,  4  and  6 - 9 , or may comprise sensors applied directly to the roof substrate, and then covered with a membrane  20 A as shown in  FIG. 2 . In either of those alternatives, the sensors can be incorporated into a scrim layer  40  as shown in  FIG. 5 , which is then either laid on the roof substrate  12  and covered with a separate water impervious membrane  20 A, or which is adhered directly onto a water impervious membrane layer  30 , as shown in  FIG. 4 . Alternatively, sensors  50  may be incorporated directly into the water impervious membrane layer  30  as shown in  FIGS. 6-9 . Preferably sensors  50  are elongated sensor strands, most preferably fiber-optic strands. Fiber-optic strands can identity water leaks by identifying temperature changes which affect the optical signal, and can identify roof strain due to deflection of the fibers, which affect the optical signal. 
         [0017]    Referring now to the drawings and the illustrative embodiments depicted therein, a roofing membrane or sheet  20  used for covering a rooftop  12  on a building  10  comprises a sensor or sensing layer  40  and a water impervious cover or coating layer or membrane  30 . Sensing layer  40  includes a plurality of fiber-optic sensors  50  adhered, sewn or woven into a geotextile fabric or other scrim  46 . Sensors  50  are configured to measure changes in temperature and/or strain. Membrane layer  30  covers a top surface  42  of sensing layer  40 . One or more sheets  20  can be installed on rooftop substrate  12  and seamlessly fused together with an additional layer of coating, providing a water tight seal over rooftop  12 . A monitoring system  60  monitors the output of sensors  50  and issues an alert to a receiving device  70  in the event of a leak in sheet  20  or excessive strain on rooftop  12  or the like. 
         [0018]    Each roofing membrane layer can come in varying sizes. Widths typically vary from 5 to 15 feet, and can be conveniently supplied in rolls as long as 300 feet. When membrane units  20  are butted endwise, the sensors  50  are connected using conventional coupling methods. The spacing within a membrane layer  20  can vary, but a spacing of one sensor  50  every 2 to 4 feet is exemplary. 
         [0019]    In the  FIG. 2  embodiment, sensors  50  are laid onto roof substrate  12 , either as individual strands, or incorporated into sensor scrim  40  as described above. Roofing membrane  20 A which does not incorporate sensors is then applied over the layer of sensors  50 . At their ends, sensors  50  are connected to a communication strand  51  and  52 , which connect them to monitor  62  via communication links  66  ( FIG. 10 ). 
         [0020]    Referring now to  FIG. 3 , sensing layer  40  is a sensor enabled geotextile, available from sources such as TenCate, a division of Royal Ten Gate of the Netherlands, under the brand name GEODETECT. Sensing layer  40  comprises a scrim or fabric  46  made from a composite geotextile material and a plurality of fiber-optic sensors  50 . Preferably, scrim  46  is porous, especially when the fiber-optic sensors are located between scrim  46  and water impervious layer  30  ( FIG. 4 ). This allows water leakage to gain access to fiber-optic sensors  50 . Alternatively, scrim  46  can be sufficiently thin that temperature variations caused by water leakage can be sensed at the fiber-optic sensors  50 . In the illustrated embodiment, sensing layer  40  is essentially rectangular in shape with four edges  48   a,    48   b,    48   c,  and  48   d.  Sensing layer  40  has a top surface  42  and a bottom surface  44 . Sensors  50  run lengthwise across top surface  42  and are adhered, sewn to or interwoven into fabric  46 . 
         [0021]    As illustrated in  FIGS. 4 and 5  membrane  30  is applied to sensing layer  40  covering at least top surface  42 . Membrane  30  is formed from a spray coating that when applied to sensing layer  40  creates a waterproof layer having a top surface  32  and a bottom surface  34 . In the illustrated embodiment, membrane  30  is generally rectangular in shape with four edges  36   a,    36   b,    36   c,  and  36   d  corresponding to edges  48   a - 48   d  of sensing layer  40 , respectively. While membrane  30  may be any number of water resistant coatings and thicknesses, the illustrated embodiment uses an 80 mil spray coating of polyurea. Polyurea spray coatings can provide fast curing, even at very low temperatures, and water resistance, along with high hardness, flexibility, and tear strength. Although sensor layer  40  and membrane layer  30  are shown in the illustrated embodiment as generally rectangular, it should be appreciated that alternative shapes, styles and configurations may be utilized. 
         [0022]    Other coating methods may be employed for applying water impervious layer  30 , e.g. via roller, squeegee, knife blade, extrusion or pultrusion. Other examples of membrane materials include without limitation EPDM, TPO, PVC and Hypalon. 
         [0023]      FIG. 6  shows an alternative embodiment roofing membrane  20  in which the water impervious layer is applied to the reverse side of scrim  46 , from that shown in  FIGS. 4 and 5 , such that sensors  50  are exposed to the roof substrate when roofing membrane  20  is applied. In the  FIG. 6  embodiment, sensors  50  are incorporated directly into the water impervious layer  30 . When encapsulated in this manner, sensors  50  are preferably sufficiently close to the bottom surface of layer  30  that they sense temperature changes due to the presence of water. In the  FIG. 7  embodiment, sensors  50  are embedded into the bottom of water impervious membrane layer  30 , such that they are partially exposed. In the  FIG. 9  embodiment, sensors  50  are simply adhered to the undersurface of water impervious layer  30 . 
         [0024]    One or more roofing sheets  20  are installed on rooftop  12  and seamlessly fused together with additional sprayed polyurea or other polymer layer or layers that are disposed over the top of the membrane layer  30 . Once installed, sheets  20  become part of a rooftop monitoring system  60  ( FIG. 5 ). Monitoring system  60  comprises one or more sheets  20 , an optical interrogator  62 , a computing unit  64 , and a communications link  68  between optical integration  62  and computing unit  64 . Sensors  50  in sheet  20  can measure conditions and/or changes in conditions, such as by measuring the strain and/or temperature on rooftop  12 . Sensors  50  incorporate one or more fiber-optic sensing technologies such as Fiber Bragg Gratings, Brillouin, and Raman technologies. These technologies are able to measure temperature and/or strain very precisely and with a relatively high spatial resolution under static or dynamic conditions. Optical interrogator  62  collects strain and temperature data from sensing layer  40  via a wired or fiber-optic connection  66 . Monitoring may be continuous or periodic. Interrogator  62  may include a number of channels for receiving data from sensing layer  40  and each channel may sample at different rates. Data received by interrogator  62  is then transmitted to computing unit  64  via communications link  68 . Computing unit  64  may be located on-site or located remotely, and communications link  68  may be a wired connection or a wireless connection. Once data is received by computing unit  64  the data is analyzed. When computing unit  64  senses a warning condition, such as a change in temperature suggestive of a leak or high strain indicating heavy snow accumulation on rooftop  12 , computing unit  64  issues an alert to a receiving device  70 . Receiving device  70  may be a personal computer, smartphone, cell phone, or the like. The alert may be in the form of an email, phone call, text message or the like. 
         [0025]    Optionally, interrogator  62  may be capable of analyzing, the data for warning conditions. In this case, interrogator  62  can issue the alert directly to receiving device  70  without the need the computing unit  64 . 
         [0026]    Changes and modifications to the specifically described embodiments may be carried out without departing from the principles of the present invention, which is intended to be limited only by the scope of the appended claims as interpreted according to the principles of patent law including the doctrine of equivalents.

Summary:
A rooting method and system in which sensors are placed on the roof substrate, and a water impermeable membrane is placed over the sensors. This can be accomplished by applying the sensors and membrane separately, or by applying a membrane which incorporates the sensors. The sensors may be selected so as to provide strain and temperature information. A system monitoring this information may provide an alert if a roof leak or excessive strain is detected.