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CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a roofing product. More specifically, the present invention is directed to a roof covering member possessing thermal expansion relief characteristics. 
     Roofing shingles are commonly used to provide a protective environmental barrier layer for a pitched roof. These shingles typically include asphalt shingles, non-asphalt engineered composite shingles, wood shake singles, slate shingles, ceramic and concrete tiles and the like. Engineered composite shingles have become popular for commercial and residential installations in recent years due to their high strength and durability, lower cost and maintenance as compared to wood and slate shingles, and relative ease of installation. Because of their composite nature, engineered composite shingles can be fabricated to imitate the look of shake, slate, tile, and many other types of shingles. One particular type of composite shingle employs a material makeup of at least a polymer component and a filler component. For instance, the polymer component may comprise one or more thermoplastic materials and the filler component may comprise one or more minerals, as examples. Coloring agents, UV inhibitors, stabilizers, and other additives may be added or applied to the material makeup to improve the characteristics of the finished shingle product. 
     When installing a shingled roof covering system on a pitched roof, a starter course, or row, is usually coupled to a roof deck along the eaves to form a base for the first course of full shingles. Additional shingle courses are applied to partially overlap the previous courses as the roofing installer works their way up to the ridgeline. 
     One particular problem faced by shingle installers is how to account for thermal expansion and contraction cycles that occur when singles are exposed to temperature extremes in the outdoor environment. This is especially problematic when a semi-rigid to rigid shingle has fixed point of attachment on a building roof structure and will become exposed to temperatures that vary greatly from the temperature of the shingle when it is installed on the roof, such a temperature differential being referred to herein as “Delta T”. As one example, consider the pair of shingles  100  illustrated in  FIG. 1  as positioned adjacent to one another in the same course on a roof deck (not shown). A fastener is inserted through one of a set of nailing zones  102  on the shingle top surface  103  and into the roof deck to rigidly affix the shingle  100  onto a building. Because these shingles  100  have side regions  104  that abut one another when installed, any thermal expansion of the shingles will cause each to expand laterally and the side regions  104  of each shingle to exert a sizeable force on the side region of the adjacent shingle. Moreover, a large Delta T causes a bowing or “pillowing” effect of the shingles  100  where a mid-region of the shingle moves upwardly off of the underlying roof deck. This bowing effect can undermine the attachment of the fasteners extending through the nailing zones  102 , potentially causing them to move out of engagement with the roof deck. Additionally, the bowing can leave areas of the underlying roof deck directly exposed to the environment, which could allow precipitation and other elements to infiltrate the structure of the roof. Furthermore, the bowing diminishes the aesthetics of the roofing product. 
     Therefore, it would be beneficial to provide a roofing product that possesses thermal expansion relief characteristics, particularly for handling situations where the product is exposed to ambient temperatures that vary significantly from the temperatures at product installation. 
     SUMMARY OF THE INVENTION 
     Improved roofing system performance is achieved through a roofing member or shingle possessing thermal expansion relief characteristics. In one aspect, the roofing member provides thermal expansion relief when mounted adjacent to other roofing members in laterally extending courses on a roof surface. Specifically, each roofing member has a main body with top and bottom surfaces, and side regions, as well as one or more spacer tabs extending outwardly from one or more of the side regions. Each spacer tabs extends outwardly from a location on one of the side regions that is adjacent to one of a set of depressions formed into the bottom surface of the main body. In this way, when thermal expansion of adjacently mounted roofing members occurs causing a compressive force to be applied against particular spacer tabs, the particular spacer tabs fail in a way that at least partially displaces the respective spacer tabs into the adjacently positioned depressions, thereby reducing the stress loads that adjacent shingles apply to one another. 
     In another aspect, the spacer tabs and corresponding adjacent depressions are configured to handle a first compressive thermal expansion load where the spacer tabs are partially displaced into the corresponding depressions and a second compressive thermal expansion load where the spacer tabs are fully displaced into the corresponding depressions. In this way, the first compressive thermal expansion load can be said to cause a first mode of failure, while the second compressive thermal expansion load can be said to cause a second mode of failure. 
     The invention of another aspect takes the form a roofing member having a main body, a cutout feature, and a spacer tab feature. Specifically, the main body includes top and bottom surfaces, and side regions, with the cutout feature formed into one or more of the side regions and spacer tab feature extending outwardly from at least one of the side regions proximal to the respective cutout feature. In this way, when thermal expansion of adjacently mounted roofing members occurs causing a compressive force to be applied against the spacer tab feature inwardly with respect to one or more of the side regions, the cutout feature and the spacer tab feature cooperatively provide stress relief through movement of the spacer tab feature at least partially into the cutout feature. 
     Additional advantages and novel features of the present invention will in part be set forth in the description that follows or become apparent to those who consider the attached figures or practice the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the accompanying drawings, which form a part of the specification and are to be read in conjunction therewith and in which like reference numerals are employed to indicate like parts in the various views: 
         FIG. 1  is a top perspective view of prior art shingles aligned in a shingle course; 
         FIG. 2  is a bottom perspective view of one embodiment of a roofing member of the present invention possessing thermal expansion relief characteristics depicted in an abutting relationship with an adjacent roofing member; 
         FIG. 3  is a close-up plan view of the roofing member generally in a region identified by the circled area in  FIG. 2 , showing a spacer tab and a corresponding depression; 
         FIG. 4  is a view similar to  FIG. 3 , with the spacer tab being partially displaced into the depression due to a compressive force being applied by the adjacent roofing member; 
         FIG. 5  is a view similar to  FIG. 3 , with the spacer tab being fully displaced into the depression due to a compressive force being applied by the adjacent roofing member; 
         FIG. 6  is a perspective view of the roofing member region depicted in  FIG. 3 ; 
         FIG. 7  is a bottom plan view of another embodiment of a roofing member of the present invention possessing thermal expansion relief characteristics depicted in an abutting relationship with an adjacent roofing member; 
         FIG. 8  is a close-up plan view of the roofing member generally in a region identified by the circled area in  FIG. 7 , showing a spacer tab and a corresponding cutout; and 
         FIG. 9  is a view similar to  FIG. 8 , with the spacer tab being partially displaced into the cutout due to a compressive force being applied by the adjacent roofing member. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a roofing system formed by roofing members or shingles possessing thermal expansion relief characteristics. The roofing system provides a degree of “play” between adjacently mounted shingles on a roof structure. Specifically, as the shingles expand in size due to the temperature of the shingles becoming elevated, spacer tabs which are typically utilized to properly align and space apart shingles for installation are allowed to be displaced inwardly into the side regions of the shingles. This allows the side regions of the shingles to avoid the high compressive loads applied by thermally expanding adjacent shingles. In certain embodiments, the spacer tabs are configured to substantially only undergo elastic deformation when thermal expansion occurs, while in other embodiments, certain modes of failure result in the spacer tabs partially or fully breaking away from connection with the side regions of the respective shingle. 
     Turning to  FIGS. 2-6 , an embodiment of a shingle  200  possessing thermal expansion relief characteristics is depicted with a spacer tab feature  202  abutting an adjacent shingle  300 . The shingle  200  has a main body  204  possessing a top surface  206 , a bottom surface  208 , and side regions  210  from which the spacer tab feature  202  extends. It should be understood that the shingle top surface  206  may take the same form as the top surface  103  of the prior art shingle  100  of  FIG. 1 , or any other form desired. The spacer tab feature  202  extends laterally outwardly from the side regions  210  adjacent to a depression feature  212  formed in the bottom surface  208  of the shingle  200 . As used herein, the term “spaced tab feature” refers to one or more individual spacer tabs  214  each located on one of the shingle side regions  210 . Similarly, the term “depression feature” refers to one or more individual depressions  216  or cavities each corresponding to one of the individual spacer tabs  214 . 
     Each spacer tab  214  has a first longitudinal end  218  and a second longitudinal end  220  moving in the longitudinal direction of a sidewall  222  of the side regions  210 . Each depression  216  is preferably located relative to the shingle sidewall and to one of the corresponding spacer tabs  214  such that the sidewall  222  is formed with a first smaller wall thickness at a location A directly between the depression  216  and the spacer tab first longitudinal end  218  and is formed with a second larger wall thickness at a location B directly between the depression  216  and the spacer tab second longitudinal end  220 , as seen in  FIG. 3 . This design serves the purpose of creating a weak point in the sidewall  222  webbing at location A to control the initial structural failure mode of the sidewall  222  as the compression force due to thermal expansion of an adjacent shingle  300  increases against the spacer tab  214 . At the initial failure mode, depicted in  FIG. 4 , the spacer tab  214  cantilevers into a first region  224  of the depression  216  while remaining attached to the sidewall  222  generally at location B. Specifically, the first longitudinal end  218  moves into contact with a depression sidewall  226  in the first region  224  while a portion of the spacer tab  214  remains outside of the depression  216  and extends outwardly from the plane of the sidewall  222  to remain in contact with the adjacent shingle  300 . Thus, the initial failure mode provides displacement of the spacer tab  214  laterally into the shingle main body  204  without completely disconnecting with the shingle sidewall  222 . 
     As can be seen in  FIG. 6 , the first longitudinal end  218  of the spacer tab  214  has a sloped intersecting edge  228  with the shingle sidewall  222 . This slope provides a tapered length for the spacer tab  214  longitudinally along the sidewall  222  such that the spacer tab length increases moving in the direction of the shingle bottom surface  208 . The sloped intersecting edge  228  aids in guiding the initial failure mode at location A on the sidewall  222  webbing so that the spacer tab  214  laterally pivots directly into the depression  216  without pivoting upwardly or downwardly towards the shingle top surface  206  or bottom surface  208 . If the sloped edge  228  were instead vertically aligned and perpendicular to an intersecting edge  230  of the bottom surface  208  and the sidewall  222  of the shingle  200 , the extra material strength added by a surface webbing  232  of the shingle main body  204  above the depression  216  would cause uneven failure of the sidewall  222  near the spacer tab first longitudinal end  218 , and thus undesirable upward or downward pivoting of the spacer tab  214 . 
     With reference to  FIGS. 4 and 5 , as the shingles  200 ,  300  continue in thermal expansion beyond the point where the initial failure mode depicted in  FIG. 4  occurs, such as on a hot day with significant sun exposure, the compressive forces on the spacer tab  214  are transferred to the shingle main body  204 , specifically to the depression sidewall  226  and to the shingle sidewall  222  in the region of location B. Continued expansion beyond this point causes a second structural failure mode depicted in  FIG. 5 . Specifically, the second longitudinal end  220  of the spacer tab will break away from the shingle sidewall  222  at location B, causing the adjacent shingle  300  to push the spacer tab  214  into the depression  216  beyond the first region  224  and into a retaining region  234  of the depression  216 . In this way, the depression  216  both serves to control the failure modes of the spacer tab  214  and compression loads that are transferred to the shingle main body  204  over a range of thermal expansion of adjacently mounted shingles, as well as serving as a retainer for the spacer tab  214  that has broken away from the shingle sidewall  222 . The particular depth of the depressions  216  measured along the sidewall  226  perpendicularly to the plane of the shingle bottom surface  208  is a matter of design choice, and in one embodiment, is at least as large as the height of the spacer tabs  214 , enabling the depressions  216  to accept the spacer tabs  214  therein when the shingle bottom surface  208  rests on top of a flat roof structure and the spacer tabs  214  experience an inwardly compressive load that results in the initial and second failure modes described herein. 
     Turning to  FIGS. 7-9 , another embodiment of a shingle  400  possessing thermal expansion relief characteristics is depicted with a spacer tab feature  402  abutting the adjacent shingle  300 . In a similar form to the embodiment of the shingle  200  illustrated in  FIGS. 2-6 , shingle  400  has a main body  404  possessing a top surface  406 , a bottom surface  408 , and side regions  410  from which the spacer tab feature  402  extends. The shingle top surface  406  may take the same form as the top surface  103  of the prior art shingle  100  of  FIG. 1 , or any other form desired. The spacer tab feature  402  extends laterally outwardly from the side regions  410  adjacent to a cutout feature  412  formed in at least one of the side regions  410  and preferably extends from the top surface  406  through the main body  404  to the bottom surface  408 . As with the embodiment of shingle  200  illustrated in  FIGS. 2-6 , the term “spaced tab feature”, as used herein, refers to one or more individual spacer tabs  414  each located on one of the shingle side regions  210 . Similarly, the term “cutout feature” refers to one or more individual cutouts  416  each corresponding to one of the individual spacer tabs  414 . 
     Each spacer tab  414  has a free end  418  and a fixed end  420 , with the fixed end  420  configured to provide resistance to the compression force provided by a sidewall  302  of the adjacent shingle  300  undergoing thermal expansion. The thickness of the spacer tab  414  at the fixed end  420  is ideally sufficient to resist laterally inward deflection of the tab  414  when being contacted by the sidewall  302  of an adjacent shingle  300  at the time of installation, but of a thickness that allows the tab  414  to elastically deflect as the compressive loads on the tab  414  provided by the thermally expanding adjacent shingle increase to prevent bowing of the shingle  400  and adjacent shingle  300 . 
     As seen in  FIG. 9 , as the compressive load applied to the spacer tab  414  increases by the sidewall  302  of the adjacent shingle  300 , the tab  414  continues to deflect into the corresponding cutout  416  until the free end  418  of the tab  414  contacts an inner wall  422  of the cutout  416 . Ideally, the spacer tab  414  and the corresponding cutout  416  are sized and configured to enable a sufficient amount of rotation of the spacer tab  414  into the cutout  416  to handle the expected range of thermal expansion of the shingles  300 ,  400 . The spacer tab  414  may optionally be configured to eventually undergo structural failure at the fixed end  420  if thermal expansion continues beyond the condition depicted in  FIG. 9 . Alternatively, the spacer tab  414  may be configured to avoid such failure, and instead resiliently return to the position depicted in  FIG. 8  when temperatures of the shingles  300 ,  400  have lowered from the temperatures at which significant or maximum thermal expansion takes place. 
     It should be understood that the adjacent shingle  300  described herein may take the form of shingle  200  of  FIGS. 2-6  or shingle  400  of  FIGS. 7-9 , such that all shingles in a given installed course possess the thermal expansion relief characteristics described herein. Alternatively, shingle courses may be installed utilizing rows of shingles that have only some of the shingles in the given row possessing the thermal expansion relief characteristics of shingles  200  and/or  400 . As one example, a given row may alternate single  200  or shingle  400  with an adjacent shingle  300  lacking at least the depression feature  212 , and optionally the spacer tab feature  202 . 
     The shingles  200  and  400  of the present invention are preferably formed from composite materials. Suitable materials include, but are not limited to, rubber (e.g., ground up tire rubber), polymers such as polyolefins (e.g., various grades of polyethylene, recycled or virgin), fillers (e.g., glass, stone, limestone, talc, mica, cellulosic materials such as wood flour, rice hulls, etc.), asphalt embedded mats, or tile. In one embodiment, the composite material makeup includes at least a polymer component and a filler component. Coloring agents may also be added to the mixture so that the composite product more closely resembles a particular type of shingle. For example, for a composite slate product, a gray color may be added to the mixture. Similarly, for a composite wood shake product, a brown color may be added to the mixture. Other additives or processing methods may be added or applied to improve reflection, heat deflection or other weathering characteristics, (e.g., UV inhibitors and stabilizers). These material combinations form the shingles  200  and  400  into semi-rigid objects. 
     The shingles  200  and  400  may be made and cut, or molded, to shape using various fabrication techniques. For example, one manner of making the starter block relies on the use of a mixer and extruder. The ingredients that are used to form the starter block are mixed in the mixer (e.g., a kinetic mixer) and then passed through the extruder. The mixture emerging from the extruder may be sliced into small pellets by a rotary knife so that the material can be more easily conveyed through piping under air pressure or suction to a storage location for use when needed (e.g., in a storage bin). Thereafter, the pellets are extracted from storage and fed to an injection-molding machine along with coloring agents where the material is injected in one or more molds that have been cast or machined, such as by digitized molding, to have the desired shape of the shingle. After curing and sufficient cooling, the molded shingle is removed from the mold and bundled or otherwise packaged with like shingles for shipment or storage. 
     As can be seen, the shingles  200 ,  400  of the present invention provide a roofing system with thermal expansion relief characteristics to reduce the compressive loads induced by adjacent shingles on one another. While particular embodiments of the invention have been shown, it will be understood, that the invention is not limited thereto, since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. Reasonable variation and modification are possible within the scope of the foregoing disclosure of the invention without departing from the spirit of the invention.

Summary:
A roofing member provides improved thermal expansion relief characteristics when mounted adjacent to other roofing members in laterally extending courses on a roof surface. According to one arrangement, the roofing member has a main body with top and bottom surfaces, and side regions, as well as one or more spacer tabs extending outwardly from one or more of the side regions. Each spacer tab extends outwardly from a location on one of the side regions that is adjacent to one of a set of depressions formed into the bottom surface of the main body. In this way, when thermal expansion of adjacently mounted roofing members occurs causing a compressive force to be applied against particular spacer tabs, the spacer tabs fail in a way that at least partially displaces the respective tabs into the adjacently positioned depressions, thereby reducing the stress loads that adjacent shingles apply to one another.