Fixing means for a structure covering system

Abstract

A fixing means 12 for securing a component to an underlying structure 46. The fixing means comprises a fastener 50 comprising a head 56 and a shank 54 extending from the head. The head comprises an up

Description

TECHNICAL FIELD OF THE INVENTION This invention relates to a fixing means for a system for covering a building or other structure, and more particularly to a system of interconnecting shingles (e.g., roof or wall shingles) that together form a sealed covering. As used herein, a “shingle” is a thin, substantially flat tile configured to be fixed with other (similar) shingles in overlapping rows to make a roof or wall covering. BACKGROUND In some constructions, roof or wall coverings are used to protect an underlying structure from the effects of weather and provide an attractive decorative finish. In particular, such coverings are used to provide protection against rainwater, wind, and UV radiation (from sunlight). These weather forces could otherwise damage the underlying weather proofing and structure. One type of roof or wall covering is a shingle. Shingles comprise substantially flat elements of material as defined above, which are arranged together in an overlapping manner to form an outermost surface (or cap) as a covering. Presently, shingles may be made from a variety of materials, such as metal, wood or slate rock, but generally form rigid elements with sufficient structural properties to provide resistance to weather forces. Shingles may be arranged over a felt or membrane, which in turn is arranged over the underlying structure. The membrane to provide some wind and water resistance is fixed to the underlying structure with fixings, for example nails. The shingles cover the membrane and provide most of the protection from direct wind, rain, and sun forces; the membrane prevents ingress of any water or wind which passes through the (unsealed) overlapping joints of the roof or wall shingles. Traditionally, shingles are made from split slates, timber or ornamental metal, and may be arranged over the membrane on wooden members, or battens. The battens are laid over the membrane and attached to the underlying structure with fixings, such as nails, which pierce the membrane. Shingles are then attached to the battens using additional fixings. Usually, the shingles are attached to battens with fixings only at an upper edge of each shingle, so that a lower edge of each shingle is unattached to the underlying structure. The inherent rigidity in the shingle material keeps the shingle flat. The shingles are arranged along the battens in rows, with upper rows overlapping lower rows. Generally, each row overlaps the lower row so that approximately two-thirds of the lower row is covered. Consequently, only the lower third of the area of each single is visible or exposed. Roof coverings using overlapping shingles as described have several disadvantages. As outlined above, the arrangement of shingles in overlapping rows results in two-thirds of each shingle being covered by at least one other, upper shingle. Therefore, only one-third of each shingle is exposed and effectively utilised in protecting against weather forces. This is an inefficient use of material and, where an expensive material is used to form the shingles, the overlapping design of shingles can present a significant cost. The overlapping arrangement of substantially flat shingles also requires a virtually flat roof or wall to be effective. Where the underlying structure has even a small curvature, the effectiveness of overlapping shingles is compromised even if smaller shingles are used. Despite their overlapping, the joints which are formed between rows of shingles are vulnerable to wind, particularly because the lower edges are usually unsecured to the underlying structure. This makes the roof covering and underlying structure susceptible to wind damage. Additionally, the unsealed joints provide a route for cold winter air or hot summer air to enter the underlying structure or building, which is undesirable. Shingles in an overlapping arrangement are also difficult to remove and replace, because their fixing to the underlying structure is covered by another shingle in the upper row. Replacing damaged individual shingles can be time-consuming and costly. The fixing of shingles, battens and membranes to the underlying structure can also cause problems. Where the weather-proofing membrane is pierced by the fixings connecting the battens to the underlying structure, the covering is vulnerable to ingress of water by capillary action along the fixing and through the membrane. Over time, this water ingress can damage the underlying structure, for example by causing rot in wood. Such water can also cause a chemical interaction between the materials of the underlying structure and roof covering. For example, water can leach acid from wood of an underlying structure, which acts with a zinc-plated nail fixing leading to rusting or rotting of the nail, and hence damaging the integrity of the roof covering itself. The fixings which connect the shingles to the underlying structure are also vulnerable to damage. For example, where a nail is used, the head and parts of the shank of the nail are exposed to weather forces infiltrating the overlapping shingles, and are therefore vulnerable to rusting or rotting. There is a need to provide a roof or wall covering which addresses some or all of these issues. SUMMARY According to one aspect of the invention, there is provided a system comprising a plurality of shingles to be used to form a covering for a structure (e.g., a roof or wall). Each shingle comprises a plurality of edges, wherein at least one channel extends along a first one of the plurality of edges, and an overlapping surface (e.g., a capping surface) extends along a second one of the plurality of edges (e.g., to form part of a cap for the channel). The system further comprises a plurality of seal members to be positioned in each channel. Each overlapping surface is configured to overlap, and optionally cap a channel of an adjacent shingle and contact a seal member positioned therein, such that the shingles are configured to interconnect to form the covering. Each shingle may comprise a thin sheet that extends to the edges of the shingle, at which point are located the channel(s) and overlapping surface(s). Each channel may be formed with a sealing surface slightly below a general plane of the sheet, and each overlapping (sealing) surface is slightly raised from the general plane of the sheet In this manner the channels and caps have sealing surfaces that deviate slightly from the general plane and are limited to the edges of the shingles, which maximises the rigidity of the thin sheet. By “thin sheet”, it is intended that the main part of the shingle (between the edges) is a substantially planar member (e.g., sheet material), albeit with perhaps some minor surface indentations / protrusions such as a pressed design or motif, or a textured surface, as discussed herein. At least the thin sheet (or all) of the shingle may be a sheet material, for example a single layer sheet material. This excludes complex geometrical features such as flanges or hooks (i.e., extensions out of the sheet), and the like, to maximise the overall rigidity as discussed above. In some embodiments the thin sheet of each shingle could be completely smooth (without any surface indentations or texture), or the system could comprise a mixture of completely smooth shingles with those having minor surface indentations / protrusions such as a pressed design or motif, or a textured surface. The above features provide an efficient and relatively inexpensive system for covering a structure to protect it from damage due to, eg., weather forces. By interconnecting thin shingles at and along the edges thereof (and only the edges), the majority of the shingle (i.e., the thin sheet part between the edges) is exposed and usable for this purpose after installation. In addition the thin sheet part of each shingle (between the edges) extends in substantially a single plane between the edges (which could be straight or curved, as described below) and provides an increased rigidity as compared to conventional shingles or other types of covering. Accordingly, the shingles can form a rigid covering exposing a large proportion of the outer surface of each shingle to weather forces, to minimise wastage of shingle material. Various other advantages will become apparent from the discussion below. The present invention is particularly beneficial for use as a roof or wall covering for a structure to prevent it from damage due to wind (or other weather). By providing a channel along an edge of each shingle, and a seal within the channel, each shingle can form a sealing joint with an adjacent shingle. The edges of adjacent / adjoining shingles may be substantially parallel. The shingles may tessellate with each other to form the covering. The term “tessellate”, as used herein, means an arrangement of shaped shingles that fit together with no spaces in between and wherein the edges of adjacent shingles remain substantially parallel with each other (even though they partially overlap). As such, the shingles fit together to form a mosaicked covering. The shingles may be made up of a number of regular or irregular polygonal shapes that fit or cooperate with each other in this manner, as will be described in more detail below. Using a tessellated / mosaicked arrangement in this manner results in a rigid covering with no wastage of material. By providing shingles that interconnect along adjacent edges, the shingles may also be used for covering an underlying structure which is not flat, i.e., is curved or irregularly shaped. One or more (or all) of the shingles may be configured to interconnect with an adjacent shingle, where the adjacent shingle, e.g., the general plane thereof (between the edges) is arranged at an angle thereto. The shingles may themselves be curved so as to form various curved shapes. The edges of curved shingles may also be curved, and form sealing joints with correspondingly shaped curved overlapping surfaces of other shingles. Each curved shingle may form a sealing joint with an adjacent curved shingle to provide a covering that is itself a continuous curve. In this manner the general plane (in this case a curved plane such as part of the surface of a sphere or ovoid) of each shingle (between the edges) could at the connecting edges thereof be substantially parallel to that of any adjacent shingle. This optimises the rigidity of the curved shingles forming the covering. The channels may be formed from the same material as the shingles, for example as a continuation of a sheet material (e.g., single layer sheet material) which forms the shingle, but shaped to form a recess. The channels may form a ‘II’ shape in cross section, having a base, with first and second opposed walls extending from the base. By forming a strong, sharp edge this particular shape of channel adds further rigidity to each shingle, and covering as a whole. The channels may extend along substantially the entire first edge of each shingle. The channels may have a substantially constant cross-section along their entire length. Each shingle may comprise a plurality of channels formed along a plurality of its edges. Two (or more) of the plurality of channels formed along different edges may be joined at vertices of the edges (e.g., corresponding to a corner of the shingle), so as to form a substantially continuous channel that extends along multiple edges of the shingle. As noted above, each shingle comprises an overlapping surface that extends along the second one of the plurality of edges. The overlapping surface may be an extension of the shingle upper surface, or each shingle could include a flange that extends from the upper surface and interconnects the upper surface and the overlapping surface, so as to raise the overlapping surface slightly from the general plane of the shingle. However it is provided, the overlapping surface is configured to overlap a channel of an adjacent shingle and contact a seal member positioned therein. In the above-described manner, each overlapping surface may cap an adjacent channel, and provide extra rigidity to the thin sheet forming each shingle when raised from the general plane thereof (due to the formation of a strong, sharp edge). There may be small angles between the planes of adjacent shingles, which may be accommodated using the channel and cap (the interaction of which would not typically require exactly parallel shingles). Should two adjacent shingles of the plurality of shingles define respective planes arranged at an angle to one another, then the overlapping surface of one of the adjacent shingles and the sealing surface of the channel of the other of the adjacent shingles may still be arranged parallel to each other, such that the cap and channel meet in a shared plane and compress the seal upon connecting the two shingles. For example, for large angles (9°) between the planes of two adjacent shingles, the channel in a first shingle can be formed at half of the angle ((0 / 2)°) to the plane of the first shingle, and the cap from the adjacent shingle can be formed at half of the angle ((0 / 2)°) in the opposed direction, so that the channel and cap interact in a plane which is offset to each of the planes of the shingles by plus or minus half of the angle (± (0 / 2)°), and the seal is compressed in a plane of 90 degrees plus or minus half of the angle (90 ± (0 / 2)°). Each shingle may comprise a plurality of overlapping surfaces (including, e.g., flanges to slightly raise the surface) formed along a plurality of edges. Two (or more) of the plurality of overlapping surfaces formed along different edges may be joined at vertices of the edges (e.g., corresponding to a corner of the shingle), so as to form a substantially continuous surface along multiple edges of the shingle. Joining the overlapping surfaces when they are slightly raised by a flange (as described above) adds significantly to the strength of the thin shingle, as does joining the channels when they are slightly sunken below the general plane (e.g., as a ‘U’ shaped channel). The overlapping surfaces may be formed from the same material as the shingles, for example as a continuation of a sheet material (e.g., single layer sheet material) which forms the shingle, wherein the edges could be shaped to form the overlapping surface. The overlapping surface, for example, may form part of a raised portion along the edge(s) of each shingle, which may form at least an ‘L’ shape with the flange, or even an inverted ‘U’ shape (or TT) in cross section, that is having a top (forming the overlapping surface) and opposed walls extending down from the top. The overlapping surfaces and / or channels may be formed as a unitary piece with the thin sheet. Each shingle may have three, four or six edges, such that each shingle could form a triangle, a rectangle (or square), or a hexagon respectively. These shapes can form a covering with a regular tessellation (as defined above), formed of shingles which all comprise the same shape, and gaining extra rigidity when provided with caps and / or channels that sit slightly above or below the general plane of the shingles as described above. Alternatively, each shingle may form part of a covering with a semi-regular tessellation, where shingles of a number of different shapes form sealing joints in the manner described above. For example, a tessellation may be formed from shingles of three different types, respectively having three edges, four edges and five edges. Alternatively, each shingle may form part of a covering with an irregular tessellation, where shingles of many different shapes form sealing joints with one another. The system may be used to cover a flat structure (such as a normal roof), using a regular or irregular tessellation of the shingles. In various embodiments, the system may be used to cover a curved structure, e.g., a concave or convex structure that forms part of a sphere, cylinder and the like. The shingles in these embodiments could each be substantially flat, and configured to meet at an angle along two opposed sides, such that the plane of each shingle is oriented parallel to a cylinder's axis of symmetry, for example, but offset so as to form a covering with a facetted appearance. Alternatively, the shingles could be curved so that they form a covering that is itself a cylinder, which is concentric with the cylindrical (or part-cylindrical) structure underneath. Various other curved structures may be covered. For example, a toroidal section, or ring-shaped structure may be covered using flat or curved shingles, in a similar manner to the cylinder above, but wherein the shingles are configured to meet at an angle along all sides (rather than two opposed sides as in the example above). A more irregular structure, for example using compound curves and / or lines of inflexion may be covered as well. It will be appreciate that the system can work with any type of curved or shaped structure, wherein the edges of the shingles can be adapted for each structure so as to provide the necessary curvature of the covering that matches that of the curved or shaped structure. In one embodiment, a covering system may comprise two or more different shapes of shingle in order to provide a covering which covers a surface having a changing curvature. One such embodiment is provided where a covering system comprises a first plurality of tessellated shingles having a first shape (e.g., hexagonal), which are configured to cover a first region of a surface (e.g., a substantially flat region of the underlying structure). The covering may further comprise a second plurality of tessellated shingles having a second shape (e.g., different to the first shape, such as rectangular), which are configured to cover a second region of the surface (e.g., a curved region of the underlying structure). The covering may further comprise a third plurality of tessellated shingles having a third shape (e.g., different to the first and second shapes, such as triangular), which are configured to cooperate with both the first and second shingles to transition the covering between the first and second regions (e.g., from a flat region to a curved region of the underlying structure). The third plurality of shingles may be triangular. The first, second and third shingles may all tessellate with each other where they connect, as defined herein. As noted above a seal member is disposed in each channel. The seal member may comprise an elongated member. The seal member may comprise a substantially constant cross-section along its entire length. The seal member may extend along substantially the entire length of the channel so as to seal along its entire edge. Each shingle may comprise more than one sealing member positioned in the channel or channels. The seal member may be formed of a resilient material, such as rubber or another polymer. The use of a resilient material allows the seal member to deform when contacted by the overlapping surface, the deformation forming a more effective sealing contact. The seal may be tubular, such that a cavity within the seal member is provided for more efficient use of material. This also helps to provide a readily-deformable shape leading to an effective sealing contact. A tube shape may be particularly easy to manufacture. Each seal member could comprise a resilient, tubular member, and each overlapping surface could be configured to compress a respective resilient, tubular member against the sealing surface of an adjacent channel when the shingles interconnect to form the covering. The seal member may comprise a plurality of longitudinal ridges extending from an outer surface, the plurality of ridges extending continuously along the length of the seal member. The plurality of ridges may be unitary with the seal member. The plurality of ridges may provide an effective seal contact with an overlapping surface and / or channel. The rigidity of one or more of the shingles may be further increased by pressing a design or motif out of the main, thin sheet part of the shingle. Preferably the design or motive is pressed in a direction away from the underlying waterproofing / structure. Adjacent shingles could alternate between pressed shingles (having the same or different designs or motifs) and unpressed shingles. In this way a customised pattern may be created. The system will typically require a means of fixing the shingles to the (underlying) surface that is to be covered. Although a particularly useful fixing means is described below, this should be regarded as beneficial, but not strictly essential for the aspects of the invention described above. The fixing means is considered advantageous in its own right and may be claimed independently. Additionally, the system may be provided as a kit of parts for covering an underlying structure (e.g., a roof or wall). Each shingle may comprise a plurality of holes extending through the shingle and configured to receive a fastening means. The holes of adjacent shingles may overlie each other, or match-up when the shingles are interconnected (i.e., when their edges overlap as described above). The fastening means may extend through the holes in adjacent shingles to secure them together, and to the underlying structure. In this manner, the shingles can be urged together with a compression force from the fastening means that compresses the seal members, forming a particularly effective sealing joint along the edges of the shingles. This arrangement means that each fastener extends through and secures multiple shingles, and, in total, only one fastener is required per shingle. This is a relatively efficient use of materials as compared to conventional arrangements. One of the plurality of holes on each shingle may be provided within the channel, and one of the plurality of holes may be provided on the overlapping surface (e.g., cap). When the shingles are interconnected the holes of adjacent shingles (one within the channel and the other on an adjacent overlapping surface) may match up, allowing the fastening means to extend through both. Providing holes within the channel and on the overlapping surface in this manner allows the compression force from the fastening means to be applied more directly to the sealing joint, providing a more effective seal. The fixing means may comprise a primary fastener (e.g., screw) configured to be secured to an underlying structure, and a secondary fastener (e.g., screw) configured to extend through the shingle(s) and be secured to the primary fastener. Using such a two-part system provides a means for creating the assembly efficiently in several stages, wherein the primary fastener is secured to the underlying structure, then shingles are overlaid on the first fastener, and then the secondary fastener is secured to the primary fastener through the holes in the shingles. Various advantages of this system will become apparent from the detailed description below. In one embodiment, the primary fastener comprises a threaded screw having a head, a shank, and a threaded hole formed in the head. The secondary fastener comprises a threaded screw having a head and a shank, the shank configured to be received in the threaded hole in the head of the primary fastener. This provides for an easy assembly, and one wherein the secondary fastener is also easily removable without removing the primary fastener from the underlying structure, e.g. for repair or replacement of the shingles. The head of the primary fastener may comprise an upper surface and a lower surface, the shank extending from the lower surface, wherein the lower surface is planar around the shank and configured to abut a surface of the underlying structure. By providing a planar lower surface, there is formed a ‘compression stop’ with the underlying structure. When the primary fastener is secured to the underlying structure, for example with a power tool, the device will only insert up to the end of the shank, because the planar surface will interact with the surface of the underlying structure to prevent the device being inserted further. The primary fastener is typically secured to the underlying structure so that substantially all of the shank is within the underlying structure (and any membrane, if present), and substantially all of the head is above the underlying structure. The effect of the compression stop is that each primary fastener can be quickly and easily secured, and such that the heads extend above the underlying surface by a common distance, allowing for the inclusion of a flexible seal, compressed to a predetermined amount. The further components assembled on top of the primary fasteners will, therefore, be level, providing a more effective covering by equal compression of the seals between adjacent shingles. The system may further comprise a plurality of spacers configured to extend between the shingles and the underlying surface, wherein each spacer forms a cap that can be positioned over a respective one of the primary fasteners, once it is secured to the underlying surface. Each spacer may comprise a crown and a wall portion extending down from the crown, wherein the crown comprises a hole configured to receive a respective secondary fastener. The spacer may be assembled with the annular wall portion surrounding the primary fastener when this is attached to the underlying structure, with the secondary fastener extending upwards through the hole in the crown of the spacer. The crown comprises a planar upper surface around the hole that is configured to support the first and / or the second shingles when they are laid thereon. The spacer may provide an increased clearance between the underlying structure and the overlaid shingles. The clearance between the structure and shingles aids airflow, which reduces potentially damaging effects of moisture on the underlying structure and the covering. The wall portion of the spacer may be annular, although this is not essential and it could be formed from multiple portions. The hole in the spacer is configured to receive the secondary fastener, so that the secondary fastener may be secured to the primary fastener whilst the spacer is positioned over the primary fastener. The spacer may, therefore, be assembled after the primary fastener is secured to the underlying structure, and before the shingles are overlaid. This provides a particularly easy means of assembly. The spacer may comprise at least one vent extending through the wall thereof. The vent allows air and trapped moisture to escape the spacer, which avoids damage that may be caused by the moisture, as mentioned above. The system may further comprise an annular seal formed from a resilient material, to be fitted to the primary fastener. The head of the primary fastener comprises a lip located around an upper surface of the head. The annular seal is configured to sit between the lip and the surface of the structure to which the primary fastener is secured, such that the seal can be compressed against the underlying surface by the lip when the primary fastener is secured to the structure. This forms a particularly effective seal between the primary fastener and the underlying structure to prevent moisture ingress into the structure. The primary fastener may define a cut-out between the lip and the lower surface of the head, and the annular seal may be configured to fit within this cut-out. The cut-out may further comprise a channel formed therein, which channel is configured as a space into which the seal may deform under compression, to prevent buckling of the seal. The system may comprise a plurality of washers for positioning between each lip and respective seal, such that each lip bears against a washer which, in turn, bears against a respective seal to compress it against the underlying structure. The washer may comprise an annular ring to be inserted around the head of the primary fastener. The washer may provide a more effective and even distribution of compression force from the lip to the seal. The system may further comprise a plurality of annular seals configured to fit around the shank of each secondary fastener, and between the head of the each secondary fastener and an outer surface of the shingles. The head of the secondary fasteners may be configured to bear against each annular seal to compress and deform the seal into the outer surface, thereby providing a seal around the holes through which the secondary fasteners are secured to the shingles. Sealing at this location limits water ingress from outside the covering assembly to under the shingles and hence the membrane over the underlying roof structure. The system may further comprise a plurality of washers, each configured to fit around the shank of a secondary fastener between the head of the secondary fastener and the annular seal. In this arrangement, the head of the secondary fastener is configured to bear against the washer, which in turn compresses the seal against the outer surface. The washers may each comprise an annular wall portion configured to extend downwards and encompass a respective annular seal. The annular wall portion may be configured to contact the outer surface when installed, in addition to compressing the seal. This configuration of washer provides some protection of the annular seals that are located around the secondary fasteners, which would otherwise be exposed to weather forces which may damage the seal, for example UV radiation from sunlight. In a further aspect of the present invention, there is provided an assembly which comprises the system described above, the plurality of shingles comprising at least a first shingle and a second adjacent shingles (or multiple pairs of first and second adjacent shingles), each having a plurality of holes formed therethrough, wherein the overlapping surface of the second shingle overlies the channel of the first shingle and contacts the seal member within the channel of the first shingle, as aforesaid. The first and second shingles may comprise any combination of the features described above. The first and second shingles may comprise different combinations of features. The assembly further comprises a fixing means as described above, that is each fixing means comprising a primary fastener configured to be secured to an underlying structure, and a secondary fastener secured to the primary fastener, the secondary fastener extending through both a hole within a channel of the first shingle and a hole on an overlapping surface of the second shingle, and fastened so as to bring the second shingle into bearing engagement with the first shingle, as well as to press the overlapping surface of the second shingle against the seal member located within the channel of the first shingle. The fixing means may comprise any of the features described above, including the spacer, annular seals and washers, and features or combinations of features described in relation thereto. In a further aspect of the present invention, there is provided a method of installing the system or assembly described above. The method comprises securing the shingles in successive rows across the underlying structure. A first row of shingles may be fitted to the structure, wherein one side of the row of shingles forms an edge of the covering. An adjacent row of shingles may then be fitted along the other side of the row of shingles. This process may continue for further rows of shingles such that successive rows are secured across the structure. Of course, the shingles could be fitted in various ways, and not necessarily in successive rows. The method comprises the step of securing a plurality of the primary fasteners to the underlying structure. All or most of the primary fasteners may be secured to the underlying structure to form a grid pattern of primary fasteners to which the rows of shingles (and other components) of the system can be assembled. The plurality of spacers can be press-fitted onto the primary fasteners once they are secured to the structure. This step may be completed concurrently with the attachment of the primary fasteners. A first shingle may be overlaid onto the primary fasteners, or spacers if present. A secondary fastener can then be secured to one of the primary fasteners through a hole of the first shingle to hold the shingle in place. A second shingle may then be overlaid on the primary fasteners and (partially) over the first shingle such that they interconnect (as described above). A secondary fastener can then be secured to one of the plurality of primary fasteners through both of the first and second shingles, such that the second shingle is secured to both the underlying structure and to the first shingle. Using the second fastener in this manner brings the second shingle into bearing engagement with the first shingle, and presses the surface of the second shingle against the seal member located within the channel of the first shingle. The method provides an effective means for assembling a covering for an underlying structure, and which ensures a consistent installation of the fixation means and shingles. According to an aspect of the invention there is provided a method of manufacturing the shingles as described herein. The method may be used to manufacture any aspects and embodiments of the shingles as described herein. One particular method that is part of the invention is to manufacture the shingles from sheet material stock (e.g., sheet metal), such as a single layer sheet material. This method would involve bending and / or pressing the sheet material to form the channel(s) and cap(s) as described herein. A design (e.g., motif) could be pressed into the thin sheet part of the shingle between the edges as described above. This method may also comprise cutting the sheet material stock, for example a first cutting process could cut the sheet material into individual shingle precursors. One or more second cutting processes could cut more intricate features into each shingle (e.g., after bending / pressing processes), such as the holes that receive fasteners, or edge features, etc. Another method that is part of the invention is to manufacture the shingles using an additive manufacturing technique (e.g., 3-D printing). This could be used for example where more complex shingles (e.g., having curved geometries) are to be manufactured. This method could involve additively manufacturing each shingle using any suitable technique known in the art, such as a 3-D printer, including the thin sheet part as well as the more complex channel(s) and cap(s) as described herein. Generally, therefore, the present invention relates to the use of shingles that are rigid, plate-like members (which could be flat or curved), and which have features along and around (and restricted to) the edges of the plate to allow them to interconnect with each other. In other words, there are no interconnecting or sealing features (or other complex geometrical features) in the area of the shingle between the edges. This maximises rigidity in an economical manner, in that the large, main sheet area between the edges is substantially planar. BRIEF DESCRIPTION OF THE DRAWINGS Various embodiments of the invention are described in detail herein, and with reference to the following figures. Fig. 1 shows a system for covering a roof or wall using a plurality of tessellated, interconnecting and overlapping shingles, according to the invention. Fig. 2 shows a system for covering a roof or wall using a plurality of tessellated, interconnecting and overlapping shingles, according to another embodiment of the invention. Fig. 3 shows a shingle from the embodiment of Fig. 1. Fig. 4 shows a sectioned view of Fig. 3. Figs. 5 and 6 show a partial cross-sectional view of a first and second shingle according to the embodiment of Fig. 1. Fig. 7 and 8 show a partial cross-sectional view of another embodiment of a first and second shingle according to the embodiment of Fig. 1. Fig. 9 shows a cross sectional view of a fixing according to the embodiment of Fig. 1. Fig. 10 shows a perspective cross sectional view of the fixing of Fig. 9. Figs. 11 to 16 show views of the embodiment of Fig. 1 in partially installed states. Figs. 17 to 19 show different types of structure and shingle arrangements, demonstrating the versatility of the system. Fig. 20 shows a shingle according to another embodiment of the invention. Fig. 21 shows a shingle according to another embodiment of the invention. Fig. 22 shows a shingle according to another embodiment of the invention. Fig. 23 shows a system for covering a roof or wall using the shingles of the embodiments of Figs. 20, 21 and 22. DETAILED DESCRIPTION OF THE DRAWINGS Fig. 1 shows a system 2a for covering a structure (e.g., roof or wall), comprising a plurality of shingles 4, and a fixing means 12. The shingles 4 are secured to an underlying structure, for example through a waterproof membrane (not shown) and by the fixing means 12. Each shingle 4 is secured to an adjacent shingle 4 by the fixing means 12. The shingles 4 are interconnected along edges 8 thereof to create a joint along the edges. In the example shown, the plurality of shingles 4 are arranged in rows 6a, 6b, and the shingles 4 are secured to adjacent shingles 4 in the same row 6a and adjacent shingles 4 in the adjacent row 6b. In the embodiment shown, the plurality of shingles 4 comprise substantially the same features as one another. The shingles 4 are rectangular, each comprising four edges 8 and four vertices 10, and the plurality of fixation means 12 are arranged at vertices 10 of each of the shingles 4. Each shingle 4 comprises a substantially thin, rigid sheet material forming the main central part, such that between its edges 8 the shingle 4 defines a substantially planar surface (although minor indentations such as a motif 5 could be pressed into this, as described herein), wherein at its edges 8 the shingle 4 is slightly deformed to provide interconnecting and overlapping features (described in more detail below). Fig. 2 shows another assembly of a similar system 2b, but with an alternative tessellation. This assembly 2b also comprises rectangular shingles 4 arranged in rows 6a, 6b, and secured and sealed to adjacent other shingles 4 at edges thereof. In the embodiment of Fig. 2, however, shingles in adjacent rows are offset by half of a width of a shingle, so that vertices 10 of shingles 4 in each row are positioned halfway along edges 8 of adjacent shingles 4 on adjacent rows. A fixing means 12 is provided at the vertex 10 of each shingle 4. It will be appreciated that various other shapes of shingle and tessellations may be provided, as noted above in the summary section of the invention. Figs. 3 and 4 show one of the shingles 4 according to the embodiment of Fig. 1. The shingle 4 comprises an outer surface 14, which is configured to face outwardly from an underlying structure for exposure to weather forces, and an inner surface 16 which is opposed to the outer surface 14 and is configured to face the underlying structure. The shingle 4 thereby defines an inner direction, extending away from the inner surface 16, and an outer direction 14 extending away from the outer surface 14. In the example shown, the shingle 4 forms a generally planar or flat shape. However, as noted previously other shapes of shingle may be used. The shingle 4 may comprise an embossment 5 formed on the outer surface 14 thereof. The shingle 4 comprises a number of edges 8. In the example shown, since the shingle 4 is rectangular there are four edges 8, including a first edge 8a and a second edge 8b which respectively oppose a third edge 8c and a fourth edge 8d. As best show in Fig. 4, the edges 8 comprise either a channel 18 sunk into the edge, or a raised cap 20. In the example shown, the first and second edges 8a, 8b each form a respective channel 18, and the third and fourth edges 8c, 8d each form a respective cap 20. The channels 18 and the caps 20 each extend along substantially the whole of their respective edges 8, and have substantially constant cross-sectional shapes. In the embodiment shown, the channels 18 of the first and second edges 8a, 8b meet at a vertex 10 of the first and second edges 8a, 8b so as to form a continuous channel extending along both the first and second edges 8a, 8b and around the vertex 10. Similarly, the caps 20 of the third and fourth edges 8c, 8d meet at a vertex 10 of the third and fourth edges 8c, 8d, so as to form a continuous cap extending along both the third and fourth edges 8c, 8d and around the vertex 10. In other embodiments, the channels 18 and caps 20 of each edge 8 could be separate rather than continuous. Where they meet, the channels and the caps are separated and form a gap 22 at each respective vertex 10. The channels 18, as best seen in Fig. 4, each form a recessed portion at the edge of the shingle 4. That is, the channels comprise an inwardly recessed shape relative to the outer surface 14 of the shingle 4 at the edges 8 thereof. In the example shown, the channels 18 each form a ‘U’ shaped recession. The ‘U’ shape comprises a base 26 and first and second walls 24, 28 extending therefrom. The first and second walls 24, 26 extend generally perpendicular to the outer surface 14. The base 26 extends substantially parallel to the outer surface 14. The caps 20 each form a raised portion of the shingle 4. That is, the caps 20 are formed by an outwardly raised projection or flange 30 at the edges 8 of each shingle 4. In the example shown, the caps 20 each form an inverted ‘U’ shape, or ‘IT, (i.e., inverted relative to the channels 18) formed by a top 32 and first and second walls 30, 34 extending therefrom. The first and second walls 30, 34 extend generally perpendicular to the outer surface 14. The top 32 extends substantially parallel to the outer surface 14. The channels 18 of each shingle 4 are shaped to cooperate and interact with caps 20 of an adjacent shingle to secure and seal the shingles 4 to each other. Figs. 5 and 6 are partial views showing an interaction between a first shingle 4a and an adjacent second shingle 4b. Each of the shingles 4a, 4b is generally as described above, and the partial view of Figs. 5 and 6 shows a channel 18 of the first shingle 4a and a cap 20 of the second shingle 4b. The first shingle 4a comprises a seal member 36a which is positioned and held within the channel 18. The seal 36a is an elongated member which extends along the channel. In some embodiments, the seal 36a extends along a whole length of the channel 18. The seal 36a is substantially constant in cross section along the channel 18. In the example shown, the seal 36a has a circular, ring shaped cross-section so as to form a tubular shape along a length of the seal 36a. The seal 36a thereby forms a cylindrical cavity 38a, which is substantially empty during and after installation of the shingles 4a, 4b. The cavity 38a may be open at lengthwise ends of the seal 36 to allow pressure equalisation of the cavity 38a with the exterior of the seal 36a. The seal 36a is formed of a resilient material, and the material and shape of the seal 36a are such that it can be deformed under an applied force. Fig. 6 shows the interaction between the first shingle 4a and the adjacent second shingle 4b during and after installation of the shingles 4a, 4b. The cap 20 is positioned to overlap with (e.g., cap) the channel 18. The second wall 34 of the cap 20 contacts the seal, and deforms the seal 36a under an applied force (the means of applying force is described below). The seal 36a deforms and thereby increases the contact area between the seal 36a and the channel 18, and also increases the contact area of the seal 36a with the cap 20. By increasing the contact area in this manner, the deformable seal 36a provides a sealing contact with both the channel 18 and the cap 20, and provides a seal between the first shingle 4a and the second shingle 4b at the edges 8 thereof. Fig. 7 and 8 are partial views which show an interaction between a first shingle 4a and an adjacent, separate second shingle 4b in a further embodiment. The embodiment is as described above, except comprising a different seal member 36b. The seal member 36b comprises a non-circular ring shaped cross section and forms a prism shape along a length of the seal 36b. The non-circular ring defines a cavity 38b which may be generally as described in relation to the embodiment of Figs. 5 and 6. The seal 36b comprises a cross-section with one or more ridges 40, which extend from an outer surface 42 of the seal 36b in a direction away from the cavity 38b. The ridges 40 extend along the length of the seal 36b. In the example shown, there are three ridges 40. The ridges 40 are unitary with the seal 36b. The seal 36b and ridges 40 are formed of the same resilient material, and are deformable under pressure. Fig. 8 shows the interaction between the channel 18 of the first shingle 4a and the cap 20 of the adjacent second shingle 4b, which is largely the same as that described in relation to the embodiment of Fig. 6. The seal 36b and ridges 40 deform under applied pressure from the cap 20. The ridges 40 may form a particularly effective line seal against the cap 20. However, it should be noted that the cylindrical seal 36a shown and described with respect to Figs. 5 and 6 would be easier to manufacture and install. For example, it does not require a specific orientation prior to being inserted within the channel. Returning to Figs. 3 and 4, the shingle 4 comprises a first hole 44a and a second hole 44b each configured to receive a fixing means. Each of the first hole 44a and the second hole 44b extend through the shingle from the outer surface 14 to the inner surface 16. In the embodiment shown, the first hole is located at the vertex 10 where the first and second edges 8a, 8b meet, and is within the channel 18 formed along the edges 8a, 8b. The first hole 44a is formed in the base 26 of the channel 18. The second hole 44b is located at the vertex 10 where the third and fourth edges 8c, 8d meet, and is formed on the top 32 of the cap 20. As described above in relation of Figs. 5 to 8, when in use, the shingle 4 is arranged next to an adjacent shingle such that the cap 20 of one shingle overlies and caps the channel 18 of the adjacent shingle. The cap 20 and channel 18 are positioned to overlap such that the hole 44a in the channel 18 aligns with the hole 44b in the cap. A fixing means is then used to apply a pressure to bring the cap 20 and channel 18 together and deform the seal 36 therein. An exemplary fixing means is described below. In the example shown, each shingle 4 comprises one first hole 44a formed in a channel 18 at a vertex 10, and one second hole 44b formed in a cap at a vertex 10. Other shingle arrangements (see, e.g., Fig. 2) may use a different number of holes as required. Figs. 9 and 10 show a detailed view of an exemplary fixing means 12 for securing shingles 4a, 4b to one another and to an underlying structure 46. The shingles 4a, 4b in the embodiment shown are largely as described in relation to Figs. 1 to 6. The fixing means 12 comprises a primary fastener 50, which is secured to the underlying structure 46, for example through a membrane 48 which covers the underlying structure 46. The fixing means 12 also comprises a secondary fastener 52 which passes through the holes 44a, 44b of the shingles, 4a, 4b and secures the shingles 4a, 4b to the primary fastener 50. The primary fastener 50 and the secondary fastener 52 are coaxial along an axis X, defined in the direction between the shingle 4a and the underlying structure 46, and intersecting a centre of the holes 44a, 44b. In the embodiment shown, the primary fastener 50 is a threaded screw which is configured for screwing into the underlying structure 46. The primary fastener 50 comprises a threaded shank 54 extending from a head 56. The threaded shank 54 extends into the underlying structure. The head 56 comprises an upper surface 58 and a lower surface 60, the threaded shank 54 extending from the lower surface 60. The lower surface 60 around the threaded shank 54 is planar, and is configured to contact the surface to be covered. The planar portion of the lower surface 60 circumscribes the threaded shank 54. The lower surface 60 thereby comprises a large, flat contact area which forms a compression stop. The contact area of the lower surface 60 and the membrane 48 is such that the primary fastener 50 cannot be inserted into the underlying structure 46 beyond the lower surface, such that during and after installation, the head 56 remains wholly above the surface to be covered. In the embodiment shown, the upper surface 58 is planar, and defines a plane parallel to that of the lower surface 60. The fixing means 12 may further comprise a primary washer 64 and a primary seal 66. The primary fastener 50 defines a longitudinal axis X along its shank 54. The washer 64 and the seal 66 are each an annular ring defined around the axis X such that they both circumscribe the head 56 of the primary fastener 50. The head 56 comprises a lip 62 formed around the upper surface 58 thereof, such that a cut-out 68 is formed in the head 56 below the lip 62. The lip 62 comprises a surface 70 configured to contact the washer 64. The seal 66 is positioned axially between and in contact with the washer 64 and the membrane 48. The washer 64 is positioned axially between and in contact with the seal 66 and the head 56. The seal 66 comprises a resilient material, for example rubber, so as to be deformable under pressure. Before the fixing means 12 is assembled, the seal and washer 66, 64 have a combined axial dimension which is slightly greater than a distance defined between the surface 70 of the lip 62 and the lower surface 60 of the head 56. As such, when the fixing means 12 is in place, the surface 70 of the lip 62 bears against the washer 64 so as to compress the seal 66 against the membrane 48. The resilient seal 66 deforms under compression, and forms a sealing contact between the seal 66 and the membrane 48. In the embodiment shown, the head 56 further comprises an annular recess 72 formed within the cut-out 68. The annular recess 72 provides space into which the seal 66 can deform, to avoid damage to the seal 66 from the compression or buckling of the seal 66 which could otherwise compromise the sealing contact with the membrane 48. The upper surface 58 of the head 56 comprises a means for receiving the secondary fastener 52. In the embodiment shown, the means is a threaded hole 74 and the secondary fastener 52 is a threaded screw. The secondary fastener 52 comprises a head 94 and a threaded shank 96 extending from the head 94. The threaded shank 96 is configured to be screwed into the threaded hole 74 of the primary fastener 50 to secure the secondary fastener 52 to the primary fastener 50. In the embodiment shown, the fixing means 12 also comprises a spacer 76, as best shown in Fig. 10. The spacer 76 comprises a hollow annular wall 78 defined about the axis X, and a crown 80, the crown 80 comprising an upper surface 82. The wall 78 extends downwards from the crown 80 to a lower surface 84. The spacer 76 is positioned on the membrane 48 adjacent to the underlying structure 46, such that the lower surface 84 contacts the membrane 48. The shingles 4a, 4b are positioned on top of the spacer 76 so that the inner surface 16 of each of the shingles 4a, 4b, contacts the upper surface 82 of the spacer 76. The spacer 76 thereby serves to separate the shingles 4a, 4b from the membrane 48 at a precise axial distance, equal to the separation between the upper and lower surfaces 82, 84 of the spacer 76. The annular wall 80 of the spacer 76 is sized to have a greater radius than that of the head 56 of the primary fastener 50, as well as the washer 64 and the seal 66, so that the spacer 76 fits around the primary fastener 50 and its associated parts. In the embodiment shown, the annular wall 80 has a radius sized such that the spacer 76 may be press-fit onto the seal 66. The lower surface 84 of the spacer 76 thereby circumscribes the primary fastener 50. The spacer 76 comprises a hole 86 through the crown 80, through which the secondary fix fastener 52 may extend, so as to be secured to the primary fastener 50. In the embodiment shown, the spacer 76 comprises vents 88 extending through the wall 80 to prevent a build-up of moisture within the spacer 76. The vents 88 may each extend from the lower surface 84 of the spacer 76, and partially but not wholly up the wall 80. As described above, the secondary fastener 52 passes through holes 44a, 44b formed in the shingles 4a, 4b, and secures to the primary fastener 50. The fixing device 12 further comprises a secondary washer 90 and a secondary seal 92, which are annular rings formed about the axis X. The washer 90 and the seal 92 circumscribe the shank 96 of the secondary fastener 52. The washer 90 and seal 92 are both positioned between the head 94 of the secondary fastener 94 and the outer surface 14 of the shingles 4a, 4b. The washer 90 is positioned, at least in part, between the head 94 and the seal 92. The seal 92 is positioned between the washer 90 and the outer surfaces 14 of the shingles. The head 94 of the secondary fastener 52 comprises a planar, inwardly facing surface 98, which bears against the washer 90 during and after installation. The secondary fastener 52 thereby provides a compression force against the washer 90 and the seal 92 to press the washer 90 and seal 92 towards the outer surfaces 14 of the shingles 4a, 4b. The seal 92 thereby provides a sealing contact with the outer surfaces 14 around the hole 44a. In the embodiment shown, the washer 90 has an annular wall 100 which extends downwards and around the seal 92, and contacts the outer surfaces 14 of the shingles 4a, 4b. The washer 90 thereby provides some protection of the seal 92 from exposure to weather forces. The wall 100 may end in a bent or curved portion 102 to provide a more even contact with the outer surfaces 14 of the shingles 4a, 4b. Figs. 11 to 16 show an exemplary method of fitting a plurality of shingles 4 to an underlying structure (e.g. with or without membrane 48) using the system described above. In a first step, a plurality of primary fasteners 50 are secured to the underlying structure, and through the membrane 48 (if one is provided). This step may include positioning a primary seal 64 and washer 66 with the primary fastener 50 in the manner described above. The primary fasteners 50 may be secured with a powered tool configured to apply a constant torque value to the primary fastener 50. The (optional) application of constant torque, in combination with the compression stop formed by the head 56 of each primary fastener 50, ensures that each head 56 extends above the membrane 48 by the same distance. In a second step, a plurality of spacers 76 are placed in a press-fit over the primary fasteners 50. In the embodiments shown in Figs. 11 to 16, the first shingle 4a will comprise an edge that also forms an edge of the covering. Two of the four spacers with which the first shingle 4a interacts may comprise an element 77 extending upwardly from the upper surfaces 82 of the spacers 76a. The element 77 is shaped to fit with the cap 20 of the shingle 4a, to support the shingle along a lower edge. The element 77 is provided as there is no shingle underlying the lower edge of the first shingle 4a (and no channel or seal on which the lower edge may rest). In a third step, a first shingle 4a is placed on top of the plurality of spacers 76. The shingle 4a is aligned so that the axial hole 86 of each spacer 76 is aligned with one of the holes 44a, 44b formed in a channel 18 and cap 20, or with one of the gaps 22 separating a channel 18 and a cap 20 as appropriate. In a fourth step, a secondary fastener 52 is secured to a primary fastener 50 through the hole 44b in the cap 20. A secondary seal 92 and washer 90 may be positioned on the secondary fastener 52 as outlined above. In a fifth step, a second shingle 4b is overlaid onto the first shingle 4a to provisionally interconnect therewith. The cap 20 of the second shingle 4b overlies or caps the channel 18 and seal (not shown) of the first shingle 4a. The second shingle 4b is positioned adjacent to the first shingle 4a and in the same row therewith. A secondary fastener 52 is secured through the hole 44b of the second shingle 4b, and through a gap 22 of the first shingle 4a, onto a primary fastener 50 so as to complete the sealing joint between the adjacent shingles 4a, 4b. Subsequently, a further shingle 4 may be fitted in the same row adjacent to the second shingle 4b, and so forth with further shingles 4 until the row of shingles is completed. In a sixth step (see Fig. 15), a third shingle 4c is overlaid onto the first shingle 4a, in an upper row which is adjacent to the row comprising the first shingle 4a and second shingle 4b. A cap 20 of the third shingle 4c overlies the channel 18 and seal (not shown) of the first shingle 4a, and provisionally interconnects therewith. A secondary fastener 52 is secured through the hole 44b of the third shingle 4c, and through a gap 22 of the first shingle 4a, onto a primary fastener 50 so as to complete the sealing joint between the adjacent shingles 4b, 4c. In a seventh step, a fourth shingle 4d is overlaid onto the second shingle 4b and the third shingle 4c. A cap 20 of the fourth shingle 4d overlies the channels 18 and seals (not shown) of both of the second and third shingles 4b, 4c. A secondary fastener 52 is secured through the hole 44b of the fourth shingle 4d, as well as through gaps 22 of each of the third shingle 4c and the second shingle 4b, and through a hole 44a in the channel 18 of the first shingle 4a, then onto a primary fastener 50 so as to complete the sealing joint between the adjacent shingles 4c, 4d. Subsequently, further adjacent shingles 4 may be fitted in the same row adjacent to the fourth shingle 4d until the row of shingles is completed. A further row may then be added above and adjacent to the row of the third and fourth shingles 4c, 4d, and so forth until the system 20a is completed and cover the underlying surface. It should be understood that particular steps such as fitting the primary fasteners 50, fitting the spacers 76, and completing the rows of shingles 4 may be partially performed, for example subsequently to other steps where possible. In other words, not all of the primary fasteners 50 etc. have to be secured before the shingles and other components of the system 20a begin to be laid down. As noted above, the system may be used to provide a covering for curved or irregular structures. By way of example, alternative structures that could be covered using the system are shown in Figs. 17 to 19. These demonstrate the capability of the various shingles 2 and fixing means 12 described above to cover a structure that is not simply flat, e.g., is curved or irregular. As shown in Fig. 17, a system 200 may be formed from planar shingles 202 which are connected at edges 204 to adjacent shingles. The shingles 202 are arranged at angles to adjacent shingles, so that planes defined by the outer surfaces 206 of the shingles 202 are at angles to one another. In the example shown, each of the shingles 202 forms the same shape with the same number of edges 204 to each shingle 202. The shingles 202 thereby form a regular tessellation. As shown in Fig. 18, a system 300 may be formed from planar shingles 302 which are connected at edges 304 to adjacent shingles. As in the previous example, outer surfaces 306 of the shingles 302 are arranged at angles to those of adjacent other shingles. In this example, several different shapes of shingles 302 are used to form the covering structure, having a different number of edges 304. As shown in Fig. 19, a system 400 may be formed from non-planar, curved shingles 402, which are connected to one another at curved edges 404. The overall system 400 therefore forms a covering having a curved outer surface. In the example shown, the shingles are curved and comprise constant radii of curvature. The degree of curvature is the same across the whole covering. In other embodiments, the shingles may have non-constant radii of curvature, so that the curvature of the covering system changes across the outer surface. Fig. 20 shows another embodiment of a shingle 504, which may form part of a covering system. The shingle 504 has a regular hexagonal shape, with six edges 508a, 508b, 508c, 508d, 508e, 508f of the same length. Three of the edges 508a, 508b, 508c each comprise a cap 520a, 520b, 520c, and three of the edges 508d, 508e, 508f each comprise a channel 518d, 518e, 518f, where the caps 520a, 520b, 520c and channels 518d, 518e, 518f are similar to those described in relation to previous embodiments. A seal member (not shown) may be positioned within each of the channels 518d, 518e, 518f, which could take the form of any of those described in relation to previous embodiments. In the illustrated embodiment, the three edges 508a, 508b, 508c comprising caps 520a, 520b, 520c are on one geometric half of the shingle 504 (such that the caps extend around three consecutive edges), and the three edges 508d, 508e, 508f comprising channels 518d, 518e, 518f are on an opposed geometric half of the shingle 504 (such that the channels extend around three consecutive edges). In other embodiments, the three edges comprising caps may be non-consecutive, e.g. each edge comprising a cap may be adjoined by two edges comprising channels. Vertices 510a, 510b are formed at meeting points of edges 508a, 508b, 508c (which each comprise a cap 520a, 520b, 520c), which two vertices 510a, 510b each comprise holes 586 for receiving fasteners (these holes may be generally as described in relation to previous embodiments). Two further vertices 51 Od, 51 Oe are formed at meeting points of edges 508d, 508e, 508f (which each comprise a channel 518d, 518e, 518f), and two further vertices 510c, 51 Of are formed at meeting points of edges 508a, 508c (which each comprise a channel 520a, 520c) and edges 508d, 508f (which each comprise a cap 518d, 518f). These four vertices 510c, 510d, 510e, 51 Of each comprise a gap 522. As will be appreciated, the holes 586 and gaps 522 match up in a manner similar to those described in relation to previous embodiments. That is, a secondary fastener may be secured through the hole of a first shingle, and through a gap of an adjacent shingle, for example onto a primary fastener so as to complete the sealing joint between adjacent shingles. The shingle 504 may comprise a decorative embossment 505 on an outerfacing surface 516. Fig. 21 shows an end shingle 604 for the covering system that may be combined with the shingle 504 shown in Fig. 20, as well as the shingles described in previous embodiments. The shingle 604 is configured to cooperate with the shingle 504 of Fig. 20 to allow it to form an end edge of a hexagonal region of the covering system, and optionally link with different shingles, such as those of the previous embodiments (see Fig. 23). The region of the covering system that predominantly comprises hexagonal shingles may be configured to have straight edges using the shingle shown in Fig. 21. This could be for transitioning between a hexagonal region of the covering system (with a generally hexagonal tessellation) to a rectangular region of the covering system (with a generally rectangular tessellation, as shown in Fig. 23 and described in more detail below. These embodiments generally show how the covering system may transition from a first region having a first tessellation to a second region having a second, different tessellation. The transition shingle 604 comprises three edges 608a, 608b, 608c, such that the shingle 604 forms an isosceles triangular shape with a first, longer edge 608a, and a second edge 608b and third edge 608c which are the same length as each other, and both shorter than the first edge 608a. The first edge 608a of the transition shingle 604 comprises a channel 618, and the second and third edges 608b, 608c each comprise a cap 620. A first hole 686 is formed at a vertex where the second and third edges 608b, 608c meet, and a second hole 686 is formed halfway along the first edge 608a. Gaps 622 are formed where the first edge 608a meets each of the second and third edges 608b, 608c. The end shingle 604 may also comprise a decorative embossment 605 formed on an outer surface 616. A second transition shingle 704 is shown in Fig. 22. The second transition shingle 704 is similar to that shown in Fig. 21, but with a different configuration of channels, caps, holes and gaps. That is, the second transition shingle 704 comprises similar first edge 708a, second edge 708b and third edge 708c, wherein the first edge 708a comprises a cap 720 and the second and third edges 708b, 708c each comprise a channel 718. A hole 786 is formed halfway along the first edge 708a. Three vertices 710 are formed at meeting points of the edges 708a, 708b, 708c, each vertex 710 comprising a gap 722. In both the transition shingles 604, 704, the caps, channels, holes and gaps are similar to those described in previous embodiments. Fig. 23 shows an example covering system 500 comprising hexagonal shingles 504 (as shown in Fig. 20), in combination with first transition shingles 604 (as shown in Fig. 21) along the top, and second transition shingles 704 (as shown in Fig. 22) along the bottom. The covering system further comprises rectangular shingles 4 generally as described in relation to Figs. 1 to 16. All of the shingles are tessellated (as defined herein), and joined at respective edges such that, at each edge, a cap of one shingle is overlaying a channel of an adjacent shingle. A plurality of fixation means are provided to join the shingles together, in the manner described above. The arrangement of triangular transition shingles 604, 704 in this embodiment provides a transition between a hexagonal tessellated region 500a, defined between lines A and B, a first rectangular tessellated region 500b defined above line A, and a second rectangular tessellated region 500c defined below line B. The first transition shingles 604 are configured to tessellate with hexagonal shingles 504 at the geometric half of the hexagonal shingles 504 with edges that each comprise a channel, and the second transition shingles 704 are configured to tessellate with hexagonal shingles 504 at the other (opposite) geometric half, where the edges each comprise a cap. The covering system 500 may be used for covering an underlying surface having a varying curvature. For example, the hexagonal tessellated region 500a between the lines A and B may be generally flat, to cover a flat section of underlying surface, for example a vertical wall. The rectangular tessellated region 500b above the line A may have a curvature, for example a convex curvature, to cover a curved section of underlying surface. The second rectangular tessellated region 500c below the line B may also have a curvature, for example a concave curvature, for covering a differently curved section of underlying surface.

Claims

19 07 245 1. A fixing means for securing a component to an underlying structure,the fixing means comprising:a fastener comprising a head and a shank extending from the head, the head comprising an upper surface, a lower surface and a lip, the shank extending from the lower surface, the lower surface being planar and configured to contact a10 surface to be covered; anda seal forming an annular ring circumscribing the head of the fastener, the seal comprising a resilient material configured to deform under compression from a surface of the lip of the fastener so as to compress against the surface to be covered.

152. The fixing means of claim 1,wherein the fastener is a threaded screw configured for screwing into an underlying structure, the shank comprising a threaded shank.20 3. The fixing means of claim 1 or 2,further comprising a washer, the washer forming an annular ring circumscribing the head of the fastener, the washer positioned axially between and in contact with the seal and the head, the surface of the lip configured to bear against the washer so as to compress the seal.

254. The fixing means of claim 3,wherein the shank extends from the lower surface to define an axis of the fastener and, before the fixing means is in place, the seal and washer have acombined axial dimension which is greater than a distance defined between the surface of the lip and the lower surface of the head.19 07 245. The fixing means of any preceding claim,5 wherein the resilient material of the seal is rubber.

6. The fixing means of any preceding claim,wherein the head comprises an annular recess, the annular recess providing a space into which the seal is configured to deform.

107. The fixing means of any preceding claim,further comprising a secondary fastener, the upper surface of thehead of the fastener comprising a means for receiving the secondary fastener.15 8. The fixing means of claim 7,wherein the means for receiving the secondary fastener is a threaded hole, the secondary fastener comprises a head and a threaded shank extending from the head, and the threaded shank is configured to be screwed into the threaded hole of the fastener.

209. The fixing means of any preceding claim,wherein the means further comprises a spacer, the spacer comprising a crown with a planar upper surface configured to be contacted by a lower surface of a component and an annular wall extending from the crown, the annular wall sized25 such that the spacer fits around the fastener.

10. The fixing means of claim 7 or 8,19 07 24wherein the means further comprises a spacer, the spacer comprising a crown with a planar upper surface configured to be contacted by a lower surface of a component and an annular wall extending from the crown, the annular wall sized such that the spacer fits around the fastener, wherein crown comprises a hole5 configured to receive the secondary fastener.

11. The fixing means of claim 10,further comprising a secondary seal forming an annular ring circumscribing a head of the secondary fastener and configured to be positioned10 between the head and an outer surface of the component, the head comprising a planar surface configured to provide a compression force against the secondary seal.

12. The fixing means of claim 11,further comprising a secondary washer forming an annular ring15 circumscribing the head of the secondary fastener and configured to be positioned at least in part between the head and the secondary seal, the planar surface of the head configured to bear against the secondary washer so as to provide the compression force against the secondary seal.20 13. The fixing means of claim 12,wherein the secondary washer comprises an annular wall which extends downwards and around the seal and is configured to contact the outer surface of the component.25 14. The fixing means of claim 13,wherein the wall of the secondary washer ends in a bent or curved portion configured to contact the outer surface of the component.19 07 2415. The fixing means of any of claims 9 to 14, wherein the annular wall of the spacer is sized such that the spacer may be press-fit onto the seal.5 16. The fixing means of any of claims 9 to 15,wherein the spacer comprises vents extending through the annularwall.

17. The fixing means of claim 16,10 wherein the vents each extend from a lower surface of the spacerpartially up the annular wall.

18. A method of installing a fixing means for securing a component to an underlying structure, the method comprising the steps of:15 positioning a seal with a fastener, the fastener comprising a head anda shank extending from the head, the head comprising an upper surface, a planar lower surface and a lip, the seal forming an annular ring circumscribing the head of the fastener; andsecuring the fastener to the underlying structure so that the shank is20 within the underlying structure and a surface of the lip of the fastener compresses the seal, the seal deforming under compression against a surface to be covered to form a sealing contact, wherein the step of securing the fastener to the underlying structure includes contacting the planar lower surface with the surface to be covered such that the head remains wholly above the surface to be covered throughout the25 step.

19. The method of claim 18,19 07 24further comprising the step of providing a membrane over the underlying structure, the membrane forming the surface to be covered, wherein the seal forms a sealing contact with the membrane upon securing the fastener to the underlying structure.

520. The method of claim 18 or 19,wherein the step of securing the fastener includes using a powered tool to apply a constant torque to the primary fastener to secure the fastener to the underlying structure.1021. The method of any of claims 18 to 20, further comprising the step of press-fitting a spacer over the fastener.

22. The method of claim 21,15 further comprising the step of overlaying a component onto the spacerso that an upper surface of the spacer contacts a lower surface of the component.

23. The method of claim 22,further comprising the step of securing a secondary fastener to the20 fastener through a hole in the component and a hole in the spacer.

Images