Fixing system

Abstract

A system for employment in building construction for the fixing of cladding elements to structural elements providing a strong, irreversible, or temporary attachment, said cladding elements being made in a variety of cross-sectional shapes with two or more parallel, linear channels moulded into their undersides, orientated parallel to their longitudinal axes and in spaced arrangement across the width of said cladding elements, the width, depth and transverse cross-sectional shaping of said channels being such as to accommodate and engage accurately with engagement elements of complementary attachment devices fixed to or formed on elongated supporting strips, said supporting strips being fixed to said structural elements, said attachment devices being regularly positioned on said supporting strips so as to register with the positions of said linear channels.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application is a Section 371 National Stage Application of International Application No. PCT / AU2023 / 000004, filed May 10, 2023, and published as WO 2024 / 207044 A1 on Oct. 10, 2024, not in English, which claims priority to and the benefit of Australian Patent Application No. 2023900989, filed Apr. 4, 2023, the contents of which are incorporated herein by reference in their entireties.FIELD OF THE INVENTION

[0002] This invention relates generally to methods of fixing planks, boards, siding, strip tiling and the like to structural elements during building construction.BACKGROUND

[0003] In architecture, planks, boards, siding, tiling and the like of a variety of cross-sectional shapings are employed to provide floors, surfaces to decking, exterior coverings to buildings and roofing. Roofing takes the form of discrete tiles, slates and the like or, not uncommonly, strips of tiling giving the appearance of discrete tiles or slates.

[0004] Planks and boards for decking and the exterior cladding of buildings have been made from natural timber, treated timber, laminated timber (including bamboo), proprietary wood-plastic composites (WPC), aluminium, unplasticised (rigid) polyvinyl chloride (uPVC), foamed PVC and, with suitable fillers, re-cycled high-density polyethylene (HDPE), polystyrene (PS) and polyethylene terephthalate (PET). Similarly, in addition to natural materials, roofing tiles are now commonly made from metals, polymers and polymer-composites. uPVC and foamed PVC are particularly suitable materials for the making of decking planks, planks and boards for exterior cladding, siding and tiling. It has excellent mechanical strength, may be treated to resist deterioration due to solar exposure and manufactured in an inexhaustible range of shapes and sizes. It is inexpensive, more or less maintenance-free and fire-resistant, having a service life of around 50 years. It may be provided in a wide range of colours, either by adding pigment to the PVC or by co-extruding a capping layer of a UV-stable, colourfast polymer around the exterior surfaces of a profile. Such polymers as acrylonitrile styrene acrylate (ASA) are commonly used as a capping layer. PVC may also be provided in a variety of surface finishes (including wood-graining), or wire brushing to achieve a non-slip surface. Importantly, PVC is 100 per cent recyclable, does not warp, is easily cut, drilled and machined and, unlike many polymers, is fire-resistant. Synthesised from chlorine (derived from sea salt) and ethylene, uPVC is effectively self-extinguishing, merely charring and contributing nothing to the combustion process.

[0005] In traditional methods of building construction, attached elements, such as flooring, decking planks, cladding and siding, and structural members, such as joists, rafters, purlins and wall studs were usually of timber or metal, the various elements being fixed together in the conventional way using nails, screws or, sometimes in the case of metal, rivets.

[0006] Subsequently, and commencing with decking, a variety of attachment methods were developed to allow planks to be fixed in place with no visible fastenings. The simplest of these is the device known colloquially as a ‘biscuit clip’. A biscuit clip is a small, stiff plate made from a variety of materials in a variety of proprietary shapes and having a central aperture to accommodate a fixing screw. Suitably shaped and spaced local recesses or linear channels are provided in each side face of decking planks and the lower surfaces of the recesses or channels of adjacent planks are engaged by laterally-extending edge parts of the biscuit clips. Fixing screws passing through the central apertures of the biscuit clips are screwed into the supporting joists, thereby urging the decking planks into contact with the joists. The fixing screws are tightened by a suitable narrow tool able to be accommodated in the spaces between adjacent planks. It has always been normal to allow a suitable spacing, typically in the range 3 to 6 millimetres, between decking planks to permit rain to drain away and to allow for expansion and contraction of the planks with changes in the weather.

[0007] Advent of the biscuit clip inspired more complex fixing methods, of which the following are typical. The Deck Board Fastener Methods taught by Brigham et al in US 2019 / 0112802 include use of a clip having a bottom and a removable top insert, the bottom being made from a material different from that of the top; the clip having a generally T shape in a side view with a central bore passing through the top member and the bottom member to receive a screw or other fastening member, and a plurality of apertures through the top surface of the bottom member that engage the top member; the body of the bottom member having a transverse planar upper member and at least one perpendicularly positioned planar lower member or keel; the deck board fastener optionally having a lip that projects upward from the upper surface of the transverse planar member, the lip being able to be positioned about an exterior edge of the transverse planar member or along the upper surface.

[0008] In the Hidden Clip for Decking taught by Demuth et al in US 2022 / 0220748, a plurality of clips can be provided in a strip, individual strips being separated by a frangible section or tab located between adjacent clips, each strip able to be provided with a hand grip portion removably attached to a proximal-most hidden clip in the strip of clips; an aperture defined in each hidden clip able to include an offset cylindrical section that causes a fastener to pivot from a vertical alignment when the fastener is driven into a joist.

[0009] The Clip and Clip Installation Apparatus taught by Chapman et al in WO2023012625 relates (not exclusively) to a decking board clip for securing decking boards to a support structure and apparatuses for installing decking board clips; the clips comprising a body having an inner part made of a first material and an outer part made of a second material, the body having a first and second retaining formations, the first retaining formation being resiliently moveable between an engaged position in which it engages in a groove of a decking board to provide a bias onto part of the groove and a disengaged position wherein it is not engaged inside the groove of the decking board and extends freely from the body, the body also having a receiving formation for receiving a fastener to fasten the clip to a support.

[0010] The Decking Clip and Heating for a Decking Board taught by Pendrill in GB2599153 is intended particularly for use with metal decking boards and comprises a first portion at a first edge of the clip shaped for clamping a foot of a decking board and preventing the release of the board, a second portion positioned at a second edge of the clip and shaped differently to the first portion for receiving a decking board by a sliding fit, and a central portion preferably comprising a hole to receive a screw; the first and second portions being preferably operable to receive a foot via a snapping fit, the first portion being able to comprise a wing with a hooked end and the second portion an unhooked open end; the first and second wings preferably extending away from the central portion and forming an obtuse angle with the central portion; a metallic decking board and a method of heating a metallic decking board structure also being claimed.

[0011] The Decking Clip and Decking Assembly Comprising a Decking Clip taught by White in WO2022002980 comprises a first decking panel, a second decking panel adjacent the first decking panel, a clip comprising a base and a retaining portion, wherein the retaining portion cooperates with the first decking panel to affix the clip thereto, the base projecting from the first decking panel to engage the second decking panel and, the base defining a fastener opening for receiving a fastener to secure the first and second decking panels to an underlying substrate.

[0012] The Decking Fastener Assembly taught by Shadbolt in AU2022203537 is broadly directed to an assembly comprising: a base mounting adapted for fixing to a support member such as a floor joist and a plurality of pivoting clips pivotally mounted to the base mounting at predetermined spacings along a strip, the pivoting clips being equally-spaced at a distance slightly greater than the width of a decking board to be placed between an adjacent pair of pivoting clips; the fastener assembly being designed whereby placement of the decking board between the adjacent pair of pivoting clips effects pivotal movement of at least one of the clips into engagement with the decking board to anchor it to the base mounting between the adjacent pair of pivoting clips.

[0013] The Decking Clip taught by Sachs in U.S. Pat. No. 5,997,209 takes the form of a fastener for timber decking, fences, pallets and the like and comprises a joist attachment plate with one or more fastening apertures therein, one or more spacing flanges locatable between joists and planks, a plank spacer extending between adjacent planks and axially aligned plank engaging teeth extending from opposed sides of the plank spacer to engage respective side surfaces of adjacent planks.

[0014] The Decking Clip taught by Tebo in US 2018 / 0127973 is directed to a single-sided deck clip that allows an approach to deck board installation with hidden fasteners, and without grooving both edges of a deck board, the non-requirement for edge grooving allowing a perimeter trim to optionally include one square finished edge on ending pieces; the single-sided clip allowing for attaching fasteners through the clip at an angle that penetrates both a deck board and an underlying joist, thereby providing a positive connection of decking to joist framing below; in another embodiment, a clip magazine being disclosed that stores, supplies, and assists in installation of single-sided deck clips and fasteners, the clip magazine being able to hold a plurality fasteners and single-sided deck clips, the magazine allowing the single-sided clips and fasteners to be positioned relative to the deck board, and fasteners to be aligned with a single-sided clip, and pushed into a deck board during installation.

[0015] In the Snap Fitting Building Components taught by Richardson in AU2019201162, a linear spacing rail for use in fixing decking boards to joists and weather boards to studs has a series of projections which engage the sides of the boards in order to space them accurately and snap fit them to the joists or studs, a method of constructing a deck and the side of a building being described.

[0016] The Deck Module Including Quick Clip Module taught by Lee in US 2019 / 0249376 includes deck panels having a plate shape extending in a first direction and having deck grooves formed in both side surfaces thereof in the first direction, a bottom structure disposed on lower portions of the deck panels in a second direction crossing the first direction, and quick clip modules connected to a side surface of the bottom structure wherein the quick clip modules comprise quick clip bases extending in the second direction; quick clip protrusions protruding from the quick clip bases in a third direction orthogonal to the first direction and the second direction and having protrusion portions formed at ends of the quick clip protrusions to protrude in the second direction and correspond to the deck grooves, and quick clip supports protruding from the quick clip protrusions in the first direction.

[0017] In the Attachment System for Decking and Siding taught by Mackenzie in US 2021 / 0131121 includes hold-down devices for attaching deck boards to deck support structures and attachment devices for mounting siding boards to wall structures; hold-down devices being attached to deck support structures by horizontally-extending fasteners and attaching the deck boards to the deck support structures without fasteners, providing paths for water to pass through the deck boards into the support structures; deck board engagement members of the hold-down device extending into slots in deck boards, siding board attachment devices being mounted on upright surfaces of wall structures using horizontally extending fasteners, siding boards being mounted with a standoff distance providing ventilation space behind and between siding boards.

[0018] In the Improvements in or Relating to Decking taught by Roberts in GB2586465, a clip includes two body portions-one body portion having a fastener area for having a fastener surface and receiving a fastener part for attaching the clip to a decking frame, the other body portion including a locking part; in use the fastener area and the locking part are separated such that the fastener area is exposed once the locking part is fitted into the decking board, the clip optionally having two locking portions one above the other in the form of barbs; also claimed is a deck board including a pair of surfaces and an installation profile between the surfaces, the installation profile including a locking portion for preventing movement of a clip away from the decking; further claimed is an assembly comprising the clip and the decking.

[0019] The Decking Clip taught by Doupe et al in US 2018 / 0238060 allows a plurality of decking members to be attached relative to a support assembly, the decking clip including an elongate plastic body strip having a body length, the body provided with a number of openings to receive fasteners there through to attach the body relative to the support assembly; a number of upstands being spaced over the body length and extending substantially perpendicularly from the body strip, substantially transversely to the body length; each upstand having at least two opposed decking board engagement arms, a first decking board engagement arm extending from a first lateral side of each upstand at an acute angle and a second decking board engagement arm extending from a second lateral side of each upstand at an acute angle, each upstand and / or engagement arm being resiliently deformable to allow portion of a decking board to pass and to retain the decking board relative to the support assembly in a spaced apart, non-overlapping configuration.

[0020] The Decking Clip taught by Doupe et al in AU2018253529 allows a plurality of decking members to be attached relative to a support assembly, the decking clip including an elongate plastic body strip having a body length, the body provided with a number of openings to receive fasteners therethrough to attach the body relative to the support assembly, a number of upstands spaced over the body length and extending substantially perpendicularly from the body strip, substantially transversely to the body length, each upstand having at least two opposed decking board engagement arms, a first decking board engagement arm extending from a first lateral side of the upstand at an acute angle and a second decking board engagement arm extending from a second lateral side of the upstand at an acute angle, at least two centering members, at least one centering member extending from the first lateral side of the upstand between the first decking board engagement arm and the body strip and at least one centering member extending from the second lateral side of the upstand between the second decking board engagement arm and the body strip, each upstand and / or engagement arm being resiliently deformable to allow a portion of a decking board to pass and to retain the decking board relative to the support assembly in a spaced apart, non-overlapping configuration.

[0021] The Step Clip Fastening System and Method taught by Schneider in US 2022 / 0136254 provides a method of assembling a deck board, the method comprising the steps of fastening the step clip fastening device onto a joist by using a plurality of fastening tools; sliding a first end of the deck board into an inner cavity of a step clip attached at a first end of the step clip fastening device; and snapping a second end of the deck board into an inner cavity of a corresponding step clip facing the step clip attached at the first end of the step clip fastening device to form a mating relationship between the deck board and the step clip fastening device.

[0022] In the Thermory decking system supplied by the Finnish company, Keila Ehituspood, two parallel, longitudinally-arranged channels are machined from end to end in the under surfaces of decking planks, the channels being located inwardly of the plank edges. Each channel is of approximately square cross-sectional shape, orientated such that an oblique axis (corner to corner) is vertically orientated with an opening of reduced width extending to the plank lower surface. Planks are secured in place by engagement of the lower, oblique surfaces of the channels by the downwardly-directed, free edges of angled, elastic, polymer sprags, the sprags being forced up through the openings of reduced width. The sprags are supported at their upper edges by upstanding elements fixed to supporting joists and extending up into the channels. The lower ends of the upstanding elements are joined by polymer elements to create a strip, somewhat similar to that employed by Doupe et al in the cited prior art examples.

[0023] Perusal of the cited prior art examples shows that, in the majority of cases, discrete fixing elements are employed to grip the lower surfaces of longitudinally-arranged recesses formed in the side surfaces of decking planks, the fixing elements being urged against supporting joists by means of conventional fastenings. The fastenings are tightened using a suitable tool passing through the aperture between adjacent planks. The use of discrete elements of the types claimed and the need to fasten each in place is fiddly work that is wasteful of labour. The zone immediately beneath the fixing elements is frequently damp and, with time, may experience dry rot around the fastenings. The fixing method is clearly inappropriate for the edge planks in a deck. In many cases, the gaps between planks permit the fixing elements to be clearly visible, which is aesthetically displeasing. The prior art inventions disclosed in US 2019 / 0112802, US 2022 / 0220748, WO 2023 / 012625, GB 2599153, WO 2022 / 002980 and GB 2586465 fall into this category.

[0024] The prior art invention disclosed in US 2021 / 0131121 is somewhat similar to those mentioned in the immediately proceeding, employing a metal clip that engages narrow channels formed in adjacent plank edges, the clip being secured in place by a short strap extending down the side of a joist with its lower end nailed to the joist. Use of the metal clip is not as convenient as the fixing elements of the prior art inventions previously mentioned, the fastenings of which can be accessed from above. The narrow channels act as water traps and may encourage dry rot. Similarly, the fixing method is inappropriate for the edge planks in a deck. In the prior art invention disclosed in AU 2019 / 201162, decking boards and moulded boards are fixed, respectively, to joists and studs by the snap-fit engagement of shaped projections forming part of polymer strips fixed to the joists and studs with moulded edges of the decking and moulded boards. As the strength of the mechanical attachment so achieved is not high, the use of adhesive and nailing is apparently expected. Similarly, this fixing method is inappropriate for the edge planks in a deck. The invention is apparently intended to be only a temporary fixing system and is therefore of limited utility. The prior art invention disclosed in U.S. Pat. No. 10,487,460 has an operating principle similar to that disclosed in AU 2019 / 201162 (shaped, projecting elements forced into engagement with the shaped edges of decking planks), except that the homologous quick clip protrusions and their supporting base are made of metal. To prevent rusting of the protrusions and base and the consequent deterioration of timber in contact with them, the metal components would require either an anti-corrosion coating or construction in a non-corrodible material. The protrusions and base are complex in arrangement and therefore expensive to manufacture. Correct alignment and fixing of the supporting base to joists is a time-consuming function requiring skills. Similarly, this fixing method is inappropriate for the edge planks in a deck. The prior art invention disclosed in AU 2022203537 utilises pivoting clips to secure decking boards to supporting joists. The clips, which are injection moulded and incorporated into a mounting strip of the same material are complex, requiring costly injection moulding dies for their production. The pivoting clips are quite delicate and liable to contact damage. Similarly, this fixing method is inappropriate for the edge planks in a deck. The mounting strip is somewhat similar in arrangement to that taught by Doupe et al in US 2018 / 0238060 and AU 2018253529.

[0025] The prior art invention disclosed in AU 2018253529 and US 2018 / 0238060 utilises decking clips to secure decking boards to joists. The decking clips are supported from regularly-spaced upstands formed integrally with a plastic body strip which is fixed to joists. The decking clips extend downwardly at an acute angle from the upper ends of the upstands and are resiliently deformable. Pressure is applied to decking boards to force them down over the decking clips which engage recesses formed in the side surfaces of the boards, thereby retaining them in place. The invention requires costly dies for its production. The decking clips are ineffective in restraining boards from longitudinal displacement. Similarly, this fixing method is inappropriate for the edge planks in a deck. The prior art invention disclosed in US 2022 / 0136254 secures decking boards to joists by means of a plurality of regularly-spaced, upstanding, resilient step clips formed on an elongated, polymer base strip. With the base strips fixed to joists, a recess formed in one side surface of a decking board is engaged with projecting edges of step clips and pressure is applied to elastically displace opposing step clips, allowing the board to be displaced downwardly and permitting projecting edges of those step clips to engage a recess formed in the opposite edge of the decking board, thereby securing the board in place. Costly dies are required for production of the invention. Similarly, this fixing method is clearly inappropriate for the edge planks in a deck. The base strip is somewhat similar in arrangement to that taught by Doupe et al in US 2018 / 0238060 and AU 2018253529.

[0026] Decking planks formed by extrusion from materials such as aluminium, wood-plastic composites and polymers offer a significant advantage in that they are able to be provided during manufacturing with shapings employed to engage complementary fixing devices.SUMMARY

[0027] An exemplary aspect of the present disclosure relates to a system offering a variety of building element fixing applications in building construction; a system in which the components have a low cost; a system that provides a strong, irreversible, or temporary attachment of building elements; a system in which all building elements are extruded or injection-moulded, allowing production using low-cost tooling; a system that positively inhibits longitudinal displacement of fixed building elements; a system that can be employed to fix building elements up to the edge of a structure; a system that does not promote dry rot in associated wooden building elements; and a system which confers ease of assembly of building elements.

[0028] During building construction, elongated cladding elements, in the form of planks or boards for the building of decking, siding for the cladding of buildings, strip tiling or the like are fixed to elongated structural elements, in the form of joists, rafters, purlins, wall studs and the like. According to the present invention, cladding elements and, where appropriate, structural elements are extruded from a suitable thermoplastic or settable material. As appropriate, cladding and structural elements are made in a variety of cross-sectional shapes, optionally with internal voids to reduce weight without compromising stiffness and beam strength of the finished item. Depending upon its face width, each cladding element is made with two or more parallel, linear channels moulded into its underside, the axes of the channels being orientated parallel to the longitudinal axes of the cladding elements, positioning of the channels across the width of a cladding element being such as to provide for its secure attachment, the width, depth and transverse cross-sectional shaping of the channels being such as to accommodate and engage accurately with complementary attachment devices fixed to structural elements, but without compromising the stiffness and beam strength of the cladding elements. The attachment devices are fixed to or formed on elongated supporting strips, regularly positioned on the strips so as to register with the linear channels of cladding elements to be fixed to them. The attachment devices are orientated normal to the longitudinal axes of the strips, the strips being fixed to structural elements by appropriate conventional means with their centrelines collinear with those of the structural elements and with the attachment devices of all parallel structural elements in a structure being aligned with planes passing through and normal to the structural elements. The strips are optionally of sufficient width to completely cover the structural elements, thereby ensuring that their vulnerable, normally-exposed faces of wooden structural elements remain dry. In the preferred embodiment, an attachment device comprises two parallel, elastic panels provided either with projecting engagement elements on their exterior surfaces to engage complementary elements on the interior surfaces of a linear channel, or projecting engagement elements on their interior surfaces to engage complementary elements on the exterior surfaces of a fixing panel of suitable thickness fixed to the inner end of a linear channels and collinear with the channel centreline. Fixing panels are made with sufficient length to extend more or less throughout the depth of linear channels, the width of linear channels being increased, as appropriate, to accommodate fixing panels and parallel elastic panels. The complementary engagement elements formed on the abutting faces of linear channels and attachment devices optionally take a variety of cross-sectional shapings, ranging from square or rectangular, through negative or minimally-angled ratchet teeth to sharply-angled ratchet teeth. Where ratchet teeth are used, they may be of a regular size or regularly graduated in size over the length of an attachment device. Depending upon the character of building elements to be joined, the engagement elements may have a projecting (engagement length) as small as 0.5 millimetre or as large as 10 millimetres. The space between pairs of elastic panels of attachment devices, the elasticity of the panels and the width of linear channels are made such that, during penetration by attachment devices of linear channels, engagement elements are able elastically ride over one another, the engagement elements engaging fully and irreversibly as the free ends of the elastic panels abut the inner ends of the linear channels. Wherever possible, one or more wedging surfaces, wedges or tongues are provided formed on the inner ends of linear channels and positioned on or parallel to the longitudinal axis of a channel. The width and degree of taper of the wedges or tongues is such that, with the free ends of the elastic panels abutting the inner ends of the linear channels, the wedges or tongues act to urge the complementary engagement elements into a position of full engagement and to maintain that position. Wedging contact of the wedges or tongues with the elastic panels further acts to inhibit any tendency towards linear displacement of attachment devices within linear channels, thereby inhibiting any resultant tendency of fixed cladding elements to be displaced longitudinally. Cladding elements are fixed to structural elements by positioning them such as to allow entry of the attachment devices into the linear channels, pressure then being applied to the cladding elements to cause the attachment devices to fully penetrate the channels with their complementary shapes engaged. Provision is made to accurately join elongated strips of supporting material end-to-end in ways that ensure maintenance of centre-line collinearity. It will be readily understood that the present invention permits cladding elements to be fixed in place right up to the edge of a structure.BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The various aspects of the present invention will be more readily understood by reference to the following description of preferred embodiments given in relation to the accompanying drawings, in which:

[0030] FIG. 1 is a fragmentary, isometric view of an extruded board or plank of the present invention;

[0031] FIG. 2 is a transverse, cross-sectional view of the board or plank of FIG. 1;

[0032] FIG. 3 is a fragmentary, transverse, cross-sectional view of a linear fixing channel of the present invention, being generally as depicted in the zone defined as B in FIG. 2;

[0033] FIG. 4 is an isometric view of attachment devices of the present invention made integrally with an elongated strip of supporting material;

[0034] FIG. 5 is a face view of the attachment devices and elongated strip of supporting material of FIG. 4;

[0035] FIG. 6 is a side view of the attachment devices and elongated strip of supporting material of FIG. 4;

[0036] FIG. 7 is a fragmentary, cross-sectional view of an attachment device of the present invention, being generally as depicted in the zone defined as A in FIG. 6;

[0037] FIG. 8 is a fragmentary, isometric view of the attachment devices and elongated strip of supporting material of FIG. 4 with the extruded board or plank of Figure 1 attached;

[0038] FIG. 9 is a face view of the upper surface of the attachment devices, elongated strip of supporting material and extruded board or plank of FIG. 8;

[0039] FIG. 10 is a side view of the attachment devices, elongated strip of supporting material and extruded board or plank of FIG. 8;

[0040] FIG. 11 is a transverse, cross-sectional view of an alternative embodiment of attachment device of the present invention fixed to a joist;

[0041] FIG. 12 is a fragmentary, transverse, cross-sectional view of an alternative embodiment of linear fixing channel of the present invention;

[0042] FIGS. 13a to 13d are schematic, transverse, cross-sectional views of alternative surface shapings of attachment devices of the present invention;

[0043] FIG. 14 is a fragmentary, transverse, cross-sectional view of an alternative embodiment of attachment device of the present invention, the device depicted as partially entered into a complementary linear fixing channel;

[0044] FIG. 15 is a fragmentary, transverse, cross-sectional view of the attachment device and complementary linear fixing channel of FIG. 14, depicted in their fully engaged situation.DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0045] With reference to FIG. 1, elongated cladding elements in the form of planks or boards for the building of decking, siding for the cladding of buildings, strip tiling or the like and structural elements, in the form of joists, rafters, purlins, wall studs and the like are extruded from a suitable thermoplastic or settable material. Extruded planks and boards are made in a variety of transverse, cross-sectional shapes, of which plain plank 1 is an example. To reduce weight, said planks, boards or the like are optionally made with voids 2, 3, the voids not compromising stiffness and beam strength of the finished item. With additional reference to FIG. 2, depending upon its face width, a cladding element is made with two or more parallel, linear channels 4 moulded into its underside, the axes of the channels being orientated parallel to the longitudinal axes of said cladding element, the positioning of said channels across the width of said cladding element, the width, depth and transverse cross-sectional shaping of said channels being such as to engage accurately with complementary attachment devices fixed to said structural elements and to not compromise the stiffness and beam strength of said cladding element.

[0046] Said cladding elements are fixed to elongated structural elements (joist depicted as 13 in FIG. 11), in the form of joists, rafters, purlins, wall studs and the like. Said structural elements are optionally made from conventional materials or are also extruded in solid, hollow or partially hollow form from a suitable thermoplastic or settable material. With additional reference to FIGS. 4 to 6, attachment devices 5 are fixed to or formed on elongated supporting strips 6 of the same material, said devices being regularly positioned along said strips such as to register with said linear channels of said cladding elements to be fixed to them. Said attachment devices are orientated normal to the longitudinal axes of said supporting strips, said strips being fixed to said structural elements by appropriate conventional means (typical fastening locations indicated as 8) with their centrelines collinear with those of said structural elements and with said attachment devices of all parallel said structural elements in a structure being aligned with planes passing through and normal to said centrelines of said structural elements. Where said structural elements are extruded, said attachment devices are optionally made integrally with them. With additional reference to FIG. 11, where said structural elements are of wood, supporting strips 6 are preferably made wider than said structural elements (joist depicted as 13), thereby protecting said structural elements from moisture-induced deterioration. Where deterioration of said structural elements is not a consideration, apertures 7 are provided in supporting strips 6 to reduce weight and save on materials.

[0047] With reference to FIGS. 3 and 7, in the preferred embodiment, attachment devices 5 comprise two parallel, elastic panels 16 separated by gap 12 and provided on their exterior surfaces with projecting engagement elements 11 adapted to engage with and grip complementary engagement elements 14 provided on the interior surfaces of linear channels 4. Also in the preferred embodiment, elastic panels 16 are either made parallel or divergent with an interior angle in the range 1 to 5 degrees. Similarly, the planes of disposition of engagement elements 14 on the interior surfaces of said linear channels are either made parallel or divergent with depth with an interior angle in the range 1 to 5 degrees. Also in the preferred embodiment, said interior angles of said elastic elements and said linear channels are adjusted such that engagement elements 11 must elastically deflect (skate) over engagement elements 14 as said attachment device penetrates said linear channels. Also in the preferred embodiment, wedges or tongues 15 are provided, formed at the inner ends of said linear channels. Said wedges or tongues are positioned on the centrelines of said linear channels, projecting towards the openings of said linear channels and of a length and degree of taper such as to be able to interact with elastic panels 16. In operation, as said elastic panels approach full penetration of said linear channels, said wedges or tongues enter gaps 12 between said panels, further inward displacement of said panels acting to urge said panels apart, thereby urging engagement elements 11 and 14 into full and irreversible engagement. The wedging engagement of said wedges or tongues between said elastic panels also acts to positively inhibit any tendency towards longitudinal displacement of said linear channels on said attachment devices and, thereby, any longitudinal displacement of attached said cladding elements across said structural elements. Attachment devices 5 are optionally made in metal or polymer materials.

[0048] With additional reference to FIGS. 8 to 10, plank 1 (fragment only depicted) is fixed in place on supporting strip 6 by engagement of linear channels 4 of said plank with attachment devices 5 formed on said supporting strip, said supporting strip being fixed to a structural element (not shown).

[0049] With reference again also to FIGS. 4 and 5, complementary shapings 9, 10 are provided formed in the ends of said supporting strips, engagement of said shapings permitting a plurality of said supporting strips to be joined end-to-end in a way that ensures maintenance of collinearity of the centrelines of said supporting strips. Those skilled in the art will understand that the same effect can be achieved through the use of a variety of such complementary shapings.

[0050] With reference to FIG. 12 and with reference again to FIG. 7, in an alternative embodiment, the width of linear channels 4 of said cladding elements is increased as appropriate to accommodate the entry of elastic panels 16 (as depicted in FIG. 7, but more widely spaced), fixing panels 17 being formed on the inner ends of said linear channels and positioned collinear with their centrelines. Said fixing panels are made with sufficient depth to extend more or less throughout the depth of said linear channels and are provided on both faces with suitable engagement elements 18. The inner surfaces (not shown) of said elastic panels are provided with complementary engagement elements to engage those of said fixing panels. In the preferred embodiment, the width of separation of said elastic panels is such that their engagement elements (not shown) must elastically deflect away from (skate over) engagement elements 18 of said fixing panels as said elastic panels penetrate said linear channels. The side walls of said linear channels are made convergent such that, in operation, as said elastic panels approach the full depth of engagement with said linear channels, said convergent side walls act to urge said elastic panels inwardly, thereby urging their said engagement elements and those of said fixing panels into full and irreversible engagement. In an alternative embodiment, for the same purpose, only the inner parts 19 of said side walls of said linear channels are made convergent with depth. In a further alternative embodiment, said fixing panels are made tapered, increasing in width with depth, and said elastic panels are made divergent with an interior angle more or less equal to the angle of taper of said fixing panels.

[0051] With reference to FIG. 13a and with reference again to FIG. 7, in an alternative embodiment, engagement elements 21 take the form of square or rectangular elements formed on the exterior surfaces of elastic panels 16, said elastic panels optionally diverging towards their free ends with an internal angle in the range 1 degree to 5 degrees; during penetration of said linear channels by said elastic panels, shoes 20 formed on the free ends of said elastic panels and having elongated, curved faces riding over said complementary engagement elements formed in the inner wall surfaces of said linear channels (not shown), said curved shoe surfaces acting to inhibit said square or rectangular engagement elements from engaging said complementary engagement elements; said shoes falling into recesses (not shown) at the inner ends of said linear channels, allowing said elastic panels to be elastically displaced outwardly and, thereby, the engagement of engagement elements 21 with said complementary engagement elements. In another alternative embodiment, said elastic panels are made parallel and, as they approach full penetration of said linear channels, are elastically deflected outwardly by the contact of their free ends with wedges or tongues (depicted as 15 in FIG. 3) provided at the inner ends of said linear channels.

[0052] With reference to FIG. 13b and with reference again to FIG. 7, in another alternative embodiment, engagement elements 22 take the form of ratchet teeth formed on the exterior surfaces of elastic panels 16, said ratchet teeth having an abutting surface normal to the longitudinal axis of said panels and a deflecting surface inclined at 45 degrees to the longitudinal axis of said elastic panels.

[0053] With reference to FIG. 13c and with reference again to FIG. 7, in another alternative embodiment, engagement elements 23 take the form of ratchet teeth formed on the exterior surfaces of elastic panels 16, said ratchet teeth having an abutting surface inclined to the longitudinal axis of said panels at acute angles in the range 85 degrees to 60 degrees and a deflecting surface inclined at 45 degrees to the longitudinal axis of said elastic panels.

[0054] With reference to FIG. 13d and with reference again to FIG. 7, in another alternative embodiment, engagement elements 25 formed on the exterior surfaces of elastic panels 16 take any of the forms described in relation to FIGS. 13a to 13c, the depth of said engagement elements (measured normal to the longitudinal axes of said elastic panels) increasing in a linear way, with elements 25 having the greatest depth positioned at the ends of said elastic panels capable of the greatest degree of elastic deflection and with elements 24 having the least depth positioned at the ends of said elastic panels capable of the least degree of elastic deflection.

[0055] With reference to FIG. 14, in an alternative embodiment, an attachment device 36 comprises two parallel, elastic panels 29 joined to or made integral with elongated supporting strip 6, the ends of said panels remote from said supporting strip being joined by jacking panel 30. Said jacking panel is either joined to said panels or made integral with them. Where said elastic panels are made integral with said supporting strip, they are thinned in zone 32 adjacent said supporting strip to permit flexural displacement of said panels in relation to said supporting strip. Where said jacking panel is made integral with said elastic panels, zone 31 at the junction of the three panels is thinned to permit the independent, flexural displacement of said jacking panel in relation to said elastic panels. Centrally-located zone 33 of said jacking panel is also thinned to permit said jacking panel to straighten permit said jacking panel to straighten from its undeployed, outwardly-projecting, acute-angular disposition. Where said elastic panels are joined to said supporting strip and / or said jacking panel is joined to said elastic panels, said joining means take the form of a simple hinge arrangement (not shown). A plurality of ratchet teeth 26 is formed in the exterior surfaces of said elastic panels, said teeth being orientated such that their abutting surfaces are positioned proximal to said supporting strip and, in the preferred embodiment, normal to the inner surfaces of said elastic panels, their deflecting surfaces being positioned distal to said supporting strip, the angle between said ratchet tooth abutting surfaces and deflecting surfaces being 45 degrees. In alternative embodiments, greater or lesser angles are employed. Also in the preferred embodiment, to facilitate entry of said attachment device into a linear channel 37 of a said cladding element, said elastic panels are made to converge towards said jacking panel, the angle of convergence between the inner faces of said elastic panels falling in the range 5 to 30 degrees. Also in the preferred embodiment, said elastic panels, said jacking panel and said supporting strip are extruded integrally from a suitable, rigidly-elastic, polymer material. In alternative embodiments, said components are made from any suitable material, including metal alloys.

[0056] With additional reference to FIG. 15, cladding elements 1 (typical form depicted in FIGS. 1 and 2) are made with linear channels 37, the depth of said channels being sufficient to fully accommodate the height of attachment device 36 with the two parts of jacking panel 30 on either side of thinned zone 33 collapsed into a straight (two parts collinear) form (as depicted in FIG. 15). In the preferred embodiment, the side walls 28 of said linear channels are made divergent with depth, the internal angle between said side walls falling in the range 10 to 45 degrees. Formed in the inner surfaces of said side walls is a plurality of complementary recesses 27 shaped to receive ratchet teeth 26, said complementary recesses being positioned such that, with said attachment device fully accommodated within a said linear channel and with elastic panels fully displaced outwardly to bring their exterior surfaces into abutment with the interior surfaces of a said linear channel (as depicted in FIG. 15), said ratchet teeth are fully accommodated within said complementary recesses.

[0057] In use, said cladding elements are fixed to said structural elements by positioning them such as to allow entry of said attachment devices into said linear channels, pressure then being applied to said cladding elements to cause their said attachment devices to penetrate said channels. Progressive penetration of a said attachment device into a said linear channel brings said jacking panel in its outwardly-projecting, folded form (as depicted in FIG. 14) into contact with the inner, end surface 34 of said linear channel. Further penetration causes said jacking panel to progressively straighten, thinned zone 33 opening and thinned zones 31 closing, the straightening of said jacking panel acting to displace said elastic panels outwardly, said displacement being accommodated by flexing of thinned zones 32. Finally, with achievement of the situation depicted in FIG. 15, with said jacking panel straight and abutting said inner, end surface of said linear channel and said ratchet teeth fully accommodated in said complementary recesses, said attachment device is positively and irreversibly fixed to said linear channel. The length of said jacking panels in their straightened form is such that elastic panels 29 are urged against the side wall 28 of said linear channel in what is, effectively, an interference fit which inhibits any tendency towards longitudinal displacement of said linear channels on said attachment devices and, thereby, any longitudinal displacement of attached said cladding elements across said structural elements. A said cladding element incorporating said linear channel is thereby restrained against displacement in any direction. Those skilled in the art will understand that the present invention permits said cladding elements to be fixed in place right up to the edge of a structure.

[0058] Also in the preferred embodiment, to facilitate entry of said attachment devices into a linear channel 37 of a said cladding element, the side surfaces of said linear channel adjacent its entry are cut back to create short splays 35, the angular difference between the inner wall surfaces of said linear channel and said splays preferably falling in the range 10 to 30 degrees.

[0059] Those skilled in the art will understand that, in alternative embodiments, the attachment device described in relation to FIGS. 14 and 15 may be made longer, or wider, or with said ratchet teeth of a greater or lesser number, or with said ratchet teeth of smaller, larger or graduated engagement depth, or with said engagement elements having a shaping different from that of said ratchet teeth.

[0060] Depending upon the character of building elements to be joined, said engagement elements of the present invention optionally have a projecting depth (measured normal to the longitudinal axes of said elastic panels) falling in the range 0.5 millimetre to 10 millimetres.

[0061] In a further alternative embodiment, said attachment devices are made double-ended and are employed to join cladding elements edge-to-edge, linear channels of the type described in relation to FIG. 3 being provided in the edges of said cladding elements.

[0062] In an alternative embodiment in which said attachment devices are intended for temporary fixing, said elastic panels are made suitably fragile, such that they break away from a said supporting strip when a moderate separation force is applied. In another alternative embodiment directed at the same application, said engagement elements taking the form of ratchet teeth are modified such that their abutting surfaces (as described in relation to FIGS. 13b to 13d) are made with a reverse inclination, being angled to a small degree towards the free ends of said elastic elements (away from said supporting strips), said reverse inclination causing said engagement elements to disengage from said complementary recesses formed in the inner wall surfaces of said linear channel when a moderate separation force is applied. In the preferred embodiment, the angle of said reverse inclination of said ratchet tooth abutting surfaces falls in the range 1 to 10 degrees, measured between said surfaces and the longitudinal axes of said elastic panels.

[0063] With reference again to FIG. 4, in another alternative embodiment, supporting strips 6 are made in long lengths which are stored in rolls on a drum. A suitable robotic device (not shown) fixes said supporting strips to structural elements such as, for example, the joists of a deck, said robotic device verifying the position of each said attachment device by optically referencing a target strip fixed to one side of the structure. Said robotic device is guided along said supporting element by guiding wheels gripping the sides of said element and propelled by said guiding wheels and / or a drive wheel acting upon the upper surface of said supporting element and having cut-outs to accommodate said attachment devices, said wheels and said drum being driven as required to obtain the correct positioning of each said attachment device.

[0064] The fact that mating or related components are depicted to a variety of scales in the figures hereto is of no significance.

[0065] The present invention should be taken to include any feasible combination of features described herein.

Claims

1-32. (canceled)33. A fixing system for employment in building construction, the fixing system comprising:at least one cladding element, each cladding element comprising two or more parallel, linear channels formed in an underside of the cladding element, said linear channels being orientated parallel to a longitudinal axis of the cladding element and in spaced arrangement across a width of said cladding element such as to provide for secure attachment;at least one elongated supporting strip;a plurality of complementary attachment devices being fixed to or formed on each elongated supporting strip which are, in turn, fixable to and alignable with longitudinal axes of structural elements used in building construction, said attachment devices being regularly positioned on said supporting strip so as to register with a transverse spacing of said linear channels, each of said attachment devices comprising:first and second elastic panels arranged parallel to or divergent from one another and provided on their lateral, exterior surfaces with a plurality of projecting engagement elements in the form of ratchet teeth shaped to engage engagement elements of complementary shaping provided on interior side surfaces of a respective one of said linear channels, said ratchet teeth being distributed along full lengths of said elastic panels and full depth of said linear channel, said first and second elastic panels being separated by a gap sufficient to allow inwards, elastic deflection of the first and second elastic panels as said projecting engagement elements of the elastic panels ride over the engagement elements on the interior side surfaces of the linear channel during penetration of said linear channel by said first and second elastic panels;a transverse, cross-sectional aspect ratio of height to width in a range 2:1 to 2.5:1; each of the first and second elastic panels comprising a length such as to extend throughout the full depth of said linear channel and such that when fully engaged with said linear channel said attachment device completely fills said linear channel, except at said gap, with said projecting engagement elements engaging fully with the engagement elements on the interior side surfaces of the linear channel as ends of said first and second elastic panels abut inner end of said linear channel.

34. The fixing system of claim 33 in which said ratchet teeth of at least one of the first and second elastic panels have:abutting surfaces arranged normal to a plane passing through a longitudinal axis of and bisecting said elastic panel;deflecting surfaces inclined at 45 degrees to said plane; anda depth of engagement, measured normal to said plane falling in a range 0.5 to 10.0 millimeters.

35. The fixing system of claim 33 in which each of said ratchet teeth of at least one of the first and second elastic panels has:an abutting surface inclined to a longitudinal axis of said panel at an acute angle in a range 85 degrees to 60 degrees; anda deflecting surface inclined at 45 degrees to the longitudinal axis of said elastic panel.

36. The fixing system of claim 33 in which said ratchet teeth of at least one of the first and second elastic panels has:a depth of engagement, measured normal to a plane passing through a longitudinal axis of and bisecting said panel, increasing in a linear way, said ratchet teeth having a greatest depth of engagement at an end of said elastic panel that is capable of a greatest degree of elastic deflection and having a least depth of engagement at an end of said elastic panel that is capable of a least degree of elastic deflection.

37. The fixing system of claim 33 in which, where said first and second elastic panels diverge from one another and form an interior angle between said panels in a range of 1.0 to 5.0 degrees.

38. The fixing system of claim 33, wherein at least one of the linear channels comprises one or more wedges or tongues are on the inner end of said linear channel, positioned on or parallel to a longitudinal axis of said linear channel and projecting towards an opening of said linear channel, the one or more wedges or tongues having a length, width and degree of taper such that, with the ends of the first and second elastic panels abutting said inner end of said linear channel, said one or more wedges or tongues act to urge said projecting engagement elements into a position of full engagement with the engagement elements on the interior side surfaces of the linear channel and to maintain said projecting engagement elements in that position; said urging by said one or more wedges or tongues of said first and second elastic panels additionally acting to inhibit any tendency towards displacement of said linear channel on said attachment device.

39. The fixing system of claim 33 in which the spaced arrangement of said linear channels in said at least one cladding element and said attachment devices on said at least one supporting strip allows said cladding element to be fixed in place by positioning the cladding element such that entry of at least one of said attachment devices into at least one of said linear channels can be effected and full penetration of said linear channels with full engagement of said engagement elements achieved, by application of pressure to an outer surface of said cladding element.

40. The fixing system of claim 33 in the at least one elongated supporting strip comprises first and second ends having complementary shapings that enable the at least one elongated supporting strip to be accurately joined end-to-end with at least one other elongated supporting strip whilst ensuring maintenance of center-line collinearity by the engagement of shapings formed on the ends of said supporting strips.

41. The fixing system of claim 33 wherein:said projecting engagement elements take a form of square or rectangular elements formed on the exterior surfaces of said first and second elastic panels;said first and second elastic panels diverge towards their free ends with an internal angle in a range 1 degree to 5 degrees;said first and second elastic panels comprise shoes formed on the free ends of said elastic panels, the shoes having elongated, curved faces which ride over the complementary engagement elements formed in the inner side surfaces of said linear channel, said curved shoe surfaces acting to inhibit said square or rectangular engagement elements from engaging said complementary engagement elements; said shoes falling into recesses at the inner ends of said linear channels at a maximum penetration of the first and second elastic panels in the linear channel, allowing said first and second elastic panels to be elastically displaced outwardly and, thereby, engagement of said complementary engagement elements.

42. The fixing system of claim 33 in which said ratchet teeth of at least one of the first and second panels comprise an abutting surface normal to a longitudinal axis of said elastic panel and a deflecting surface inclined at 45 degrees to the longitudinal axis of said elastic panel.

43. The fixing system of claim 33 in which said ratchet teeth of at least one of the first and second panels comprise an abutting surface inclined to a longitudinal axis of said elastic panel at acute angles in a range 85 degrees to 60 degrees and a deflecting surface inclined at 45 degrees to the longitudinal axis of said elastic panel.

44. The fixing system of claim 33 wherein:said first and second elastic panels are pivotally joined to or made integral with said elongated supporting strip, the ends of said panels remote from said supporting strip being either pivotally joined to or made integral with a jacking panel;junctions of said first and second elastic panels with said jacking panel permit independent displacement of said jacking panel in relation to said first and second elastic panels, a centrally-located zone of said jacking panel being thinned to permit said jacking panel to straighten from an undeployed, outwardly-projecting, acute-angular disposition;said ratchet teeth being orientated such that their abutting surfaces are positioned proximal to said supporting strip and more or less normal to inner surfaces of said elastic panels, their deflecting surfaces being positioned distal to said supporting strip, an angle between said abutting surfaces and deflecting surfaces being 45 degrees;to facilitate entry of said attachment device into said linear channel, said first and second elastic panels converge towards said jacking panel in the undeployed, outwardly-projecting, acute-angular disposition, an angle of convergence between the inner surfaces of said first and second elastic panels falling in a range 5 to 30 degrees; the depth of said linear channel being sufficient to fully accommodate a height of said attachment device with parts of said jacking panel on either side of said centrally-located, thinned zone collapsed such that a axes of the parts are collinear; said side walls of said linear channels being divergent with depth, an internal angle between said side walls falling in a range 10 to 45 degrees, said side wall convergence and positioning of said engagement elements on the interior side surfaces of the linear channel being such that, with said attachment device fully accommodated within said linear channel and with said first and second elastic panels fully displaced outwardly by said jacking panel, said ratchet teeth are fully accommodated within complementary recesses of the engagement elements on the interior side surfaces of the linear channel.

45. The fixing system of claim 44 in which said spacing of said linear channels in said cladding element and said attachment devices on said supporting strip allows said cladding element to be fixed in place by positioning the cladding element such that entry of said attachment device into said linear channel can be effected, pressure being applied to outer surfaces of said cladding elements to cause said attachment device to penetrate said channel, progressive penetration of said attachment device into said linear channel bringing said jacking panel in the outwardly-projecting, acute-angular form into contact with an inner, end surface of said linear channel, additional penetration causing said jacking panel to progressively straighten, the straightening of said jacking panel acting to displace said first and second elastic panels outwardly; full penetration of said attachment device being achieved with said jacking panel straight and abutting said inner, end surface of said linear channel and said ratchet teeth fully accommodated in said complementary recesses, said attachment device being positively and irreversibly fixed to said linear channel, a length of said jacking panel in said straightened form being such that said first and second elastic panels are urged against the interior side surfaces of said linear channel in an interference fit, wherein frictional engagement is achieved inhibiting any tendency towards longitudinal displacement of said linear channel on said attachment device, thereby positively restraining said cladding element.

46. The fixing system of claim 44 in which said first and second elastic panels, said jacking panel and said supporting strip are extruded integrally from a suitable, rigidly-elastic, polymer material.

47. The fixing system of claim 44 in which, to facilitate entry of said attachment device into said linear channel, the interior side surfaces of said linear channel adjacent their entry are cut back to create short splays, and angular difference between the interior side surfaces of said linear channel and said splays falling in a range 10 to 30 degrees.

48. The fixing system of claim 33 further comprising a further attachment device made double-ended and employed to join first and second cladding elements edge-to-edge, said linear channels being provided in edges of said first and second cladding elements.

49. The fixing system of claim 33 in which said attachment devices are intended for temporary fixing, and wherein:attachment points of said first and second elastic panels are made suitably fragile, such that the attachment points break away from said supporting strip when a separation force is applied; orthe ratchet teeth have inclined abutting surfaces with inner ends angled towards said at least one supporting strip, said inclined abutting surfaces causing said projecting engagement elements to disengage from said engagement elements formed in the interior side surfaces of said linear channel when a moderate separation force is applied; wherein an angle inclination of said ratchet teeth abutting surfaces falls in a range 1.0 to 10.0 degrees, measured between said abutting surfaces and planes normal to longitudinal axes of said first and second elastic panels.

50. A fixing system for employment in building construction, the fixing system comprising:at least one cladding element, each cladding element comprising two or more parallel, linear channels formed in an underside of the cladding element, said linear channels being orientated parallel to a longitudinal axis of the cladding element and in spaced arrangement across a width of said cladding element such as to provide for secure attachment, each linear channel comprising a fixing panel which extends from an inner end of the linear channel and is colinear with the linear channel;at least one elongated supporting strip;a plurality of complementary attachment devices being fixed to or formed on each elongated supporting strip which are, in turn, fixable to and alignable with longitudinal axes of structural elements used in building construction, said attachment devices being regularly positioned on said supporting strip so as to register with a transverse spacing of said linear channels, each of said attachment devices comprising:first and second elastic panels arranged parallel to or divergent from one another and provided on their lateral, interior surfaces with a plurality of projecting engagement elements in the form of ratchet teeth shaped to engage engagement elements of complementary shaping provided on lateral surfaces of the fixing panel, said ratchet teeth being distributed along full lengths of said first and second elastic panels and full depth of said fixing panel, said first and second elastic panels being separated by a gap sufficient to allow elastic deflection of the first and second elastic panels as said projecting engagement elements of the elastic panels ride over the engagement elements on the fixing panel during penetration of said linear channel by said first and second elastic panels;a transverse, cross-sectional aspect ratio of height to width in a range 2:1 to 2.5:1; each of the first and second elastic panels comprising a length such as to extend throughout the full depth of said linear channel, with said projecting engagement elements engaging fully with the engagement elements on the fixing panel as ends of said first and second elastic panels abut the inner end of said linear channel.

51. The fixing system of claim 50 in which each of the linear channels comprises side walls, and a whole of or inner parts of said side walls are made convergent such that, in operation, as said first and second elastic panels approach their full depth of engagement with said linear channel, said convergent side walls act to urge said elastic panels inwardly, thereby urging said projecting engagement elements and the complementary engagement elements of said fixing panel into full and irreversible engagement.

52. The fixing system of claim 50 in which said fixing panel is made tapered, increasing in width with depth, and said first and second elastic panels are made divergent with an interior angle more or less equal to an angle of the taper of said fixing panel.

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