GB2448148A

GB2448148A - Method of constructing a building skin, building skin installation and panels for use therein

Info

Publication number: GB2448148A
Application number: GB0706485A
Authority: GB
Inventors: Robert Telfer Mcneil
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-04-03
Filing date: 2007-04-03
Publication date: 2008-10-08
Also published as: GB0706485D0

Abstract

The invention relates to a building skin for a roof or a wall constructed using prefabricated panels 101, 102, 103, 104 comprising rigid steel substrate material (500 figure 5a) with a polyisobutylene (PIB) coating (502 figure 5a). The plurality of panels 101, 102, 103, 104 are of a size and shape to be laid side-by-side to form said skin. Prior to installation, the panels are provided with pliable lap pieces 134, 136, 138 of material along at least two edges of each panel, projecting a distance beyond the substrate along at least one edge. The panels 101, 102 are installed on a supporting structure so that the lap pieces 134, 136 of the two panels 101, 102 overlap. The overlapping pieces are bonded to one another to affect a continuous sealed join between the polymer surfaces of the panels. Bonding may be by heat and/or by low molecular weight PIB self-welding.

Description

METHOD OF CONSTRUCTING A BUILDING SKIN, BUILDING SKIN

INSTALLATION AND PANELS FOR USE THEREIN

The invention relates to methods and component panels for use in installing a building skin, meaning the outer layer of a roof structure or wall.

Various materials are known for providing a weatherproof skin to a building, be it a flat or inclined root or a vertical wall. Functional performance, durability, cost of materials, cost of labour/equipment for installation are all factors in the choice of method and materials. Tiles (shingles) and sheet materials are the common alternatives. Where aesthetic appearance is important, traditional materials may be used, or modern materials adapted to provide the look of traditional materials.

The look of a traditional material, for example a lead sheet roof, is a function not only of the material, but also the way it is shaped and applied to the supporting structure.

Modern sheet materials include bituminous felts, polymer membranes such as PVC and the more modern PIB (polyisobutylene). PIB and other polymers are also available as coatings on rigid substrate materials, such as steel sheeting. The polymer coating provides a barrier to corrosion of the metal, and can also provide an aesthetically pleasing finish. PIB materials can be obtained in various forms for example from the company Flachdach Technologie GmbH, represented in the UK by FDT (UK) Limited, under the trade mark Rhepanol. The PIB coating on the metal can be sealed to the membrane without the use of separate adhesives, either by application of heat from a hot air gun, or by providing a "self-sealing" interface layer of low molecular weight PIB. This self-sealing layer fuses spontaneously with another PIB surface to which it is applied, even at ambient temperature. In a conventional application, PIB-coated metal may be used as the flashing, for example, around a skin of reinforced PIB membrane.

The applicant has devised a novel method of using modern materials such as polymer-coated panels and membranes, which uses panels of polymer-coated substrate, with polymer membrane lap pieces to seal the skin at joins between panels. The novel panel components are pre-fabricated to provide a rapid installation, yet one which can achieve a high integrity, and a high aesthetic quality.

In one embodiment, the finished installation closely resembles a traditional lead sheet roof.

The invention provides a method of constructing a building skin using prefabricated panels of rigid substrate material with a polymer coating, the method comprising: -forming a plurality of panels from a substrate to which a polymer layer has been applied, the panels being of a size and shape to be laid side-by-side to form said skin; -prior to installation, providing said panels with pliable lap pieces of material along at least two edges of each panel and projecting a distance beyond the substrate along at least one edge -installing two panels on a supporting structure with said lap pieces of two panels overlapping; and -bonding the overlapping lap pieces to one another, thereby to effect a continuous sealed join between the polymer surfaces of the panels.

The substrate material may be metal, for example steel.

The polymer coating material may be polyisobutylene (PIB) or a derivative thereof.

The lap pieces may of substantially the same polymer material as the coating on the substrate material. For example, in a preferred embodiment, the panel is of steel coated with PIB, and the lap pieces are ribbons of PIB, of which a part is bonded to the FIB coating. The material of the lap pieces may including reinforcing fibres, while still comprising substantially PIB. Different grades of PIB may be used for the different parts, while remaining compatible. For example, lower molecular weight PIB can be used on the lap pieces to increase pliability and facilitate joining, at the expense of reduced hardness. Very low molecular weight PIB can even be used as a self-sealing surface, which will fuse to another piece of PIB without special application of heat.

One of the said lap pieces may comprise a continuation of the polymer coating beyond the edge of the substrate material. (In a preferred embodiment, this feature provides a third lap piece along an edge orthogonal to the two edges mentioned above.) PIB is used as an example, and other polymer formulations may be suitable for application in the invention, whether known at the present date or to be developed inthefuture.

The step of bonding the lap pieces of neighbouring panels together may be performed by heat fusion or welding. One or both lap pieces may alternatively or in addition be provided with a layer of polymer having molecular weight low enough to permit self-bonding between the overlapping pieces. Alternatively, the bonding may be performed by use of an adhesive, or a liquid version of the same polymer, but this detracts from the simplicity of the installation method which the invention permits.

At least one of said lap pieces may be effectively bonded to an underside of the substrate, notwithstanding that the coating is applied only to a front surface of the substrate material, by providing a hemmed portion along the substrate edge whereby a portion of the coated surface is turned under the panel edge.

The method may further comprise a step of bonding the joined lap pieces to the coating of the adjacent substrate, after the lapping pieces have been bonded together. It is easier to obtain a good seal when joining the pliable lap pieces to one another in the first instance, rather than trying to bond the lap piece directly to coated substrate material.

In a first type of join, a first panel is formed with a first lap piece set back from the edge of the panel and partially bonded to its face while leaving a free edge unbonded, while a second panel is provided with a second lap piece projecting from an edge of the second panel substrate, the edge of the second panel substrate in the finished installation overlying the edge of the first panel substrate, while free edges of the first and second lap pieces lie one over the other for bonding together.

The first type of join may be used where the second panel is mounted above the first panel on an inclined or vertical skin. The overlying of the substrates in that arrangement provides an additional barrier to ingress of water running down the building skin, and provides an aesthetic appearance similar to traditional lead sheet roofing. The lower edge of the second panel may be referred to as the "eaves" edge in that case.

The method may include applying fasteners through the first panel substrate and into the supporting structure prior to installation of the second panel, the fasteners in the finished installation being covered by the overlying portion of the second panel substrate.

In the preferred embodiment of the first type of join, the second panel has a jogged portion toward said lower edge, which can lie over the upper edge of the substrate of the lower panel while the remainder of the upper panel lies flush with the lower panel.

Also in the preferred embodiment of the first type of join, the lapping piece on the second panel edge projects beyond the free edge of the lapping piece on the first panel, the method comprising bonding the free edge of the second lapping piece to the coating of the first panel, after bonding the first and second lapping pieces together.

In a second type of join, a third lap piece projecting from an edge of the first panel overlaps and is bonded to an edge of a third panel, the overlapping lap pieces occupying a gap between the substrates of the first and third panels. The term "third" lap piece is used here to distinguish from the first and second lap pieces of the first type of join, mentioned above, without meaning to imply that both types of join are present in a given embodiment.

The third lap piece may in installation be bonded directly to the coated substrate of the third panel, or else to a fourth lap piece projecting from an edge of the third panel. The third lap piece may comprise a portion of said polymer coating projecting beyond the edge of the panel substrate.

The join may include a substantial gap between the substrates (greater than 20mm, say), or the substrates may be close to abutting (less than 10mm).

The method may further comprise bonding a covering piece to cover the join between the first and third panel substrates.

The cover piece may for example comprise a strip of compatible polymer material on the outside of the bonded lap pieces.

In a preferred embodiment, the cover piece comprises a relatively rigid extrusion of polymer material having a raised architectural profile, with self-sealing polymer material on an underside thereof. As well as protecting the join, the architectural profile of this extrusion can be designed to enhance the aesthetic appearance of the skin, for example to simulate battens or rolls in a traditional lead roofing system.

In a complete skin structure according to the preferred embodiment of the invention, panels are arrayed in a first row on said supporting structure with joins of the second type between adjacent panels in said row, and one or more similar rows of panels are mounted above the first row, with joins between panels of adjacent rows being joins of the first type.

The invention further provides a set of prefabricated panels of a size and shape to be laid side-by-side on a supporting structure to form a building skin, wherein each panel comprises primarily a sheet of rigid substrate material with a polymer coating, further provided with pliable lap pieces bonded to the polymer coating of the rigid panel along at least two edges of each panel and projecting a distance beyond the substrate along at least one edge.

The substrate material may be metal, for example steel.

The lap pieces may be of substantially the same polymer material as the coating on the substrate material. One of the said lap pieces may comprise a portion of said polymer coating projecting beyond the edge of the substrate.

The material of the lap pieces may be selected such that bonding between them can be performed by application of hot air and pressure. One or both lap pieces may alternatively or in addition be provided with a layer of polymer having molecular weight low enough to permit selfbonding between the overlapping pieces.

At least one of said lap pieces may be effectively bonded to an underside of the panel, by providing a hemmed portion along the substrate edge whereby a portion of the coated surface is turned under the panel edge.

Each panel may be formed with a first lap piece set back from a first edge of the panel and partially bonded to its face while leaving a free edge unbonded, and a second lap piece projecting from a second edge of the panel substrate, such that the second edge of the panel may overlie the first edge of a similar panel, while free edges of the first and second lap pieces of the respective panels lie one over the other for bonding together.

In a preferred embodiment the second edge of each panel has a jogged portion, which can lie over the first edge of the substrate of the similar panel while major portions of the panels lie flush with one another.

Also in the preferred embodiment, the lapping piece on the second edge has a free portion substantially wider than a free portion of the lapping piece set back from the first edge.

Whatever the arrangement at the first and second edges, each panel may be further provided with a third lap piece projecting from a third edge orthogonal to the first edge and a fourth lap piece projecting from a fourth edge opposite the first edge, such that two of said panels can be laid side-by-by side with their respective third and fourth lap pieces overlapping while a gap remains between their substrates.

Alternatively each panel may further be provided with a third lap piece projecting from a third edge orthogonal to the first edge, such that two of said panels can be laid side-by-side with the third lap piece of one panel overlying the edge of the coated substrate of the other panel, with a relatively small gap between their substrates.

The first or third lap piece may comprise a portion of said polymer coating projecting beyond the edge of the panel substrate.

The set of panels may be provided in combination with a covering piece or pieces sized to cover the gap between the third and fourth edges of said panel substrates.

In a preferred embodiment, the cover piece comprises a relatively rigid extrusion of polymer material having a raised architectural profile, with self-sealing polymer material on an underside thereof.

The features of the first and second edges and the features of the third and fourth edges mentioned above may be combined in each panel of the set of panels.

The invention yet further provides prefabricated panel for use in forming a building skin, the panel comprising a substantially rigid, rectangular panel of polymer-coated substrate, the panel having along at least two of its four edges a lap piece of pliable material having a free edge for bonding to another panel of the same form, the lap piece along at least a first edge projecting beyond the edge of the substrate and while the lap piece along at least a second edge is set back from the edge of the substrate, the setting back of the second edge lap piece serving to create an overlap between the substrate materials as well as the lap pieces when free edges of the lap pieces of two such panels are lain together.

In one preferred embodiment, first, third and fourth edges have projecting lap pieces while the second edge has the set back lap piece. In another preferred embodiment, first and third edges have projecting lap pieces, while the second edge has the set back lap piece and a fourth edge has no lap piece.

In the preferred embodiments, the substrate of each panel includes a jogged portion along the edge which lies opposite the second edge, the jogged portion having a width sufficient to accommodate the overlapping portion of the adjacent panel's second edge.

In one preferred embodiment at least one of said lap pieces comprises a portion of said polymer coating projecting beyond the edge of the panel substrate. This lap piece in the preferred embodiment is said third lap piece, but it could in principle be any of the lap pieces.

The invention yet further provides a building skin installation comprising an array of panels according to the invention as set forth above, each panel being mounted on a supporting structure with at least one of said lap pieces bonded to a lap piece of an adjacent panel.

The invention yet further provides a building skin installation made by a method according to the invention as set forth above.

The above and other features and advantages of the invention will be apparent from a consideration of the following description of specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, by reference to the accompanying drawings, in which: Fig. 1 represents a roof formed from an array of panels fabricated and assembled in accordance with a first embodiment of the present invention; Fig. 2 is a cut-away diagram of the roof of Fig. 1, showing the principle features of construction in both longitudinal and transverse joints; Fig. 3 is an exploded diagram showing the formation of longitudinal and transverse joints in more detail; Fig. 4 shows in more detail the structure of an extruded cover piece applied to a longitudinal join, where it crosses a transverse joint; Fig. 5 shows in longitudinal cross-section three stages (a) -(c) of the formation of the transverse joint in the embodiment of Figs. 1 to 4; Fig. 6 shows the formation of a longitudinal join in a second embodiment of the invention; and Fig. 7 is a cut-away detail of a transverse joint formed in the second embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 shows in schematic form the roof constructed from an array of panels made of metal (for example, steel) sheet coated with PIB polymer. Where the intention is to simulate a traditional lead sheet roof, the P18 material will have a mid grey colour, and the panels may have width W roughly 0.6 m wide and length L roughly 1.3 m. A larger size panel might be 1.4m wide and 2.5m long. Because it is not corrugated, however, such a large sheet may be difficult to handle unless made of thicker steel than would otherwise be needed. There is no reason why the panels should not be square, or have W greater than L. Four representative panels are labelled 101, 102, 103 and 104, it being understood that, apart from edge features, a rectangular roof can be made from a set of identical panels, of which these four are chosen for the sake of this explanation. In the installation method to be described, a first row of panels 101, 103 etc. are mounted in turn. Each panel is fastened at its upper edge to a supporting structure, not shown in Fig. 1.

Subsequently, a next row of panels, 102, 104 etc. are added, with their lower edges overlapping the tops of the first row of panels by 50mm or more, and covering the fastener heads in the process.

As will be explained in more detail below, longitudinal gaps between the coated metal panels in this installation are bridged by the provision of lap pieces along their long edges, these lap pieces comprising strips of pliable PIB membrane. The strips of neighbouring panels extend approximately 30mm from each panel, so as to overlap and be sealed together, in a manner to be described further below.

Longitudinal cover pieces 110 are fixed along the longitudinal joins. As will be seen later, these cover pieces have a raised profile, providing a robust protection of the membrane join, and contributing aesthetically by mimicking the traditional rolled seams of a lead roof. The transverse joins (between the rows of panels) are of a different form because the metal panels here overlap instead of having a gap between them. These joins are also sealed with lap pieces of pliable PIB membrane, but in a different arrangement, as will be seen below.

Referring to Fig. 2, we see a cut-away section of the roof of Fig. 1, centred on the joins between the four panels 101-104. A supporting structure can be seen, which comprises structural beam 112 overlaid with inner skin 114, vapour barrier 116, a depth of insulation 118 and a breather layer 120. Breather layer 120 and insulation 118 are fastened to deck 114 by fasteners 122. The heads of the fasteners will be covered by the outer skin in the finished installation, and are shown exposed in this cut-away diagram purely for illustration. The particular forms of beam, deck and insulation are relatively conventional, and are shown only as one example of a supporting structure. Concrete or plywood deck material are also acceptable, Separate purlins may be provided running across the supporting beams at intervals, instead of a continuous deck. The structure may be purpose built, or the outer skin may be applied to a pre-existing roof structure, either to restore a failing roof, or simply to improve its aesthetic and/or insulation qualities. The size of the prefabricated panels may be adapted to suit the spacing of beams and purlins in an existing supporting structure.

Referring also now to the exploded detail of Fig.3, each rectangular panel 101 -104 is of the same form and has four straight edges. The main part of each panel is in steel or other metal sheet, coated with a skin of polyisobutylene (PIB). The metal along the side edges and the bottom edge of each panel is hemmed, that is folded over so that the RIB coating extends around the edge of the panel and for a short distance on the underside. Coupled with the overlapping of another panel over the remaining (upper) edge, this avoids exposure of uncoated metal to the elements.

The upper edge could also be hemmed, if desired. The hemmed portion also provides a ready means of bonding polymer strips to the underside of the panel edges, as will be described shortly.

In terms of the language of the claims and introduction of the present specification, edges lOla and 103a represent the first (upper) edge of each panel, edges 102b and 1 04b represent the second (lower or "eaves') edge, the third (right) edge is represented by the edges 1 03c and 1 04c, and the fourth (left) edges by edges 101 d and 102d. The lower edge of each panel includes a jogged" portion, formed by a small step or jog 124, 50mm or so away from the bottom edge. The jogged portion allows the panels 102, 104 in the second row to overlie the topmost portion of the first row panels 101, 103, while the major part of each panel lies flat on the breather layer 120. Pan head fixings 130 fasten the top edges of the first row of panels 101, 103 to the supporting structure, while the jogged portions of the panels 102, 104 in the second row cover these fixings, so that they do not present a route for the ingress of water. Crosses 132 mark the locations of the concealed fixings 130, for the purposes of illustration only.

To facilitate the assembly and sealing of the metal panels to form a watertight and aesthetically pleasing roof, lap pieces comprising strips or ribbons of pliable polymer material (not on rigid metal substrate) are pre-assembled onto the panels, preferably at a factory location.

Along the bottom edge, a strip 134 is attached to the hem of the jogged portion 125 of the panels, and projects as a "tail" 30 mm or so beyond the edge of the panels.

This is seen in Fig. 2 on panels 102 and 104. At the top edges of the panels, as seen at the top of panel 101 in Fig. 2, a further strip of 136 of PIB material is bonded on to the upper face of the panel, where it is held also under the panhead fixings 130. Strip 136 has a free edge 1 36a which is not bonded to the surface of panel 101/103. In contrast to the lapping strips at the other three edges of the panel, the free edge in this case is at the side of the strip which is inboard of the panel edge. A free edge of strip 136 is set back from the edge of panel 101, so as to lie in contact with the free portion of strip 134 on the panel above when the substrates overlap in the longitudinal direction. These strips can be bonded together to form a seal between the panels along the transverse joint. A preferred sequence for forming the transverse seals will be described below, with reference to Fig. 5.

on the longitudinal edges of the panels, further lapping strips 138 and 140 are fitted on opposite sides of the panel (adjacent sides of panels 101, 103). The longitudinal joins between panels 101, 103 etc along each row are formed by mounting the panels with a gap between them. This gap, which may for example be 30mm between the substrates, is filled by the overlap of the projecting portions 138a and 140a of strips 138, 140. (The equivalent strips, also labelled 138, 140 are present along the longitudinal edges of the panels 102, 104.) As shown in more detail in Fig. 3, the transverse lapping strips 134 on the jogged portions 125 of the panel lower edges extend beyond the longitudinal edges of the panels, to form corner portions 1 34b and 1 34c at their two ends. These are welded together when lain over the gap between the strips 136 in the lower row of panels 101, 103. Depending on the detailed construction and the thickness of the materials, it may be desirable to trim one or both corner portions, to avoid excessive thickness or stiffness in the join, which must remain flexible enough to accommodate thermal expansion.

Fig. 4 shows the completed join between four panels, with the longitudinal join capped by a separate cover piece 142. This capping piece is conveniently formed from solid FIB by an extruding process, so as to be hollow with reinforcing ribs 144 along its interior, and wings 146 extending from its base along either side. Cover piece 142 is applied along the longitudinal joins between adjacent panels, and may be fabricated in a length so as to extend along several rows of panels, without joins.

The wings and base 146 of the extrusion are flexible enough that they can be deform to bond closely with the slight steps encountered when crossing the transverse seals, as shown in Fig. 4. The underside of the extrusion including the wing portions is coated with low molecular weight FIB material 148, which is pre-bonded to the material of the extrusion, and covered by a peelable film when supplied. Upon peeling off this film and pressing the cover piece to the exposed FIB surfaces of the assembled panel roof, an effective seal is formed automatically by fusion of the low molecular weight PIB with the underlying FIB material of the coated metal and lapping strips 140, without the need for application of heat, nor any adhesive or solvent. The P16 material of cover piece 142 is also a mid-grey colour, matching the other PIB materials, thereby to mimic the traditional roll of a lead sheet roof. As an alternative to an extrusion of plastic material, a solid batten or shaped metal sheet may be formed into a suitable cover piece, which compatible material under and around it for bonding and aesthetic compatibility.

Fig. 5 shows in steps (a) to (C) some detail of the assembly of one row of panels on top of a row already present, to form the transverse join mentioned above. The same reference numbers are used for features shown already in Figs. 2, 3 and 4.

Referng firstly to Fig. 5(a), a lower panel, for example panel 101 is already fixed by a panhead nail 130 to a supporting structure (not shown) as seen in this cross-section, each panel, 101, 102 consists of a metal substrate 500 and a thin P16 layer 502. Toward the lower edge 1 02b of panel 102, the jog 124 and jogged portion 125 can be seen, along with the hem 504 by which the edge of the coated substrate is folded to ensure continuity of coating 502 around the exposed edge 1 02b of the pre-fabricated panel 102. Pre-attached to the coating in the region of the hem 504 is the lap piece comprising strip 134 of fibre-reinforced PIB material, with its free edge 134a providing a "tail" to the panel 102. This tail may extend 50mm or so beyond the hemmed edge 1 02b.

On the panel 101, below the jogged portion of panel 102, lap piece 136 is bonded to the PIB coating 502 near the top edge lOla of the panel, while having a free, pliable portion 136a facing away from the edge, and spaced from it. The free portion 1 36a lies under the tail' 1 34a of the upper panel, but extends only 30mm or so, so that the tail 1 34a overhangs somewhat. Fixing 130 passes through both the bonded portion of lap strip 136 and the substrate 500 at the top edge of panel 101.

This reinforces the bonding of the strip to the panel coating, and provides a suitable thickness and cushion for the fastener 130. In other embodiments, the material of strip 136 could stop short of the edge, to align for example with the edge of hem 504.

In Fig. 5(b), a first step of sealing the transverse join is illustrated. Using the pliable nature of the strips 134, 136, they are prised up to permit the nozzle of a hot air gun 510 to enter. This heats the strips from below, while pressure is supplied via a roller or similar device 512. By this facility to apply heat from below the strips and press from above, a reliable heating and bonding of the free edges 134a, 136a of the strips can be achieved on site. It will also be appreciated that the free edges being joined are not being bonded at this point to the metal substrate, which would act as a heat sink and frustrate the heating and bonding process. The bond between the strips 134 and 136 in this step forms the main seal against water ingress along the transverse joints. Subsequently, as shown in Fig. 5(c), the free edge of the tail piece formed by strip 134 can be bonded down, where it extends beyond the edgeof strip 136, to form a bond with the P16 coating 502 of the lower panellOl.

The same heat gun 510 and roller 512 can be applied along the longitudinal seams, joining the free edges 138a and 140a of the strips on the longitudinal edges of adjacent panels. As these are not supported on any metal substrate, the problem of heat sinking does not prevent a good seal being achieved. As mentioned already, the self-sealing cover piece 142 provides both additional sealing and mechanical protection for this more delicate join.

Fig. 6 and 7 illustrate a second example, having a modified form of longitudinal edge and join. In this example, it may be that the panels have a width (W) greater than their length (L), depending on the width of coated steel available as a starting material. It will be understood that the coated steel sheet, or other substrate is formed by bonding and over-sized polymer film to the surface of the steel sheet, such that an unbonded portion of polymer film projects beyond the edge of the steel sheet, along the "selvedge". This selvedge would normally be trimmed to provide a neat edge to the coated substrate. The sheet may be cut already into rectangles before coating, or may be made by coating continuous steel sheet on a roll, and cutting and straightening lengths from the roll as desired. In examples 6 and 7, this projecting portion of polymer film is used to form one of the lap pieces. Other differences from the first example will be become apparent from the following brief

description.

In Fig. 6, two lower corners of representative panels of 600 and 600' are shown.

The near panel 600 is shown at its bottom left corner, with bottom edge 600b and left edge 600d. Compared with the first example, it can be seen that edge 600d has no lap piece, and is merely the cut edge of a coated steel sheet, held to the supporting structure with a pan-head fixing 630. As before, a jog 124 is provided some distance back from edge 600b, and a hem labelled 504. Beneath the hem a lower lap piece 634 is provided, similar to the piece 134 in the first example. As shown 643c, the end of the strip 634 does not project beyond edge 600d but is rather folded back and bonded to itself and to the upper coated surface of panel 600, forming a barrier against water penetration by capillary action. The opposite end of the tail strip 634 can be seen at 634b on the second panel 600'. This projects beyond the edge of 600c of the steel substrate of panel 600' as before.

Whereas no lap piece is provided at edge 600d of panel 600, the lap piece 640 is provided, projecting from the edge 600c of the panel. Rather than being a strip of PIB material bonded separately to the hemmed coating of the panel 600', however, this lap piece is merely the selvedge continuation of the PIB coating, extending beyond the edge 600c of the steel sheet beneath. A "weld" 642 is formed where the hemmed portion at the lower edge 600b of the panel leads into a hemmed portion of the extended coating.

At the top edge of each panel 600, not shown, a lap piece 636 is bonded a distance back from the upper edge 600a, this being the same as in the first example.

Fig. 7 shows four panels 701-704 of the type shown in Fig. 6 joined together to form a building skin such as a roof or wall. The transverse join in this case is formed in a manner very similar to that of the first example: panel 702 is laid with its jogged portion 125 over the upper edge as lap piece 636 of panel 701. A portion of panel 102 is cut away in the diagram, to show the upper edge 600a and lap pieces 636 of panel 701 beneath. Strip 634 is bonded first to strip 636, and then bonded to the coated surface of panel 701 to complete the transverse join. On the other hand, the example of Fig. 6 and 7 differs markedly from the example of Figs. 1-5 in the formation of the longitudinal join. As can be seen in Fig. 7, the right and left edges 600c and 600d of the panel substrates are more or less abutting, with a gap of less than, say, 5mm, perhaps as little as 2mm. The strip 640, which is the portion of the coating of panel 704 projecting beyond the edge 600c of the substrate sheet, overties the edge 600d of panel 702, where it is welded securely to the coating panel 702. This action covers the fixings 630.

The second example exploits the projecting portion of the polymer coating along the selvedge to simplify the fabrication of the panels. The dimensions of the panels can be chosen to exploit the maximum dimension of the source material. In one example, the width of the panels is approximately 1.4m, and the length 1.25m, which is half of the 2.5m x 1.4m panel discussed in relation to Figure 1. Halving the size of the panel increases the number of joins to be made, but naturally makes the panels easier to handle, particularly where they are of relatively thin sheet material.

Numerous further variations are possible compared with the above described embodiments, without departing from the spirit or scope of the invention. Although it is in advantage of the preferred embodiment that all bonds can be made simply by the application of heat and/or with self-sealing materials, the invention does not exclude the application of adhesive or liquid polymer at appropriate points in the installation process. While projecting selvedge material has been shown utilised for the congitudinal join, it could be adapted to form either the tail or the set-back lap piece, if convenient.

The provision of self-sealing (low molecular weight) polymer layers can be extended not just to the cover piece 142, but to any or all of the lap pieces represented by strips 134-140. If this is done, the need for application of heat may be avoided altogether, or the heat may still be applied to increase the integrity of the seals at the same or another place. Where a self-sealing is provided, it will typically be protected by the presence of a peelable paper or foil, which can be removed from its location, conveniently at the time of installation. Application of pressure using roller 512 may aid the bonding process, as required.

While PIB material is ideal for an aesthetically pleasing and robust implementation, the invention does not exclude the use of other polymer coatings. Suitable materials are those available from Flachdach Technologie GmbH, mentioned above.

While a simple rectangular roof has been shown formed from rectangular panels in a two-dimensional array, the shape of the panels can be adapted either individually or as a group, to fit other shapes and contours of roof. The rectangular panels can of course be applied on any pitch of roof, up to a vertical wall. The simple rectangular panels illustrated can also be applied on a barrel vault profile of as tight as 10 m radius.

Claims

1. A method of constructing a building skin using prefabricated panels of rigid substrate material with a polymer coating, the method comprising: -forming a plurality of panels from a substrate to which a polymer layer has been applied, the panels being of a size and shape to be laid side-by-side to form said skin; -prior to installation, providing said panels with pliable lap pieces of material along at least two edges of each panel and projecting a distance beyond the substrate along at least one edge -installing two panels on a supporting structure with said lap pieces of two panels overlapping; and -bonding the overlapping lap pieces to one another, thereby to effect a CO continuous sealed join between the polymer surfaces of the panels.

2. A method as claimed in claim I wherein the substrate material is metal, for

example steel. C)

3. A method as claimed in claim I or 2 wherein the polymer coating material is polyisobutylene (PIB) or a derivative thereof.

4. A method as claimed in any preceding claim wherein the lap pieces are of substantially the same polymer material as the coating on the substrate material.

5. A method as claimed in claim 4 wherein lower molecular weight materials are used on the lap pieces than on the coating.

6. A method as claimed in any preceding claim wherein one of the said lap pieces comprises a continuation of the polymer coating beyond the edge of the substrate material.

7. A method as claimed in any preceding claim wherein the step of bonding the lap pieces of neighbouring panels together is performed by heat fusion or welding.

8. A method as claimed in any preceding claim wherein one or both lap pieces is provided with a layer of polymer having molecular weight low enough to permit self-bonding between the overlapping pieces.

9. A method as claimed in any preceding claim wherein at least one of said lap pieces is effectively bonded to an underside of the substrate, notwithstanding that the coating is applied only to a front surface of the substrate material, by providing a hemmed portion along the substrate edge whereby a portion of the coated surface is turned under the panel edge.

CO

10. A method as claimed in any preceding claim further comprising a step of bonding the joined lap pieces to the coating of the adjacent substrate, after, the lapping pieces have been bonded together.

11. A method as claimed in any preceding claim wherein in a first type of join, a first panel is formed with a first lap piece set back from the edge of the panel and partially bonded to its face while leaving a free edge unbonded, while a second panel is provided with a second lap piece projecting from an edge of the second panel substrate, the edge of the second panel substrate in the finished installation overlying the edge of the first panel substrate, while free edges of the first and second lap pieces lie one over the other for bonding together.

12. A method as claimed in claim 11 wherein in the first type of join, the second panel has a jogged portion toward said lower edge, which lies over the upper edge of the substrate of the lower panel while the remainder of the upper panel lies flush with the lower panel.

13. A method as claimed in claim 11 or 12 wherein in the first type of join, the lapping piece on the second panel edge projects beyond the free edge of the lapping piece on the first panel, the method comprising bonding the free edge of the second lapping piece to the coating of the first panel, after bonding the first and second lapping pieces together.

14. A method as claimed in any preceding claim which includes applying fasteners through the first panel substrate and into the supporting structure prior to installation of the second panel, the fasteners in the finished installation being covered by the overlying portion of the second panel substrate.

15. A method as claimed in any preceding claim wherein in a second type of join, a third lap piece projecting from an edge of the first panel overlaps and is bonded to an edge of a third panel, the overlapping lap pieces occupying a gap between the substrates of the first and third panels. Co

16. A method as claimed in claim 15 wherein the third lap piece is bonded directly to the coated substrate of the third panel, or else to a fourth lap piece projecting from an edge of the third panel.

Q

17. A method as claimed in claim 16 wherein the second type of join includes a substantial gap between the substrates (greater than 20mm, say).

18. A method as claimed in claim 15, 16 or 17 further comprising bonding a covering piece to cover the join between the first and third panel substrates.

19. A method as claimed in claim 18 where the cover piece comprises a relatively rigid extrusion of polymer material having a raised architectural profile, with self-sealing polymer material on an underside thereof.

20. A method as claimed in claims 11 and 15 combined, wherein panels are arrayed in a first row on said supporting structure with joins of the second type between adjacent panels in said row, and one or more similar rows of panels are mounted above the first row, with joins between panels of adjacent rows being joins of the first type.

21. A set of prefabricated panels of a size and shape to be laid side-by-side on a supporting structure to form a building skin, wherein each panel comprises primarily a sheet of rigid substrate material with a polymer coating, further provided with pliable lap pieces bonded to the polymer coating of the rigid panel along at least two edges of each panel and projecting a distance beyond the substrate along at least one edge.

22. A set as claimed in claim 21 wherein the substrate material is metal, for

example steel.

00

23. A set as claimed in claim 21 or 22 wherein the polymer coating material is polyisobutylene (PIB) or a derivative thereof.

24. A set as claimed in claim 21, 22 or 23 wherein the lap pieces are of substantially the same polymer material as the coating on the substrate material.

25. A set as claimed in claim 24 wherein One of the said lap pieces comprises a portion of said polymer coating projecting beyond the edge of the substrate.

26. A set as claimed in any of claims 21 to 24 wherein the material of the lap pieces is selected such that bonding between them can be performed by application of hot air and pressure.

27. A set as claimed in any of claims 21 to 25 wherein at least one of said lap pieces is effectively bonded to an underside of the panel, by providing a hemmed portion along the substrate edge whereby a portion of the coated surface is turned under the panel edge.

28. A set as claimed in any of claims 21 to 27 wherein each panel is formed with a first lap piece set back from a first edge of the panel and partially bonded to its face while leaving a free edge unbonded, and a second lap piece projecting from a second edge of the panel substrate, such that the second edge of the panel can overlie the first edge of a similar panel, while free edges of the first and second lap pieces of the respective panels lie one over the other for bonding together.

29. A set as claimed in any of claims 21 to 28 wherein the second edge of each panel has a jogged portion, which can lie over the first edge of the substrate of the similar panel while major portions of the panels lie flush with one another.

30. A set as claimed in claim 28 or 29 wherein the lapping piece on the second edge has a free portion substantially wider than a free portion of the lapping piece CO set back from the first edge.

31. A set as claimed in any of claims 21 to 30 wherein each panel is further provided with a third lap piece projecting from a third edge orthogonal to the first edge and a fourth lap piece projecting from a fourth edge opposite the first edge, such that two of said panels can be laid side-by-by side with their respective third and fourth lap pieces overlapping while a gap remains between their substrates.

32. A set as claimed in any of claims 21 to 30 wherein each panel is further provided with a third lap piece projecting from a third edge orthogonal to the first edge, such that two of said panels can be laid side-by-side with the third lap piece of one panel overlying the edge of the coated substrate of the other panel, with a relatively small gap between their substrates.

33. A set as claimed in claim 32 wherein one of the first and third lap pieces comprise a portion of said polymer coating projecting beyond the edge of the panel substrate.

34. A set as claimed in any of claims 31 to 33 wherein in combination with a covering piece or pieces sized to cover the gap between the third and fourth edges of said panel substrates.

35. A set as claimed in claim 34 wherein the cover piece comprises a relatively rigid extrusion of polymer material having a raised architectural profile, with self-sealing polymer material on an underside thereof.

36. A prefabricated panel for use in forming a building skin, the panel comprising a substantially rigid, rectangular panel of polymer-coated substrate, the panel having along at least two of its four edges a lap piece of pliable material having a free edge for bonding to another panel of the same form, the lap piece along at least a first edge projecting beyond the edge of the substrate and while the CO lap piece along at least a second edge is set back from the edge of the substrate, the setting back of the second edge lap piece serving to create an overlap between the substrate materials as well as the lap pieces when free edges of the lap pieces of two such panels are lain together.

37. A panel as claimed in claim 36 wherein first, third and fourth edges have projecting lap pieces while the second edge has the set back lap piece.

38. A panel as claimed in claim 36 wherein first and third edges have projecting lap pieces, while the second edge has the set back lap piece and a fourth edge has no lap piece.

39. A panel as claimed in claim 36, 37 or 38 wherein the substrate of the panel includes a jogged portion along the edge which lies opposite the second edge, the jogged portion having a width sufficient to accommodate the overlapping portion of an adjacent panel's second edge.

40. A panel as claimed in any of claims 36 to 39 wherein at least one of said lap pieces comprises a portion of said polymer coating projecting beyond the edge of the panel substrate.

41. A building skin installation comprising an array of panels according to any of claims 36 to 40, each panel being mounted on a supporting structure with at least one of said lap pieces bonded to a lap piece of an adjacent panel. Co