PLAIN ROOF TILES

Abstract: A plain roof tile has an upper surface (21) of which a lower surface area is visible when the tile is laid with other such tiles to form a roof, an under surface (28), and being shaped during manufacture to enable the visible surface area, when a plurality of such tiles are stacked one on top of another to form a stack, to be spaced from, and remain out of contact with, an oppositely facing under surface (28) area of the immediate overlying tile of the stack.

Description: PLAIN ROOF TILES The present invention relates to cambered and flat plain roofing and cladding tiles, referred to generically herein as plain roof tiles. Plain roof tiles are of generally rectangular shape with upper and under (in use) surfaces, opposite side edges, upper (head) edges and lower (leading) edges and optionally, each tile is formed on its under surface along or adjacent its head edge with one or more hanging nibs by means of which the tiles are supported from roof battens when the tiles are laid to form a roof. Plain roof tiles may be made from a variety of materials such as clay, polymer bound aggregates and cementitious materials such as concrete. Such tiles are conveniently made by extrusion, moulding or a pressing operation. Typically, cementitious mixtures include sand and/or other aggregate, cement, colouring pigment and water plus optionally one or more other additives to facilitate moulding, pressing or extrusion, prevent growth of fungus etc. Tiles of cementitious materials have been produced in an extrusion process for around fifty years with apparatus including an extrusion head comprising a hopper-like box which is disposed above a conveyor path and which is charged with the cementitious mixture. The flow of the cementitious mixture is assisted in the box by means of a rotating paddle. A succession of pallets for moulding the under surface of the tiles are driven along the conveyor path and past the box so that the cementitious mixture from the box forms on the pallets and is compressed thereon by means of a rotating roller mounted within the box downstream of the paddle, and having a shape which corresponds to the upper surface of the tiles to be formed. The cementitious mixture is further compressed on the pallets as they pass out of the box by means of a slipper which is disposed downstream of the roller and also has a shape which corresponds to that of the upper surface of the tile to form a continuous extruded ribbon of cementitious mixture on the pallets. The ribbon is subsequently cut into tile forming lengths (tiles) downstream of the box by means of a suitable cutting knife, optionally with nail holes being formed in the tile forming lengths at the same time. The pallets with the formed tiles thereon are then conveyed to a curing location. At the curing location, the tiles are conveyed through a curing chamber which is maintained at a desired relative humidity and temperature. The curing time is usually in excess of 6 hours. The tiles undergo only a partial curing in the curing chamber from where they are conveyed to, and stacked, out-of-doors to complete the curing process. After partial curing, the tiles are depalleted, for example by means of rotating depalleting wheels disposed on opposite sides of the conveyor path. In operation, the wheels successively enter in between the pallets and tiles, with the tiles continuing along the original conveyor path, and the pallets being carried downwards along a different conveyor path, thereby separating the tiles from the pallets. Known typically longitudinally cambered plain tiles and typically planar (flat) plain tiles (and slates) have several disadvantages which will now be discussed with reference to Figs. 1 to 4 and Figs. 5 to 8 respectively. A longitudinally cambered plain tile la (Figs. 1 to 4) has an upper surface 1, a lower surface 2, side edges 3, a leading (lower) edge 4 which is visible when laid, a head (upper) edge 5 which is covered from view when laid and optional hanging nibs 5a (only one nib 5a for each tile is visible in the drawings). In the part-sectional side elevation of Fig. 3 of a roof structure 100a, roof rafters 6 are covered with roofing felt 7 and fixed with tiling battens 8 on which the tiles la are hung to form an overlapping array of cambered plain tiles la laid in broken bond/double lapped format, i.e. overlapping leading edge to head edge and side-by-side relationship to form a roof. Because the tiles are cambered along their longitudinal length and are laid on an array of battens 8 in a sensibly flat plane, with each overlying tile la in one course lav, lax and lay above being in contact with its immediate underlying tile la in the next adjacent course lax, lay, laz below, only along a line or plane 9 where the bottom of the leading edge 4 meets the under surface 2 of the overlying tile, or where the bottom of the leading edge 4 and adjacent elongate narrow portion of the under surface 2, of the overlying tile la rests on the upper surface 1 of the underlying tile. For clarity of illustration, the lines or narrow planes 9 are shown as being slightly out of contact with the immediate underlying tile la. The line or narrow plane 9 contact creates two weaknesses in the tile array, namely:- i) an unsupported gap 11 between overlying pairs of cambered plain tiles of the courses lax and lay because the plain tiles of the courses lax and lay are laid in double lapped format such that any water entering this area through gapping between successive tiles la in the course can easily be blown over the head edge 5 of the tile of course lax which consequently necessitates such conventional plain tiles being restricted to roof pitches of 35° and above; ii) the position of the line or narrow plane of contact 9 directly above the unsupported gap 11 is such that if any force such as foot traffic is applied at point 10 on any of the cambered plain tiles such as that in course lav, the load is directly applied to an approximate midpoint of the underlying tile la of the course lax, the mid-point being the weakest region of the tile and likely to cause breakage. Such breakage can be expensive to repair. Only the lower area 13 of the upper surface 1 of each cambered plain tile la is visible when laid, being that area which is not covered by an overlying tile. Figures 5 to 8 show a sensibly, longitudinally, flat plain tile lb (slate) having an upper surface 1, a lower surface 2, side edges 3, a leading edge 4, a head edge 5 and optional hanging nibs 5a. In the part-sectional-side elevation of Fig. 7 of a roof structure 100b, roof rafters 6 are covered with roofing felt 7 and fixed with tiling battens 8 on which the slates lb are hung to form an overlapping array of flat plain tiles lb laid in broken bond/double lapped format, ie overlapping leading edge to head edge and side-by-side relationship, to form a roof. Because the plain tiles lb are flat along their longitudinal length and are laid on an array of battens 8 in a sensibly flat plane each underlying tile lb of the courses lbx, lby, lbz, is in frictional contact with the overlying tile lb of the courses lbv, lbx, lby respectively for the entire overlapping region 14 where the lower surface 2 of particular overlying tile lb is adjacent to the upper surface 1 of the associated underlying tile lb. This frictional contact is a disadvantage in use in that water entering this area via capillarity within areas 14 between flat plain tiles lb in the course can migrate over the sides 3 caused by creep, this phenomenon being well known in the use of slates and limiting their use; Indeed, slates are limited to roof pitches of 27.5° and above, even in areas of low driving rain exposure. Only the lower area 15 of the upper surface 1 of each flat plain tile lb is visible when laid, being that area which is not covered by an overlying flat plain tile lb. Figures 4 and 8 show cambered and flat plain tiles la and lb stacked into respective stacks 4a and 8a, which are packaged as shown in Figs. 4a and 8a respectively by applying a strap or band 46 transversely around the mid-region of the stack 4a or 8a, to form a respective pack 4b or 8b for transportation and delivery to a customer. Alternate tiles la, lb in the respective packs are turned through 180° such that the nib 5a of the overlying tile la, lb is hung over the leading edge 4 of the underlying tile la, lb. This method is traditional and well proven to allow tiles la, lb to arrive at their final destination intact and with a minimum of breakage. There is, however, a problem with all cambered and flat plain tiles la, lb that have to be packaged in this manner, in that the individual tiles la, lb of the tile packs 4b, 8b move relative to each other in transport. Accordingly, because the upper and lower surfaces 1 and 2 of successive tiles are in frictional contact, the upper surfaces 1 including the visible areas 13 and 15 of the laid tiles la, lb respectively are abraded leaving unsightly marks on the visible areas 13 and 15 of the upper surfaces 1, which are not masked from view even when laid in a double format tile array to form a roof. The main object of the present invention is to provide a plain roof tile in which unsightly marks appearing on the visible surface region as a result of abrasion in a stack or pack during storage and/or transportation are avoided. Another object of the present invention is to reduce breakage of tiles in a laid roof of plain roof tiles due to foot traffic and thus the expense of replacing broken tiles. From one aspect of the present invention, there is provided a plain roof tile having an upper surface of which a lower surface area is visible when the tile is laid with other such tiles to form a roof and an under surface, characterised in that the tile is shaped during manufacture to enable the visible surface area, when a plurality of such tiles are stacked one on top of another to form a stack, to be spaced from, and remain out of contact with, an oppositely facing under surface area of the immediate overlying tile of the stack. From another aspect of the present invention, there is provided a method of making a plain roof tile having an upper surface and an under surface, characterised by forming the tile with a shape which enables a lower visible surface area on the upper surface when the tiles are stacked with other such tiles one on top of the other to form a stack, to be spaced from, and remain out of contact with, an oppositely facing under surface area of the immediate overlying tile of the stack. By shaping the tile in this way, the visible surface area of the upper surface is not abraded or scuffed so that the visible surface area is free of unsightly marks and is therefore aesthetically pleasing. Whilst applicants have considered modifying the shape of the under surface area which lies opposite the visible upper surface area of the tile in the pack, modification of the shape of the visible upper surface area is preferred to minimise the risk of breakage from foot traffic when the tiles are laid to form a roof. This is because the under surface of the tile opposite the visible upper surface area should desirably contact, and be supported on, the upper, non- visible area of the upper surface, to avoid so far as is possible, gapping and the expense of breakage from foot traffic which would happen with inadequately supported tiles. Accordingly, expressed in another way, the invention provides a plain roof tile having an upper surface of which a lower area, which is visible when the tiles are laid, has a shape which is produced during manufacture of the tile and which, when stacked with other such tiles one on top of the other to form a stack, is spaced from, and remains out of contact with, an oppositely facing under surface area of the immediate overlying tile of the stack. The invention also comprises a method of making a plain roof tile having an upper surface of which a lower area, which is visible when the tiles are laid, has a shape, which when stacked with other such tiles one on top of the other to form a stack , is spaced from, and remains out of contact with, an oppositely facing under surface area of the immediate overlying tile of the stack. Another advantage of the present invention is that plain tiles made in accordance therewith may serve as longitudinally cambered plain tiles or as slates. The shape of the visible upper surface area may be any suitable shape consistent with achieving spacing from the oppositely facing under surface area in the stack. The shape may be achieved by tapering the visible upper surface area in the direction from the head edge to the leading edge, or by providing the visible upper surface with an arcuate shape or camber in the direction from the head edge to the leading edge such that in both instances the leading edge is of reduced thickness compared to either of the known forms of plain tiles referred to hereinabove or what would have otherwise been the case without the tapered or arcuate shape. A reduced thickness leading edge enhances the aesthetic appearance of the laid tile. By shaping a plain tile in any of these ways, a plain tile roof can be formed of a plurality of such tiles laid in overlapping leading edge to head edge and side-by-side relationship having a rafter pitch below 35° and preferably below 27.5° which has hitherto not been possible with the conventional longitudinally cambered plain tiles of Figs. 1 to 4 and the longitudinally flat plain tiles of Figs. 5 to 8 respectively. Accordingly, from another aspect the present invention provides a plain roof tile which is shaped during manufacture to provide a plain tile roof formed of a plurality of such tiles laid in overlapping leading edge to head edge and side-by-side relationship and having a rafter pitch below 35° and preferably below 27.5°. Applicants have found that the combination of a substantially flat upper non-visible upper surface area which receives, and supports, the lower under surface area of the overlying tile of a laid roof with a shaped visible upper surface area , eg a tapered or arcuate visible upper surface area, as previously mentioned, is particularly advantageous. This can be even more so when the lower under surface area is provided with regions that present substantially flat supporting surfaces which rest on the substantially flat non- visible upper surface area because this increases the resistance of the tiles to breakage due to foot traffic and the expense of replacing broken tiles. Such substantially flat supporting surface regions preferably extend into the upper area of the under surface so as to provide support for the tile substantially from the tiling battens to the leading edge. In one embodiment, such substantially flat supporting surface regions extend from a recess for receiving at least one hanging nib to the leading edge and lie in the same plane as the free end of the or each hanging nib and present the lowest point of the tile. In another embodiment, such substantially flat supporting surface regions extend from the head edge to the leading edge with the free end of the or each hanging nib presenting the lowest point of the tile. Further support and resistance against breakage can be provided by the provision of transversely extending substantially flat supporting surface regions. The supporting function of the transversely extending supporting surface regions may be enhanced by providing a transversely extending flat supporting surface region comprising an intermediate region that rests on the substantially flat upper non-visible area of the underlying laid tile adjacent the head edge. For ease of manufacture and to reduce weight, the supporting regions are preferably in the form of strengthening ridges which have recesses therebetween and at least some of which may be provided with a pressure- moderating and anti-capillarity groove. In order to facilitate depalletting when the tiles are made by extrusion, the under surface is provided with a substantially flat area adjacent the head edge thereby providing, for extruded tiles, a depalleting region for the tiles from the pallets in production. Moreover, when more than one hanging nib is provided, such nibs are less prone to damage during depalletting than is a single hanging nib. In tiles in which the free end of the or each hanging nib presents the lowest point of the tile, the invention further provides a recess in the upper surface of the tile adjacent the head edge for accommodating at least one hanging nib when a plurality of such tiles are stacked one on top of the other to form a stack with the head edges of the tiles being disposed immediately one above the other, preferably in a substantially vertical line. The invention also enables the production of so-called one-piece double plain tiles which are, in effect twins, of any of the tiles as defined hereinabove according to the invention. Accordingly, the present invention also provides a one-piece double-tile comprising any two of the same tiles as defined hereinabove according to the invention, in which a dummy groove is provided in the tile upper surface and leading edge to simulate the effect of two closely spaced apart tiles. From another aspect the invention also provides a method of making a one-piece double tile, in which the tile is created on a single pallet which forms the under surface shape of two single tiles at a time and forming, as by moulding, pressing or extruding in a dummy groove to simulate the effect of two closely spaced apart tiles. From yet another aspect of the present invention, there is provided a roof structure comprising a plurality of any of the plain tiles according to the invention as defined hereinabove, laid in overlapping leading edge to head edge and side-by-side relationship to form a roof. Such a plain tile roof may have a rafter pitch of below 35° for tiles having a width greater than 160 mm or below 27.5° in the case of tiles having a width greater than 205 mm. From a further aspect of the present invention, there is provided a stack formed from a plurality of any of the plain tiles according to the invention as defined hereinabove, laid one above the other, wherein a visible surface area on an upper surface of a tile is spaced from, and remains out of contact with, an oppositely facing under surface area of the immediate overlying tile of the stack. The tiles of the stack can be stacked, in a preferred embodiment, with their leading edges disposed immediately one above the other, preferably in a substantially vertical line. By means of this aspect of the invention, there is no need for alternate tiles to be turned through 180° to be stacked as is the case with the known plain tiles la, and lb, thereby achieving a much simpler stacking arrangement. In order to stack tiles in which the free end of the or each hanging nib presents the lowest point of the tile, at least one hanging nib of each overlying tile of the stack is accommodated in a recess in the upper surface adjacent the head edge of the immediate underlying tile with the leading edges of the stacked tiles being disposed immediately one above the other, preferably in a substantially vertical line. Preferably, the tiles of the stack are in frictional contact with the non-visible flat upper surface area of each underlying tile which has the added advantage of providing good support and strength to withstand the force applied when a stack of such tiles are made into a pack by the application of packaging means such as shrink wrap or at least one length of flexible material, say in the form of one or more straps or bands, around the stack. Conveniently, the pack comprises a strap or band which extends around the stack in the mid-region of the overall length of the tiles of the stack or two straps or bands in the mid- region, and towards the head region respectively, of the tiles of the stack. In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which:- Fig. 1 is a side elevation view of a conventional longitudinally cambered plain tile; Fig. 2 is a perspective view from the upper surface, one side edge and the leading edge of the tile of Figure 1; Fig. 3 is a side elevation of a roof showing a typical installation of the longitudinally cambered plain tiles of Figures 1 and 2; Fig. 4 is side elevation of a plurality of the longitudinally cambered plain tiles of Figures 1 and 2, formed into a stack for packaging; Fig. 4a shows the stack of tiles of Fig. 4 formed into a pack for storage and/or transportation; Fig. 5 is a side elevation of a conventional longitudinally flat plain tile; Fig. 6 is a perspective view from the upper surface, one side edge and the leading edge of the tile of Figure 5; Fig. 7 is a side elevation of a roof showing a typical installation of the longitudinally flat tiles of Figures 5 and 6; Fig. 8 is a side elevation of a plurality of the longitudinally flat plain tiles of Figures 4 and 5, formed into a stack for packaging; Fig. 8a shows the stack of tiles of Fig. 8 formed into a pack for storage and/or transportation; Fig. 9 is a perspective view from the upper surface, one side edge and the leading edge of one embodiment of a plain tile made in accordance with the invention; Fig. 9a is a perspective view from the upper surface, one side edge and the leading edge of a shortened version of one embodiment of plain tile made in accordance with the invention, to accommodate its use as a top or eaves course tile; Fig. 9b is a perspective view from the upper surface, one side edge and the leading edge of another embodiment of a plain tile made in accordance with the invention that has had part of its leading edge removed to form a decorative tile; Fig. 10 is a perspective view from the under surface, other side edge and the leading edge of the tile of Figure 9; Fig. 11 is a side elevation of the tile of Fig. 9; Fig. 12 is a longitudinal sectional view of the tile of Figs. 9 to 11; Fig. 12a is a longitudinal sectional view of the top or eaves course tile of figure 9a; Fig. 13 is a horizontal cross-sectional view of the tile of Figures 9 to 12; Fig. 14 is a side elevation of a stack formed of a plurality of the plain tiles of Figs. 9, 10, 11, 12 and 13 for storage and/or packaging and illustrating the visible area of the tiles when laid; Fig. 14a shows the stack of tiles of Fig.14, packaged into one embodiment of pack for storage and/or transportation; Fig. 14b shows the stack of tiles of Fig.14, packaged into another embodiment of pack for storage and/or transportation; Fig. 15 is a part-sectional side elevation of a roof structure similar to those of Figs. 3 and 7, showing a typical installation of the plain tiles of Figs. 9, 9a, 10, 11, 12, 12a and 13, with the rows of tiles being alternately in side elevation and in longitudinal section; Fig. 16 is a horizontal cross-sectional view of a typical installation of plain tiles as shown in Figs. 9, 10, 11, 12 and 13, or Figs. 17 and 18. Fig. 17 is a longitudinal sectional view of the tile of Fig. 18; Fig. 18 is a perspective view from the under surface, one side edge and the leading edge, and one side view of the plain tile of Figs. 9, 10, 11, 12 and 13, modified by an alternative hanging nib arrangement; Fig. 19 is a perspective view from the upper surface, one side edge and the leading edge of a double plain tile made in accordance with the invention and being a twin form of the plain tile of Figs. 9, 10, 11, 12 and 13; Fig. 20 is a perspective view from the under surface, other side edge and the leading edge of the tile of Fig. 19; Fig. 21 is a perspective view from the upper surface, one side edge and the leading edge of a further embodiment of plain tile made in accordance with the invention; Fig. 22 is a perspective view from the under surface, other side edge and leading edge of the tile of Fig. 21; Fig. 23 is a side elevation of the tile of Figs. 21 and 22; Fig. 24 is a longitudinal cross-sectional view of the tile of Figs. 21 to 23; Fig. 25 is a horizontal cross-sectional view of the tile of Figs. 21 to 24; Fig. 26 is a side elevation of a plurality of the plain tiles of Figs. 21 to 25, formed into a stack for storage and/packaging and illustrating the visible area of the tiles, when laid; Fig. 26a shows the stack of tiles of Fig. 26, packaged into one embodiment of pack for storage and/or transportation; Fig. 26b shows the stack of tiles of Fig. 26, packaged into another embodiment of pack for storage and/or transportation; Fig. 27 is a part-sectional side elevation of a roof structure showing a typical installation of the plain tiles of Figs. 21 to 25 with the rows of tiles being alternatively in side elevation and in longitudinal section; Fig. 28 is a longitudinal sectional view of the tile of Figs. 21 to 26 but modified by having an alternative under surface profile; Fig. 29 is a perspective view from the upper surface, one side edge and the leading edge of a double plain tile made in accordance with the invention and being a twin form of the tile ofFigs. 21 to 25; Fig. 30 is a perspective view from the under surface, other side edge and leading edge of the tile of Fig. 29; Fig. 31 is a front elevation of a roof structure showing a roof formed from a plurality of the tiles of Figs. 9, 10, 11, 12 and 13, Figs. 17 and 18, Figs. 21 to 25 , or Fig. 28 laid in broken bond (ie in overlapping leading edge to head upper edge and side-by-side relationship); Fig. 32 is a perspective view of the underside of a single- width tile corresponding to the tile of Fig. 18 but modified by the provision of cut-outs in the ribs or ridges on the underside of the tile and showing airflow patterns through the cut-outs; Fig. 33 is a perspective view of the underside of a double-width tile corresponding to the tile of Fig. 20 but modified, in the manner of the tile of Fig. 32, by the provision of cut-outs in the ribs or ridges on the underside of the tile, thus effectively being a twin form of the tile of Fig. 32; Fig. 34 is a longitudinal section through a tile as illustrated in Fig. 32 or Fig. 33; Fig. 35 is an end view of the single-width tile of Fig. 32 cut through line A-A of Fig. 32 to form a top and eave tile; Fig. 36 is a longitudinal section through the top and eave tile of Fig. 35; Fig. 37 is a horizontal section through a laid roof of tiles in accordance with Figs. 32, 34 and 35, showing the end view of a top tile as shown in Fig. 36; Fig. 38 is an enlarged detail view of part of Fig. 37; Fig. 39 is a longitudinal section through the laid roof of Fig. 37 and Fig 38; Fig. 40 is a view from underneath a further modified tile provided with cut-outs akin to those of Fig. 32 et seq.; Fig. 41 is a top plan view of the tile of Fig. 40; Fig. 42 is an end view of the tile of Figs. 40 and 41; Fig. 43 is a side view of the tile of Figs. 40, 41 and 42; Fig. 44 is a transverse sectional view taken on line A-A of Fig. 40; Fig. 45 is a transverse sectional view taken on line B-B of Fig. 40; Fig. 46 is a transverse sectional view taken on line C-C of Fig. 40; Fig. 47 is a transverse sectional view taken on line D-D of Fig. 40; Fig. 48 is a longitudinal sectional view taken on line E-E of Fig. 40; Fig. 49 is a longitudinal sectional view taken on line F-F of Fig. 40; and Fig. 50 is a longitudinal sectional view taken on line G-G of Fig. 40. Referring to Figs. 9, 10, 11, 12 and 13, a plain tile 20 has an upper surface 21, an under surface 22, side edges 23, a leading edge 24, a head edge 25, and a single hanging nib 25a extending all the way across the tile from one side edge 23 to the other side edge 23. As will be apparent from Figs. 9, 11 and 12, the upper surface 21 has an area 21a of generally flat (planar) configuration extending in the direction from the head edge 25 to the leading edge 24 (ie down the length of the illustrated tile 20) for a distance of between one half and two thirds the overall length of the tile where it changes to an area 21b of arcuate configuration. The generally planar area 21a is non- visible and serves to support an overlying tile 20 from the under surface area immediately beneath or disposed opposite to the arcuate upper surface area 21b which is visible when the tiles 20 are laid to form a roof. The arcuate area 21b also extends in the direction from the head edge 25 to the leading edge 24 (ie down the length of the illustrated tile 20) until it meets the leading edge 24 such that the thickness of the leading edge 24 is less that that of the head edge 25. From each side edge 23 can be seen an angled recess 26 extending from the upper end 27 of the straight under side 28 of side 23 to the base 29 of the nib 25a. This recess 26 is for accommodating a tiling batten 8 (see Fig. 15). Referring more particularly to Fig. 10, the under surface 22 has several flat supporting surface regions which rest on and support the tile 20 from the non-visible upper surface area 21a, which regions are in the form of strengthening and supporting ridges 30, 31, 32 and 33. The ridges 30 present the side edges 23 and the straight under sides 28. The ridges 30 also present ramped ridge portions 26a which terminate just short of the nib base 29 so that together with flat under surface portions 26b leading from the ramped ridge portions to the base of the nib 25a define the hanging nib recess 26. The ridges 30 extend longitudinally of the tile 20 from a lower transverse ridge 31 extending all the way across the tile 20 and presenting the leading edge 24. The under surface 22 also has an intermediate strengthening ridge 32 extending transversely between, and merging into, the two longitudinal ridges 30. The purpose of the intermediate ridge 32 is to allow for the manufacture of a shorter tile, to be used with other such tiles, as an eaves or top course and to be hereinafter described with reference to, and as shown in, Figs. 9a and 12a. Optionally, the lower region of the under surface 22 features inclined ridges 33 which extend between, and merge into, the lower transverse ridge 31 and opposite side ridges 30. Such inclined ridges are to enable the formation of differently profiled (featured) leading edges, eg of beaver tail shape, arrow head shape (Fig. 9b) etc. The side ridges 30 are provided with pressure moderating and anti-capillarity grooves 34, the lower ridge 31 is provided with a pressure moderating and anti-capillarity groove 35, and the intermediate ridge 32 is provided with a pressure moderating and anti-capillarity groove 36. The ridges 30, 31, 32 and 33 create recesses 37, 38, 39 in the under surface 22 of the tile 20. It will be seen from Fig. 12 that the under surface area 40 represented by the undersides 28, ridges 30, bottom of recess 37, intermediate ridge 32, lower ridge 31 and optional inclined ridges 33 are generally parallel to the upper surface 21 of the tile 20. Fig. 13 shows the upper surface 21, under surface 22, hanging nib 25a, ridges 30 with their pressure- moderating and anti-capillarity grooves 34 and the under surface area 40 represented by the bottom of the recess 37. As will be appreciated from Fig. 14 to which reference will now be made, the tiles 20 have the benefit of a simpler packaging arrangement as compared with the known plain tiles la and lb of Figs. 1 to 6. This is because a plurality of tiles 20 can merely be stacked in a simple array to form a stack 41 without the need for alternate tiles 20 to be turned through 180 ° as is the case with the plain tiles la, and lb. The under side 28 of the side edge 23 of the tile defining the lowest point of the side wall 30 and thus of the tile 20 of each overlying tile 20 is in frictional contact with the flat planar portion 21a of the upper surface 21 of each underlying tile 20, providing good support and strength to withstand the force applied when the stack 41 of such tiles 20 are made into a pack. Conversely, and advantageously, the arcuate visible area 21b of the upper surface 21 of each underlying tile 20 is spaced apart from the underside 28 with the consequence that there is no frictional contact and no scuffing or abrasion of the visible surface area 21b of the upper surface 21 of the tiles due to handling transportation of individual and collective packs 45 (Figs. 14a and 14b) A pack 45 is formed by the application of packaging means consisting of one strap or band 47, as shown in Fig. 14a or two straps or bands and 47 and 47a as shown in Fig. 14b around the stack 41. In Fig. 14a, the strap or band 47 extends transversely around the pack 45 in the mid-region of the overall length of each tile 20. The two straps or bands 47 and 47a in Fig. 14b extend transversely around the pack respectively in the mid-region of the overall length of each tile and towards the head region around or adjacent the upper end 27 of the straight side 28 before the inclined tiling batten receiving recess 26. Referring more particularly to Figs. 9a and 12a , these show views of a tile 20a that is manufactured in the same way, and with the same means as the tile shown in Figs. 9, 10, 11, 12 and 13 but are then shortened in overall length, downstream of the extrusion head by cutting, pressing or stamping in a horizontal plane across the width of the tile and in the region of the intermediate strengthening and supporting ridges 32. This provides a tile of shortened length having a thicker leading edge 24a than the corresponding tile 20 and that has a specific use to form either the eaves course or the top course in a completed roof such as is shown in Fig. 15.The tile 20g of Fig. 9b, is manufactured in the same way and with the same means as the tile shown in Figs. 9, 10, 11, 12 and 13 but is then provided with a featured upper surface 21 downstream of the extrusion head by cutting, pressing or stamping means to form sloping leading edges 23a which terminate at an apex which is all that is left of the leading edge 24 of the tile 20. The sloping leading edges 23a are determined in the region of the inclined strengthening and supporting ridges 33 and the particular example is known as an Arrowhead Tile in the trade. Tiles 20g are generally used in band courses within a roof including a plurality of tiles 20 to create an attractive feature to the completed roof. In the roof structure 100c of Figs. 15 and 16, a plurality of the plain tiles 20 are hung from roof battens 8 to form an overlapping array of plain tiles 20 laid in broken bond/double lapped format, ie overlapping leading edge to head edge and side-by-side relationship to form a roof. Fig. 15 shows the arcuate area 21b of the upper surface 21 of tiles 20 as being the only area of the upper surface 21 which is visible when the tiles are in laid and which presents, in situ, a clean, unscuffed, undamaged and therefore aesthetically pleasing appearance. The overlapping array of tile starts at the eaves 41 and finishes at the ridge 43 with the cut-down in length special top and eaves course plain tiles 20a. The section presented in Fig. 16 is through the gaps between abutting tiles in the eaves course of tiles 20a and then through the centre of the tiles 20 in the overlying course, through the gaps between abutting tiles 20 in the next course immediately above and so on. In all areas where the tiles 20 overlap, the flat under surfaces of the lower ridges 30, 31, 32, and 33 of the under surface of the overlying tile are in frictional contact with the flat portion 21a of the upper surface 21 of its immediate underlying tile 20. Thus, if a load is applied on the exposed visible area of a tile 20, such as by way of foot traffic, that load is carried by fully supported underlying tiles and by the tiling batten 8 on which the lower underlying tile is hung, thereby minimising the risk of tile breakage caused by the imposition of such loads. A further benefit is that of increased protection against wind driven rain which can be appreciated from Figs. 15 and 16. Any water which passes through the gaps 56 (Fig.16) between adjacent tiles in an overlying course enters a cavity 55 created by the upper surface 21a of the underlying course, the ridge 30, lower ridge 31 and intermediate ridge 32 and the lower surface 40 of the overlying course. Pressure from the wind is then moderated when it enters the cavity 55 by the action of passing under the ridges 30, 31 and 32 with their built- in pressure-moderating and anti-capillarity grooves 34, 35 and 36. Thus water is prevented from blowing over the head 25 of the tile 20 and thereby allows the use of the tiles 20 at lower roof pitches than is legislated for plain tiles. Further, and advantageously, the presence of the cavity 55 in a laid array of tiles 20 prevents the migration due to creep of water over the sides 23 of the tiles, a disadvantage that is associated with substantially flat plain tiles (slates). Again, this allows the tiles 20 to be hung at lower roof pitches than is legislated for slates. Figs. 17 and 18 show an embodiment of plain tile 20b that differs from the tile 20 of Figs. 9, 10, 11 and 13 by a modification of the under surface 22 which merely involves the replacement of the single hanging nib 25a by two hanging nibs 25b which are spaced inwardly of the side edges 23 and are spaced inwardly of the head edge 24 of the tile 20b to provide a flat area 48. This embodiment has the advantages of the flat area 48 providing a depalleting region for the tiles 20b from the pallets in production and the nibs 25b are therefore less prone to damage than is the single nib 25a. The embodiment of Figs. 19 and 20 is a twin of the plain tile 20 of Figs. 9, 10, 11, 12 and 13 and is a one-piece double tile 20c which is created on a single pallet which forms the under surface shape of two single tiles at a time. The effect of a double tile is achieved by moulding, pressing or extruding in a dummy groove 49 to simulate the effect of two closely spaced apart tiles 20. Unlike the tile 20, in the under surface 22a, the two ridges 30 of two single plain tiles 20 are merged together to form a single double ridge 30a with a double- ramped ridge portion 26c, with there being two pressure-moderating and anti-capillarity grooves 34 in the double ridge 30a. The single nib 25a and single ridge 31 with its single pressure-moderating and anti-capillarity groove 35 extend the full width of the double tile 20c. The embodiment of plain tile 20d shown in Figs. 21 to 25 differs from the plain tile 20 of Figs. 9, 10, 11, 12 and 13 and the plain tile 20b of Figs. 17 and 18 by modifications of the head region of the tile 20/20b both on its under surface 22 and upper surface 21 to provide another way of accommodating the hanging nib(s) when the tiles are stacked into a stack and packed to form a pack for storage, handling and transport. Thus, the upper surface 21 in the head region of the plain tile 20d is provided with an L-shaped recess 61, leaving the head edge 25c much narrower than the head edge 25. As with the tile 20b of Figs.17 and 18, the under surface 22 has two hanging nibs 25b. However, un-like the tile 20b where the free ends of the hanging nibs 25b lie in the same plane as the underside 28 which constitutes the lowest point of the tile 20, the nibs 25b in the tile 20d project beyond the underside 28a (equivalent to underside 28) and their free ends constitute the lowest point of the tile 20d (see Figs. 23 to 25). As will be apparent from Fig. 22, the nibs 25b project from an elongate head portion 62 of the under surface 22 to accommodate the tiling battens 8 (Fig. 27) along the bases 29 of the nibs. The under surface head portion 62 also forms an upper wall 37a of the recess 37 and lies in the same plane as that of the straight underside 28a which extends all the way from the leading edge 24 to the head edge 25c. Thus, the inclined hanging nib recess 26 of the embodiments of Figs. 9, 10, 11, 12 and 13, 9a and 12a, 9b, 17 and 18 and 19 and 20 is omitted. Referring now to Fig. 26, it will be seen that a plurality of tiles 20d are stacked one upon the other to form a stack 63 in the same manner as the tiles 20 are stacked into a stack 41 in Fig. 14 except that the hanging nibs 25b are accommodated in the recesses 61. As with the stack 41 and pack 45 of Fig. 14a, the stack 63 is formed into a pack 65 with the band or strap 47 and, like the stack 41 and pack 45 of Fig. 14b, there are two bands or straps 47 and 47a. Because there are no hanging nib recesses 27 in the tile 20d, the band or strap 47a can be secured around the pack 65 much nearer the head edges 25c than the head edges 25 of the pack 45 in Fig. 14b, which more readily maintains the integrity of the pack 65. All the advantages and benefits of the stack 41 of Fig.14 and pack 45 of Figs. 14a and 14b, also apply to stack 63 of Fig.26 and packs 65 of Figs. 26a and 26b. The laid array of roof tiles 20d in the roof structure lOOd of Fig. 27 functions in the same way, and has the same benefits and advantages, as the laid array of roof tiles 20 in the roof structure 100c of Figs. 15 and 16. The top and eaves course tiles 20a described with reference to Fig. 15 are designated 64 in Fig.27. Referring to Fig.28, this shows a plain roof tile 20e which is like the tile 20d shown in Figs.20 to 27 but has a modified under surface 22c. The under surface 22c of the tile 20e is thickened in the mid-region 21c to provide even greater strength and therefore resistance to breakage from foot traffic in the laid roof. This thickening is achieved by curving the bottom 40a (straight in Fig.24) of the recess 37 and accentuating the curve already present in the bottom of the recess 38 to produce an intermediate ridge 32a of considerably lesser depth with a considerably more shallow pressure-moderating and anti-capillarity groove 36a than those of the ridge 32 and groove 36 shown in Fig. 24. The one-piece double plain tile 20f of the embodiment of Figs. 29 and 30 corresponds to, and is made in the same way as, the double tile 20c of Figs. 19 and 20 but is a twin of the plain tile 20d of Figs.21 to 25. Unlike the tile 20d, in the under surface 22d of the double tile 20f, the two ridges 30 of two single plain tiles 20d are merged together to form a single double ridge 30a having two pressure-moderating and anti-capillarity grooves 34 therein. The tile 20f has four spaced apart hanging nibs 25b projecting from the under surface head portion 62 which, as well as the L-shaped recess 61 in the upper surface 21, in this embodiment extends over the full width of the double tile. In Fig. 31 a roof structure comprises a roof 50 formed of a plurality of plain tiles 20, 20b, 20d or 20e and laid like the tiles 20 in the roof structure 100c of Fig. 15 and the tiles 20d in the roof structure lOOd in Fig. 27 in overlapping trailing edge to head edge 24 and side-by- side relationship, ie in a double lapped array. The roof tiles 20, 20b, 20d or 20e are laid in six courses at a rafter pitch of below 35° or below 27.5° and for clarity of illustration the shortened eaves and top course tiles 20a of Figs. 15 and 27 are omitted. All that can be seen by a viewer of the roof 50, are the aesthetically pleasing non-scuffed arcuate visible areas 21b and narrow leading edges 24. Referring now to Figs. 32 to 39, tile variants 51, 52, 53 are shown in which grooves or cutouts 54 are provided in the ridges or ribs 30, 31, 32 on the underside of the tiles 51, 52, 53. Like numerals are used for like parts but, with specific reference to the tile 51 of Fig. 32, it will be noted that the pressure-moderating and anti-capillarity grooves 34, 35, 36 divide the respective ridges 30, 31, 32 in which they are situated into parallel ridge portions. In particular, it will be noted that the intermediate ridge 32 is divided into an upper intermediate ridge portion 32u and a lower intermediate ridge portion 321, and that four cutouts 54 are provided in the upper intermediate ridge portion 32u. These cut-outs 54 splay outwardly and downwardly from the recess 37 to the groove 36, enabling air to flow between the recess 37 and the groove 36. Similarly, the side ridges 30 are each divided into an inner side ridge portion 30i and an outer side ridge portion 30o. Five cut-outs 54 are provided in each inner side ridge portion 30i. Three outwardly- and downwardly-angled cut-outs 54 are situated in each inner side ridge portion 30i above the intermediate ridge 32, allowing air to flow between the recess 37 and the grooves 34. Two inwardly- and downwardly-angled cut-outs 54 are situated in each inner side ridge portion 30i below the intermediate ridge 32, allowing air to flow between the recess 38 and the grooves 34. Fig. 33 illustrates the twin form 52 of the tile 51 of Fig. 32 which, like the twin-form tile of Fig. 20, has longitudinal ridges 30 conjoined or siamesed in a double ridge 30a divided by two parallel pressure-moderating and anti-capillarity grooves 34 and thus having two inner ridge portions 30i, one each side of the double ridge 30a. That understood, it will be evident that the cut-outs 54 are disposed in a manner akin to those of the single- width tile 51 of Fig. 32. As best seen in the horizontal and end views of Figs. 35, 37 and 38, the outer side ridge portions 30o and the lower intermediate ridge portion 321 are shallower than their counterparts, namely the inner side ridge portions 30i and the upper intermediate ridge portion 32u. Thus, when laid in a roof structure, only the inner side ridge portions 30i of the side ridges 30 and the upper intermediate ridge portion 32u of the intermediate ridge 32 are in contact with the upper surface of the underlying tile. Accordingly, air can flow between the underlying tile and the overlying outer side ridge portions 30o and lower intermediate ridge portion 321 while the cut-outs 54 allow free movement of air through the inner side ridge portions 30i and the upper intermediate ridge portion 32u and thus across the ridges 30 and 32. Figs. 32 to 39 show typical airflow patterns across the ridges 30, 32 by reference to the arrow-headed lines in those figures. It will be evident that, in the general areas of the laid roof, air is free to flow from the underside of each tile 51, 52, 53, through the cut-outs 54 in the ridges or ribs 30, 32, across and/or along the pressure-moderating and anti- capillarity grooves 34 and 36, under the outer side ridge portions 30o, and then to atmosphere via the gaps between adjacent tiles 51, 52, 53. In the case of the top tile 53 of Figs. 35 and 36, which is cut centrally along the pressure-moderating and anti-capillarity groove 36, air is free to flow from the underside of the tile, through the cut-outs 54 and immediately to atmosphere as shown. In the event that wind flowing over a completed roof creates an area of low pressure above a section of tiling, the embodiments of Figs. 32 to 39 provide freedom for air to flow across the underside of the tiles and vent to the upper side, hence reducing the pressure differential between the upper and lower surface of the tiles. This action effectively increases the dead- weight resistance of the tiles and reduces the need for mechanical fixings. The embodiments of Figs. 32 to 39 also provide high-level ventilation of roof spaces. By creating a top tile that has an in-built ventilation capability, and by providing a means for air to escape from the roof space to the underside of the tiling in the region of the top tile, the required high level ventilation can be achieved without resorting to specialist ventilation devices. Referring now to Figs. 40 to 50, a further tile variant 70 is akin to the ventilated tiles 51, 52, 53 of Figs. 32 to 39 and so, again, like numerals are used for like parts. It will be noted, in particular, that grooves or cut-outs 54 are provided in the ridges or ribs 30, 31, 32 on the underside of the tile 70 as before and that, similarly, pressure-moderating and anti- capillarity grooves 34, 35, 36 divide the respective ridges 30, 31, 32 in which they are situated into parallel ridge portions. The tile 70 of Fig. 40 is particularly akin to tile 52 of Fig. 33 in that the tile 70 is also of twin form and has a dummy groove 49 on the part of its upper side that will be exposed in a tiled roof structure. Nevertheless, it will be evident to the skilled reader how the features of tile 70 could be transferred to a single tile, like tile 51 of Fig. 32. In common with the twin-form tile 52 of Fig. 33, tile 70 of Fig. 40 has central longitudinal ridges conjoined or siamesed to form a double ridge 30a divided by two parallel pressure- moderating and anti-capillarity grooves 34. In this instance, however, further ridges or ribs 71 extend parallel to and lie between the side ridges 30 and the double ridge 30a, the ridges 71 extending above and below the intermediate ridge 32 and being disposed generally perpendicularly with respect thereto. As before, the intermediate ridge 32 divides the underside of the tile into upper and lower recesses 37 and 38; it will therefore be apparent that the ridges 71 divide each of the recesses 37 and 38 into first and second upper and lower recess portions 37a, 37b and 38a, 38b respectively. The ridges 71 cooperate with the inner side ridge portions 30i and with the intermediate ridge 32 to defme the lowest part of the underside of the tile 70, thus serving as supporting formations. As before, the outer side ridge portions 30o and the central portion of the double ridge 30a lying between the parallel grooves 34 are shallower than the supporting formations. Accordingly, when a plurality of tiles 70 are laid in a roof structure, gaps coincident with the outer side ridge portions 30o and the central portion of the double ridge 30a provide a path for air to flow across the underside of the tiles 70 and around their periphery. Additionally, it will be noted that the pressure-moderating and anti-capillarity grooves 34, 36 are themselves divided into groove portions by the intermediate ridge 32 and the ridges 71. More specifically, grooves 34 are each divided into an upper groove portion 34u and a lower groove portion 341 by interruptions 72 defined by the intermediate ridge 32, and groove 36 is divided by interruptions 73 defined by the ridges 71, thus defining a series of four groove portions 36a, 36b, 36c and 36d. As before, the intermediate ridge 32 is divided into an upper intermediate ridge portion 32u and a lower intermediate ridge portion 321, but in this instance four groups of four cut-outs 54 cross the upper intermediate ridge portion 32u. Each group of cut-outs 54 links a respective groove portion 36a, 36b, 36c and 36d with a respective one of the upper recess portions 37a, 37b. The cut-outs 54 of each group splay outwardly and downwardly from the respective upper recess portions 37a, 37b to the respective groove portions 36a, 36b, 36c, 36d. Four further groups of four cut-outs 54 each link one of the upper recess portions 37a, 37b to a respective one of the upper groove portions 34u. The cut-outs 54 of each of these groups are mutually parallel and are inclined downwardly from the upper recess portions 37a, 37b to the associated upper groove portions 34u. Finally, four pairs of cut-outs 54 link each lower recess portion 38a, 38b with a respective one of the lower groove portions 341. The cut-outs of each of these pairs are mutually parallel and are inclined downwardly from the lower groove portions 341 to the lower recess portions 38a, 38b. The cut-outs 54, and the groove portions 34u, 341, 36a, 36b, 36c, 36d and recesses 37a, 37b, 38a, 38b with which the cut-outs 54 communicate, provide a path for air to flow through or around the supporting formations. Various modifications may be made without departing from the scope of the invention as defined in the appended claims. For example, instead of the arcuate shape imparted to the visible area 21b of the upper surface 21 to avoid scuffing, each and every tile described may be provided with any other suitable shape consistent with producing a non-scuffed visible surface area of aesthetically pleasing appearance on the laid roof. The modified under surface of Fig.28 may be employed on any of the embodiments of Figs. 9, 10, 11, 12 and 13, Figs. 9a and 12a, Fig 9b, Figs. 17 and 18 and Figs. 19 and 20. The configuration, shape and arrangement of the under surface ridges and pressure-moderating and anti- capillarity grooves may be varied as desired or necessary to optimize support on the tile upper surfaces 21a and resistance to breakage.

Claims: CLALMS 1. A plain roof tile having an upper surface of which a lower surface area is visible when the tile is laid with other such tiles to form a roof, and an under surface, characterised in that the tile is shaped during manufacture to enable the visible surface area, when a plurality of such tiles are stacked one on top of another to form a stack, to be spaced from, and remain out of contact with, an oppositely facing under surface area of the immediate overlying tile of the stack. 2. A plain roof tile having an upper surface of which a lower surface area that is visible when the tiles are laid has a shape which is produced during manufacture of the tile and which, when stacked with other such tiles one on top of the other to form a stack, is spaced from, and remains out of contact with, an oppositely facing under surface area of the immediate overlying tile of the stack. 3. A method of making a plain roof tile having an upper surface and an under surface, characterized by forming the tile with a shape which enables a lower visible surface area on the upper surface when the tiles are stacked with other such tiles one on top of the other to form a stack, to be spaced from, and remain out of contact with, an oppositely facing under surface area of the immediate overlying tile of the stack. 4. A method of making a plain roof tile having an upper surface of which a lower area is visible when the tiles are laid, characterized by forming the visible surface area with a shape, which when stacked with other such tiles one on top of the other to form a stack, is spaced from, and remains out of contact with, an oppositely facing under surface area of the immediate overlying tile of the stack. 5. A plain roof tile as claimed in claim 1 or 2, wherein the visible surface area has a tapered shape with the taper extending in the direction from the head edge to the leading edge. 6. A plain roof tile as claimed in claim 5, wherein the taper is such that the leading edge is of reduced thickness. 7. A plain roof tile as claimed in claim 1 or 2, wherein the visible surface area has a curved, cambered or arcuate shape with the curve, camber or arc extending in the direction from the head edge to the leading edge. 8. A plain roof tile as claimed in claim 7, wherein the curve, camber or arc is such that the leading edge is of reduced thickness. 9. A plain roof tile as claimed in any one of claims 1, 2, 5, 6, 7 or 8, and having a substantially fiat upper non-visible upper surface area which receives, and supports, the lower under surface area of the overlying tile of a laid roof. 10. A plain roof tile as claimed in claim 9, and having an under surface with regions that present substantially flat supporting surfaces which rest, when a plurality of such tiles are laid to form a roof, on the non-visible upper surface area of the immediate underlying tile. 11. A plain roof tile as claimed in claim 10, wherein the supporting under surface regions extend into the upper area of the under surface so as to provide support for the tile substantially from the tiling battens to the leading edge when a plurality of such tiles are laid to form a roof. 12. A plain roof tile as claimed in claim 10 or 11, wherein the supporting under surface regions extend from a recess for receiving at least one hanging nib to the leading edge and lie in the same plane as the free end of the or each hanging nib and present the lowest point of the tile. 13. A plain roof tile as claimed in claim 10 or 11, and having at least one hanging nib, wherein the supporting surface regions extend from the head edge to the leading edge, with the free end of the or each hanging nib presenting the lowest point of the tile. 14. A plain roof tile as claimed in any one of claims 10 to 13, wherein the substantially flat supporting surface regions include at least one transversely extending supporting surface region. 15. A plain roof tile as claimed in claim 14, wherein the transversely extending flat supporting surface region comprises an intermediate region that rests on the substantially flat upper non-visible area of an underlying laid tile adjacent the head edge of that tile. 16. A plain roof tile as claimed in any one of claims 10 to 15, wherein the supporting surface regions are in the form of strengthening ridges which have weight reducing recesses therebetween. 17. A plain roof tile as claimed in claim 16, wherein at least some of said ridges are provided with a pressure-moderating and anti-capillarity groove. 18. A plain roof tile as claimed in claim 16 or claim 17, wherein at least one cut-out is provided in at least one of said ridges and is adapted to permit air to flow across or through the ridge when the ridge lies upon and is supported by an underlying tile in a roof structure. 19. A plain roof tile as claimed in claim 18 when appendant to claim 17, wherein the cutout communicates with the groove. 20. A plain roof tile as claimed in claim 18 or claim 19, wherein the cut-out communicates with a recess. 21. A plain roof tile as claimed in any of claims 16 to 20, wherein the ridge includes a first relatively deep portion and a second relatively shallow portion, the arrangement being such that when the first portion lies upon an underlying and supporting tile in a roof structure, a gap is maintained between the second portion and the underlying tile to permit air to flow between said tiles through said gap. 22. A plain roof tile as claimed in claim 21 when appendant to claim 18, wherein the cutout communicates directly or indirectly with the gap. 23. A plain roof tile as claimed in claim 21 or claim 22, wherein the first and second portions extend beside each other along the ridge. 24. A plain roof tile as claimed in claim 23, wherein the second portion is outboard of the first portion. 25. A plain roof tile as claimed in any one of claims 1, 2 and 5 to 24, and having a substantially flat area on the tile upper surface adjacent the head edge to provide a depalleting region for tiles made on pallets in production. 26. A plain roof tile as claimed in claim 13 or any claim dependent thereon and having a recess in the upper surface of the tile adjacent the head edge for accommodating said at least one hanging nib whose free end presents the lowest point of the tile when a plurality of such tiles are stacked one on top of the other to form a stack, with the head edges of the tiles being disposed immediately one above the other. 27. A plain roof tile as claimed in claim 26, wherein the head edges lie in a substantially vertical line. 28. A plain roof tile having an upper surface of which a lower surface is visible when the tile is laid with other such tiles to form a roof, and an undersurface, characterised in that said undersurface is formed in such manner as substantially to equalise pressure of air on said upper and under surfaces when air flows over said roof. 29. A plain roof tile as claimed in claim 28, wherein the undersurface is shaped to define at least one supporting formation which in use rests on the upper surface of an underlying laid tile, and wherein said formation is provided with airways permitting air to flow across, around or through said formation substantially to equalise pressure of air on said upper and under surfaces. 30. A plain roof tile as claimed in claim 29, wherein said formation is provided with a pressure-moderating and anti-capillarity groove. 31. A plain roof tile as claimed in claim 29 or claim 30, wherein at least one cut-out is provided in said formation and is adapted to permit air to flow across or through the formation when the formation lies upon and is supported in use by an underlying laid tile. 32. A plain roof tile as claimed in claim 31 when appendant to claim 30, wherein the cutout communicates with the groove. 33. A plain roof tile as claimed in claim 31 or claim 32, wherein the cut-out communicates with a recess in said undersurface. 34. A plain roof tile as claimed in any of claims 29 to 33, wherein the formation includes a first relatively deep portion and a second relatively shallow portion, the arrangement being such that when the first portion lies in use upon an underlying and supporting laid tile, a gap is maintained between the second portion and the underlying tile to permit air to flow between said tiles through said gap. 35. A plain roof tile as claimed in claim 34 when appendant to claim 31, wherein the cutout communicates directly or indirectly with the gap. 36. A plain roof tile as claimed in claim 34 or claim 35, wherein the first and second portions extend beside each other along said formation. 37. A plain roof tile as claimed in claim 36, wherein the second portion is outboard of the first portion. 38. A plain roof tile as claimed in any of claims 28 to 37 and being in the form of a top and/or eave tile. 39. A plain roof tile substantially as hereinbefore described with reference to Figs. 9, 10, 11, 12 and 13, 9a and 12a , Fig. 9b, Figs. 17 and 18, Figs 21 to 26, or any of Figs 9, 10, 11, 12 and 13, Fig. 9b, Figs. 17 and 18, or Figs 21 to 25, as modified by Fig. 28 of the accompanying drawings, or Figs. 32 to 39, or Figs. 40 to 50. 40. A one-piece double plain roof tile comprising two tiles as claimed in any one of claims 1, 2 and 5 to 29 and having a central groove in its upper surface and leading edge to simulate the effect of two closely spaced apart plain tiles. 41. A one-piece double plain roof tile substantially as hereinbefore described with reference to Figs. 19 and 20, Figs. 29 and 30, Fig. 33 or Figs. 40 to 50 of the accompanying drawings. 42. A method of making a one-piece double plain roof tile as claimed in claim 40 or 41, comprising creating the double tile on a single pallet to form the under surface shape of two single tiles at a time and moulding, pressing or extruding in said groove to simulate the effect of two closely spaced apart tiles. 43. A method of making a plain roof tile as claimed in claim 3 or 4 and substantially as hereinbefore described. 44. A method of making a plain roof tile as claimed in claim 3 or 4 and substantially as hereinbefore described with reference to Figs. 9, 10, 11, 12 and 13, Figs. 9a and 12a, Fig.9b, Figs. 17 and 18, Figs 21 to 25, or any of Figs. 9, 10, 11, 12 and 13, Fig.9b, Figs. 17 and 18, or Figs 21 to 25, as modified by Fig. 28 of the accompanying drawings, or Figs. 32 to 39, of Figs. 40 to 50. 45. A method of making a one-piece double plain roof tile substantially as hereinbefore described with reference to Figs. 19 and 20, Figs. 29 and 30, Fig. 33 or Figs. 40 to 50 of the accompanying drawings. 5 46. A stack of plain roof tiles as claimed in any one of claims 1, 2 and 5 to 28 or made by the method as claimed in claims 3 or 4 or of one-piece double plain roof tiles as claimed in claim 29 or 30 or made by the method as claimed in claim 34, disposed one above the other, wherein a visible surface area on an upper surface of a tile is spaced from, and remains out of contact with, an oppositely facing under surface area of the immediate o overlying tile of the stack. 47. A stack as claimed in claim 46, wherein the leading edges of the tiles of the stack are disposed immediately one above one another. 5 48. A stack as claimed in claim 47, wherein the leading edges of the tiles are disposed in a substantially vertical line. 49. A stack as claimed in any one of claims 46 to 48, wherein each overlying tile is in frictional contact with a non-visible flat upper surface area of each underlying tile. 0 50. A stack as claimed in any one of claims 46 to 49, wherein each tile has at least one hanging nib having a free end which presents the lowest point of the tile and wherein at least one hanging nib of each overlying tile is accommodated in a recess in the upper surface adjacent the head edge of the immediate underlying tile with the tile leading edges 5 being disposed immediately above one another. 51. A stack as claimed in claim 50, wherein the leading edges of the stacked tiles are disposed in a substantially vertical line. 0 52. A stack of plain roof tiles substantially as hereinbefore described with reference to Fig. 14 or Fig. 26 of the accompanying drawings. 53. A pack formed by packaging a stack of plain roof tiles as claimed in any one of claims 35 to 41. 54. A pack as claimed in claim 53, wherein a length of flexible material extends transversely around the stack in the mid-region of the tiles to package the tiles in the stack. 55. A pack as claimed in claim 54, wherein two lengths of flexible material respectively extend transversely around the stack in the mid-region and head regions of the tiles to package the tiles in the stack. 56. A pack of plain roof tiles substantially as hereinbefore described with reference to Fig. Fig. 14a, Fig.l4b, Fig. 26a or Fig. 26b of the accompanying drawings. 57. A roof structure comprising a plurality of plain roof tiles as claimed in any one of claims 1, 2 and 5 to 39 or made by the method as claimed in claim 3 or 4, or a one-piece double plain roof tile as claimed in claim 40 or 41 or made by the method as claimed in claim 45, laid in overlapping leading edge to head edge and side-by-side relationship to form a roof. 58. A roof structure comprising a plurality of plain roof tiles that have a width of more than 160 mm and as claimed in any one of claims 1, 2 and 5 to 39 or made by the method as claimed in claim 3 or 4, or a one-piece double plain roof tile that has a width of more than 320 mm and as claimed in claim 40 or 41 or made by the method as claimed in claim 45, laid in overlapping leading edge to head edge and side-by-side relationship to form a roof having a rafter pitch of below 35°. 59. A roof structure comprising a plurality of plain roof tiles that have a width of more than 205 mm and as claimed in any one of claims 1, 2 and 5 to 39 or made by the method as claimed in claim 3 or 4, or a one-piece double plain roof tile that has a width of more than 410 mm and as claimed in claim 40 or 41 or made by the method as claimed in claim 45, laid in overlapping leading edge to head edge and side-by-side relationship to form a roof, having a rafter pitch of below 27.5°. 60. A method of ventilating a roof structure comprising a plurality of roof tiles each having an upper surface and an undersurface, the method being characterised by the provision of a plurality of tiles each having an undersurface adapted such that said plurality of tiles permits a ventilating flow of air from the eaves to the ridge. 61. A method as claimed in claim 60, wherein the ventilating flow passes through a plurality of airways on the underside of the roof structure defined by the undersurfaces of the tiles. 62. A method of preventing or at least substantially reducing uplift of roof tiles in a roof structure comprising a plurality of said tiles each having an upper surface and an undersurface, the method being characterised by the provision of at least one tile having an undersurface adapted to permit a flow of air from below the roof structure to above the roof structure whereby substantially to equalise pressures above and below the roof structure . 63. A method as claimed in claim 62, wherein the flow of air is generally in a direction from the eaves to the ridge of the roof structure. 64. A roof structure comprising a plurality of plain roof tiles substantially as hereinbefore described with reference to Figs. 15 and 16, Fig. 27, Fig. 31, Fig. 37 or Fig. 38 of the accompanying drawings.

Inventors: BAMBER BARRY HUGH, FIFIELD JOHN ALFRED, BAMBER, BARRY, HUGH, FIFIELD, JOHN, ALFRED
Applicants: BAMBER BARRY HUGH, FIFIELD JOHN ALFRED, SCOTT TOOMEBRIDGE LIMITED, BAMBER, BARRY, HUGH, FIFIELD, JOHN, ALFRED, SCOTT (TOOMEBRIDGE) LIMITED
Application year: 1998
Main classification: E04D1
IPC codes: E04D1