GB2496424A - Roofing system comprising components with a projection and co-operating rebate. - Google Patents

Abstract

The system comprises first and second roofing components where the first component comprises a rebate and the second component comprises a projection that corresponds to the said rebate. The components are designed such that the projection abuts against the rebate in use. In various embodiments of the invention the respective first and second components are: i) a floor cassette and a roof support; ii) a spandrel and a roof panel; iii) a spandrel and a floor cassette and iv) a roof panel component and a roof panel component. In the first embodiment the floor cassette 27 may have a number of wall plates 86a and 86b which include at least one but preferably several rebates 88 which receive the projections 94 made by a series of rafters 90 in a roof support. The roofing system may comprise a pair of spandrels. Also claimed is a method of locating the projection within a rebate and the rebate supporting the weight of the first component at the abutment point of the projection on the rebate. The rebate may be tapered or arcuate.

Description

ROOFING SYSTEM

The present invention relates to a roofing system for use in building construction and in particular, though not exclusively, to a roofing system wherein at least two roofing system components can engage and co-operate with one another to provided support and to facilitate an efficient roofing system assembly and a securely assembled roof.

Until recently habitable room in the roof space of a building was only possible using trussed rafters or loose cut roofs.

Both of these methods provide structurally sound solutions but involve most of the work being performed on-site and at height.

Panelised roofs have been introduced in recent years and are now growing in popularity and sophistication. The principal drivers are speed of consuruction, assured levels of performance through improved quality control, the desire for improved health and safety and the minimisacion of waste on-site.

One known system is Smartroof® produced by Smartroof Ltd and described in GB 2391026. This is a prefabricated, modular roofing system comprising main roof panels which can span the distance between gable ends and can be supported thereby and intermediate panels which do not span the whole roof and are supported by, and cooperate with, the main roof panels. One side of the roof system preferably comprises at least two main roof panels, one set of intermediate panels arranged between the main roof panels to provide window openings, an cave panel and an apex panel. The cooperating surfaces may extend across the full length of the panels. The roof is preferably attached by a tongue and groove system, wherein the groove is provided along a sloping edge at the gable ends, or spandrels if used, and the tongues are located on the ends of the roof panels. A method of assembling the roof using bracing means Is also disclosed whereby a spandrel once affixed to the brickwork of the end walls of the building is braced to the side walls to prevent sideways movement during roof construction. In this roof system substantially all the weight of the roof is supported by the end walls as compared to other roofing systems where the weight of the panels is at least partially supported on the side walls which tends to foroe the side walls apart due to the lateral loading applied.

There are a number of disadvantages In this roofing system.

The panels must be manufactured to a high tolerance and the spandrels separated by an equally high tolerance, so that the toncue and grooves mate correctly. A considerable amount of screwing and nailing is required to restrain the roof panels from sliding down the roof line. This lateral loading down the pitch of the roof is increased by the use of closed roof panels which are made heavier by the inclusion of insulation and surrounded boarding. Additional time is required when the spandrels are craned into position, as the cranes must bear the weight of the spandrels until such time as the bracing arrangement is fitted.

GB 2475539 to F4ITek Holdings, Inc. describes a method of constructing a roof on top of a building comprising; fixing two lower spandrels, one on each of the other two sides of the top of the building, the lower spandrels each having a trapezoidal shape having two parallel sides and two sloping sides; fixing ceiling panels to the upper sides of the spandrels to form a platform; fitting upper spandrels above the respective lower spandrels on the ceiling panels; and fitting gable tc gable roofing panels to bridge the gap between the sloping sides of the spandrels to form a roof. The method may comprise constructing a small wall atong two opposite sides of the top of the building and the ceiling panels may be closed panels with insulation. A groove may be provided in the sloping edge of one of the spandrels for locating the roofing panels. The roofing panels may comprise at least one flitch beam attached to the spandrel to transfer the load which may comprise a sheet of steel sandwiched between two wooden beams.

This roofing system uses ohe well-known piggy back' arrangement of spandrels and locates a ceiling between the lower and top-hat spandrels. While it identifies the disadvantages in the earlier patent application, it fails to mitigate some while introducing others. This roofing system describes the construction of two small timber walls on the side walls, these are matched to snubbed ends of the lower spandrels. It is not clear if these are tied together to form a brace, but it does require specially shaped spandrels. This roofing system also uses locators on the roof panels to lie in a groove along the sloping edge of the spandrel and thus has the same disadvantages to tight tolerances as the prior art roofing system, though the presence of, and the width of, the small wall may assist this, if it is constructed to a tight tolerance. The roofing panels are lighter weight than those detailed in GB2391026, having no insulation and the locators set the panels so as to be spaced apart from the spandrels.

This arrangement means that flitch beams are incorporated to screw the panels to the spandrels and transfer the load.

However, the beams add extra time and components to the construction, do not prevent the panels from sliding down the roof line during construction and provide a substantial air gap between the panels and the spandrels. This air gap must be filled to seal the roof, adding further time and construction materials. Additionally, insulation needs to be added to the roof panels and, although there is a greater space to add more insulation, this merely increases the load of the roof which is entirely transferred to the end walls.

An additional disadvantage is in the arrangement of the ceiling onto the lower spandrel. The ceiling cassette is designed to sit over the upper parallel sides of the lower spandrels and to locate in the groove on the sloping edges of the spandrels. This arrangement means that the roof panels cannot be fitted directly against the spandrels to create a seal as ceiling noggins are located over the spandrels. The roofing panels require locators to span the ceiling noggins and as discussed above, the resulting air gap provides disadvantages in construction.

It is an object of the present invention to provide a roofing system for use on a building wherein at least part of the roofing system is efficient to assemble and secure upon as s e mb 1 y.

It is a further object of at least one embodiment of the present invention to provide a roof system for use on a building which distributes the load of the roof arrangement assembled thereon.

It is a further object of at least one embodiment of the present invention to provide a roofing syscem for use on a building which may be assembled with at least a reduced requirement for additional fixings such as nails and screws.

According to a first aspect of the present invention there is provided a roofing system for use in a roof of a building, the roofing system comprising at least one first roofing system component and at least one second roofing system component, wherein the at least one first roofing system component is provided with a surface having at least one rebate and the at least one second roofing system component is provided with a surface having a projection which corresponds to the said rebate such that said rebate and projection co-operate with one another such that a surface of the projection abuts against a surface of the rebate to provide support to a portion of the roofing system.

In this way, the roofing system can be assembled such that the first roofing system component projection can co-operate with a rebate of the second roofing system component such that the components can be assembled together guickly, simply and efficiently. In addition, the co-operation of the components means that less, if any, additional securing means such as screws and nails are reguired to secure the components together therefore reducing the cost and time associated with assembling the roofing system as well as minimising the reguirement for a skilled tradesperson to be involved in the assembly of the roofing system on the building. In addition, the abutting surfaces of the corresponding components provide support to one another which facilitates the distribution of the weight of the roofing system more effectively across the footprint of the assembled roof.

Preferably, said first roofing system component is a floor cassette and said second roofing system component is a roof support. Further preferably, said floor cassette comprises a floor panel having a lower surface arranged for location upon a building surface area on which a roof arrangement is to be provided; a substantially planar upper surface; a plurality of side edges and at least one wall plate wherein said wall plate is arranged on said upper surface such that an cuter edge cf said wail plate corresponds to a side edge of said floor panel and an inner edge of said wall plate comprises at least one rebate to provide an abutting surface to support at least a portion of a projection of a roof support.

In uhis way, a floor cassette can be arranged in a roofing system such that the wall plate retains and provides support to a roof support such as a rafter, joist or spandrel. In this way, the floor cassette bears, and distributes, the weight of the joist or spandrel and any roof panels arranged thereon across the roof cassette thus reducing lateral or outward pressure of the roof arrangement on the walls of the building or lower roof arrangement on which it is assembled.

In addition, the rebates act to provide support to said roof support therefore minimising, if not eliminating, the addition securing means, such as ties, supports, nails or screws, which are required as well as the manpower needed for the assembly of the roof when using such fastenings. The rebates further ensure that a snug secure arrangement is created during assembly of the roof such that there are minimal gaps left during construction which may need filled later.

Preferably the floor cassette is provided with wall plates arranged at opposing side edges of the floor panel. By arranging wall plates to oppose one another the load of the structures secured thereto will be distributed more effectively across the whole floor cassette.

Each floor cassette rebate may have a tapered profile. A tapered profile will mean that the roof support projection received into, and abutting against, the rebate may be wedged into position by the weight of the roof assembly. This will result in a more secure construction and ensure effective support is provided by the floor cassette assembly.

Preferably, each rebate has an abutting surface which is arcuate in profile. By having a rounded abutting surface, the rebate is able to provide a greater degree of tolerance in the positioning of the portion of the abutting roof support and can facilitate the guiding of the roof support into position in the rebate of the floor cassette.

Alternatively, said first roofing system component is a spandrel and said second roofing system component is a roof panel. Preferably, the spandrel comprises a solid timber frame having at least three sides; a first side arranged for location upon a wall of a building; second and third sides being inclined towards opposite ends of the first side, respectively; the second and third sides each providing an upwardly facing sloping surface for affixing roof panels; and the sloping surfaces having a plurality of rebates arranged along their length, with each rebate located substantially perpendicular to the incline to provide an abutting surface to support at least a portion of projection of a roof panel.

In this way, a series of step-shaped recesses are provided down each sloping surface. A roof panel, provided with at least one corresponding projection, when lowered onto the sloping surface will therefore naturally slide down the incline and be stopped at the ridge created by the stepped shape recess. The ridge prevents movement of the roof panel while supporting its weight. In providing multiple ridges on a spandrel, a number of roof panels can be positioned and their weight will be distributed along the length of the side of the spandrel.

S

Alternatively, the first roofing system component is a spandrel and said second roofing system component is a floor cassette. Preferably, the spandrel comprises a solid timber frame having at least four sides; a first side arranged for location upon a wall of a building; second and third sides being inclined towards opposite ends of the first side, respectively; and a fourth side arranged parallel to the first side such that the spandrel is trapezoidal, the fourth side providing an upwardly facing horizontal surface for affixing a floor cassette, a plurality of rebates arranged along the horizontal surface with each rebate providing an abutting surface to support at least a portion of a projection of a floor cassette.

This arrangement provides a lower spandrel for use with a floor cassette onto which an upper or top hat spandrel can be built. Such spandrels provide ease of transportation for roofs of increased height. By having rebates provided in the horizontal surface, and corresponding projections formed on a floor cassette, the floor cassette can be abutted against the lower spandrel securely without the requirement for further fixing means such as screws or nails. In addition, the arrangement will minimise the likelihood of gaps being left in the assembled spandrel and floor cassette arrangement thus reducing the need for subsequent filling of gaps.

Furthermore, the assembled floor cassette and spandrel arrangement will be advantageous over prior art systems in that the placement of the roof panels will not he impeded by the floor cassette arrangement.

Alternatively, the first roofing system component is a roof panel component and said second roofing system component is a roof panel component. Preferably, the roof panel components are rafter ridge components wherein each rafter ridge component is provided with at least one projection and at least one rebate such that a first rafter ridge component rebate corresponds with a second rafter ridge component projection with each rebate providing an abutting surface to suppcrt at least a portion of a corresponding projection.

In this way, the rafter ridge panel components can be abutted against one and other such that they co-operate with each other efficientiy and simply to provide a secure assemble which minimises the reguirement for other securing components such as nails and screws. In addition, such an arrangement does not require a skilled tradesman thus the cost associated with on site assembly of the roof system is reduced.

Preferably, the roofing system comprises a first floor cassette; at least two spandrels and at least two roof panels wherein each roof panel is provided with at least one projection which corresponds with a rebate provided in one of said floor cassette, one of said spandrels and another of said roof panels such that said rebate and projection co-operate with one another to provide support to a portion of the roofing system.

In this way, a roof panel of the roofing system will be able to be engaged with at least one other component of the roofing system in such a way that the components can he assembled together quickly, simply and efficiently. In addition, the co-operation of the roofing panel and another component means that less, if any, additional securing means such as screws and nails are required to secure the roofing panel to the corresponding component thus reducing the cost and time associated with assembling the roofing system as well as minimising the requirement for a skilled tradesperson to be involved in the assembly of the roofing system on the building.

The roofing system may further be provided with a second floor cassette which is provided with at least one projection which corresponds with, and co-operates with, a rebate provided in one of said spandrels such that said rebate and projection co-operate with one another to provide support to said second floor oassette.

Such an arrangement faoilitates the assembly of a roofing system as the second floor cassette can be used for a "piggy-back" roofing system arrangement. In addition, the provision of rebates and corresponding projections in the assembly of the second floor cassette on the spandrels ensures that the components can be assembled simply with minimal, if any, additional securing means reguired. A second floor cassette which can be assembled on top of the spandrels using a projection and rebate technique will further ensure that the second floor cassette can be integrated into the roof assembly without creating any unnecessary air gaps which would have to be filled by a skilled tradesman once the components of the roofing system had been assembled.

According to a second aspect of the present invention there is provided a method of constructing a roof of a building comprising the steps: (a) locating a first roofing system component having a rebate, according to the first aspect, on a suitable surface area; (b) locating a second roofing system component having a projection, according to the first aspect, such that the projection thereof correspcnds with a rebate of the said first roofing system component; (c) directing said second roofing system component towards said first roofing system component until said rebate and projection co-operate with one another such that a surface of the projection abuts against a surface of the rebate; and (d) supporting said second roofing system component weight at the abutting surface of the rebate and distributing said weight.

In this way, roofing system components can be located and supported simply by using a crane, thus removing the need for highly skilled workers at the location of building construction to locate and affix roofing system components to the building structure. This saves considerable time and cost in the build and also increases safety.

Embodiments of the present invention will now be described, by way of example only, in which: Figure 1 is an expanded illustration of a roof system for a building including a floor cassette according to an embodiment of the present invention; Figure 2 is a schematic illustration of a castellated spandrel with a roof panel according to further embodiment of the present invention; Figure 3 is a side view of a portion of a roof system according to a further embodiment of the present invention; Figure 4 is a perspective view of a floor cassette according to further embodiment of the present invention; Figure 5 is a perspective view of a portion cf a roof panel according to a further embodiment of the present invention; Figure 6 is a perspective view of a portion of a roof panel according to a further embodiment of the present invention; Figure 7 is a cross section of a roof system according to a further embodiment of the present invention; Figure 8 (a) is a perspective view of a floor cassette according to a further embodiment of the present invention; Figure 8 (b) is a cross section of a portion of a roof system according to a yet further embodiment of the present invention; and Figure 9 illustrates an assembled roofing system according to a further embodiment of the present invention.

Referring initially to Figure 1 of the drawings there is illustrated a roofing system, generally indicated by reference numeral 10, comprising floor cassette, spandrels 12a,b and roofing panels 14a-g, according to an embodiment of the present invention.

Roofing system 10 is located upon a building 16 formed of end walls 18 (one shown) and side walls 20 (one shown) . End and side walls 18,20 are typically constructed of block or brickwork and form the storeys of the building 16 as is known in the art. At the roof level 22, a floor level 24 is constructed formed of one or more floor cassettes 26, in this case, the roofing system is formed with one floor cassette 26.

It will be appreciated that, although not shown, floor level 24 may alternatively be formed of joists laid aoross the opposite walls 18,20 and covered in boarding.

In this embodiment, floor cassette 26 comprIses an array of joists (not shown) which are braced together preferably with a Strongbridge® recessed brace. Boarding is nailed to the upper surface to create a floor 27 and rim boards are arranged around the perimeter such that when the floor cassette 26 is lifted onto the building 10, the rim 28 aligns with the outer face 30 of the walls 18,20. The floor cassette 26 can have an access hole arranged there through for positioning of a staircase or a hatch.

The floor cassette 26 is further provided with, In this case, two wall plates 82 (one shown) arranged on the upper surface, or floor, 27 with each wall plate 82 having an outer edge 84 which corresponds with the rim 28 aligned with walls 20. The wall plate 82 is further provided with an inner edge 86.

Floor cassettes speed up construction time on-site, reduce the requirement to have skilled labour on-site to construct a floor and create minimal on-site waste.

Each spandrel 12 is formed of three timbers 32,34,36 placed in a triangular arrangement with a base timber 32 and two inclined timbers 34,36 meeting at an apex 38.

The roofing system 10 is further provided with a plurality of panels 14a-g. As can be seen, panels 14a and 14g at least, are constructed from a plurality of rafters 90 on which a panel surface has been arranged. Panels 14a-14d abut against one another and are arranged such as to span, and be supported by spandrels 12a and l2b across timbers 34a and 34b. Panels 14d' -14g abut against one another and are arranged such as to span, and be supported by spandrels 12a and 12b across timbers 36a and 36b. Roof panels l4a and 14g are eaves roof panels which form the eaves of the roofing system 10. Roof panels 14d and 14d' are apex roof panels which meet to form apex 38 of the roofing system.

Referring now to Figure 2 of the drawings, a portion of a timber 34 is shown in greater detail together with a roof panel 14. Timber 34 is formed in two parts, an upper 42 and a lower 44 section. This provides a strengthened timber 34 but the timber 34 could be a single piece if desired.

The lower section 44 is standard rectangular cross-section solid timber. The upper section 42 has an upper face 46 which is a sloping surface arranged down an incline of the spandrel 12. On the face 46 there are machined a series of grooves 48.

Three grooves 48 are illustrated but there could be any number along the length of the face 46.

Each groove 48 is a rectangular cross-sectional bed edged by a high abutting surface 52 and low abutting surface 54. Each groove, or rebate, 48 is machined from the face 46 across the timber section 42, so that the abutting surfaces 52,54 are perpendicular with the sloping edge and incline of the timber 34. Bed surface 50 is in parallel with, but recessed from, sloping surface and incline of the timber 34. The series of grooves 48 present on the upper face 46 of the inclined timbers 34,36, give the spandrel 12 a casteilated appearance.

The roof panel 14 has, at the outside edge of the panel 14, an outer edge rim 56 which is formed to correspond to the upper surface 46 of inclined timber 34 of the spandrel 12. It will be appreciated that each side edge of a roof panel 14 will be provided with an outer edge rim 56 which corresponds with a respective inclined timber 34,36 of a spandrel 12. The outer edge rim 56 is formed of a single piece of timber and has an upper rim surface 58, which is planar, and a tower rim surface 60. Lower rim surface 0 is provided with ridges 62. In this case two ridges 62 are shown however, there could be any number of ridges provided along the length of the lower rim surface 60.

Each ridge 62 has a rectangular cross section and is edged by a first abutting surface 64 and a second abutting surface 66.

Each ridge 62 is formed by a recess 68 being machined from the timber of the outer edge rim 56 such that abutting surfaces 64, 66 are perpendicular with the sloping surface and incline of the lower rim surface 56. Ridge surface 70 is in parallel with, but projecting from, sloping surface and incline of the lower rim surface 60 of outer edge rim 56. Tn a preferred embodiment, the ridges 62 project from the lower rim surface to a depth which corresponds to the depth of grooves 48 in the corresponding spandrel timber 34, 36 so that when assembled there is no gap between the ridge surface 70 and the bed surface 80. The series of ridge projections 62 present on the lower rim surface 60 give the outer edged rim 56 a casteliated appearance.

In Figure 3, there is shown cross section of an arrangement of portions of the outer edge rim 56 of two roofing panels 14a, l4b co-operating with castellated spandrel timber 34. Two ridge projections 62 are shown on lower panel 14a. As can be seen, the first abutting surface 64 of each ridge 62 is abutted against the low abutting surface 54 of the corresponding rebate 48, and ridge surface 70 rests against bed surface 50.

For the ridges 62 arranged centrally on the outer edge rim 56 of the roofing panel 14a and l4b, when first abutting surface of each ridge 62 is abutted against low abutting surface 54, a void 72, in this case a small rectangular void, is created between the high abutting surface 52, the second abutting surface 66, the bed 50 and the rim recess 68. After the roof has been assembled, voids 72 can simply be filled by one of the construction team.

As can be seen, where upper panel 14b is arranged to co-operate with lower panel 14a as well as spandrel timber 34, the first abutting surface 64 of the leading edge 74 of the panel 14b abuts against the seoond abutting surface 66 of the rear edge 76 of the panel 14a with first abutting surface of panel i4a abutting against the lower abutting surface 52 of groove 48 and the second abutting surface 66 of panel 14b adjacent to, and in this case abutting against high abutting surface 52 of groove 48. The arrangement of the leading edge 74 and rear edge 76 of co-operating roof panels abutting against one another ensures a snug fit between adjacent roofing panels is achieved.

Reference is now made to Figure 4 which shows floor cassette 26 which comprises floor 27 and rim 28, in this case rim panels 28a and 28b. Floor 27 is provided with two wall plates 82a, 82b, formed of a strap of timber each of which have an outer edge 84a, 84b respectively which is aligned with rim panels 82a, 82b respectively. Each wall plate 82a, 82b is further provided with an inner edge 86a, 86b from which rebates 88 have been machined such that they extend into the wall plate 82 towards outer edge 86. Each rebate 88 is provided with two opposing rebate side walls 87 and an abutting edge 89. In this case opposing rebate side walls 87 are tapered such that they are closer together as they reach the abutting edge 89 than they were at outer edge 86.

In Figure 5, there is shown a portion of leading edge 74 of a panel 14, which is an eaves roof panel such as a roof panels 14a or 14g from Figure 1 which will form the eaves of a roofing system, shown upside down. Panel 14 comprises a plurality of roof supports which in this case is rafters 90 arranged in parallel to and spaced apart from one another and to which panel surface 92 is affixed. In this case, five rafters 90 have been shown but it will be appreciated that any number of rafters may be used depending on the dimensions of the roof arrangement being constructed.

At leading edge 74, each rafter, or roof joist, 90 is provided with an angled surface 91 which a projection 94 projects from.

Each end projection 94 has an oval cross section and in this case projections 94 were formed by machining each rafter end 91 prior to assembly of roof panel 14. Each projection has an end face 100, an abutting face 102 and opposing side faces 104. The panel 14 is further provided with a facing plate 96.

Facing plate 96 is a planar sheet of timber having a width which extends the width of leading edge 74 of the panel 14 and a length which corresponds to the length of each rafter end 91. The facing plate 96 is further provided with a plurality of voids 98 which are spaced apart to correspond to projects 94 such that when assembled, inner surface 96b of facing plate 96 abuts against rafter ends 91 and projections 94 project through voids such that end face 100 of projection 94 projects away from outer surface 96a of facing plate 96.

In Figure 6 there is shown a portion of rear edge 76 of a panel 14, which is a rafter roof panel such as a roof panel 14d or 14d' from Figure 1 which will form the apex of a roofing system. Panel 14 comprises a plurality of roof supports which in this case is rafters 90 arranged in parallel to and spaced apart from one another and to which panel surface 92 is affixed. In this case, five rafters 90 have been shown but it will be appreciated that any number of rafters may be used depending on the dimensions of the roof arrangement being constructed.

At rear edge 76, each rafter, or roof joist, 90 is provided with an angled surface 105 from some of the angled surfaces, in This case surfaces 105a and 105b, have a projection 106 which projects therefrom. Each projection 106 has an oval cross section and in this case projections 106 were formed by machining each angled surface 105 prior to assembly of roof panel 14. Each projection has an end face 110, an abutting face 112 and opposing side faces 114.

The panel 14 is further provided with a facing plate 107.

Facing plate 107 is a planar sheet of timber having a width which extends the width of leading edge 74 of the panel 14 and a length which corresponds to the length of each angled surface 105. The facing plate 107 is further provided with a plurality of voids 108 which are spaced apart to correspond to projections 106. When assembled, inner surface iO7b of facing plate 107 abuts against angled surface 105 and projections 106 project through voids 108 such that end face 110 of projection 106 projects away from outer surface 107a of facing plate 107.

The angled surfaces 105 of joists 90 which are not provided with projections are instead provided with rebates 109. The facing plate 107 is provided with voids 108 which are spaced apart to correspond with rebates 109 such that they form an extension to rebates 109. The rebate surface 119 closest to apex 38 will, upon assembly, act as an abutting surface.

The rebates 109 are arranged such as to correspond with, and be able to receive, projections extending from another opposing roof panel which will cc-operate with the panel shown to form the apex of a roofing system (not shown) In Figure 7 there is shown a cross section of a roof system, and which includes the features of the arrangements shown in Figures 4, 5 and 6. The roof system 10 includes the floor cassette 26 described with reference to Figure 4 and roof panel 14 which is a single roof panel which includes the eaves roof panel features and apex roof panel features described with reference to Figures 5 and Figure 6.

As can be seen, when assembled, projections 94 are arranged such that they extend into corresponding rebates 88 so that abutting face 102 of projection 94 abuts against abutting surface 89 (not shown) Facing plate 96 acts to ensure that the roof panel 14 and floor cassette 26 are abutted against one another in such a way that no gaps or spaces are created which will require filling by a tradesman in order to ensure the roof is sealed.

In addition, although not seen, at apex 138, projections 106 are received by rebates 109 such that outer surfaces lO7a of facing plates 107 abut against one another. When this happens, abutting faces 112 will abut against rebate surfaces 119 thus providing support to the assembled roof panels 14.

To assemble the roof system id shown in Figure 7, the floor cassette 26 is located such that rims 28a and 28b correspond with and supported upon walls 20. Although not illustrated, it will be appreciated that rims 28c and 28d may correspond with walls 18. Roof panels 14 are arranged such that projections 94 of rafters 90 are arranged to correspond with a rebate 88 in floor cassette 26. Projections 94 are directed towards a side edge 84 of floor panel 27 of the floor cassette 26 such that the abutting face 102 of each projection 94 meets the corresponding abutting surface 89 of the rebate 88. Opposing rebate side wall 87 co-operate frictionally with opposing side faces 104 of projections 94. Tn this way, each rebate supports the weight of the corresponding rafter 90 at abutting surface 89 thus facilitating the distribution of the said weight across the structure of the floor cassette 26.

Rafters 90 also meet and are secured together at apex 38 such that the roof panels 14 form a continuous roof surface.

At the same time, projections 106 on a roof panel 14 are arranged to correspond with a rebate 109 on the opposing roof panel 42. The projections 106 are directed into rebates 109 such that when the roof panels 14 are assembled, the abutting face 112 of each projection 106 abuts against rebate surface 119.

In this way, roof supports, in this case rafters 90 formed as part of roof panels 14, can be located and supported simply by using a crane, thus removing the need for highly skilled workers at the location of building construction to locate and affix roof supports to the building structure. This saves considerable time and cost in the build and also increases safety.

Referring now to Figure 8 (a) shows a perspective view of a portion of a further embodiment of a floor cassette 126 and Figure 8 (b) which shows a cross section view of a portion of a roofing system including a floor cassette 126, it can be seen that in this embodiment, floor cassette 126 comprises an array of joists 128 which are braced together preferably with a Strcngbridgeo recessed brace (not shown) . Boarding is nailed to the upper surface to create a floor 127. At end 140 of each joist 128 there is formed a stepped projection 142 having an abutting face 144.

Such a floor cassette 126 is of particular use in a "piggy-back" roofing system which includes lower spandrels 12a and upper spandrels 12b. Lower spandrel 12a will include a fourth timber 35 and has a trapezoidal shape. Upper spandrel 12b has a triangular shape. The floor 127 of cassette 126 will be formed to correspond with the spandrel timber 32b such that it does not extend beyond the extent of surface 37 of spandrel timber 35.

Fourth timber 35 is, on an upper surface 37, provided with a series of machined grooves:48. Three grooves 148 are illustrated but there could be any number along the length of the upper surface 136.

Each groove 148 is a rectangular cross-sectional bed edged by an abutting surface 150 and opposing side surfaces 152. Each groove, or rebate, 148 is machined from the face 137 across the width of the timber 35 When floor cassette 126 is provided on a spandrel timber 35, the abutting surface 144 of projections 142 correspond with, and abut against abutting surfaces 150 of grooves 148 in spandrel timber 35. As can be seen, this arrangement ensures that the floor cassette 126 does not project beyond the extent of spandrel timber 32b and therefore does not impinge on the placement of roof panel 14. Upon assembly, this means that a small gap 154 will be formed between roof panel 14, spandrel timber 35 and spandrel timber 32b which will be filled easily by an on site builder following assembly of the roofing system 10.

Referring now to Figures 9, the build sequence of arranging a roofing system 10 according to an embodiment of the present invention is detailed. The assembly oommences with provision of a floor cassette 26, such as that detailed in Figures 4 and 5, followed by erection of lower spandrels 12a (one shown) which have a trapezoidal shape, with the lower base edge 32a arranged upon floor oassette 26 such that the spandrels 12a are upon end walls 18 (one shown) . A ceiling cassette 126, such as that detailed in Figure 8(a) and 8(b), is then arranged upon upper surface 37 of timber 35 of spandrels 12a such that it extends between spandrels 12a across the roof space to form a ceiling platform. Upper spandrels i2b are then secured to ceiling cassette 126 so that they are arranged above lower spandrels l2a. The sloping edges 34a, 36a; 34b, 36b are formed from the assembly of spandrels 12a and 12b.

In order to arrange the roofing panels on the spandrel, an eaves roofing panel, in this case panel 14a, which extends from spandrel timber 134b across the roof void 80 to spandrel timber 134b is put in a position so that outer edge rims 56a, 56b is parallel with but slightly spaced apart from the spandrel timbers 34a,34b such that the roof panel Ha is slichtly closer to the apex 38 of the roofing system 10 than It will finally be arranged. Once arranged in a desirable position, the roof panel Ha is then allowed to come into contact with spandrel timber 34 and slide into position in relation to timber 34. Projections 62 move into a groove 48 and first abutting surface 64 abuts against the lower abutting surface 54. The abutting surfaces 64, 54 then act to support the roof panel 14a In position in the roofing system 10 without the need for any further securing using nails or screws. Tn addition, projections 94 at the leading edge 74a of the roofing panel abut against rebates 88 of floor cassette 26 to form the bottom edge, or eaves, of the roof system 10.

A subsequent panel, such as intermediate roofing panel l4b, which in this case includes a void for use in including a window in the assembled roof, is then to be added to the roof system. The panel 14b is put in a position relative to the spandrel timber 34, such that it is between the rear edge 76 of panel Ha and apex 38, lying approximately parallel to and spaced apart from spandrel timber 34, slighuly closer to the apex 38 than it will finally be arranged. The leading edge 74 of panel 14b is adjacent the rear edge 76 of panel 14a. Once arranged in a desirable position, the roof panel 14b is then allowed to come into contact with spandrel timber 34 and slide into position in relation to timber 34 and roof panel i4a.

The lower roof panel l4b is manoeuvred into such a position that the projection 62 at the leading edge 74 moves into a groove 48 and gravity acts on the roof panel 14b to ensure that leading edge 74 abuts against rear edge 76 and projection 62 of panel 14a. The remaining projections 62 on panel l4b move into corresponding grooves 48 and first abutting surface 64 abuts against the lower abutting surface 54. As above, the panel 14b is then securely in position without the requirement of further securing means such as nails or screws to prevent the panels 14a or lAb from sliding down the roof line.

Subsequent roof panels 14c, 14d, which are an intermediate roofing panel and an apex roofing panel respectively, are then arranged in the same manner as detailed in relation to panels Ha and 14b above such that, when in place, the rear edge 76d of panel lAd contributes to the formation of apex 18.

The same assembly process is carried out for the roof panels arranged to correspond with sloping spandrel timber 36. Rear edge 76d' of panel lAd' then corresponds with rear edge 76d of panel 14d to create apex 38. Projections 106 are arranged to correspond with opposing rebates 109 and are directed into rebates 109 such that when assembled, the abutting face 112 of projections 106 abuts against rebate surface 119.

Once the roof panels 14a-g are in place and the roofing system 10 is assembled using the technique detailed above, a plurality of small voids 72, 154 will remain between the assembled roof panels 14a-g and the spandrels 34, 36 and these can be simply filled to complete the roof.

The principal advantage of the present invention is that it provides a roofing system in which the roofing components are provided with corresponding rebates and projections which abut together to provide support to one another at abutting surfaces and act to distribute the weight of the assembled roof more evenly across the footprint of the roofing system assembly and therefore spread the weight across the extent of the supporting walls. This reduces the pressure placed upon the side walls or end walls of a building thus minimising the potential for damage being caused to the walls through supporting the weight of the roofing system.

Another advantage of an embodiment of the present invention is that once slotted into place, the roofing components provided with corresponding rebates and projections require minimal additional securing means to be used in affixing them together the spandrels, this can minimise the cost and time associated with construction.

A further advantage of present invention is that the roof components can be simply arranged to create the roofing system without the need on-site for complex machinery or highly skilled workers.

A yet further advantage of the present invention is that only very smaiLl voids remain after the assembly of the roofing system and these can be simply and easily filled by a suitable tradesman. This improves the wind and water tightness of the roof system during the construction phase and also results in a minimal cost being incurred in sealing the roof system upon oompletion.

It will be appreciated to those skilled in the art that various modifications may be made to the invention herein described without departing from the soope thereof. For example, whilst the rebates and the projections have been detailed as being tapered, triangular or rectangular in cross section, they may have any suitable cross sectional shape, including but not limited to rhomboid and square. The roof panels may, or may not be provided with a void designed for inclusion of a window. The leading edges and rear edges of the roof panels may be arranged to correspond with any part of, or sit apart from, a projection. The roof supports have been detailed as being roof joists or rafters, however it will be appreciated that the spandrels of the roofing system may be provided with projections which correspond to a rebate in the floor cassette and thus may be secured to a floor cassette in a manner as detailed herein. Whilst in the arrangement detailed, the spandrels and floor cassette have been detailed as being provided with rebates and the roof panels provided with corresponding projections, it will be easily understood that the roof panels could instead be provided with rebates and the spandrels and floor cassette provided with corresponding projections.