Improvements in or relating to a roof cassette

Abstract

The roof cassette 100 comprises thermal insulation 170 between structural upper 110 and lower 120 layers (e.g., comprising OSB). The upper layer is thermally insulative and has an upper surface 112 which supports a thermally conductive weatherproof layer 140. A thermally conductive element 150 is located on the upper surface in contact with the weatherproof layer. A photovoltaic module 160 (e.g., a thin-film photovoltaic module) is provided on an upper surface 142 of the weatherproof layer and is separated from the upper layer by the weatherproof layer. The thermally conductive element may be recessed into the upper surface, may comprise a flat surface 152 in contact with the weatherproof layer, may be a channel for conveying a fluid, and may be non-linear (e.g., tortuous). The upper layer may comprise a structural layer 114 and an insulative layer 116. The weatherproof layer may be metal and / or comprise upturned sides 146. The cassette may comprise a vapour permeable membrane 180, structural members 132,133 and / or a fire-resistant layer 190.

Description

FIELD OF THE INVENTION The present invention relates to improvements in or relating to a roof cassette and, more specifically, to a fully integrated and structural roof cassette comprising insulation, weatherproofing, a photovoltaic module and / or a solar thermal system including both heat harvesting and photovoltaic cooling capabilities. BACKGROUND TO THE INVENTION Simple roof cassettes comprising traditional tiles and battens are known. It is also possible to affix Photovoltaic (PV) modules to these simple cassettes using brackets and / or other such fasteners post installation. However, such roof cassettes are somewhat inefficient in terms of installation, through roof fittings, energy generation and usage, structural performance, weight and cost. Similarly, standard roof construction using trusses, membrane, battens and tiles do not have PV or insulation designed in and such additions are generally fitted post roof completion. It is against this background that the present invention has arisen. SUMMARY OF THE INVENTION According to the present invention there is provided a fully integrated and structural roof cassette comprising: a structural upper layer and a structural lower layer having thermal insulation therebetween, wherein the upper layer is thermally insulative and comprises an upper surface that supports a structural and thermally conductive weatherproof layer. The roof cassette may comprise a photovoltaic module located on an upper surface of the weatherproof layer, such that the weatherproof layer separates the upper layer from the photovoltaic module. There is also provided fully integrated and structural roof cassette comprising: a structural upper layer and a structural lower layer having thermal insulation therebetween, wherein the upper layer is thermally insulative and comprises an upper surface that supports a structural and thermally conductive weatherproof layer; a thermally conductive element located on the upper surface of the upper layer, such that the thermally conductive element is in contact with the weatherproof layer; and a photovoltaic module located on an upper surface of the weatherproof layer, such that the weatherproof layer separates the upper layer from the photovoltaic module. In the context of this application, 'thermally insulative' means having a thermal conductivity less than 10 W / m-K and 'thermally conductive' means having a thermal conductivity of 10 W / m-K or greater. Also, in the context of this application, 'structural' means load bearing, in use; and 'weatherproof' means impermeable to water, such as rain. Consequently, a 'structural' feature is subjected to a compressive and / or tensile force. The force may be generated by an external load, such as wind, snow and / or another feature of the roof cassette, when the roof cassette is in use. The roof cassette may comprise a web. The web may extend between the upper layer and the lower layer. The upper layer may be structurally connected to the web. The lower layer may be structurally connected to the web. A structural connection may result in the connected features acting as one composite structural feature. In other words, a structural connection enables the connected features to resist load by a joint action (i.e. by pooling their respective strengths). A structural connection may be generated using any suitable connecting means, such as glue, adhesive, screws, bolts, and / or dowels. In particular, screwed, glued and / or doweled connections provide a highly robust and lightweight structure. Preferably, a glue or adhesive may be used. The web may be an integrated structural element. The web may comprise a plurality of monocoque boxes. The monocoque boxes may be interconnected boxes. Each box may comprise four side members. Of the four side members, two may be longitudinal members and two may be cross members. Each side member may form part of the web. At least one side member of a first box may be contiguous with a side member of an adjacent boxes. More specifically, each monocoque box may comprise six planar members. The six planar members may include four side members configured to form a web, the structural upper layer, and the structural lower layer. The upper layer and lower layer may be contiguous across a plurality of boxes. The longitudinal side members may also form part of the adjacent box. In fact, any of the side members may extend as one element and continue to become the side of the next connected monocoque box. For example, the cross (or latitudinal) side members may form the cross (or latitudinal) side member of the adjacent monocoque box. At all junctions of the upper layer, lower layer, and side members there may be a structural connection. The structural connection may provide a fully integrated and contiguous or composite structure. Consequently, the fully integrated and structural roof cassette may be a monocoque roof cassette. More specifically, the fully integrated and structural roof cassette may bean interconnecting system of monocoque boxes arranged as a grid. In other words, the roof cassette may comprisea shell structure deriving bi-directional bending resistance or strength from intersecting planar surfaces. The intersecting planar surfaces may comprise the upper layer, lower layer and web. The resulting structure may be a 3D planar shell structure. The whole structure, comprising the upper layer, lower layer and web, may act as a composite section having structural properties analogous to the terminology of a structural steel beam. For example, the upper layer may be an upper flange, the lower layer may be a lower flange and the web may extend there between. The upper layer provides rigidity to the roof cassette whilst restricting the transfer of thermal energy through the roof cassette. For example, the upper layer comprises timber such as 0SB3 or plywood that may be 15 mm or 18mm or 20mm thick. Timber is a poor conductor of thermal energy and, in the context of this application, is thermally insulative. Alternatively, the upper layer may be a pultrusions made of Glass Reinforced Plastic (GRP) or Carbon Fibre Reinforced Plastic (CFRP). The weatherproof layer provides further rigidity whilst also enabling thermal energy to be transferred between the photovoltaic (PV) module and the thermally conductive element. Consequently, excess thermal energy can be transferred from the PV module to the thermally conductive element, via the weatherproof layer. This can be used to reduce the temperature of the PV module and maintain its operating efficiency. The thermal energy transferred into the thermally conductive element may be recycled. For example, the energy may be used within a building heating system. Alternatively, or in addition, the thermal energy transferred into the thermally conductive element may be used within at least one of a mechanical ventilation and heat recovery system; a heat pump; and a water cylinder. The mechanical ventilation and heat recovery system may include a heat pump. The heat pump may be driven by electricity from the photovoltaic (PV) module. The heat pump may heat or cool incoming / outgoing air. Alternatively, or in addition, the heat pump may use energy from the thermally conductive layer to provide a thermal energy source for the heat pump or to lose excess heat out to the thermally conductive element as described below. The heat pump may deliver hot water and / or heating to a building or, in conjunction with the mechanical ventilation and heat recovery system heat, cool or moderate the internal temperature or climate of a building. Thermal energy can also be transferred from the thermally conductive element to the PV module, via the weatherproof layer. This process may be used to melt snow and / or ice located on the PV module, for example. Doing so effectively clears the surface of the PV module and maintains the operating efficiency thereof. Transferring thermal energy from the thermally conductive element to the PV module, via the weatherproof layer, can also be used to remove heat energy from a space, such as from within a house. This may be achieved using a heat pump. More specifically, this may be achieved using a mechanical ventilation and heat recovery (MVHR) system integrated with a heat pump. Locating the thermally conductive element on the upper surface of the upper layer increases the amount of thermal energy transferred to the thermally conductive element. This is because the material surrounding the conductive element is relatively insulating compared to the thermally conductive element, thus minimising the amount of thermal energy transferred into the upper layer. The roof cassette may be at least 1 metre (m) in length. Alternatively, the roof cassette may at least 2m, 3m, 4m, 5m, 6m, 8m, 10m, 12m, 15m or 20m in length. The roof cassette may be up to 0.4m, 0.8m, lm, 1.2m, 1.8m, 2.4m, 3.6m or more than 3.6m wide. This enables the roof cassette to be used on roofs having a variety of different geometries. The roof cassette, while having parallel sides, may be manufactured such that its top (ridge) end and lower (eave) end may be set at angles from 90 degrees in order to accommodate roofs that have valleys and hips. As previously disclosed, the web may be an integrated structural element comprising a plurality of monocoque boxes. The web may be made from timber, such as OSB. The web may comprise a plurality of planar members. Each member may be made from timber, such as OSB. The planar members may form a plurality of monocoque boxes, as previously described. At least one planar member may be at least lm, 2m, 3m, 4m, 5m, 6m, 8m, 10m, 12m, 15m or 20m in length. Alternatively, or in addition, at least one planar member may be up to 10mm, up to 12mm or up to 18mm thick. In some embodiments, the at least one planar member may be more than 19mm thick. However, preferably, each planar member is 11mm thick. Each end of the roof cassette structure may rest on a support plate or pad. The support plate or pad may be the wall plate at the eave end of the cassette. At the ridge end of the cassette, the support plate or pad may be a timber or steel beam that spans from side wall to side wall or some form of truss. In the case of a timber or steel beam, the combination of the roof cassettes and beam comprises a large warm roof space that can be used as a further room in the roof. In contrast to traditional PV modules and / or solar collector systems and / or PVT systems attached to a standard roof, the present invention does not require additional brackets, through roof fixings, tiles, battens, fixings, membrane, rafters or purlins. Instead, the present roof cassette only requires a single support pad along the ridge of the roof structure, whilst the eaves ends of the present roof cassette simply sit on the wall plate. Thus, not only is material eliminated, but the time to deliver a water tight roof is significantly reduced and the time spent "working at height" during the installation process is also greatly reduced. The weatherproof layer may be structurally connected to the upper layer. Consequently, the waterproof layer and upper layer may form a composite structural layer. A composite structural layer comprising the upper layer and the weatherproof layer provides increased strength compared to the sum of the individual layers. The weatherproof layer may be structurally connected to the upper layer via glue. Alternatively, or in addition, the weatherproof layer may be structurally connected to the upper layer via an adhesive and / or construction quality double sided tape, such as SIGA Twinet® 20. The thermally conductive element may be recessed into the upper surface of the upper layer. This enables the weatherproof layer to be located directly adjacent to (i.e. in contact with) the upper layer, thus enabling a more secure connection there between. Alternatively, the thermally conductive element may be located within a groove located in the upper surface of the upper layer. The weatherproof layer may be made of metal. For example, the weatherproof layer may be made of steel. Steel is a strong and weatherproof material, thus enabling a single layer of material to provide multiple beneficial functions for the roof cassette. However, other materials may be used. For example, the weatherproof layer may be made of other metals, such as copper, zinc, aluminium (and alloys thereof), and titanium. Alternatively, the weatherproof layer may be made of a composite material, such as carbon fibre reinforced plastic (CFRP). Moreover, in some embodiments, the weatherproof layer may comprise one or more cooling channel. This may be implemented if pultrusions are employed. The weatherproof layer may be a standard industrial roofing or cladding product for which no further treatment will be necessary. However, in some embodiments, the upper surface of the weatherproof layer may comprise a coating. The coating may be configured to prevent the weatherproof layer from rusting. The coating may comprise a plastisol layer, a zinc layer and / or a primer layer. Moreover, the coating may be thin enough not to significantly alter the thermal conductivity of the weatherproof layer. The weatherproof layer may comprise a lower surface in contact with the upper surface of the upper layer. In other words, the lower surface of the weatherproof layer may be opposed to the upper surface of the weatherproof layer. The lower surface of the weatherproof layer may comprise a coating. Again, this coating may be configured to prevent the weatherproof layer from rusting. The coating may comprise a protective zinc layer and / or layer of paint. As before, the coating may be thin enough not to significantly alter the thermal conductivity of the weatherproof layer. The weatherproof layer may comprise a flat base and upturned sides. The upturned sides may be substantially perpendicular to the flat base. For example, the weatherproof layer may have a substantially U-shaped cross-section. The base of the 'U' may comprise the flat base. The flat base may be approximately 800 millimetres (mm) wide; the upturned sides of the weatherproof layer may be approximately 65 mm high; and each of the base and the sides may be up to 0.7mm thick. This geometry may provide additional stiffness to the roof cassette. Alternatively, in some embodiments, the flat base may be up to 400mm, 600mm, 1,000mm or more than 1,000mm wide. In fact, the flat base may be any width conforming to regular building practices. The weatherproof layer may be manufactured from standard rolled material. The upturned sides enable the waterproof layer to be connected to the waterproof layer of an adjacent roof cassette. The connection between two adjacent upturned sides may also be waterproof. Alternatively, or additionally, the cassette may comprise a weatherproof seal between two adjacent weatherproof layers. The weatherproof seal may be a steel capping channel, membrane, tape, mastic or adhesive. The upturned sides and weatherproof seal may provide the impression of a rising seam roof. In some embodiments, a standing seam closer may be used to provide the weatherproof seal. The standing seam closer may be zinc, aluminium or copper. This may provide additional integrity to the weather tightness of the roof. For example, the weatherproof layer may be a TATA steel® Catnic® Urban (formally Colorcoat Urban) section with its proprietary standing seam means of jointing. Similarly, each roof cassette may comprise a waterproof layer having a plurality of adjacent structural and waterproof sections. Each section may comprise a flat base and upturned sides. Two or more adjacent sections may be connected at their upturned sides to provide a waterproof joint. Consequently, the weatherproof layer may be bound by proprietary upstand members that form a closure at the joint between each weatherproof section. Each weatherproof section may be an 800mm wide steel sheet having upturned sides. In some embodiments, the upturned sides may extend along each long edge of the cassette, thus forming a U-shaped weatherproof section spanning from one end of the cassette (i.e. a roof ridge end, in use) to the other end (i.e. a roof eaves end, in use). The thermally conductive element may comprise a flat surface that is at least 3mm in length and in contact with the weatherproof layer. However, in some embodiments, the flat surface of the thermally conductive element may be at least 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 8mm, or at least 10mm in length. The flat surface increases the surface area of the thermally conductive element in contact with the weatherproof layer. This increases the rate that thermal energy can be transferred therebetween. For example the thermally conductive element may be a D-shaped element, such as a D-shaped pipe or tube. The thermally conductive element may be metallic. In particular, the thermally conductive element may be copper. The thermally conductive element may be at least 10mm in diameter and / or 10mm in width. Therefore, the groove may be at least 10mm wide and / or 10mm deep. For example, the groove may be half-cylindrical. The base radius of the groove may comprise a base radius of 5mm. Alternatively, in some embodiments, the thermally conductive element may be up to 10mm, or 15mm in diameter and / or width. Therefore, the groove may be up to 10mm, or 15mm wide and / or up to 10mm, or 15mm deep. The thermally conductive element may be fixed within the groove. For example, the thermally conductive element may be glued within the groove or may be a simple interference fit. The thermally conductive element may comprise a second flat surface opposed to the first flat surface. The second flat surface may be shorter than the first flat surface. For example, the second flat surface may be less than 3mm in length. The second flat surface may be in contact with the base of the groove. In some embodiments, the thermally conductive element is a pipe having a 10mm outer diameter, wherein the pipe comprises a flattened top and bottom surface. The flattened top and bottom surface may be generated by passing the thermally conductive element through a roller press. The thermally conductive element may be a fluid channel configured to convey a fluid. The fluid may be configured to store thermal energy. For example, the fluid may be water. The fluid may comprise at least 10%, more preferably 20%, and most preferably 30% by concentration antifreeze and / or inhibitors. This may prevent the fluid from freezing when exposed to low temperatures. It may also counter any sludge build up. Fluid, such as water, flowing within the fluid channel may be used to transfer heat efficiently to or from the PV module. In particular, water has a high specific heat capacity, thus making it a particularly effective fluid for use in the fluid channel. However, other fluids may also be used. For example, the fluid may comprise oil. The thermally conductive element may be non-linear. A non-linear thermally conductive element may be used to increase the area of the element in contact with the weatherproof layer, which increases the amount of thermally energy that can transfer therebetween. More specifically, the thermally conductive element may be tortuous. As such, the thermally conductive element may comprise at least one curve having an apex. The upper surface of the upper layer comprises at least one expansion void configured to allow the thermally conductive element to expand there into. More specifically, the recess (or groove) comprising the thermally conductive element may comprise at least one expansion void configured to allow the thermally conductive element to expand when subjected to increased temperatures. This reduces the likelihood of the thermally conductive element breaking, cracking and / or otherwise failing. There may be a plurality of expansion voids. The recess (or groove) comprising the thermally conductive element may comprise at least one expansion zone located at the apex of the at least one curve. This helps to control the thermal expansion of the conductive element, which reduces the likelihood of fluid leaking therefrom. The thermally conductive element may be a single element. The thermally conductive element may be void of any connections or joints beneath the waterproof layer. In other words, the thermally conductive element may be void of any connections (or joints) located between the waterproof layer and the upper layer. As such, leakage of any fluid from a joint or connection in the thermally conductive element will occur above the waterproof layer and will run down the outside of the roof cassette. The upper layer may be Oriented Strand Board (OSB). In particular, the OSB may be 0SB3. The OSB layer may be up to 15mm, up to 18mm thick or more than 18mm thick. Alternatively, or in addition, the upper layer may comprise a wood fibre material or plywood layer. The upper layer may be continuous. As such, the upper layer may comprise a single timber sheet extending across the entire surface area of the roof cassette. The upper layer may comprise a structural layer and a thermally insulative layer. The structural layer of the upper layer may be a timber layer. More specifically, the timber layer may be 0SB3. The structural layer may up to 15mm thick, up to 20mm thick, or up to 30mm thick. The thermally insulative layer of the upper layer may be a wood fibre layer. The thermally insulative layer may be up to 20mm thick, up to 30mm thick or up to 50mm thick. The structural layer may be structurally connected to the thermally insulative layer. As such, the upper layer may be a composite upper layer. The upper surface of the thermally insulative layer may be the upper surface of the upper layer. As such, the thermally conductive element may be located on the upper surface of the thermally insulative layer. The structural layer may be continuous. As such, the structural layer may comprise a single timber sheet extending across the entire surface area of the roof cassette. The lower layer may be Oriented Strand Board (OSB). In particular, the lower layer may be 0SB3. The lower layer may be up to 11mm or 15mm thick. Alternatively, the lower layer may be a pultrusions made of Glass Reinforced Plastic (GRP) or Carbon Fibre Reinforced Plastic (CFRP). The roof cassette may further comprises a fascia board configured to provide a substantially vertical fascia when the roof cassette in in use. Alternatively, or in addition, the roof cassette may further comprises a soffit board configured to provide a substantially horizontal soffit when the roof cassette in in use. The photovoltaic (PV) module may be a thin film photovoltaic module. The PV module may comprise a plurality of copper indium gallium selenide (CIGS) PV cells. Alternatively, or in addition, the PV module may comprise one or more silicon wafer PV cells. This may increase the efficiency of the PV module whilst minimising cost. Alternatively, or in addition, the PV module may comprise perovskite. In some embodiments, the PV module comprises a solar enhancing coating. The solar enhancing coating may be configured to alter the composition of the spectrum of light from the sun. This may enhance efficiency. The PV module may be connected directly to the weatherproof layer. No other fixings may be required. In general "thin film" photovoltaic modules will be used. However, it is recognised that as technology advances there will be more efficient and more economic products marketed that could also be used in the present invention. There may be a plurality of PV modules. Each PV module may be as described above. As previously described, the web may comprise two or more longitudinal structural members extending between the upper layer and lower layer. The longitudinal structural members may be side members. The web may also comprise at least one structural cross member extending between two longitudinal members. There may be a plurality of longitudinal members. There may be a plurality of cross members. Each cross member may connect between two longitudinal members. The longitudinal members and cross members may form the plurality of monocoque boxes. Each cross member may provide lateral bracing. A plurality of cross members may be positioned at various intervals and / or at each end of a longitudinal member. The intervals may be at 400mm, 600mm, 800mm, 1,000mm, 1,200mm or more than 1,200mm centres, for example, depending on the design requirements of the roof cassette. Each cross member may be fabricated to fit accurately and closely to the longitudinal member. Each cross member may be connected to a longitudinal member using adhesive, glue, one or more screw and / or one or more dowel. Other connection means may also be used. Alternatively, or in additionally, each cross member may be connected to at least one of the upper layer and or lower layer using adhesive, glue, one or more screw and / or one or more dowel. Again, other connection means may also be used. In some embodiments, the roof cassette may comprise two substantially parallel longitudinal members having one or more cross member extending therebetween. In some embodiments, the roof cassette may comprise more than two substantially parallel longitudinal members having one or more cross member extending therebetween. In some embodiments, there is at least two cross members. Incorporation of a plurality of cross members creates a strong box section. The roof cassette may comprise a U-value of 0.2 W / m2-K or less. More preferably, the roof cassette may comprise a U-value of 0.15 W / m2-K or less. Most preferably, the roof cassette may comprise a U-value of 0.1 W / m2-K or less. A U-value of 0.1 W / m2-K meets Passivhaus requirements. The thermal insulation may be configured to provide the roof cassette with the desired U-value. More specifically, the thickness and thermal resistance of the thermal insulation may be configured to provide the roof cassette with the desired U-value. The thermal insulation may be integrated between the structural upper layer and the structural lower layer. More specifically, the thermal insulation may be located within one or more of the monocoque boxes. In particular, the thermal insulation may be located within each of the monocoque boxes. The thermal insulation may be conformable. The thermal insulation may be mineral fibre, wool or fibrebased insulation. Alternatively, the thermal insulation may be rigid foam insulation. For example, the thermal insulation may be rigid closed cell foam, such as such as Polyisocyanurate (PIR), extruded polystyrene insulation (XPS) or expanded polystyrene (EPS). In some embodiments, thermal insulation may also be provided on an external face of the web structure, such that two cassettes positioned directly adjacent to each other do not comprise an uninsulated void therebetween. The roof cassette may comprise a vapour permeable membrane. The vapour permeable membrane may be configured to prevent water vapour from entering the roof cassette therethrough. Alternatively, or in addition, the vapour permeable membrane may be configured to allow water vapour to exit the roof cassette therethrough. The vapour permeable membrane may be positioned below the lower surface of the lower layer. The vapour permeable membrane may wrap up around the sides of the lower layer. The roof cassette may further comprise a fire resistant layer. The fire resistant layer may have a fire resistance duration of at least 30 minutes. More preferably, the fire resistant layer may have a fire resistance duration of at least 60 minutes. Most preferably, the fire resistant layer may have a fire resistance duration of at least 90 minutes. The fire resistant layer may be located below the lower layer and / or vapour permeable membrane. The fire resistant layer may be the lowermost layer. The fire resistant layer may be plasterboard. The fire resistant layer may be up to 15mm or 18mm thick. The fire resistant layer may comprise a fire resistant paint. In some embodiments, the fire resistance layer may comprise the lower layer. The average weight of the cassette may be less than 200kg per Im length. Preferably, the average weight of the cassette is less than 175kg per Im length. More preferably, the average weight of the cassette is less than 150kg per lm length, and, most preferably, the average weight of the cassette is less than 140kg per lm length. This means that the cassette can be installed on the roof of the majority of domestic homes by a small crane, thus minimising cost of installation. Moreover, the cassette can be fitted onto the roof of the majority of domestic homes without additional strengthening of walls or the building. The roof cassette is therefore usable for retrofit, refurbishment or new build housing. This enables an average house to be provided with a complete roof structure in a matter hours, thus minimising the period when a house is open to the weather and minimising the amount of time working at height. The PV module may cover at least 80% of the weatherproof layer. However, in some embodiments, the PV module covers at least 50%, 60% 70%, 80%, or 90% of the weatherproof layer. The PV module may comprise one or more PV elements. Each PV elements may be configured to generate electricity. The PV module may be configured to generate an average of at least 1320 Watts peak in the UK. Consequently, the PV module may produce enough energy for the roof cassette to pay for itself over period less than 10 years, preferably, less than 8 years, and most preferably less than 6 years. In some embodiments, a UK-based south facing roof cassette may generate 1185 kWhs in one year. However, the amount of energy generated throughout the ear may vary between 0.5 - 5.4 kWh. In summary, the roof cassette is specifically designed to utilise all of its materials in the most efficient way and to eliminate any unnecessary fittings or fixtures. Thus the PV is affixed directly to the weatherproof layer, which is affixed directly to the upper layer, which comprises the thermally conductive element. The thermal insulation is then integrated beneath the upper layer and the lower layer is affixed beneath the thermal insulation. The whole underside is wrapped in the membrane. The invention will now be further and more particularly described, by way of example only, with reference to the accompanying drawings FIGURES Figure 1 shows a cross-section of one embodiment of the roof cassette. Figure 2 shows an exploded cross-section of an embodiment of the roof cassette. Figure 3 shows the web of the roof cassette according to some embodiments of the present invention. Figure 4 shows two adjacent weatherproof sections connected via their upturned sides. Figure 5 shows a roof cassette according to some embodiments of the invention. DETAILED DESCRIPTION Figure 1 shows a roof cassette 100 according to some embodiments of the present invention. The roof cassette 100 comprises a structural upper layer 110 and a structural lower layer 120. A web 130 extends between the upper layer 110 and lower layer 120. More specifically, the web 130 comprises side members 132 extending between the upper layer 110 and lower layer 120. The side members are 11mm 0SB3. The side members 132 are connected to the upper layer 110 and lower layer 120 via connecting blocks 135. The connection blocks 135 are planed timber. More specificaIly, the connection blocks are 35mm by 35mm C24 planed timber blocks. The connection blocks 135 may each be up to 8m long. However, other means of connecting the side members 132 to the upper layer 110 and / or lower layer 120 may be used. Moreover, in some embodiments, as shown in figure 3, the web 130 comprises at least one structural cross member 133 extending between one or more longitudinal side members 132. The upper layer 110 is thermally insulative. In some embodiments, the upper layer 110 is made from timber. In some embodiments, the upper layer 110 is Oriented Strand Board (OSB) and, in some embodiments, the OSB is 0SB3. Also, in some embodiments, such as the embodiment shown in figure 1, the upper layer 110 is a composite layer comprising two or more layers. In particular, the upper layer 110 comprises a structural layer 114 and a thermally insulative layer 116. The lower layer 120 is thermally insulative. In some embodiments, the lower layer 120 is made from timber. In some embodiments, the lower layer 120 is Oriented Strand Board (OSB) and, in some embodiments, the OSB is 0SB3. The upper layer 110 comprises an upper surface 112. The upper surface 112 supports a structural and thermally conductive weatherproof layer 140. The weatherproof layer 140 is structurally connected to the upper layer 110. Consequently, the waterproof layer 140 and upper layer 110 form a composite structural layer. In some embodiments, the upper surface 112 is the upper surface of the thermally insulative layer 116. In some embodiments, the weatherproof layer 140 is made of steel. Also, in some embodiments, the weatherproof layer 140 comprises a flat base 144 and upturned sides 146. The roof cassette 100 further comprises a thermally conductive element 150 located on the upper surface 112 of the upper layer 110. More specifically, the thermally conductive element 150 is recessed into the upper surface 112 of the upper layer 110. The upper surface 112 of the upper layer 110 comprises at least one expansion void (not shown) configured to allow the thermally conductive element 150 to expand there into. This provides room for the thermally conductive element 150 to expand and contract as its temperature raises and lowers. The thermally conductive element 150 is a fluid channel configured to convey a fluid. The thermally conductive element 150 is non-linear. More specifically, the thermally conductive element 150 is a tortuous pipe configured to convey a fluid, such as water. The thermally conductive element 150 is in contact with the weatherproof layer 140. More specifically, the thermally conductive element 150 comprises a flat surface 152. The flat surface 152 is at least 3mm in length. The flat surface 152 is in contact with the weatherproof layer 140. The roof cassette 100 further comprises a photovoltaic module 160 located on an upper surface 142 of the weatherproof layer 140. The weatherproof layer 140 separates the upper layer 110 from the photovoltaic module 160. The photovoltaic module 160 is a thin film photovoltaic module. More specifically, there are two photovoltaic modules 160. Each photovoltaic module 160 is a thin film photovoltaic module. The PV module(s) 160 covers at least 50% of the upper surface 142 of the weatherproof layer 140. The roof cassette further comprises thermal insulation 170. The thermal insulation 170 is located in the void created between the upper layer 110, lower layer 120 and web 130. The thermal insulation 170 is configured to provide the roof cassette with a U-value less than 0.1 W / m2 K. Moreover, in some embodiments, as shown by the dashed line in figure 1, the roof cassette further comprises a vapour permeable membrane 180. The vapour permeable membrane is configured to prevent water vapour from entering the roof cassette therethrough. Moreover, the vapour permeable membrane 180 is configured to allow water vapour to exit the roof cassette therethrough. Some embodiments also comprise a fire resistant layer 190, as shown in figure 1. In some embodiments, the fire resistant layer 190 is a plasterboard layer. In some embodiments, including the embodiment shown in figures 1, the roof cassette 100 is a composite structure capable of spanning a roof lengthwise (eaves to ridge) and / or crosswise (side to side). It does this by utilising the structural upper layer 110 and structural lower layer 120 to resist compression and tension. The compressions and tension may be generated by the bending effects caused by at least one of dynamic loads during lifting and / or transport; snow load; access load (such as personnel); and wind suction load. Compressive stress may be transferred to any adjacent features by direct compression. Conversely, tensile stresses are transferred to structurally connected features via the connection there between. The roof cassette 100 further comprises a web 130 extending between the upper layer 110 and lower layer 120. In some embodiments, the web 130 is an integrated structural element comprising a plurality of interconnected monocoque boxes. The web 130 is configured to transfer shear stress to the supports. Alternatively, or additionally, the web 130 is configured to resist the longitudinal and 'rolling' shears. For instance, when the roof cassette 100 is spanning from ridge to eaves (of a roof), the vertical reactions at the ridge and eaves are balanced by shear stresses in the web 130. Also, the opposing forces in the upper layer 110 and lower layer 120 react against the web 130, thus preventing differential strain. This strain is termed rolling shear. When the roof cassette 100 is spanning longitudinally (such as between the ridge and eaves of a roof) and resisting vertical loads (such as snow or access loading), the upper layer 110 is typically placed in compression and the lower layer 120 is typically placed in tension. The upper layer 110 and lower layer 120 thus resist the bending effect caused by the gravitational actions of the loads. When subjected to wind uplift the bending may be reversed and the upper layer 110 placed in tension and the lower layer 120 in compression. More specifically, the web 130 may comprises a plurality of structurally connected members 132,133. The connections may comprise splices pieces. The splice pieces may transfer the stress between the individual members 132,133. These connections may be positioned at locations of low stress transfer. The upper layer 130 is also configured to support foot traffic for maintenance. This is achieved by virtue of a continuous upper layer, which spans up to 800mm between two adjacent side members 132. Consequently, the roof cassette 100 is capable of resisting a variety of load and support arrangements that induce stresses as such stresses are resisted and transferred throughout the roof cassette in an efficient manner. This results in a robust roof cassette 100. Figure 2 shows an exploded cross-section of an embodiment of a roof cassette 200. The embodiment shown in Figure 2 has all the same features as the embodiment shown in figure 1, as indicated by the accompanying reference numbers. Figure 3 shows the web 130 of the roof cassette 100 according to some embodiments of the present invention. In particular, figure 3 shows a basic monocoque box structure and how the upper layer 110, lower layer 120, longitudinal side members 132 and cross members 133 may overlap to adjacent boxes. Figure 4 shows a weatherproof layer 140 comprises two adjacent weatherproof sections 141 connected via their upturned sides. Each weatherproof section 141 comprises a flat base 144 and at least one upturned side 146. Each weatherproof section 141 is made of steel. Each section 141 may be up to 2mm thick or, more specifically, up to 1.6mm thick. Figure 5 shows a roof cassette 500 according to some embodiments of the invention. The roof cassette 500 comprises a plurality of longitudinal side members 132 and at least one cross side member 133. The roof cassette 500 also comprises a structural upper layer 110, a structural lower layer 120, a weatherproof layer 140, at least one thermally conductive element 150, and at least one photovoltaic module 160. Other features as described with respect to the previous figures may also be present in the embodiment shown in figure 5. Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure, "and / or" where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example, "A and / or B" is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein. Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments that are described. It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments, it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.

Claims

1. A fully integrated and structural roof cassette comprising:a structural upper layer and a structural lower layer having thermal insulation therebetween, wherein the upper layer is thermally insulative and comprises an upper surface that supports a structural and thermally conductive weatherproof layer;a thermally conductive element located on the upper surface of the upper layer, such that the thermally conductive element is in contact with the weatherproof layer; anda photovoltaic module integrated on an upper surface of the weatherproof layer, such that the weatherproof layer separates the upper layer from the photovoltaic module.

2. The roof cassette according to claim 1, wherein the weatherproof layer is structurally connected to the upper layer, such that the waterproof layer and upper layer form a composite structural layer.

3. The roof cassette according to any preceding claim, wherein the thermally conductive element is recessed into the upper surface of the upper layer.

4. The roof cassette according to any preceding claim, wherein the weatherproof layer is made of metal.

5. The roof cassette according to any preceding claim, wherein the weatherproof layer comprises a flat base and upturned sides.

6. The roof cassette according to any preceding claim, wherein the thermally conductive element comprises a flat surface that is at least 3mm in length and in contact with the weatherproof layer.

7. The roof cassette according to any preceding claim, wherein the thermally conductive element is a fluid channel configured to convey a fluid.

8. The roof cassette according to any preceding claim, wherein the thermally conductive element is non-linear.

9. The roof cassette according to any preceding claim, wherein the upper surface of the upper layer comprises at least one expansion void configured to allow the thermally conductive element to expand there into.

10. The roof cassette according to any preceding claim, wherein the upper layer is Oriented Strand Board (OSB).

11. The roof cassette according to any of claims 1 to 9, wherein the upper layer comprises a structural layer and a thermally insulative layer.

12. The roof cassette according to any preceding claim, wherein the lower layer is Oriented Strand Board (OSB).

13. The roof cassette according to any preceding claim, wherein the photovoltaic module is a thin film photovoltaic module.

14. The roof cassette according to any preceding claim, comprising two or more longitudinal structural members extending between the upper layer and lower layer and at least one structural cross member extending therebetween.

15. The roof cassette according to any preceding claim, wherein the roof cassette comprises a U-value of 0.1 W / m2-K or less.

16. The roof cassette according to any preceding claim, further comprising a vapour permeable membrane configured to prevent water vapour from entering the roof cassette and allow water vapour to exit the roof cassette therethrough.

17. The roof cassette according to any preceding claim, further comprising a fire resistant layer.

18. The roof cassette according to any preceding claim, wherein the average weight of the cassette is less than 200kg per lm length.

19. The roof cassette according to any preceding claim, wherein the PV module covers at least 80% of the weatherproof layer.

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