A roofing sheet assembly

Abstract

A clip for attaching a roofing sheet onto an underlying support structure, comprising: a base having a first end, the first end comprises a tapped hole extending along the length of the base for recei

Description

Field The present application relates to a roofing sheet assembly, and in particular to a clip, a roofing sheet assembly, and a method for forming the roofing sheet assembly. Background Roofing sheets, otherwise used also as cladding sheets, are cost-effective solutions for sheltering outdoor areas and outbuildings. In some applications, particularly greenhouses and conservatories, double-glazed roofing sheets are utilized to improve thermal insulation and thereby reduce energy loss. However, such an installation requires the use of expensive glazing bars to be mounted on top of an underlying support structure, such as a purlin, which significantly increases its weight, cost and complexity, carrying some risk to the installers. In more general applications, corrugated plastic or metal sheets are typically used which offer improved mechanical strength and durability. Furthermore, the troughs at the corrugated sheets facilitate effective rainwater drainage. Through many large predrilled holes distributed throughout the roofing sheets, they are directly secured to the top of the purlins by special capped screws. Specifically, the capped screws overlap the large predrilled holes to create seals that prevent rainwater from leaking therethrough. However, the seals offered by the capped screws can deteriorate and move off-centre over time and so they may require frequent maintenance or replacement. Moreover, the large predrilled holes formed at the roofing sheets may not perfectly align with the screws or the purlins, which undermines the quality of the installation. Critically, conventional installations require an installer to access the top of the purlins. For example, the installer will have to climb on top of every purlin to screw the roofing sheets or glazing bars onto their upper surfaces. Such practice not only puts additional stress on the purlins during installation but working at height also carries considerable risks, especially for inexperienced installers. Therefore, a roofing sheet assembly that offers an efficient installation, without requiring large holes to be drilled in the roofing sheets, or the installer to access the top of the purlins, are highly desirable. Summary The present invention provides a specially designed clip allowing an installer to attach a roofing sheet when working below an underlying support structure. Specifically, the clip is arranged to be fixedly attached to an upper surface of the support structure by a threaded fastener extending through the support structure, thereby dispensing with the need for large holes to be drilled in the roofing sheets, or requiring the installer to access the top of the purlins. In most embodiments, the clip may be fixedly attached to the upper surface of the support structure after the assembled roofing sheet has been laid at the desired position, thereby minimising the likelihood of misalignment, or risk to the installers. The present invention is also very suited for emergency dwellings to be erected in many areas of the world, following natural disasters, the installers requiring few erecting skills and only basic tools, readily available. According to a first aspect of the presently-claimed invention, there is provided a roofing sheet assembly, comprising: a roofing sheet having a plurality of longitudinally extending channels distributed along the width of the roofing sheet, each of the channels comprises two opposing sidewalls having adjoining upper and lower curved sections in reverse curve arrangement each having a substantially constant radius of curvature; and at least one support structure supporting the roofing sheet at one of the channels, the support structure comprises an attachment portion having cross-sectional profile substantially complementary to the upper and lower curved sections of the channel, and thereby allowing the roofing sheet to removably attach to the support structure. The width of the roofing sheet in this application may refer to a dimension of the roofing sheet extending in a direction perpendicular to the length of the support structure, whereas the length of the roofing sheet may refer to a dimension of the roofing sheet extending in a direction parallel to the length of the support structure. In other words, in these embodiments, the channels extend parallel to the support structure. Each of the sidewalls of the channel may comprise continuous upper and lower curved sections with their respective radii residing on different sides of the sidewall, hence they generally exhibit a reverse curve arrangement. Specifically, the radii of the upper curved sections are located inside the channel and the radii of the lower curved sections are positioned outside the channel. In other words, when viewed along the length of the roofing sheet, each sidewall may be an S-shaped element, and the channel may have a cross-section profile that resembles an Omega, □. Similarly, each of the sidewalls of the attachment portion of the support structure, or purlin, may comprise continuous upper and lower curved sections corresponding to that of the channel, with their respective radii residing on different sides of the sidewall, hence they generally exhibit a reverse curve arrangement. Specifically, the radii of the upper curved sections are located within the support structure and the radii of the lower curved sections are positioned outside the support structure. Thus, the upper part of the attachment portion of the support structure may comprise side protrusions having rounded ends that engage the upper curved sections of the corresponding channel, wherein the sides of the attachment portion are each provided with a groove for receiving the lower curved section of a corresponding channel. In other words, when viewed along the length of the support structure, each sidewall of the attachment portion may be an S-shaped element, and the channel may have a cross-section profile that resembles an Omega, Q. Optionally, the support structure comprises the same cross-sectional profile along its length. Optionally, the roofing sheet is removably attached to the support structure by snap fit attachment formed between the upper and lower curved sections of the channel and the attachment portion of the support structure. That is, once attached, the rounded ends of the side protrusions at the support structure may engage at least the upper curve sections of the sidewalls of the channel. The lower curved sections of the sidewalls of the channel, on the other hand, form a slot opening for retaining the rounded ends of the side protrusions of the support structure within the upper curved sections. The upper and lower curved sections at the channel of the roofing sheets are each provided with a substantially constant radius of curvature. Thus, when viewed along the length of the roofing sheet, the upper and lower curved sections may be seen as two stacked semicircles. Such an arrangement may offer a secured interlock between the sidewalls of the channel and the corresponding side protrusions of the support structure. In some embodiments, the upper curved sections of each of the channels adjoin each other to form a top section. That is, in these embodiments, the upper curved sections have a continuous curvature when viewed along the length of the roofing sheet, akin to a supporting glazing bar which is no longer required with the inventive method described herein. Alternatively and preferably, each of the channels comprises a top section adjoining the two opposite upper curved sections, wherein the top section is substantially flat. The width of the top section corresponds to the length of the anchor at the clip. Optionally the flat top section of the channel abuts an upper surface of the corresponding support structure, thereby increasing the support provided to the roofing sheet. Optionally, the upper curved sections of the channel have a greater radius of curvature than the corresponding lower curved sections. Advantageously, such an arrangement may widen the slot between the lower curved sections of the channel, thereby allowing the snap attachment to be performed more easily. Optionally, the plurality of channels comprises: a first channel adjacent to a leading side edge of the roofing sheet; and a second channel adjacent to a trailing side edge of the roofing sheet opposite to the leading side edge; wherein the first channel is configured to fully overlap a second channel of a second roofing sheet to attach both the roofing sheet and the second roofing sheet by the corresponding support structure within. The roofing sheet is configured to adjoin with other identical roofing sheets, widthwise, in a roofing assembly. Specifically, the first channel that is closest to the leading side edge of the roofing sheet is configured to overlap a second channel that is closest to a trailing side edge of a second, or preceding, roofing sheet. The first channel of each roofing sheet may be sized slightly larger than the second channel, so as to accommodate the second channel of the second roofing sheet therein, along their respective lengths. Thus, the roofing sheet and the second roofing sheet may be attached to the same support structure within the channels. Similarly, the second channel at the trailing side edge of the roofing sheet is configured to be overlapped by a first channel that is closest to a leading side edge of a subsequent roofing sheet. Thus, the roofing sheet and the subsequent overlapping roofing sheet may be attached to the same support structure. Since the first channel in each roofing sheet fully overlaps the second channel of the adjoining roofing sheet, it may advantageously eliminate leakage between the adjoining sheets. If necessary a sealant may be spread along the overlapping edge to guarantee no leakage. Furthermore, the overlapped first and second channels increases the rigidity of the joint between the roofing sheet and the second roofing sheets, akin to a supporting glazing bar which is no longer required with the inventive method described herein. Optionally, the plurality of channels further comprises intermediate channels distributed between the first and second channels, wherein the intermediate channels are identical to the second channel. Thus, the roofing sheet may comprise a single first channel provided towards its leading side edge with a plurality of second channels evenly distributed along the width of the roofing sheet. Optionally, the second channel comprises gripping rails extending along the opposing sidewalls for gripping onto the attachment portion of the support structure. For example, when viewed along the length of the roofing sheet, the gripping rails may deviate and extend from the upper curve sections and may comprise a cross-section profile complementing the curvature of the lobed ends of the side protrusions. Advantageously, the gripping arms may offer improved grip onto their corresponding rounded ends of the attachment portion of the support structure, thereby enhancing the security of the attachment. In some embodiments, the roofing sheet may be fixedly attached to the attachment portion of the support structure by a threaded fastener. For example, the threaded fastener may extend through the flat top section of the roofing sheet and screwed into the upper surface of the purlin to fixedly secure the two together. In other word, the support structure, e.g. a purlin or a joist, may function as a glazing bar. Optionally, each of the channels comprises a first end and a narrowed second end opposite to the first end, the narrowed second end of the roofing sheet is arranged to be overlapped by the first end of a corresponding channel of a third roofing sheet, along their lengths. The roofing sheet is configured to adjoin with other substantially identical roofing sheets, lengthwise, in a roofing assembly. Specifically, the second end of each channel has a slightly reduced external dimension, such that it is insertable into the corresponding first end of the channel at the third roofing sheet. Advantageously, such an arrangement may ensure the joint between the roofing sheet and the third roofing sheet is substantially level, and fully engaged along their length. Optionally, the roofing sheet is at least partially double-glazed or triple-glazed, as such improving the thermal insulation offered by the roofing sheet. Optionally, a side edge of the roofing sheet is folded lengthwise to form an edging portion, and wherein the edging portion extends perpendicularly to the roofing sheet for covering at least a sidewall of the support structure, merging with side cladding as necessary for protection. Optionally, the support structure is arranged to attach to an upper surface of a second support structure, with the support structure extending in a direction perpendicular to the second support structure when viewed along a vertical axis. That is, in these embodiments, the support structure (e.g. a purlin) may be supported across a plurality of perpendicularly extending second support strucutures (e.g. a joist), and wherein the support structure and the second support structure may be fixedly attached to each other by conventional joinery methods such as threaded fasteners or nails extending therebetween. According to a second aspect of the presently-claimed invention, there is provided a method of removably attaching the roofing sheet to the support structure of the third aspect, comprising the step of: positioning the roofing sheet such that one of the channels aligns with the attachment portion of the support structure; and biasing the channel towards the attachment portion so as to cause the upper and lower curved sections of the channel to grip onto the attachment portion of the support structure.. Features from any one of the first to the fourth aspects of the present invention may be applicable to any other feature from the other aspects. Brief Description of the Drawings Certain embodiments of the presently-claimed invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure lisa truncated front view of a roofing assembly according to a first embodiment of the present invention; Figure 2 is a truncated side view of a roofing assembly of Figure 1; Figure 3 is a truncated perspective view of a roofing sheet for forming the roofing assembly as shown in Figures 1 and 2; Figures 4A to 4D are truncated side views illustrating various steps of forming the roofing assembly of Figure 1; Figure 5A is a truncated plan view of a roofing assembly of the first embodiment; Figure 5B is a truncated front section view of a joint comprising four adjoining roofing sheets of the first embodiment; Figure 6 is a side view of a clip according to a second embodiment of the present invention; Figure 7 is a truncated front view of a roofing assembly according to a third embodiment of the present invention; Figure 8 is a truncated perspective view of a roofing sheet according to a fourth embodiment of the present invention; Figure 9 is a truncated front view of a roofing assembly according to a fifth embodiment of the present invention; Figure 10 is a truncated side view of a roofing assembly of Figure 9; and Figure 11 is a truncated side view of a roofing assembly according to a sixth embodiment of the present invention. Detailed Description Figures 1 and 2 are respectively truncated front and side views of a roofing assembly 510 according to a first embodiment of the present invention. In the illustrated embodiment, the roofing assembly 510 comprises two substantially identical roofing sheets 520a, 520b overlaying across a pair of parallelly extending purlins 2, e.g. underlying support structures. The two roofing sheets 520a, 520b, adjoined widthwise, are jointly attached to each of the purlins 2 by a single T-shaped clip 550. In other embodiments, the roofing assembly may comprise any number of adjoining roofing sheets and clips as required to overlay the full length of the underlying purlins. The clip 550 is configured to fixedly attach to an upper surface of the purlin 2 at its first end, or lower end. More specifically, the clip 550 comprises a base 552 having a tapped hole 554 opened at its first end, through which a threaded fastener 4, in this example a bolt extending through a through-hole 6 in the purlin 2, extends to secure the clip to the upper surface of the purlin 2. The tapped hole 554 extends along the length of the base 552, and partially through the clip 550. The base 552 further comprises an anchor provided at its second end, or upper end. The anchor comprises two side protrusions 556 extending parallel to the purlin 2 each having a lobed end 558 for engaging sidewalls of a channel 524 at the roofing sheet 520. Thus, the clip 550 is generally a T-shaped member. Moreover, the two side protrusions 550 are symmetrically provided on two sides of the clip 550. As illustrated Figure 1, the curvature of the lobed end 558 has a substantially constant radius, which partially corresponds to a cross-section profile of the sidewalls of the channel 524, otherwise referred to as a second channel or an inner channel. The lobed end 558 forms the thickest part of the side protrusion 556. Specifically, the top of the lobed end 558 levels with the top surface of the side protrusion 556, whilst its bottom extends beneath the floor of the side protrusion 556 to increase its reach. Thus, the centre of each lobed end 558 is vertically offset from the centreline of the corresponding side protrusion 556. Such an arrangement enables the sidewalls of the second channel 524 to grip onto the side protrusions 526 more securely. Figure 3 is a truncated perspective view of the roofing sheet 520 for forming the roofing assembly. The roofing sheet 520 comprises a first channel 522 and a plurality of second channels 524 evenly distributed along the width of the roofing sheet 520. Specifically, the roofing sheet 520 comprises a floor 521 proximal to the purlin 2 when the roofing sheet 520 is attached, and the first and second channels 522, 524 each extends upwardly from the said floor 521. The first and second channels 522, 524 extend along the length of the roofing sheet and are parallel to each other. More specifically, the first channel 522 is positioned adjacent to a leading side edge 526a of the roofing sheet 520 and the opposite trailing side edge of the roofing sheet 520 is provided with a second channel 524. Referring back to the roofing assembly 510 of Figure 1, the leading side edge 526a of the roofing sheet 520a covers the trailing side edge 526b of a second roofing sheet 520b. More specifically, the first channel 522 or outer channel of the roofing sheet 520a is configured to completely overlap the second channel 524 or inner channel of the second roofing sheet 520b, thus allowing both the roofing sheet 520a and the second roofing sheet 520b to be secured on the purlin 2 by the same clip 550. In order to accommodate the second channel 524, the internal dimensions of the first channel 522 correspond to the external dimensions of second channels 524, i.e. the first channel 522 is sized slightly larger than the second channels 522, and the first and second channels 522, 524 have generally complementary cross-sectional profiles. By reference to their relative positions, the second roofing sheet 520b can be referred to as a leading roofing sheet and the roofing sheet 520a can be referred to as a trailing roofing sheet. Each of the first and second channels 522, 524 comprises a pair of opposing S-shaped sidewalls. More specifically, each of the S-shaped sidewalls comprises an upper curved section 530 and a lower curved section 532 in a reverse curve arrangement. The radii of the upper curved sections 530 are positioned inside the channels 522, 524, thus they bulge outwardly to form an enlarged cavity for accommodating and engaging the lobed ends 558 of the side protrusions 556, of clip 550. In contrast, the radii of the lower curved sections 532 are located outside the channels 522, 524 and therefore they cave inwardly to form a slot opening, or a neck, which retains the lobed ends of the side protrusions 556 within the cavity formed by the upper curved sections 530. The width of the said slot opening is equal to, or larger than, the depth of the clip 550, as such the anchor of the clip 550 can slide into the channels 522, 524 through the central slot opening. The upper curved sections 530 is shown having a greater radius of curvature than the corresponding lower curved sections 532. The radius of curvature of the lower curved sections 532 generally relates to the extent of the base 550, and therefore the elevation of the roofing sheets 520a, 520b. As shown in Figure 1, a comparatively small radius of curvature at the lower curved sections 532 reduces the profile of the channels at the roofing sheet. As shown in Figure 1, the bottom of the lobed ends 558 abuts and biases against the upper curved sections 530 of the second channel 524, which on their own are sufficient to retain the roofing sheet 520 in place. To enhance the security of the attachment, the second channels 524 are additionally provided with gripping rails 536 extending along their length. In the illustrated embodiment, the gripping rail 536 protrudes from the joint between the upper and lower curved sections 530, 532. The gripping rail 536 is curved upwardly along its length and has a crosssection profile complementing the curvature of the lobed ends 558 of the side protrusions 556. Specifically, the gipping rail 536 has the same radius of curvature as the upper curved section 530 and can be taken as a continuation of the upper curved section 530. The curved gripping rails 536 grip onto the corresponding lobed ends 558 to prevent them from accidental detachment, e.g. under high winds. The pair of the upper curved sections 530 of the first and second channels 522, 524 are joined by a planar top section 534. The top section 534 extends the width of the channel for accommodating the elongated anchor. Thus, when viewed along the length of the roofing sheet, the first and second channels 522, 524 each resembles an Omega, Q. Being double overlap thickness together, the joined strength is greatly increased, thus resembling a glazing bar, not now necessary or required. In contrast to known installations, the clip 550 can be fixedly attached to the purlin 2 after the roofing sheet 520 is fitted in place, and therefore eliminates any misalignment. Figures 4A to 4D are truncated side views illustrating various steps of forming the roofing assembly 510. In Figure 4A, the roofing sheet 520a is positioned at a desired location above the purlin 2, with its first channel overlapping a second channel of the second roofing sheet 520b. For example, the installer may slide the roofing sheets 520a, 520b into position when standing underneath the purlin 2. Once the roofing sheets 520a, 520b are in place, the installer may drill through the purlin 2 to form the through-hole 6 at a position in alignment with the channels 520a, 520b. That is, the through-hole 6 is positioned directly underneath the channels 520a, 520b. Thereafter, the clip 550 is put in a first orientation where its side protrusions 556 are parallel to the overlapped channels 522, 524, before aligning it with the central slot openings of both channels 522, 524. This allows the anchor of the clip 550 to slide through the slot openings and be inserted in the cavity of the channels 522, 524 to a position where the tapped hole 554 aligns with the through hole 6, as shown in Figure 4B. In Figure 4C, the clip 550 is rotated 90° about the vertical axis to convert into a second orientation, in which its side protrusions 56 extend parallel to the purlin 2, with their lobed ends abut the sidewalls of the second channel 524 to form an interference fit. Finally, a bolt 4 is inserted through the through-hole 6, such that it can be screwed into the tapped hole 554 of at the first end of its base 552 to form the attachment. Advantageously, the entire installation can be accomplished without needing the installer to climb on top of the purlin 2. Thus, such a method significantly increases the efficiency of the installation, whilst minimising the risks posed to the installer. Furthermore, the clip 550 can be precisely attached in place after the roofing sheet has been laid down at a desired position, thus the two can be in perfect alignment with each other. In some other embodiments, the sidewalls of the channel may be attached to the clip by a snap attachment. For example, during installation the sidewalls of the channel may be biased away from each other so as to widen the slot opening, thereby allowing the channel to directly snap onto the clip to removably attach the roofing sheet onto the support structure. In these embodiments, the gripping arms 536 as shown in Figure 1 may optionally be absent to facilitate the snap attachment. This way, the roofing sheet may be secured onto the clip after the clip has already been fixedly attached to a predetermined position at the support structure. In addition to joining roofing sheets 520a, 520b widthwise as shown in Figure 1, the roofing sheets of the present invention can also be jointed lengthwise as required. Figure 5A is a truncated plan view of a roofing assembly of the first embodiment where a leading edge 527a of a third roofing sheet 520c, overlaps the trailing edge 527b of the roofing sheet 520a. The third roofing sheet 520c is shown in dotted lines to improve the clarity of the illustration. By reference to their relative positions, the roofing sheet 520a can be referred to as a front roofing sheet and the third roofing sheet can be referred to as a rear roofing sheet. More specifically, the channels 522, 524 are narrowed towards the trailing edge 527b of the roofing sheet 520a such that their external dimensions are matched with the internal dimensions of corresponding channels 522, 524 provided towards the leading edge 527a of the third roofing sheet 520c. Thus, the narrowed portions of the channels 522, 524 at the roofing sheet 520a can be completely overlapped by their corresponding channels 522, 524 at the third roofing sheet 520c. Such an arrangement provides a substantially seamless connection between the roofing sheet 520a and roofing sheet 520c, the narrowed portion of the sheet being part of the extrusion or forming process, whether plastic or metal is used. In the illustrated embodiment, the channels 522, 524 are tapered and so their widths are reduced gradually towards the trailing edge 527b of the roofing sheet 520a. The tapering can be achieved by the use of a suitable extrusion die. In some other embodiments, the channels 522, 524 may exhibit a step change in size reduction, e.g. one or both ends of each channel 522, 524 may be narrowed to suit engagement. Together, by the overlapped channels 522, 524, both the roofing sheet 520a and the third roofing sheet 520c can be supported by a single clip 550b. Since the clips 550b are fitted to the narrowed portion of the second channels 524, they are sized smaller than the other clips 550 in the roofing assembly. Specifically, the external dimensions of the clip 550b correspond to the internal dimensions of the narrowed ends of the second channels 524. Figure 5B is a truncated front section view of a joint comprising four adjoining roofing sheets 520a-520d along theirlengths. Specifically, a front leading roofing sheet 520b is joined lengthwise with a rear leading roofing sheet 520d, wherein the front leading roofing sheet 520b having the narrowed end of its second channel overlapped by a corresponding second channel of a rear leading roofing sheet 520d. Furthermore, a front trailing roofing sheet 20a is joined lengthwise with a rear trailing roofing sheet 520c, wherein the front trailing roofing sheet 520a having the narrowed end of its first channel overlapped by a corresponding first channel of a rear trailing roofing sheet 520c. Together, the first channels of the stacked front and rear trailing roofing sheets 520a, 520c overlap the second channels of the stacked front and rear trailing sheets 520b, 520d to form the joint. Figure 6 is a side view of a clip according to a second embodiment of the present invention. The clip 650 is structurally and functionally similar to the clip 550 of the first embodiment, except in that the clip 650 of the second embodiment is configured to fixedly attached to a leading purlin 2b, e.g. one that is adjacent to the drip-edge or eaves of a building, and comprises a gutter bracket 670 for supporting a gutter section 672 beneath the drip-edge of the roofing sheet 620. To aid rainwater drainage, the roofing sheet 620 is inclined to the horizontal plane. Specifically, the gutter bracket 670 extends from a sidewall of the base of the clip 650 and is perpendicular to the purlin 2b. The gutter bracket 670 is curved along its length and complements the curvature of the gutter section 672 supported thereon. The gutter section 672 may be a gutter extending along the entire length of the drip-edge or eaves of the building, or it may be a discrete section for forming the said gutter. In the illustrated embodiment, the gutter bracket 670 is integrally formed with the clip 650. In some other embodiments, the clip may comprise a tapped hole at its sidewall to which the gutter section may attach. In some other embodiments, the clip may be integrally formed with the gutter section. Advantageously, such an arrangement allows the roofing sheet 620 and the gutter section 672 to be attached to the purlin 2b by the same clip 650, thereby significantly reducing the work involved in the installation. Figure 7 is a truncated front view of a roofing assembly 710 according to a third embodiment of the present invention. The roofing assembly 710 is structurally and functionally similar to the roofing assembly 510 of the first embodiment, except in that the clip 750 is fixedly attached towards an end of a purlin 2, e.g. towards the eaves of the building, and a perimeter roofing sheet 720e comprises an edging portion 740 that fully covers the edge of the purlin 2, along the length of the sheet. The perimeter roofing sheet 720e comprises only a single first channel 722 configured to cover a second channel 724 of a leading roofing sheet 720b, thus together the leading roofing sheet 720b and the perimeter roofing sheet 720e are attached to the purlin 2 by a clip 750. As shown in Figure 7, the floor 721 of the perimeter roofing sheet 720e bends around the edge of the purlin 2 and extends downwardly to form the edging portion 740. The said edging portion 740 at least fully covers the side of the purlin 2. The edging portion 740 may be pre-fabricated with a predetermined separation between its first channel 722 and the edging portion 740, or it may be formed by heat bending the floor 721 of the perimeter roofing sheet 720e after it has already been attached to the clip 750, as such tailoring the separation between the first channel 722 and the edging portion 740 for each particular application. Figure 8 is a truncated perspective view of a pair of adjoining roofing sheets 420a, 420b according to a fourth embodiment of the present invention. The roofing sheets 420a, 420b are structurally and functionally similar to the roofing sheet 520 of the first embodiment shown in Figure 3, except in that the roofing sheets 420a, 420b are partially double-glazed roofing sheets for an improved thermal insulation, and that a leading lowered curved section of the sidewall at their first channels 422 are truncated to allow for an increased floor thickness of a preceeding roofing sheet. More specifically, the floors 421 of each of the roofing sheets 420a, 420b comprises an upper layer 421a and a lower layer 421b, with a gap sandwiched therebetween. The gap extends between, and parallel to, the channels 422, 424. The gap is sealed around its perimeter to limit air convection therein, as well as eliminating any rainwater leakage. As shown in Figure 8, the first channel 422 of the roofing sheet 420a overlaps the second channel 424 of a preceding roofing sheet 420b. The sidewalls and the top sections of the channels 422, 424 comprise only a single layer of material and therefore the channels 422, 424 are not double-glazed. Taking into account an increased floor thickness of a preceeding roofing sheet, a leading lowered curved section of the sidewall at each of the first channels 422 is truncated. Tie illustrated embodiment shows partially double-glazed roofing sheets 420a, 420b. In some other embodiments, the roofing sheet may be triple-glazed compising an intermeditate layer between an upper layer and a lower layer, with a gap sandwiched between each of the layers. Figure 9 is a truncated front view of a roofing assembly 810 according to a fifth embodiment of the present invention and Figure 10 is a truncated side view of a roofing assembly of Figure 9. The roofing assembly 810 comprises the same roofing sheets 820a, 820b as roofing assembly 510 of the first embodiment. That is, the roofing sheets 820a, 820b are structurally and functionally identical to the roofing sheets 520a, 520b of the first embodiment, and the first channel 822 or outer channel of the roofing sheet 820a is configured to overlap the second channel 824 or inner channel of the second roofing sheet 820b to join the two widthwise. For conciseness, like features are not repeated. In contrast to the roofing assembly 510 of the first embodiment which features a clip, the roofing sheets 820a, 820b directly grips onto an attachment portion of a purlin, or a joist 2c. Furthermore, as shown in Figures 9 and 10, the channels 822, 824 of the roofing sheets 820a, 820b extends parallel to the purlin 2c. That is, relative to the purlin, the roofing sheets 820a, 820b of this embodiment are perpendicularly orientated in comparison to the roofing sheets 520a, 520b of the first embodiment. Referring back to the cross-sectional view of Figure 9, the attachment portion is provided at the upper end of the purlin 2c. Similar to the first and second channels 822, 824 of the roofing sheets 820a, 820b, when viewed along the length of the support structure, each sidewall of the attachment portion may be an S-shaped element, and the channel may have a cross-section profile that resembles an Omega, □. Such a cross-sectional profile of the purlin 2c may be machined along its length, and therefore, the purlin 2c comprises the same cross-sectional profile along its length. The upper part of the attachment portion comprises side protrusions 856 having rounded ends 858 that engage the upper curved sections 830 of the second channel 824. Moreover, the curvature of each rounded end 858 has a substantially constant radius, and partially corresponds to a cross-section profile of the upper curved section 830 of the second channel 824. The sides of the attachment portion are each provided with a groove 859 for receiving the lower curved section 832 of the second channel 824. Specifically, the curvature of each of the grooves 859 has a substantially constant radius, and partially corresponds to a cross-section profile of the lower curved section of the second channel 824. During installation, the roofing sheets 820a, 820b are first positioned on the purlin 2c such that the second channel 824 of the roofing sheet 820b aligns with the attachment portion of the purlin 2c. The roofing sheets 820a, 820b are then pushed downwardly towards the purlin 2c, which forces the slot opening formed between the sidewalls of the channels 822, 824 to widen, thereby allowing the upper and lower curved sections 830, 832 of the channels 822, 824 to slide onto the attachment portion of the purlin 2c to form a snap attachment. Once attached, the planar top section 834 of the second channel 824 abuts the upper surface of the purlin 2c, thereby providing additional support for the roofing sheets 820a, 820b. Furthermore, the gripping rail 836 protruding from the joint between the upper and lower curved sections 830, 832 grips onto the corresponding rounded ends 858 at the side protrusions 856 of the purlin 2c, thereby improving strength of the snap attachment. In some other embodiments, the gripping rail may be omitted to ease the process of snap attachment. In some other embodiments, the roofing sheet may be fixedly attached to the attachment portion of the support structure by a threaded fastener and / or an adhesive. For example, the threaded fastener may extend through the flat top section of the roofing sheet and screwed into the upper surface of the purlin to fixedly secure the two together. This allows the roofing sheets to be fixed on the support structure more securely. Figure 11 is a truncated side view of a roofing assembly 910 according to a sixth embodiment of the present invention. The roofing assembly 910 is structurally and functionally identical to the roofing assembly 810 of the fifth embodiment, in that the roofing sheets 920a, 920b are releasably attached to the attachment portion of the purlin 2c by a snap-fit attachment, and optionally by additional fasteners and / or adhesive. For conciseness, like features are not repeated. In contrast to the roofing assembly 810 of the fifth embodiment, the purlin 2c and the roofing sheets 920a, 920b fitted thereon are supported on, and fixedly attached to, a second support structure or a joist 2. More specifically, a pluarality of joists 2 extend perpendicular to the purlin 2c when viewed along the vertical axis, whenin the two are fixedly attached by threaded fasteners 4 extending through the joists 2 and into the purlin 2c. Effectively, the purlins 2c functions as a glazing bar to which the roofing sheets 920a, 920b are snap-fitted thereto. During installation, an installer may, whilst working underneath the joist 2, assemble the roofing sheets 920a, 920b onto the purlin 2c on top of the joist 2. Thereafter, the purlin 2c with the roofing sheets 920a, 920b mounted thereon, can be slide to a predetermined position on the joist 2, before being fixedly attached to the joist 2. Alternatively, the purlin may be fixedly attached to the joist before the roofing sheets are snap-fitted to purlin. Either way, similar to the other embodiments of the present invention, such installation methods do not require the installer to work above the joist, and therefore significantly improve the safety of installation. In some embodiments, the clip 650 of the second embodiment as shown in Figure 6 may be inserted into the channel of the roofing sheet and abut an end wall of a leading purlin 2c, e.g. one that is adjacent to the drip-edge or eaves of a building, such that the gutter bracket 670 may extends from a sidewall of the base of the clip 650 and parallel to the purlin 2c. As such, the weight of the gutter bracket 670, and the gutter section 672 held thereon, is supported through the lobed ends of the clip, by the sidewall of the channels of the roofing sheet. Furthermore, the clip may be fixedly attached to the end wall of the leading purlin 2c to provide addition support.

Claims

1. A roofing sheet assembly, comprising:a roofing sheet having a plurality of longitudinally extending channels distributed along the width of the roofing sheet, each of the channels comprises two opposing sidewalls having adjoining upper and lower curved sections in reverse curve arrangement each having a substantially constant radius of curvature; andat least one support structure supporting the roofing sheet at one of the channels, the support structure comprises an attachment portion having cross-sectional profile substantially complementary to the upper and lower curved sections of the channel, and thereby allowing the roofing sheet to removably attach to the support structure.

2. The roofing sheet assembly of claim 1, wherein the support structure is arranged to attach to an upper surface of a second support structure, with the support structure extending in a direction perpendicular to the second support structure when viewed along a vertical axis.

3. The roofing sheet assembly of claim 1 or claim 2, wherein roofing sheet is removably attached to the support structure by snap fit attachment formed between the upper and lower curved sections of the channel and the attachment portion of the support structure.

4. The roofing sheet assembly of any one of the claims 1 to 3, wherein the sides of the attachment portion are each provided with a groove for receiving the lower curved section of a corresponding channel.

5. The roofing sheet assembly of any one of the claims 1 to 4, wherein upper curved sections at the channel of the roofing sheet have a greater radius of curvature than corresponding lower curved sections.

6. The roofing sheet assembly of any one of the claims 1 to 5, wherein each of the channelscomprises a substantially flat top section adjoining the two opposite upper curved sections and optionally the flat top section of the channel abuts an upper surface of the corresponding support structure, or the upper curved sections of each of the channels adjoin each other to form a top section.

7. The roofing sheet assembly of any one of the claims 1 to 6, wherein the plurality of channels comprises:a first channel adjacent to a leading side edge of the roofing sheet; anda second channel adjacent to a trailing side edge of the roofing sheet opposite to the leading side edge;wherein the first channel is configured to fully overlap a second channel of a second roofing sheet to attach both the roofing sheet and the second roofing sheet by the corresponding support structure within.

8. The roofing sheet assembly of claim 7, wherein the second channel comprises gripping rails extending along the opposing sidewalls for gripping onto the attachment portion of the corresponding support structure.

9. The roofing sheet assembly of claim 7 or claim 8, wherein the plurality of channels further comprise intermediate channels distributed between the first and second channels, wherein the intermediate channels are identical to the second channel.

10. The roofing sheet assembly of any one of the claims 7 to 9, wherein each of the channelscomprises a first end and a narrowed second end opposite to the first end, the narrowed second end of roofing sheet is arranged to be overlapped by a first end of a corresponding channel of a third roofing sheet.

11. The roofing sheet assembly of any one of the claims 1 to 10, wherein the roofing sheet is at least partially double-glazed or triple-glazed.

12. The roofing sheet assembly of any one of the claim 1 to claim 11, wherein a side edge of the roofing sheet is folded lengthwise to form an edging portion, and wherein a part of the the edging portion extends perpendicularly to the roofing sheet for covering at least the side of support structure.

13. A method of removably attaching the roofing sheet to the underlying support structure of any one of the claims 1 to 12, comprising the step of:positioning the roofing sheet such that one of the channels aligns with the attachment portion of the support structure; andbiasing the channel towards the attachment portion so as to cause the upper and lower curved sections of the channel to grip onto the attachment portion of the support structure.18 11 24

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