GB2464331A

GB2464331A - Glazing

Info

Publication number: GB2464331A
Application number: GB0812210A
Authority: GB
Inventors: David John Anderson
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-07-03
Filing date: 2008-07-03
Publication date: 2010-04-21
Also published as: GB0812210D0

Abstract

A glazing panel for building structures such as conservatories comprises an assembly of at least two cellular glazing sheets (10) that each have a hollow cellular structure defining a plurality of cells (14). The glazing sheets (10) are disposed in a generally face to face relation such that the glazing panel has a thickness equal to at least the sum of the thicknesses of the glazing sheets. The cells may be defined by intermediate walls 14 and transverse walls 18. The cells may be further divided by inclined webs 20. The glazing sheet may be an integral transparent or translucent plastics such as polycarbonate, PVC, glass reinforced plastic (GRP), polymethyl methacrylate or polyurethane or glass. The glazing sheets of panels may be laminated together (figure 2) or separated by a perimeter spacing system 52 or 82 (figures 3 and 4). The gaps 54, 84 may be filled with heat insulating, absorbing or reflecting material.

Description

Glazing

Field of the Invention

The invention relates to glazing and particularly, but not exclusively, to glazing panels for building structures such as conservatories and the like.

Background to the Invention

It is known to use hollow plastics glazing panels for glazing structures such as conservatories and the like. One of the parameters affecting the choice of glazing panel is the reduction of thermal transmission to allow for comfortable use of the conservatory and economic heating during the winter months. Known single sheet panels typically have a depth of 25, 32 or 35 mm. Typical thermal transmittance (U) values for such sheets are 1.4 W/m2 or above. Single thickness sheets having a depth of 55mm and a U value of less than 1 W1m2 are known. However, the depth of these sheets is such that they are only suitable for lean to roofs' and cannot be readily installed on conservatories having shaped ends, such as those having Victorian and Edwardian-style roofs. The reason for this is that this depth of sheet cannot be fitted in standard size glazing bar covers and increasing the glazing bar cover width to accommodate such depths would result in cumbersome and unattractive designs.

Another parameter influencing the choice of glazing is the need to provide protection against summer heat to allow conservatories to be used in comfort during the summer months. A reduction in solar heat entering the roof or side glazing of 70% or more is desirable to provide a comfortable environment within a conservatory. To achieve this, the glazing needs to exclude solar heat before it enters the conservatory.

Glazing for conservatories also needs to provide glare protection, particularly during the summer months, to alleviate discomfort to the eye. The complex internal structure of at least some known glazing sheets can be a cause of glare due to multiple internal reflections of the sun's rays leading to the production of an arc, or band of brightness and light scattering.

An undesirable feature of conventional hollow plastics glazing sheets is the drumming noise produced by rain and hail striking the sheet. This is one of the most undesirable features of this type of glazing sheet.

An object of the invention is to provide glazing that provides improved performance in at least one of these areas, or at least provide an alternative to existing products on the market.

Summary of the Invention

The invention provides a glazing panel comprising an assembly of at least two cellular glazing sheets that each have a hollow cellular structure defining a plurality of cells, said glazing sheets being disposed in a generally face to face relation such that the glazing panel has a thickness equal to at least the sum of the thicknesses of the glazing sheets.

The invention also includes a method of forming a curved roof structure comprised of glazing panels as specified in the last preceding paragraph, wherein each said cellular glazing sheet of the glazing panels is formed with a required curvature and the curved glazing sheets are positioned in said generally face to face relationship.

The invention also includes a structure having a glazed roof comprising framing and a plurality of glazing panels as specified in the last but one preceding paragraph.

The invention also includes a cellular plastics glazing sheet comprising a first outer surface element, a second outer surface element, at least one intermediate wall disposed between and spaced from said first and second outer surface elements and a plurality of wall elements interconnecting said first and second outer surface elements and said at least one intermediate wall to define a hollow interior region comprising a plurality of cells, said first and second outer surface elements forming major external surfaces of the glazing sheet and the arrangement being such that at least a plurality of said plurality of cells have a height not substantially greater than 4mm.

Brief Description of the Drawings

In order that the invention may be well understood, some embodiments thereof, which are given by way of example only, will now be described with reference to the drawings in which: Figure 1 is a schematic cross-section through a cellular glazing sheet; Figure 2 is a schematic of a glazing panel comprising two of the cellular glazing sheets of Figure 1; Figure 3 is a schematic of a glazing panel comprising two of the cellular glazing sheets of Figure 1 separated by a spacer system to provide an air gap between the glazing sheets; Figure 4 is a schematic of a glazing panel comprising two of the cellular glazing sheets of Figure 1 separated by a spacer system to provide an air gap between the glazing sheets with a heat absorbing or reflecting layer contained in the air gap; and Figure 5 is a schematic of a barrel roof comprising glazing panels as shown in Figure 2,3or4.

Detailed Description of the Illustrated Embodiments Figure 1 is a schematic cross-section through a hollow plastics cellular glazing sheet 10. The glazing sheet 10 comprises opposed outer surface elements 12 that form the major surfaces of the glazing panel. The space, or volume, between the outer surface elements 12 is divided into a plurality of generally rectangular section cells 14 by three equi-spaced layers of intermediate walls 16 that are disposed between and extend generally parallel to the outer surface elements and a series of transverse walls 18 that extend transverse (in this embodiment generally perpendicular) to the outer surface elements and intermediate walls 16. Although not essential, in the illustrated embodiment, the transverse walls 18 are thinner than the outer surface elements 12.

The intermediate walls 16 are thinner than the transverse walls 18 since they are not required to contribute to the strength of the structure.

The height 22 of the cells 14 is determined by the mutual spacing between adjacent outer surface elements 12 and intermediate walls 16 and the width of the cells is determined by the mutual spacing between adjacent transverse walls 18. In the illustrated embodiment, the arrangement of the outer surface elements 12, intermediate walls 16 and transverse walls 18 is such that the cells 14 have a width that is greater than their height and are arranged in a regular pattern of four layers of cells with the cells of the layers disposed one above the other. The cells 14 may be further subdivided by inclined webs such as the webs 20 shown in Figure 1.

The glazing sheet 10 is typically an integral transparent or translucent plastics unit made, for example, of a highly transparent polycarbonate, PVC, glass reinforced plastic (GRP), Perspex (polymethyl methacrylate) or polyurethane. Typically, the glazing sheet 10 will be manufactured by a plastics extrusion process. However, the glazing sheet could also be made from glass by a similar process.

The five horizontal walls 12, 18 of the glazing sheet 10 may be configured to provide a glazing sheet having a thickness 24 of approximately 16mm with the result the cell height 22 is not greater than 4mm. It has been found that a cell height of less than 4mm provides enhanced insulation properties as compared with conventional structures. For use in conservatories and similar structures, a roof depth of 32 or 35mm is typical, although, other thicknesses can be used. Glazing panels having a 32 or 35mm thickness with improved insulation properties as compared with conventional panels of the same thickness can be provided in the form of a glazing panel 40 as shown in Figure 2, a glazing panel 50 as shown in Figure 3 and a glazing panel 80 as shown in Figure 4, each of which is an assembly comprising two glazing sheets 10.

Referring to Figure 2, the glazing pane! 40 is a laminate of two glazing sheets 10. The laminate can be formed by bonding the two glazing sheets 10 at the interface 42 between them, or by securing them together at their edges 44 by means of tape or clips (see the description below relating to Figure 3). The resultant glazing panel 40 has a thickness 46 of approximately 32mm that can be used in place of conventional 32mm glazing panels. The eight-high cell structure of the glazing panel 40 can provide a U-value of approximately 1.0 W/m2.

Referring to Figure 3, the glazing panel 50 comprises two glazing panels 10 separated by a perimeter spacer system 52 comprising at least one spacer member. The spacer system 52 has a thickness of approximately 3mm and separates the two glazing sheets 10 so as to provide a 3mm gap 54 between them. The configuration and positioning of the spacer systems is such that the gap 54 extends over substantially the entire length and width of the glazing panel 50. The gap effectively provides an additional cell having a height of approximately 3mm. In this embodiment, the gap 54 is left empty as an air gap. However, as described in more detail below, the gap 54 may be completely or partially filled by a material selected to further enhance the performance of the glazing panel.

The two glazing sheets 10 could be bonded to the spacer system 52. However, due to the relatively small contact areas provided by the spacer system 52, a more durable structure can be produced by uniting the three layers 10, 52, 10 by means of suitable adhesive tape 56 or other securing system such as U-shaped plastics clips 58 bonded to the glazing sheets 10. The securing system can extend around the entire circumference of the glazing panel or just along selected side portions. Where adhesive tape is used, the tape may attach to the sides of the glazing panel and the adjacent major surfaces of the glazing sheets 10, or may just attach to the sides of the glazing panel. The adhesive tape may be an adhesive aluminium tape. The securing system is not limited to an adhesive tape or generally U-shaped clips as shown in Figure 3. In principle, any suitable clamping or fixing system could be used. For example, the securing system may comprise perimeter strips or channels running around the circumference of the glazing panel.

The glazing panel 50 has a nine-high cell structure and a thickness of approximately 3 5mm. The incorporation of an additional cell in the form of the air gap 54 can provide some improvement on the insulation values achieved as compared with the glazing panel 40, with values of approximately 0.9 W/m2 being achievable.

The member or members of the spacer system 52 are preferably made of an insulating material. Suitable materials include polystyrene and similar hollow extruded plastics, natural or synthetic rubber, PVC, nylon, polyethylene, polypropylene, GRP, fibre glass, polyester, polycarbonate, wood, composite, hollow glass or other solid highly insulating material. Alternatively, a poor insulator such as metal, for example aluminium, could be used.

The glazing panel 50 can be modified by filling, or partially filling the gap 54 with a transparent or translucent insulating material, which can be in sheet or loose form. A portion of a sheet, or layer, of insulating material 60 filling the gap 54 is shown in Figure 3. The insulating materials can be incorporated in a variety of forms, such as bubbles, sheets and amorphous woolly' or fibrous structures. Suitable insulating materials include a sheet or layer of expanded polystyrene, fibreglass, mineral wool, plastics foam, including polyurethane foam and isocyanides foam, or other foam or fibrous structures. Other insulating materials that could be used include solid or hollow plastics or glass beads. By filling the gap 54 with such an insulating material, it is possible to further improve the insulating properties of the glazing panel 50 and reduce the U value to around 0.8 W/m2.

In embodiments of the glazing panel 50 in which the gap 54 is filled with an insulating material in sheet or layer form, the sheet or layer of insulating material can be bonded to either or both of the cellular glazing sheets 10 and the spacer system 52 can be omitted. However, a bonded insulation layer, or sheet, and spacer system can be used to obtain good acoustic (sound insulation) properties. A further advantage of bonding, which applies to both of the glazing panels 40, 50 is that the resultant structure has complete integrity and can, therefore, be easily cut on conventional plastics roof cutting tables.

The glazing panels 40, 50 are configured to provide improved insulation properties as compared with conventional glazing panels. In addition to providing good insulation properties, the glazing panels can be arranged to provide improved solar protection against glare and summer heat. For example, inserts 70 (see Figure 1) comprising strips of heat absorbing or heat reflecting material may be inserted in the cells 14 of the cellular glazing sheet 10. To achieve the best results, the inserts 70 should be placed in the cells 14 closest to one of the outer surface elements 12 and in use, that outside surface element should be at the side of the glazing panel 40 that faces the external environment. By arranging the inserts 70 in this way it is possible to exclude up to approximately 90% of the solar heat received, depending on the grade of material the inserts are made from. The solar protection provided will progressively diminish the closer the inserts 70 are to the side of the glazing panel that faces into the building interior. A further improvement in the solar protection provided can be obtained by incorporating a layer of heat absorbing or reflecting material between the two cellular glazing sheets 10 of the glazing panel 40.

The inserts 70 may comprise any material suitable for the solar protection they are intended to provide. For example, the inserts could be strips of thin metal sheet or transparent metallised plastic (polyester, polycarbonate, PVC or PVF). The strips may be embossed to increase their stiffness, perforated and/or have a width greater than the width of the cells they are intended for so that as they are inserted, they are forced to curve to form an arch. For heat reflecting duty, the strips may be aluminium strips. For heat absorbing duty, the inserts may be dark mesh strips made of a suitable metal. Although not essential, using the insert structures disclosed by GB2 279 142 will facilitate installation.

The glazing panel 50 can be provided with improved solar protection by incorporating inserts 70 in one of the cellular glazing sheets 10 in the way described above and/or providing a sheet or layer of transparent, translucent, opaque or perforated heat reflecting or heat absorbing material between the cellular glazing sheets 10. Figure 4, shows a glazing panel 80 having a structure similar to the structure of the glazing panel 50 and provided with enhanced solar protection. In the same way as the glazing panel 50, the glazing panel 80 comprises two cellular glazing sheets 10 separated by a spacer system 82 to provide a gap 84 between the two cellular glazing sheets. The gap 84 is defined by the opposed faces of the cellular glazing sheets 10 and bounded by the spacer system 82. The gap 84 contains a layer of a heat absorbing or heat reflecting material 86. The layer of transparent, translucent, opaque or perforated heat absorbing or reflecting material may be loose in the gap 84, adhered to the either of the opposed faces of the cellular glazing sheets 10 that define the gap or suspended in the gap. By arranging the layer of heat absorbing or reflecting material 86 in this way, it is possible to exclude up to 70% of solar heat received. If inserts 70 as described above are also provided, the combination can exclude up to 95% of solar heat received.

It will be understood that embodiments of the glazing panel 50 that have the air gap 54 occupied by an insulating material, may also be provided with a layer of transparent, translucent, opaque or perforated heat absorbing or heat reflecting material such as the layer of heat absorbing or reflecting material 86. The heat absorbing or heat reflecting material may be assembled loose into the structure or pre-bonded to one of the cellular glazing sheets 10 and/or the layer of insulation material.

The glazing panels 40, 50, 80 are configured to provide good heat insulation properties and/or enhanced solar protection. These glazing panels can also provide improved acoustic characteristics as compared with conventional plastics glazing panels. Specifically, the glazing panels may reduce the transmission of noise resulting from impact by rain, hail and the like. For example, in embodiments in which two cellular glazing sheets 10 are separated by a spacer system. If left empty, the gap will provide acoustic deadening. The spacer systems can additionally be made of a soft, acoustically dead, material. For example, many of the materials mentioned above as insulators are also relatively soft and acoustically dead (for example rubber). Furthermore, where an insulating sheet or layer or other insulating material, is provided between the cellular glazing sheets, whether in a gap between the glazing sheets or as a sheet or layer sandwiched between and separating the glazing sheets, that material will typically reduce noise transmission between the sheets.

Where the cellular glazing sheet andlor the glazing panel is provided with heat absorbing or reflecting materials as described above, the heat that is collected can be used to heat a building or structure in which the cellular glazing sheet or glazing panel is incorporated. For example, in the case of a glazing panel such as the glazing panel in which the gap is not completely filled, the presence of a heat absorbing or reflecting sheet or layer in the gap 84 will lead to the collection of heat in much the same way as in a solar panel. The space left in the gap 84 by only partially filling it allows air movement through the gap 84 so that the heat can be captured and transported to a heat exchanger by air flowing through the gap 84. The airflow may be natural or forced. To allow the airflow, suitable porting (not shown) is provided in the closed sides of the glazing panels and, if necessary, the spacer system, typically at opposite side locations of the glazing panel.

By way of an example of the heat that can be harvested by roofing comprising suitable embodiments of the glazing panels, up to 0.8KW/rn2 of heat falls upon glazing that is at 90° to the solar radiation. For a typical size of conservatory, the peak solar energy falling onto the surface of the glazing may be up to around 8KW and that figure can be greater for larger conservatories. A similar result could be obtained by making use of inserts 70 as shown in Figure 1. Heat will be collected in the cells 14 fitted with the inserts and can be captured by means of a suitable airflow as previously described. For this purpose, it is believed the best result will be obtained if the inserts are put in the cells closest to the gap between the glazing sheets. In this case the side regions of the glazing panel would be provided with porting arranged to allow airflow through the cells provided with the inserts.

For a glazing panels such as the glazing panel 40 in which there is no gap provided between the cellular glazing sheets, inserts 70 can be provided in the cells 14 and the heat collected captured by an airflow through the cells. Indeed, a single glazing sheet fitted with inserts can be used in this way as a solar collector by directed an airflow along the cells fitted with the inserts 70. In this case, it is preferred that the inserts are provided in the centre layer of cells, although, this is not essential. Typically for these arrangements, cells that do not contain a heat absorbing or reflecting material are blanked off so that the air flow is specifically directed over the heat absorbing or reflecting material.

By using the glazing panels 40, 50, 80 to glaze the roof of a conservatory or similar such structure, the room can be turned into a passive heat collector and used to heat the main building. Potentially a conservatory can be used to collect much greater amounts of heat energy than a solar roof panel fitted to the roof of a house. A typical conventional conservatory loses the majority of its heat through the roof. The U value of a conventional conservatory roof is typically 3W/rn2. As described above, the glazing panels 40, 50, 80 can bring this value to below 1.0W/rn2. When the sun is low in the sky and shines through the east, west and south facing side windows of a conservatory in late autumn or early spring, the heat equivalent of up to around 0.5KW/rn2 enters the conservatory. For a conservatory glazed with conventional glazing panels, most of this heat goes to waste through the conservatory roof. In the case of a conservatory having a roof glazed with the glazing panels 40, 50, 80, this heat cannot easily escape through the roof and becomes available to heat the house, or other connected building. There is no need for complex piping, heat recovery systems and similar such elements associated with solar panels and photo-voltaics. The solar heat collected in the conservatory can be liberated to the whole house by natural ventilation by simply opening the conservatory house door. The heat flow into the main building, and individual rooms within it, can be controlled by the extent to which the door to the conservatory and doors within the building are opened.

In roofing installations in which the glazing panels are used to harvest solar energy, it may be desirable to locate a heat reflector or reflectors, which may be transparent or translucent, inwardly of the glazing panels in order to reflect any solar energy not absorbed in the first pass through the glazing panels.

Where the glazing sheets and resultant glazing panel are intended to fulfil a heat harvesting function, metal heat absorbers, such as the dark metal mesh heat absorbers should provide better results than film. This is because the metal mesh inserts can achieve higher temperatures than films, which typically distort at relatively low temperatures (typically 100 -120°C). The metal mesh would work particularly well in combination with glass glazing sheets as extremely high temperatures could be achieved.

Plastics roof glazing requires periodic upgrading and replacement. This can be done on site, either with pre-prepared panels or by assembling the glazing panels and then installing them within the glazing bars and the like of the structure. One advantage of the glazing panels of the embodiments is that they can be assembled on site allowing them to be used in barrel roof lights, such as the barrel roof light 100 shown in Figure 5. Fitting a full depth single panel would be impossible because a panel of that thickness could not be flexed and formed into the barrel shape on site. However, with the glazing panels such as the glazing panels 40, 50, 80 of the embodiments, the individual elements can simply be formed and assembled sequentially in situ since the individual elements do not have the rigidity of a full depth sheet. Similar considerations apply to the use of the glazing panels for curved roofing generally.

Although not described in any detail herein, it will be appreciated that the glazing panels may be fitted into roof structures made up of conventional framing often without the need to modify the components of the framing. Since such framing components, such as glazing bars, are well known to those skilled in the art, they will not be described in further detail therein.

It has been found that having a cell height approximating to 4mm produces improved insulation properties in glazing panels made up of two cellular glazing sheets 10 and having a thickness of approximately 32 or 35mm. A cell height of 3mm or below will provide a further improvement in insulation capability. For a glazing panel having a 35mm nominal thickness, this implies a structure with ten cells. It is believed the optimal cell height is approximately 2.3mm and there is unlikely to be any benefit in significantly further reducing the height of the cells.

It will be understood that the embodiments provide hollow glazing panels that allow the possibility of improvements in thermal insulation, solar glare and acoustic properties as compared with conventional panels. It will also be appreciated that these improvements in performance can be obtained while retaining standard 32 and 35mm thicknesses.

The embodiments also provide the possibility of the conversion of glazed areas into passive solar heaters. In summer, up to 0.8KW! m2 of heat enters the through the roof of a conservatory. In winter, when the sun is lower in the sky, up to 0.5KW/rn2 of heat enters through the side windows. The embodiments allow the collection of some of this heat to provide a heat source for the domestic or commercial premises.

In Figure 1, the glazing sheet is shown as having a cell structure in* which the layers of cells are arranged such the cells of the layers are disposed one above the other. This is not essential. Instead the cells of the layers could be offset.

In Figure 1, the cells are shown as all having the same height. This is not essential.

For example, in a glazing sheet having a nominal cell height of 4mm, there may be a layer of cells having a height substantially less than 4mm to allow the incorporation of an additional cell layer, while keeping the overall thickness of the glazing sheet within a particular nominal thickness, for example 16mm. It is also possible, there may be cells or a row of cells having a height greater than 4mm. For example and referring to Figure 1, the intermediate walls 16 could be omitted in the spaces between the transverse walls 18 where the webs 20 are provided so that the cellular structure comprises a mixture of cells having a height of 4mm or less and cells having a height that varies with the slope of the web. Similarly, it is not essential that the cells all have the same width. For example, the positioning of the transverse walls may be arranged to provide columns or layers of cells having respective different widths.

In Figure 1, the glazing sheet comprises the outer surface elements, intermediate walls between the outer surface elements and transverse walls that extend transverse to the outer surface element and intermediate walls. It will be appreciated that the transverse walls could be omitted. In this case, the glazing sheet can comprise a plurality of spaced sheets of plastics material or glass.

In the embodiments, the glazing panels are shown as comprising two glazing sheets.

It will be appreciated that this is not essential. The glazing panels may comprise three or more glazing panels as desired and the structure of, for example the glazing panel and the glazing panel 50 integrated in a single glazing panel.

In the embodiments, solar protection is provided by materials positioned in the cells of the cellular glazing sheets and/or between the glazing panels. It is envisaged that the heat absorbing and/or heat reflecting function could be obtained by incorporating suitable materials in the polymer structure of the glazing sheets. Thus, for example, a heat reflecting material in the form of a metal strip or amorphous metal forms could be incorporated into the walls of the glazing sheet during an extrusion process.

Alternatively, suitable tints and dyes could be introduced to the plastics mix to absorb and/or reflect solar heat and light generally, or tailored to a specific solar heat (microwave/radiation) absorbing function.

It will be understood that the glazing panels of the embodiments are suitable for many building applications, including, for example, use in roof lights and in glazing the roofs and side walls of conservatories and similar glazed roof/wall structures.

It will be appreciated that when configuring a glazing panel, account will have to be taken of the amount of light that panel is to be transmit as well as the insulation, heat capture and heat reflection capabilities described above and in some cases, it may not be possible to optimise those capabilities and obtain the desired light transmissibility.

Claims

Claims 1. A glazing panel comprising an assembly of at least two cellular glazing sheets that each have a hollow cellular structure defining a plurality of cells, said glazing sheets being disposed in a generally face to face relation such that the glazing panel has a thickness equal to at least the sum of the thicknesses of the glazing sheets.
2. A glazing panel as claimed in claim 1, wherein the or at least two of said cellular glazing sheets have the same structure.
3. A glazing panel as claimed in claim 1 or 2, wherein a said cellular glazing sheet comprises opposed outer surface elements forming major external surfaces of the cellular glazing sheet and a plurality of intermediate walls disposed between said outer surface elements and extending generally parallel to said outer surface elements, the mutual spacing between adjacent said outer surface elements and intermediate walls defining the height of the cells.
4. A glazing panel as claimed in claim 3, further comprising a plurality of connecting elements extending between said outer surface elements, the width of said cells being defined by the mutual spacing of adjacent said connecting elements.
5. A glazing panel as claimed in claim 3 or 4, wherein the cells of said cellular glazing sheet have a height not substantially greater than 4mm.
6. A glazing panel as claimed in any one of the preceding claims, wherein said cellular glazing sheets are disposed in face to face contact.
7. A glazing panel as claimed in any one of claims I to 5, comprising two said cellular glazing sheets separated by at least one separating member to define a gap therebetween.
8. A glazing panel as claimed in claim 7, wherein said gap is at least partially filled by an insulating material and/or a heat absorbing or heat reflecting material.
9. A glazing panel as claimed in as claimed in claim 8, wherein said gap is partially filled by a said heat absorbing or heat reflecting material and at least one side region of the glazing panel is provided with porting to permit the flow of warm air from said partially filled gap.
10. A glazing panel as claimed in any one of claims I to 5, comprising two said cellular glazing sheets separated by a translucent or transparent insulating material.
11. A glazing panel as claimed in claim 10, wherein said cellular glazing sheets are further separated by a heat absorbing or heat reflecting material.
12. A glazing panel as claimed in claim 10 or 11, further comprising at least one separating member separating said two cellular glazing sheets, said at least one separating member being disposed adjacent the periphery of the cellular glazing sheets.
13. A glazing panel as claimed in any one of the preceding claims, further comprising at least one clamping device or an adhesive tape arranged to hold said at least two cellular glazing panels in a fixed relationship.
14. A glazing panel as claimed in any one of the preceding claims, wherein said at least two cellular glazing sheets are held in a fixed relationship by bonding between members of the glazing panel.
15. A glazing panel as claimed in any one of the preceding claims, wherein at least one cell of at least one said cellular glazing sheet contains a heat absorbing or heat reflecting material.
16. A glazing panel as claimed in claim 15, wherein the or each cell containing a heat absorbing or heat reflecting material defines a flowpath extending between a first side region of the glazing panel and a second side region of the glazing panel, at least one of said side regions being closed and provided with porting to permit the flow of warm air from said flowpath.
17. A glazing panel as claimed in claim 15 or 16 when dependent on claim 3, wherein each cell of a layer of cells adjacent a said outer surface element contains a said heat absorbing or heat reflecting material.
18. A structure having a glazed roof comprising framing and a plurality of glazing panels as claimed in any one of the preceding claims.
19. A structure as claimed in claim 18 when dependent on claim 17, wherein each said glazing panel is arranged such that said layer of cells is closest to the roof exterior.
20. A cellular plastics glazing sheet comprising a first outer surface element, a second outer surface element, at least one intermediate wall disposed between and spaced from said first and second outer surface elements and a plurality of wall elements interconnecting said first and second outer surface elements and said at least one intermediate wall to define a hollow interior region comprising a plurality of cells, said first and second outer surface elements forming major external surfaces of the glazing sheet and the arrangement being such that at least a plurality of said plurality of cells have a height not substantially greater than 4mm.
21. A cellular plastics glazing sheet as claimed in claim 20, wherein said first and second outer surface elements and the or at least one intermediate wall are mutually spaced apart by a distance not substantially greater than 4mm.
22. A cellular plastics glazing sheet as claimed in claim 20 or 21 having a nominal height measured between said major external surfaces of substantially 25mm, 32mm or 35 mm.
23. A cellular plastics glazing sheet as claimed in claim 20, 21 or 22 having a thermal transmittance value not substantially greater than 1.0 W/m2.
24. A cellular plastics glazing sheet as claimed in any one of claims 20 to 23 that is a plastics extrusion.
25. A cellular plastics glazing sheet as claimed in any one of claims 20 to 24 made of a plastics material and having a heat absorbing or heat reflecting material incorporated in said plastics material.
26. A cellular plastics glazing sheet as claimed in claim 25, wherein said heat absorbing or heat reflecting material comprises a metallic film or metal particles.
27. A cellular plastics glazing sheet as claimed in any one of claims 20 to 26 made of a plastics material and having a heat absorbing component incorporated in said plastics material.
28 A cellular plastics glazing sheet as claimed in claim 27, wherein said heat absorbing component comprises a dye.
29. A cellular plastics glazing sheet as claimed in any one of claims 20 to 28, comprising heat absorbing or heat reflecting inserts inserted in at least one of said cells.
30. A cellular plastics glazing sheet as claimed in any one of claims 20 to 29, wherein the height of each said cell is in the range 2.3 to 4.0 mm.
31. A cellular plastics glazing sheet as claimed in any one of claims 20 to 30, comprising at least one row of said cells having a height not substantially greater than 4mm.
32 A glazing panel comprising at least two cellular glazing sheets as claimed in any one of claims 20 to 31, the glazing sheets being disposed and held in a generally face to face relationship.
33. A glazed structure comprising framing and a plurality of glazing panels as claimed in claim 32.
34. A method of forming a curved roof structure comprised of glazing panels as claimed in any one of claims 1 to 17 or claim 32, wherein each said cellular glazing sheet of the glazing panels is formed with a required curvature and the curved glazing sheets are positioned in said generally face to face relationship.
35. A glazing panel substantially as herein described with reference to the drawings.
36. A cellular plastics glazing sheet substantially as herein described with reference to Figure 1 of the drawings.
37. A glazed structure comprising a glazing panel and/or cellular glazing sheet substantially as herein described with reference to the drawings.
38. A method of forming a curved roof structure substantially as herein described with reference to the drawings.