GB2296279A

GB2296279A - Multiple glazing unit with channel-shaped fixing element

Info

Publication number: GB2296279A
Application number: GB9425952A
Authority: GB
Inventors: Jan Mangelschots
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 1994-12-22
Filing date: 1994-12-22
Publication date: 1996-06-26
Anticipated expiration: 2014-12-22
Also published as: GB9425952D0; LU88686A1; DE19547444A1; FR2728616A1; FR2728616B1; GB2296279B

Description

1 is 2296279 - 1 A MULTIPLE GLAZING UNIT AND METHOD FOR ITS CONSTRUCTION

The present invention relates to a multiple glazing unit, in particular to such a unit comprising two vitreous material panels positioned in faceto-face spaced apart relationship, having a gas space therebetween delimited by a peripherally extending spacer. The present invention also relates to a method for constructing such a unit.

Multiple glazing units, for example double glazing units, are very useful for increasing thermal and sound insulation of the interior of buildings and therefore for increasing the comfort of the occupants of the building compared to the weak insulation provided by ordinary simple glazing units.

Simple double glazing units are constituted by two sheets of vitreous material such as glass fixed and maintained in a spaced relationship one to the other, usually at their edges, by the intervention of a spacer. The spacer is usually a metallic profile which is adhered to the sheets, along the length of the four edges thereof. An hermetically sealed hollow space is formed between the sheets, delimited by the spacer. This space is filled with a dry gas such as dry air. It is important t hat the gas confined within the space should be maintained in a dry state in order to avoid any condensation of water at the interior of the double glazing during changes in temperature. If there is condensation of water vapour on the internal walls of the sheets, the transparency of the glazing will be reduced and the visibility through the glazing will be affected.

A multiple glazing unit is known comprising two vitreous material panels positioned in face-to-face spaced apart relationship. A gas space between the panels is delimited by a peripherally extending spacer. A cordon of resin extends at least between the spacer and each of the panels to hold the panels in place. Usually, the unit is mounted in a frame of Usectioned profile in which the edges of the panel are retained, this frame then being fixed to a support structure, for example, within the opening in the wall of a building.

The commercial demand is more and more to install the glazing units in bays by adhesively securing the panels to the support structure instead of mounting the panels in a U-section profile frame. This recent technique of panel installation is often referred to as "exterior panel adhesive fixing" or (somewhat improperly) as to structural glazing". This technique allows one to form fagades which appear to be totally glazed. It also allows one to install the units in a flush manner with the body- work of a vehicle for example. This technique allows one to obtain advantageous aesthetic effects.

In a method of installation currently practised, the multiple glazing unit is firstly assembled in the. factory. It is then passed to a workshop where a frame is adhesively secured to the periphery of the glazing unit. The assembly is then transferred to the building site to be fixed to the structure of the building. In an alternative method the unit is glued together on site.

Both such methods rely on operations carried out away from the factory where it may not be easy to control the quality of the finished product and may require additional onerous steps.

German patent application DE 3626194 (SchUco) shows a double-glazed unit fixed to the structure of a building in such a manner as to constitute a totally glazed fagade. The external sheet is larger than the internal sheet and a fixing element, fixed to the structure of the building, is secured to the internal peripheral face of the external sheet. One branch of the fixing element is inserted in a U-shaped profile which is immersed in the centre of the adhesive sealing resin of the unit. This fixing system is relatively complex and onerous. Amongst other things, it complicates the construction of the unit and increases costs, in particular because the unit cannot be constructed on a production line of the type used for conventional double-glazed units. The insertion of the profile into the hardened resin after injection or the injection of the resin around the profile are very difficult delicate operations to perform on a large scale. Further, there is a risk of an interruption in the continuity of the adhesive resin, particularly at the corners of the unit, which may drastically reduce the durability of the unit.

Another system for mounting double-glazed units on the fagade of a building by "structural glazing" is described in French Utility Certificate FR 2577274 (SchUco). The spacer of a double-glazed unit is disposed in a recess and a U-shaped profile is disposed at the periphery of the unit in the slot between the sheets of glass. The on-line construction of this unit is difficult, because the removal of excess adhesive sealing resin for 4 - 1 r% accommodating the U-shaped profile is a delicate operation to perform on a production line. Further, there is a risk of the ingress.of moisture between the external sheet and the profile. Among other things, the profile leads to a modification of the external appearance at the periphery of the unit which is undesirable from the aesthetic point of view when the faqade of the building is observed.

It is an object of the present invention to provide a multiple glazing unit and a method for constructing such a unit where the operations can be performed in a factory so as to more easily control the quality of the finished product and to provide a multiple glazing unit which is ready for installation by a structural glazing technique.

According to a first aspect of the invention, there is provided a multiple glazing unit comprising at least two vitreous material panels positioned in face-to-face spaced apart relationship, having a gas space therebetween delimited by a peripherally extending spacer, a cordon of resin securing the panels together, and a fixing element immersed in the resin to constitute means for fixing the glazing unit to a support structure, the fixing element defining a channel open towards the exterior, wherein the fixing element is positioned closely adjacent the first of the panels, while being spaced from the second of the panels.

According to a second aspect of the invention, there is provided a glazed structure, at least one fagade of which incorporates a plurality of glazing units as defined above.

- It might be thought that the presence of the fixing elements may create an obstacle to the application of the resin, resulting in the presence of bubbles at the glassspacer interface, or the risk of weak bonding between the two sheets of the unit.

It is therefore surprising that the invention leads to the formation of a unit of high quality which may be directly fixed to the structure of a building.

The fixing element can be fixed directly to the unit on an automatic production line for the construction of double-glazed units, at the same time as the unit is glued together. This can be carried out under the control of an expert in the factory, instead for example of relying on operations carried out at the building site or at a supplementary workshop. It is therefore easier to control the quality of the finished product.

Furthermore, the invention provides a multiple glazing unit which is ready for installation by a structural glazing technique and which may be easily constructed in a factory with carefully controlled application of the resin.

Preferably, the fixing element is in the form of a Usectioned profile which may comprise, in cross-section, two leg portions joined by a bridging portion, the free ends of the leg portions lying not beyond the level of the edge of the first panel, but ideally substantially flush with both the edge of the first panel and the edge of the second panel. The bridging portion is preferably inclined in such a manner that the leg portion adjacent said first panel is longer than the other leg portion. The angle of inclination may be more than 100, for example between 10 and 451, advantageously between 250 and 4C, such as about 35.

Preferably, the fixing element has a width which is less than half the spacing between the first and second panels, thereby providing sufficient space between the fixing element and the second panel for the introduction of the resin. Furthermore, the fixing element preferably has a depth which is between 25% and 75% of the depth of the space to be occupied by the resin, i.e. the distance of the spacer from the edges of the panels. This ensures that the resin contacts sufficient surface area of the first panel to provide a reliable bond therewith, while enabling the channel in the fixing element to have sufficient depth to ensure secure fixing of the unit in use.

It is possible for a number of fixing elements to be provided, which together extend around the glazing unit. It is preferred that a number of fixing elements are provided which together extend substantially fully around the periphery of the unit. This has the advantage of providing the best fixation of the glazing unit to the carrying structure. Where, for example, the unit has a generally rectangular shape, preferably four fixing elements are provided each extending along a respective edge of the unit, the fixing elements being disposed at right angles to each other. Alternatively, fixing elements may be provided only at two opposite edges of the unit, no fixing elements being associated with the other opposite edges of the unit. The fixing element may be formed of aluminium, stainless steel or a rigid plastics material such as PVC.

To enable the glazing unit according to the invention to be mounted using a "structural glazing" technique, it is preferred that the fixing elements do not extend beyond the plane of that vitreous sheet of the unit which is intended to be placed in the exterior position when the unit is assembled, together with others, in a structure such as a building.

In order to provide the greatest rigidity to the spacer panels / fixing element assembly, the cordon of resin preferably extends at least between the spacer and each of the panels.

Preferably, the resin is an adhesive material which exhibits, at 200C, an elongation of not more than 12.5% when subjected to a tensile stress of 0. 1 MPa, advantageously 0.14 MPa, as measured according to ISO 8339. The adhesive material preferably also exhibits, at 20C, an elongation of not more than 12.5% when subjected to a tensile stress of 0.1 MPa after ageing for 500 hours in water at 55C, especially when subjected to a tensile stress of 0.14 MPa after ageing in water for 1000 hours at 450C. We mostly prefer that the adhesive material exhibits an elongation of not more than 12.5% when subjected to a tensile stress of 0.1 MPa, preferably of 0.14 MPa over a temperature range of -200C to 550C, preferably over a temperature range of -400C to 700C. We prefer that the adhesive material exhibits a rupture strength at 200C of more than 0.70 MPa, preferably at least 0.84 MPa, and a deformation at rupture of greater 8 than 50%. The most preferred adhesive material exhibits cohesive rupture when subjected to a tensile stress in excess of the rupture strength thereof.

Preferably, the adhesive material is selected from silicone adhesive materials, but polysulphide and polyurethane adhesive materials may also be used. When a polysulphide or other light sensitive material is used, it is preferred to include in the glazing unit means to shield the adhesive material from sunlight. Such means may comprise, for example, a UV shield coating on the exterior sheet of vitreous material or a band of vitreous enamel formed by silk-screen printing.

Preferably, layers of sealant are positioned between the spacer and each of the panels. Thus, a water tight joint may be achieved with the aid of two different materials. The first material, which is highly water impermeable, but relatively flexible, is referred to generally herein as a "sealant", and may for example be a polyisobutylene. The second material which is highly adhesive and relatively rigid, is referred to generally herein as the "resin".

The spacer may be formed of a metal or of a plastics material. The spacer may be hollow, the hollow interior of the spacer being in gas communication with the gas space. When the hollow interior of the spacer is in gas communication with the gas space, a desiccant may be located in the hollow interior. Such a spacer may have a trapezium shaped crosssection.

Alternatively, the spacer has a cross-section which may is - 9 be open to the gas space. For example, the cross-section of the spacer has a flared "U" shape. Such a crosssection may comprise two flared arm portions interconnected by a base portion. The flared arm portions may be deformably connected to the base portion to enable some flexibility of the cross-sectional shape of the spacer which serves to take up some of the stresses that result from temperature increases or other causes. In these embodiments, a desiccant may be located within the spacer. Alternatively or additionally, the sealant may contain a desiccant.

In another embodiment, the spacer is essentially formed by a polymeric material. A suitable spacer is known as a "Swiggle Strip" (Trade Mark) ex TREMCO SA, of F-75643 Paris, Cedex 13, which is a pre-extruded butyl ribbon having a metal core and containing a molecular sieve desiccant powder. The spacer acts additionally as a moisture barrier.

The first and/or second panel may be constituted by a composite glazing panel, that is a glazing panel which consists of or includes a pair of vitreous sheets adherent to an intervening layer of polymeric material. The intervening layer may, for example, be PVB to constitute a safety laminated panel. Other suitab le intervening layer materials, such as acrylate polymers, may be used to provide exceptional acoustic properties to the composite panel due to their viscoelastic properties.

A composite panel may be formed from two or more vitreous sheets which are of equal thickness, or there may be an inequality of thickness between the sheets, the latter - arrangement leading to different acoustic isolation properties.

If a composite panel formed with an intervening polymeric layer with viscoelastic properties to provide acoustic isolation is placed in the external position, it is preferable that the sheets of the composite panel are held together with the aid of the cordon of resin. This can be achieved where the edges of the sheets are displaced relative to each other in such a manner that the cordon of resin may be in contact with both sheets of the composite panel, thereby to secure retention of the external sheet.

Advantageously, the second panel of the glazing unit according to the invention consists of a single unlaminated sheet of vitreous material. Such a sheet is very much less costly to produce than a composite panel. Preferably, the vitreous sheets of the unit have been subjected to a thermal tempering treatment. It is preferable however that the internal vitreous sheet is thermally toughened, instead of being tempered, so that the external panel is continued to be retained at its periphery should the internal panel become broken.

According to a further aspect of the invention, there is provided a method of constructing a multiple glazing unit comprising the steps of:

(i) providing two vitreous material panels; (ii) securing a fixing element to the first of said panels on the marginal portion thereof to constitute means for fixing the glazing unit to a support structure, said fixing element defining a channel open towards the exterior and positioning both said vitreous panels in face-to-face spaced apart relationship, with a gas space therebetween delimited by a peripherally extending spacer so that the fixing element is in a position closely adjacent to the first of said panels while being spaced from the second of said panels; (iii) applying a cordon of resin to the space defined by the panels, the spacer and the fixing element to immerse the fixing element and to secure the panels together.

This simple construction method may be carried out online under a controlled atmosphere, to ensure that the fixing element is correctly and securely bonded to the unit for fixing the unit in its intended place in a secure manner, and, at the same time, to ensure that the gas space has a sufficiently low humidity. The unit comes from the factory in a readyto-install condition, requiring substantially no further construction on site, other than fixing of the unit to the supporting structure of a building for example.

Preferably, the fixing element is secured to the first panel by means of double-sided adhesive tape, but other securing means such as glue may be used. Where doublesided adhesive tape is used, this preferably has a portion which extends beyond the edge of the first panel, the extending portion being folded over to cover the open mouth of the channel before step (iii) of the method is carried out to prevent the channel being filled with 12 resin. The folded over portion of the double-sided tape may be folded back or removed before the unit is mounted in a supporting structure.

is As the fixing element is already secured against one of the panels, the injection of the resin need only be made on one side of the fixing element which allows one to carry out the assembly by machine on a conventional production line. This also avoids the need to force the fixing element into the joint after gluing the unit together.

After polymerisation of the resin, the unit leaving the factory may be sent directly to the building site to be fixed to the structure of the building where complementary fixing pieces are inserted into the channel of the fixing elements.

In order to fix the unit to the fagade, one may for example make use of pivotable fixing pieces having a length of 25 mm and being distributed at every 20 cm around the bay into which the unit is to be fixed. The unit is positioned in place and then one pivots the fixing pieces through 90 to engage them in the channels formed by the fixing element, in a manner to maintain the unit in place.

The invention will now be further described with reference to the accompanying drawings, in which:

Figure 1 shows in partial cross-section a double glazing unit according to a first embodiment of the invention; Figure 2 shows in partial cross-section a double glazing unit according to a second embodiment of the invention; Figure 3 shows in partial cross-section a double glazing unit according to a third embodiment of the invention; Figure 4 shows in partial cross-section the manner in which two adjacent glazing units as shown in Figure 1 are fixed to the fagade of a building; and Figure 5 shows in partial plan view a number of glazing units as shown in Figure 1 secured to the fagade of a building.

Referring to Figure 1, there is shown a multiple glazing unit comprising two glass panels 7, 8 positioned in faceto-face spaced apart relationship. The first sheet 7 constitutes the interior sheet of the glazing unit. A gas space 9 between the panels is delimited by a peripherally extending spacer 3 formed of galvanised steel of 0.4 mm thickness. Layers of polyisobutylene sealant 5 are positioned between the spacer 3 and each of the sheets 7, 8. The polyisobutylene used has a permeability of about 0. 11 g water x mm. thickness per M2 x 24 h x kPa water vapour.

A cordon of resin 6 fills the space between the spacer 3 and each of the panels 7, 8 and secures the panels together. A fixing element 2 is immersed in the resin to constitute means for fixing the glazing unit to a support structure. The fixing element defines a channel 25 open towards the exterior. The fixing element is positioned closely adjacent the first panel 7 and is secured 14 thereto, while being spaced from the second panel 8. The fixing element 2 is in the form of a U-sectioned profile comprising, in cross-section, two leg portions 21, 22 joined by a bridging portion 23 which is inclined at an angle of about 35 in order that the resin may completely fill the space. The free ends 21a, 22a of the leg portions lie substantially flush with the edge 71 of the first panel 7 and with the edge 81 of the second panel 8.

The fixing element 2 is secured to the first panel 6 by means of doublesided adhesive tape 1, such as Glazing Tape VG 132 (ex Qualitape, Belgium).

The fixing element 2 has a width which is less than half the spacing between the first and second panels 7, 8. For example, where the panels 7 and 8 are spaced apart by 12 mm, the overall width of the fixing element 2 is 5 mm. Furthermore, where the spacer 3 is positioned 16 mm from the edges 71, 81 of the panels 7, 8, the fixing element 2 suitably has an overall depth of about 10 mm, to ensure that the resin 6 contacts sufficient surface area of the first panel 7 to provide a reliable bond therewith, while enabling the channel 25 in the fixing element 2 to have sufficient depth to ensure secure fixing of the unit in use.

The resin 6 is a silicone adhesive material which exhibits, at 20C, an elongation of not more than 12.5% when subjected to a tensile stress of 0. 1 MPa, as measured according to ISO 8339. The preferred silicone bonding adhesive material is "Q 3362" ex Dow Corning, having an elongation of 12. 5 % when subjected to a tensile stress of 0.27 MPa, before ageing and an elongation of 12.5 % when subjected to a tensile stress of 0.2 MPa, after ageing for 21 days in water at 550C, as measured according to method A of ISO 8339. The rupture strength of this material is 1.08 MPa before ageing, and 0.92 MPa after ageing, the elongation at rupture being more than 50% and the rupture being cohesive, both before and after ageing. The resin 6 is in contact with one face of the first sheet 7 and also with one face of the second sheet 8.

In use, the sealant 5 provides a barrier to the penetration of water vapour into the gas space 9 while the resin 6 serves to retain the sheets 7, 8 in their face-to-face relationship.

The method of constructing the multiple glazing unit is as follows. Firstly, the fixing element 2 is positioned closely against the first panel 7 and secured thereto by means of double sided adhesive tape 1. In a second step, sealing tubes of polyisobutylene are disposed on the side faces of the spacer 3 to an adequate extent, the spacer is disposed along the marginal zone of the sheet of glass 7 and the other sheet of glass 8 is disposed thereover. The sheets of glass are then pressed together to squash the butyl sealant to the desired extent between the sheets of glass. The fixing element 2 is thus positioned closely against the first panel 7 while being spaced from the second panel 8.

Thereafter, the cordon of resin 6 is injected into the space defined by the panels 7, 8, the spacer 3 and the fixing element 2 to immerse the fixing element 2 and 16 hardened or allowed to harden to secure the panels 7, 8 together.

The double-sided adhesive tape 1 has a portion 11 which extends beyond the edge 71 of the first panel 7, the portion 11 being folded over ( as shown by the broken lines in Figure 1) to cover the open mouth of the channel 25 before the resin is injected, to prevent the channel being filled with resin. The folded over portion 11 of the double-sided tape is removed before the unit is mounted in a supporting structure.

In the embodiment shown in Figure 2, the first panel 7 is constituted by a composite glazing panel having a pair of vitreous sheets 72, 73 adhered to an intervening layer 74 of polymeric material sandwiched therebetween.

The first sheet 72 is formed of thermally toughened glass having a thickness of 6 mm and carrying a solar screening coating of STOPSOL (Trade Mark), on the internal face thereof. The second sheet 73 is formed of thermally toughened glass having a thickness of 5 min and carrying a low emissivity coating. A low emissivity coating is provided on that face of the sheet 73 which is disposed remote from the sheet 72. The first sheet 72 constitutes the interior sheet of the glazing unit.

The acrylic polymer layer 74 has viscoelastic properties such that the critical frequency of coincidence of the panel 7 is greater than the critical frequency of coincidence of a notional monolithic vitreous sheet which is of the same shape and area as the panel 7 and has a mass equal to the total mass of vitreous material in the panel 7. A suitable acrylic polymer is UVEKOL (Trade Mark) ex UCB SA, of B-1620 Drogenbos, Belgium.

The glazing unit shown in Figure 2 is in the form of a double-glazed unit including a second glazing panel 8, formed of 5 mm thermally tempered glass, positioned in face-to-face relationship to sheet 73 of the composite panel 7, and spaced therefrom to provide an air space 9 of 12 mm.

The method of constructing the glazing unit according to Figure 2 comprises the following steps. Firstly, the pair of vitreous sheets 72, 73 are positioned in face-toface spaced relationship to each other. A ribbon 75 of butyl sealing material having a width of 8 mm is disposed between the sheets 72 and 73 at a distance of approximately 8 mm from the peripheral edge 71 of the sheets. This ribbon is formed by placing a cylindrical cordon of the butyl sealing material on one of the vitreous sheets and squeezing the cordon into a ribbon of the specified width by pressing the two sheets together. The ribbon 75 is continuous save for two interruptions (not shown) to enable, respectively, the evacuation of the space between the vitreous sheets and the injection into that space of an acrylic polymer precursor, the ribbon delimiting the area occupied by the polymeric material in the composite panel 7. After the injection of the precursor, the interruption in the ribbon of sealing material is closed by the provision of further sealing material. The acrylic polymer precursor is then caused to polymerise to the polymer by exposure to ultraviolet radiation.

18 - is The next step of the process is the positioning of the fixing element 2, followed by the steps outlined above with respect to the embodiment shown in Figure 1.

In a variation, the film 74 extends to the edge 71 (i.e. the ribbon 75 of butyl sealing material is omitted) and is constituted by PVB.

In another variation, the spacer 3 and the sealant 5 are replaced by a "Swiggle Strip".

In the embodiment shown in Figure 3, the glazing unit is in the form of a double-glazed unit including a first glazing panel 7 in the form of a single sheet and a second panel 8 constituted by a composite glazing panel. The composite glazing panel 8 has a pair of vitreous sheets 83, 82 adhered to an intervening layer 84 of polymeric material having viscoelastic properties sandwiched therebetween. A ribbon 85 of butyl sealing material is disposed between the sheets 83 and 82. The first panel 7 is positioned in face-to-face relationship to sheet 82 of the composite panel 8, and spaced therefrom to provide an air space 9. The first sheet 83 constitutes the exterior sheet of the glazing unit.

A portion of the first sheet 83 overlaps the edge of the second sheet 82. The overlapping marginal portion extends around the periphery of the composite panel 8. The resin 6 is in contact with one face of the first sheet 83 and also with one face and the edge of the second sheet 82. The resin 6 not only serves to secure both panels together, but also serves to secure both sheets of the composite panel 8.

The free ends 21a, 22a of the leg portions of the Usectioned profile section fixing element 2 lie substantially flush with the edge 71 of the first panel 7 and with the edge 81 of the exterior sheet 83 of the second panel 9.

Figure 4 shows the manner in which two adjacent units 41, 42 are fixed to the structure of a building. The spacing between the units is about 20 mm. Sealing joints 44 are provided between the units and a support member 43 fixed to the structure of the building. Pivotable fixing pieces 45, carried on the support member 43 with the aid of the screw 46 are turned through 90', after the unit is placed in position, to be engaged in thefixing element 2. The spacing of the unit from the support member 43 is determined by a cylindrical distance piece 47 surrounding the screw 46. The internal sheet of the unit is thereby pressed against the sealing joints 44. Foam filler material 48 covers the head of the screw 46 and is in turn protected by a silicone sealing joint 49.

The mass of each unit should be supported by at least two wedges per unit which are fixed to the structure of the building. These wedges are not shown in Figure 4 for the sake of clarity.

Figure 5 shows the units 41 and 42, together with adjacent units 411 and 421 in partial plan view. Figure 5 shows the distribution of the fixing pieces 45 around the units, and the disposition of the fixing elements 2. Only four corners of four adjacent units are shown, with the broken lines indicating the positioning of the fixing elements and the pivotable fixing pieces 45, which are - 20 turned upwardly to fix the upper unit, downwardly to fix the lower unit, and to the left or right to fix the left hand and right hand units respectively.

Claims

1. A multiple glazing unit comprising at least two vitreous material panels positioned in face-to-face spaced apart relationship, having a gas space (9) therebetween delimited by a peripherally extending spacer (3), a cordon of resin (6) securing said panels together, and a fixing element (2) immersed in said resin to constitute means for fixing the glazing unit to a support structure, said fixing element defining a channel (25) open towards the exterior, wherein said fixing element i positioned closely adjacent the first of said panels (7), while being spaced from the second of said panels (9).

2. A multiple glazing unit according to claim 1, wherein said fixing element is secured to said first panel (7), preferably by means of doublesided adhesive tape (1).

3. A multiple glazing unit according to claim 1 or 2, wherein said fixing element is in the form of a Usectioned profile.

4. A multiple glazing unit according to claim 3, wherein said fixing element (2) comprises, in crosssection, two leg portions (21, 22) joined by a bridging portion (23), the free ends (21a, 22a) of said leg portions lying not beyond the level of the edge (71) of said first panel (7).

22 - 5. A multiple glazing unit according to claim 4, wherein said bridging portion (23) is inclined in such a manner that the leg portion (22) adjacent said first panel (7) is longer than the other leg portion (21).

6. A multiple glazing unit according to any preceding claim, wherein the free ends (21a, 22a) of said leg portions lie substantially flush with both the edge (71) of said first panel (7) and the edge (81) of said second panel (8).

7. A multiple glazing unit according to any preceding claim, wherein said fixing element (2) has a width which is less than half the spacing between said first and second panels (7, 8).

8. A glazing unit according to any preceding claim, wherein said cordon of resin (6) extends at least between said spacer (3) and each of said panels (7, 8).

9. A glazing unit according to any preceding claim, wherein said resin (6) is an adhesive material which exhibits, at 20C, an elongation of not more than 12.5% when subjected to a tensile stress of 0.1 MPa, as measured according to ISO 8339.

10. A glazing unit according to claim 9, wherein said adhesive material exhibits, at 20'C, an elongation of not more than 12.5% when subjected to a tensile stress of 0.14 MPa.

23 - 11. A glazing unit according to claim 9 or 10, wherein said adhesive material exhibits, at 2CC, an elongation of not more than 12.5% when subjected to a tensile stress of 0.1 MPa after ageing for 500 hours in water at 550C.

12. A glazing unit according any one of claims 9 to 11t wherein said adhesive material exhibits said elongation of not more than 12.5% when subjected to a tensile stress of 0.14 MPa after ageing in water for 1000 hours at 451C.

13. A glazing unit according to any one of claims 9 to 12, wherein the adhesive material. exhibits a rupture strength at 200C of more than 0.70 MPa and a deformation at rupture of greater than 50%.

14. A glazing unit according to any preceding claim, wherein said resin (6) is selected from silicone adhesive materials.

15. A glazing unit according to any preceding claim, wherein one of said panels is constituted by a composite glazing panel having a pair of vitreous sheets (72, 73; 82, 83) adhered to an intervening layer (.74; 84) of polymeric material sandwiched therebetween.

16. A glazing unit according to claim 15, wherein the intervening polymeric layer (74; 84) is selected from acrylate polymers.

- 24 17. A glazing unit according to any preceding claim, wherein layers of sealant (5) are positioned between said spacer (3) and each of said panels (7, 8).

is. A glazing unit according to any preceding claim, wherein a number of fixing elements are provided, which together extend around the glazing unit.

19. A glazing unit according to claim 18, wherein said glazing unit has a generally rectangular shape, four fixing elements being provided each extending along a respective edge of the unit, the fixing elements being disposed at right angles to each other.

20. A glazed structure, at least one fagade of which incorporates a plurality of glazing units as claimed in any one of claims 1 to 19.

- 25 21. A method of constructing a multiple glazing unit comprising the steps of:

(i) providing two vitreous material panels (7, 8); (ii) securing a fixing element (2) to the first of said panels (7) on the marginal portion thereof to constitute means for fixing the glazing unit to a support structure, said fixing element defining a channel (25) open towards the exterior and positioning both said vitreous panels in face-to- face spaced apart relationship, with a gas space (9) therebetween delimited by a peripherally extending spacer (3) so that the fixing element (2) is in a position closely adjacent to the first of said panels (7) while being spaced from the second of said panels (8); (iii) applying a cordon of resin (6) to the space defined by said panels (7, 8), said spacer (3) and said fixing element (2) to immerse said fixing element (2) and to secure said panels (7, 8) together.

22. A method according to claim 21, wherein step (ii) includes securing said fixing element (2) to said first panel (7) by means of double-sided adhesive.tape (1) - 23. A method according to claim 22, wherein said double-sided adhesive tape (1) has a portion (11) which extends beyond the edge (71) of said first panel (7), said portion (11) being folded over to cover the open mouth of said channel (25) before step (iii) to prevent said channel being filled with resin.

26 - 24. A method according to claim 23, further comprising removing said folded over portion (11) of said double-sided tape before the unit is mounted in a supporting structure.

25. A method according to any one of claims 21 to 24, wherein step (ii) includes securing a fixing element (2) along each edge of said first panel (7).