GB2521418A

GB2521418A - Thermal Management for metal framed windows

Info

Publication number: GB2521418A
Application number: GB1322498.5A
Authority: GB
Inventors: Peter Daniel
Original assignee: Metal Window Co Ltd
Current assignee: Metal Window Co Ltd
Priority date: 2013-12-18
Filing date: 2013-12-18
Publication date: 2015-06-24
Anticipated expiration: 2033-12-18
Also published as: GB2521418B; GB201322498D0

Abstract

A window assembly includes a casement (20, fig 4) having a glazing unit 25 mounted in a casement frame (22, fig 4). The glazing unit comprises a sealed unit with an outer pane extending on one side beyond the inner pane to form a projecting outer pane edge 28. The casement has a window bar (40, fig 4) arranged on the outer pane and integrated with the outside of the casement frame to demarcate adjacent panels of the glazing unit. Each window bar includes an inverted T-shaped member 42 on the external surface of the outer pane and terminating in abutment with a window bar end piece 44. The end piece has a T-shaped section to align with the inverted T-shaped member and a U-shaped section arranged to hook over the projecting outer pane edge. In a second aspect a window includes a thermal insulation wall.

Description

TlinRMAL MANAGEMENT FOR METAL FRA1D WINDOWS

Technical Field

The present invention relates to a window assembly comprising a casement mountable to a base frame; to a building having such a window assembly installed in or on the building; and to a method of glazing a building with such window assemblies.

Background Art

A window assembly consists of two parts, a base structure or frame which is fixed to the structure of the wall or roof opening, and a casement which is typically attached via a hinge to the base structure. Glazing is carried by the structure of the casement frame.

This invention relates to such window assemblies in general, and in particular to metal roof lights, that is to say a window or skylight fitted in a roof and comprising glazing which is carried on the roof structure through at least one metallic frame.

The glazing typically consists of a double glazed unit fixed in the casement frame and seated on an angled seating element of the latter. The casement frame is normally arranged to be opened outwards and to close on to the base frame of the rooflight, by which it is typically carried directly, being for example articulated through hinges on the base.

Metal rooflights share with other metal-framed windows the problem of condensation from the atmosphere under certain conditions of temperature and humidity. Water which condenses on the frames is at best a nuisance, but can also lead to corrosion of the metal.

Building regulations (or code) is typically used to specify legal standards for structural elements of buildings, including windows. In the UK, Part L of the Building Regulations includes a requirement that the minimum area weighted average thermal conductivity for window units in new dwellings must not exceed 2.0 W/m2.K and for replacement windows in existing dwellings must not exceed 1.6 W/m2.K. A suggested target of 0.9 W/m2.K was published by the Department for Communities and Local Government, London, in 2007 (Building Regulations: Energy efficiency requirements for new dwellings -A forward look at what standards may be in 2010 and 2013) . It is likely that future revision of Building regulations and codes will result in increasingly stringent requirements relating to thermal conductivity and air permeability.

The thermal conductivity of an entire window assembly results from a combination of the thermal conductivities of the frame and the glazing. Where the frame has a relatively high thermal conductivity, it will impose a lower limit on the achievable thermal conductivity for the window as whole. It is therefore desirable that window frames have a sufficiently low thermal conductivity for the glazing to dominate the overall thermal conductivity.

GB 2 306 545 A discloses a thermal shield for a roof light with a metal frame in which a thermal shield is interposed between the base frame and the opening. The thermal shield both limits the thermal conductivity of the frame and prevents condensation thereon from becoming a problem by forming a channel that carries the condensate outside.

GB 2 492 380 A aims to provide an improved thermal shield to provide an adjustable level of thermal inslation, and to provide a roof light with very low levels of air permeability.

One particular type of metal window is a so-called conservation roof light, which is a roof light intended to replicate with historical accuracy the appearance of traditional single-paned roof lights with the aim of conserving the external appearance of buildings in areas where planning regulations or aesthetic preference dictate that new window assemblies should look the same as the traditional roof lights. One challenge is to achieve the necessary thermal performance for such conservation roof lights, in particular where historically accurate features such as window bars that used to hold smaller single panes of glass in place are to be replicated, as these features tend to result in undesirable thermal conduction pathways that lead to heat loss.

Another challenge in the case of opening window assemblies is to provide a mechanical or structural connection between the insulated internal environment and the casement frame which carries the glazing unit, so as to permit actuation of the frame to open and close it.

Typically, the thermally insulative materials used to thermally decouple the inside space from the window frame do not have the requisite structural strength or rigidity to support repeated actuation of the casement between open and closed positions. At the same time, providing a direct structural or mechanical connection typically results in creating a thermal conduction path from the inside space to the metal frame of the window assembly, potentially resulting in significant heat loss.

Suimitary of the Invention According to a first aspect of the present invention, there is provided a window assembly comprising: a casement comprising a glazing unit mounted in a casement frame, the glazing unit comprising a sealed unit having at least an inner pane and an outer pane, with the outer pane extending on one side beyond the end of the inner pane to form a projecting outer pane edge; wherein the casement is arranged to be mounted on a base frame to be installed in or on a building such that the base frame defines an opening in a wall or roof of the building, wherein the casement further comprises one or more window bars arranged at least on the external surface of the outer pane and integrated with the outside of the casement frame to demarcate adjacent panels of the glazing unit on opposite sides of each window bar, and wherein each window bar includes an inverted T-shaped member on the external surface of the outer pane extending at one end from one side of the casement frame and terminating at its opposite end in abutment with a window bar end piece, which end piece has a T-shaped section to align with the inverted T-shaped member and a generally U-shaped section arranged to hook over the projecting outer pane edge and connect on the underside thereof with another side of the casement frame opposite said one side.

According to a second aspect of the present invention, there is provided a window assembly comprising: a casement comprising a glazing unit mounted in a casement frame; and a base frame for installation in or on a building to define an opening in a wall or roof of the building, wherein the casement is arranged to be mounted to the base frame to be moveable relative to the base frame for opening away from and closing onto the base frame, wherein said base frame includes a base plate and a base wall extending outwardly from the base plate around said opening, wherein the casement further includes a thermal insulation wall on the interior side of the casement extending inwardly, around the inside of the perimeter of the casement frame, such that, when the casement is closed onto the base frame, the thermal insulation wall is positioned inside the opening defined by said base wall, spaced from the base wall, to act as a barrier to conduction of heat between the space on the interior side of the window assembly and the base wall, and wherein the window assembly further includes an actuation bracket for opening and closing the casement, the actuation bracket being mounted on the interior side of the thermal insulation wall and structurally connected to the casement frame by a connecting member that passes through the thermal insulation wall, the connection member being enclosed along a section of its length by a thermal insulator, in the region between the actuation bracket and the casement frame.

The present invention also provides a building comprising a window assembly according to the first or second aspect installed in or on the building.

Furthermore, the invention provides a method of glazing a building comprising installing a window assembly according to the first or second aspect in or on the building.

Brief Description of the Drawings

To -enable a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:-Fig. 1 is a perspective view from the exterior side of an embodiment of a window assembly according to the present invention, in the form of a roof light; Fig. 2 is a perspective view from the exterior side of a base frame of the roof light of Fig. 1; Fig. 3 is a perspective view from the exterior side of a casement of the roof light of Fig. 1; Fig. 4 is a perspective view from the exterior side of the bottom end of the roof light of Figs. 1 to 3; Fig. 5 is a perspective view from the bottom end of the roof light of Figs. 1 to 4, showing in detail the construction of the window bars; Fig. 6 is a view similar to Fig. 5, of the same roof light, in which the sealant fillets along the length of the roof bars have been removed; Fig. 7 is a similar view to Figs. 5 and 6, of the sante roof light, in which the glazing unit has been removed, in addition to the sealant fillets; Fig. 8 is a perspective cross-sectional view through the actuation bracket (and connection member) located on the inside of the rooflight of Figs. 1 to 7; Fig. 9 is an end-on cross-sectional view through the seine section of the rooflight shown in Fig. 8; Fig. 10 is a perspective view of a portion of the casement of the rooflight of Figs. 1 to 9, showing the glazing unit having been removed from the casement and detailing the construction of the casement frame; Fig. 11 is a similar view of the casement to that of Fig. 10, showing a cross-section through the glazing ledges of the casement frame; Fig. 12 is a perspective end-on view showing the hinges at the top end of the rooflight of Figs. 1 to 11; Fig. 13 is a cross-sectional perspective view through the base hinge member shown in Fig. 12, detailing the hinge construction; and Fig. 14 is cross-sectional view through a casement hinge member of the roof light of Figs. 1 to 13, detailing further elements of the construction of the hinge member of the rooflight of Figs. 1 to 13.

Detailed Description

In the following, exterior or external is used to refer generally to the side of the window assembly which is in contact with the outside environment external to the building in which the window assembly is installed, and references to the outward direction or outer side or surface should be construed accordingly, unless dictated otherwise by context. Similarly, interior or internal is used to refer generally to the side of the window assembly which is in contact with the space inside the building in which the window assembly is installed, and references to the inward direction or inner side should be construed accordingly, unless dictated otherwise by context.

Reference is made in general to metal windows, this meaning that the base frame and/or casement frame of the window is made of metal. These frames may be of any suitable metal, such as steel or aluminium, although not limited to this.

The metal frames may be in the form of castings or forgings, or be made by press-forming or by fabrication from pieces made in any of these ways, or by extrusion.

However, presently preferred is for the metal frames to be fabricated from pieces that are laser cut from sheet metal, preferably steel or aluminium.

Figs. 1 to 3 show a roof light which is an embodiment of a window assembly 1 according to the present invention.

The window assembly 1 includes a base frame 10, which is designed to be installed in the roof or wall of a building, and to define an opening, i.e., the window opening, in that roof or wall. As can be seen in Fig 2, and in Figs. 9, 12 and 13, the base frame 10 includes base mounting ribs 16 extending along two opposite longitudinal edges of the base frame 10. The base mounting ribs 16 are desirably spaced so that they can be attached to the rafters in the roof of a building, which are typically spaced apart at standard intervals. Holes, which are visible in the base mounting ribs 16 in Figs. 2, 9, 12 and 13, can be used for securing the base frame to the rafters or other structure of the building, for example using screws or bolts. However, any suitable alternative means for securing the base frame 10 in place may also be used.

With continuing reference to Fig. 2, the base frame 10 is otherwise constituted by a base plate 17, and a base wall 18 which extends outwardly from the base plate 17 to define the opening in base frame 10. Also shown in Fig. 2 are the base hinge members 13, by which the casement 20 shown in Figs. 1 and 3 is pivotably mounted or mountable onto the base frame 10.

Fig. 1 shows the casement 20 mounted to the base frame 10 via the hinges 12, of which base hinge members 13 form part.

With reference to Fig. 3, the casement 20 includes a casement frame 22 having a glazing unit 25 mounted or otherwise installed therein. A sealant 26 is provided around the perimeter of the casement frame 22, on the upper, exterior surface of the glazing unit 25, in order to fill in a gap between the casement frame 22 and the glazing unit 25. This seals the glazing unit 25 within the casement frame 22, and prevents the ingress of air, water or other fluids into the casement from the exterior side of the casement 20.

As is visible in Figs. 8, 9, 13 and 14, the glazing unit 25 is a sealed double glazing unit containing an inert gas between upper (outer) and lower (inner) panes of glass. In the roof light of the present example, the upper pane of glass extends at its bottom end (the end mounted lowest down when the roof light is installed in a pitched roof) beyond the bottom end of the lower pane of glass, so as to provide a projecting edge 28 of the upper pane. This is done to maintain the appearance of a single-paned glass roof light, for historical accuracy, whilst a sealed double-glazing unit is actually contained within the perimeter wall 23 of the casement frame 22 in order to meet modern requirements for thermal efficiency.

A silvered masking strip 34 is provided along the exterior side of the glazing unit (on the exterior surface of the outer or upper glass pane), at the position of the bottom edge of the lower or inner pane, in order to cover the seal at the bottom edge of the glazing unit 25 between the upper and lower glass panes.

The three other edges of the glazing unit are covered by the sealant fillet 26 which seals the glazing unit 25 in the casement frame 22. The glazing unit seal is preferably covered in this or another way to prevent degradation of the material used to seal the upper and lower panes of the glazing unit due to exposure to the tJV rays in sunlight shining on the rooflight. In other embodiments, a UV-resistant sealant may be used to seal between the upper and lower panes of the glazing unit 25.

Casement 20 also includes window bars 40 which are also provided to give a historically accurate external visual impression of a single-paned roof light. Such a roof light would traditionally have been formed from three separate glass panels arranged side-by-side in respective recesses defined by the casement frame 22 and window bars 40.

However, in the disclosed embodiments of the present invent ion, the window bars 40 do not physically divide the glazing unit 25 into three separate panels, but instead are provided on the exterior and interior surfaces of the upper and lower glass panes of the glazing unit 25, so that the thermal performance of the glazing unit 25 will not be compromised.

In particular, a traditional casement is made of steel, and window bars having the traditional form, whereby the window opening is divided into three separate sections side-by-side, have the effect of creating a thermal pathway between the inside and the outside of the casement, resulting in significant heat loss. By providing window bars 40 having components disposed only on the interior and exterior surfaces of the glazing unit 25, no such conduction pathway is provided which allows heat to be conducted directly from the inside to the outside of the glazing unit 25.

Glazing unit 25 is installed within casement frame 22.

Casement frame 22 includes an outer perimeter wall 23 and a glazing ledge 24 which runs around the inside of the perimeter wall 23. Glazing unit 25 is mounted or otherwise installed so as to be supported on the glazing ledge 24.

As is best seen in Figs. 8, 9, 10 and 11, to create a thermal conduction barrier between warm air on the inside of the roof light 1 and the casement frame 22, an insulation wall 50 is mounted to the inside perimeter of the glazing ledge 24 and extends around the inside of the casement frame 22 so as to provide a thermal barrier between the interior space inside the rooflight and the casement frame 22. The insulation wall 50 is arranged so as to run along the inside of the opening of the window assembly as defined by the base wall 18, and so provides a thermal barrier between the interior space and both the casement 20 and the base frame 10, when the roof light is installed in a building. Seal member 52 is provided around the upper or outer edge of the insulation wall 50, to provide a seal between the bottom or inner pane, i.e., the interior surface, of the glazing unit 25 and the upper or outer surface of the insulation wall SO.

The insulation wall 50 serves a dual purpose as both a thermal insulator and as a fascia piece around the inside of the roof light opening. It should therefore present an attractive appearance, or be susceptible of decoration.

It is contemplated that the insulation wall may have a composite or layered structure, including an insulation layer of thermally non-conductive material and a fascia layer of decorative material. For this purpose, the fascia layer may comprise a material selected from: wood, plastics material, plaster board or plaster but is not limited thereto. A thermally non-conductive material covered by the fascia layer may comprise a polyisocyanurate foam, or may comprise alternative polymer foams comprising for example polyurethane, polystyrene or phenolic resin. Alternatively the thermally non-conductive material may comprise an aerogel or other thermal insulating material. However, in the presently preferred embodiment, the insulation wall 50 may be formed as a single layer of decorative wood, since wood is typically a good thermal insulator.

Fig. 3 also details the casement hinge members 15, which are arranged at locations to correspond with base hinge members 13 on base frame 10, for mounting the casement 20 to the base frame 10 by coupling the hinge members 13 and together using hinge pins (not shown). In this way, the casement 20 can be opened outwardly away from the base frame 10 and closed onto the base frame 10, for opening and closing the roof light, i.e., by pivoting the casement 20 relative to the base frame 10.

Turning now to Figs. 4 to 7, further details of the window bars 40 will be described. Window bars 40, as explained above, are provided to give a historically accurate appearance to the roof light, as though it were a traditional single-paned roof light formed of several adjacent glass panels (in the present example, three glass panels are demarcated by the window bars 40, although the window may be divided into a greater or lesser number of glass panels depending on its width and aesthetic preference).

In order to maintain the historically accurate external appearance of a single-paned roof light formed of adjacent glass panels, the glazing unit 25 is formed with an upper or outer glass pane which extends at the bottom end of the glazing unit 25 beyond the bottom edge of the lower or inner glass pane, so as to create a projecting edge 28 which extends beyond the bottom wall of the casement frame 22. window bars 40 are formed on the exterior surface of the glazing unit 25 and include an inverted T-shaped member 42 which is attached onto the exterior surface of the outer glass pane by adhesive strips 43.

The inverted T-shaped member 42 extends from the casement perimeter wall 23 at the top end of the casement 20 (i.e., the end mounted highest when the rooflight is installed on a pitched roof) and terminates at its opposite end, at the bottom end of the casement 20 (i.e., the end mounted lowest when the roof light is installed on a pitched roof), in abutment with an end piece 44. End piece 44 has an inverted T-shaped section, which is aligned and in abutment with the inverted T-shaped member 42, and a generally U-shaped section which is arranged to hook around the projecting end 28 of the upper glass pane of the glazing unit 25. The U-shaped section of the end piece 44 is then connected, underneath the projecting edge 28 of the upper glass pane, with the casement perimeter wall 23 at the bottom end of the casement 20.

This is most easily seen in Figs. 6 and 7.

As shown in Fig. 4 and Fig. 5, after the end piece 44 and the inverted T-shaped member 42 have been attached to the exterior surface of the upper glass pane, a sealant fillet 46 is applied along both sides of the T-shaped member, creating the impression of individual glass panels having been installed and sealed between each adjacent pair of window bars 40 or between the outer window bars 40 and the adjacent long edge of the casement frame 22. Sealant fillets 46 are typically applied at the same time as the sealant 26, when sealing the glazing unit 25 inside the casement frame 22.

By forming the window bars 40 in this way, the inverted T-shaped member 42 and the end pieces 44 can be formed from the same traditional material, i.e. steel, from which the casement frame and base frame are both also preferably formed. This ensures that the completed window assembly 1 will have the desired authentic appearance of a steel framed window, but does not create a conduction pathway through the steel window bars from the inside of the glazing unit 25 to the external environment. Furthermore, the use of the window bar end pieces 44 allows an authentic appearance to be maintained at the bottom end of the roof light whilst providing a simple and effective assembly process by which the window bars 40 may be provided to the casement 20. A similar effect is achieved where aluminium is used in place of steel.

Window bars 40 may also be provided with a corresponding window bar piece or strip 48 on the interior surface of the glazing unit 25, i.e. on the lower or interior surface of the lower glass pane. The lower window bar strip 48 is connected to the casement frame 22, as best seen in Figs. 7 and 8, and is provided on its upper or outer surface with adhesive strips 49 which are used to attach the lower window bar strip 48 to the interior surface of the glazing unit 25 when this is mounted in the casement frame 22.

As can be appreciated from Figs. 7 and 8, pre-cut grooves or notches may be used to align and orientate the lower window bar strips 48. The glazing unit 25 is then installed within the perimeter of the casement frame 22, and the upper, exterior T-shaped members 42 are then applied onto the exterior surface of the upper glass pane in alignment with the lower window bar strips 48.

Figs. 8 and 9 detail another feature of the rootlight of Figs. 1 to 14, which is intended to reduce the thermal conduction of heat from the interior space on the inside of the roof light to the exterior environment outside the roof light. Specifically, Figs. 8 and 9 show how the insulation wall 50 is arranged to inhibit lateral transfer of heat from the interior environment to the casement frame 22 (including outer perimeter wall 23 and glazing ledge 24), as well as the base frame 10 (including base plate 17 and base wall 18). However, the position of the insulation wall 50 around the inside of the opening defined by the base wall 18 leaves no connection point to which a handle or other actuation member can be connected in order to open the casement 20 away from the base frame 10.

In prior embodiments, a notch or cut-out was provided in the insulation wall 50 and the handle or other actuation member was mounted directly to, and in intimate contact with, the glazing ledge 24 or other component of the casement frame 22. However, such arrangements may provide a direct conduction pathway for heat to transfer from the interior space inside the roof light through to the exterior environment, in particular via conduction along the glazing ledge 24 and perimeter wall 23, which are typically made from steel or aluminium.

In the arrangement shown in Figs. 8 and 9, an actuation bracket 60 is attached to the interior surface of the insulation wall 50, which as discussed above may be wood or another appropriate thermally insulative material or combination of materials (i.e., a material which is more thermally insulative than the steel or aluminium or other material from which the casement frame is made) However, the insulation wall 50 will typically not have sufficient rigidity or mechanical strength to permit the repeated transfer of forces needed to repeatedly open and close the casement 20 of the roof light. Accordingly, a connection member, in this case two bolts or other threaded fasteners 62, are used to provide a direct mechanical and structural connection between the actuation bracket 60 and the casement frame 22, in particular the glazing ledge 24. In order to improve mechanical and structural rigidity, the threaded fasteners 62 are provided with insulator elements 64, in this case in the form of nylon sleeves, which surround the fasteners. The nylon sleeves 64 provide structural rigidity, due to being under compression along the length of the fasteners 62 between actuation bracket 60 and glazing ledge 24, and also provide thermal insulation of the fasteners.

Furthermore, as the threaded fasteners 62 are of a relatively small diameter, only a small thermal conduction pathway is provided from the actuation bracket through to the glazing ledge 24 along the threaded fasteners 62, which will typically be of steel or aluminium or another similar metal. This arrangement therefore further reduces heat losses through the structural elements of the window assembly 1 to the exterior environment.

Figs. 8 and 9, as well as Figs. 13 and 14, also show an additional beneficial feature of the roof light of Figs. 1 to 14. Specifically, located between the glazing ledge 24 and the outer edge of the base wall 18 is a seal member 27. In the present example, seal member 27 is shown mounted to the inner side of the glazing ledge 24, although it could alternatively be mounted to the outer edge of the base wall 18.

In the illustrated configuration, the seal member 27 is mounted to the underside or inner side of the glazing ledge 24, i.e. the side which faces towards the interior of the building to which the roof light would be mounted, and is provided with two or more substantially parallel flexible ribs which extend, when the casement 20 is open, inwardly towards the outer edge of the base wall 18. In the closed position of the casement 20 shown in Figs. 8, 9, 13 and 14, the ribs are squashed flat, so as to provide a seal with the outer edge of the base wall 18.

Advantageously, the seal member 27 is arranged so that the ribs will project laterally outwardly towards the exterior, in a direction away from the opening defined by base wall 18, when they are compressed by the outer edge of the base wall 18. This has the effect that, when wind blows against the window assembly in a lateral direction, it will tend to force the ribs of the seal member 27 more strongly against the outer edge of the base wall 18, thereby increasing the downward sealing force and improving the seal. By contrast, if the seal member 27 were to be mounted in the opposite orientation, so that the squashed ribs project laterally inwardly towards the opening defined by the base wall 18, then lateral gusts of wind may tend to blow the rib members flat and create an opening or pathway into which air and/or water may flow. Indeed, in particular environments, significant amounts of water have been known to be blown through seals which have not been designed to take account of and accommodate such lateral wind forces, which may lead to damp ingress and/or corrosion.

Turning next to Figs. 10 and 11, constructional details of the casement frame 22 are shown. Fig. 10 is a perspective view of the casement frame 22, from which the glazing unit 25 has been removed. It can be seen that the perimeter wall 23 of the casement 22 is formed from four separate wall pieces, which are joined at their corners. Running along the inside of the perimeter wall 23 is the casing ledge 24, on which the glazing unit 25 is supported when installed in the casement frame 22.

The glazing ledge 24 is similarly formed of four glazing ledge pieces, one running along the entire length of each of the longer sides of the casement frame 22, and two shorter members extending across the gap between these glazing ledges at the top and bottom ends of the casement 20. Each glazing ledge piece is formed to include tabs 73 which project outwardly from the mating edge of the glazing ledge piece which runs along the inner surface of the perimeter wall 23. Perimeter wall 23 includes slots 74 into which the tabs 73 are arranged to be located, for positioning the glazing ledge pieces in the correct position with respect to the perimeter wall pieces.

Slots 74 are also visible, for example, in Figs. 1 and 3, although they are not visible in the final product as these elements would be hidden following welding to secure the ledge pieces to the wall pieces and/or painted over or otherwise covered by an anti-corrosive coating.

As is also clearly shown in Figs. 10 and 11, cut-outs are provided along portions of the mating edges of the glazing ledge pieces, which cut-outs have dual purposes.

The cut-outs may be of two different depths into the ledge pieces from their mating edges, with deeper cut-outs 76 being provided to act as drainage holes, through which water may be drained out of the casement 20 from the gap between the glazing unit 25 and the outer perimeter wall 23. That gap is sealed by the sealant 26, which is used to seal the exterior surface of the casement in order to prevent ingress of water. However, S significant amounts of condensation may still occur within the gap between the glazing unit 25 and the casement perimeter wall 23, and this water must be removed to the outside. Accordingly, drainage holes 76 are provided by providing cut-outs of an appropriate depth into the ledge pieces from the mating edges of the ledge pieces.

Each drainage hole cut-out preferably has a depth from the mating edge of the ledge piece (the edge which contacts the inner surface of the perimeter wall 23) of from 3 mm to 10 mm, preferably from 3.5 mm to 5 mm, and most preferably 4 torn, as shown in the present example.

Similarly, the length of the drainage holes along the mating edge has to be selected so that, when taking account of the combined length and width of the drainage holes 76, an opening is provided which will allow water to pass through it, without the water accumulating and bridging the hole without passing through it due to its surface tension. The drainage holes 76 preferably have a length along the mating edge of the ledge pieces of 2.5 cm to 7.5 cm, preferably 4 cm to 6 cm, most preferably 5 cm as shown in the illustrated example.

In addition to the drainage holes 76, shallower cut-outs 75 are also provided along portions of the mating edge of each ledge piece. The shallower cut-outs 75 provide welding channels, into which welding material may flow during welding of the ledge pieces onto the wall pieces.

The shallower cut-outs 75 for the welding channels preferably have a depth from the mating edge of from 1.5 mm to 2.5 mm, preferably 2 mm as shown in the illustrated example. Similarly, the shallower cut-outs preferably have lengths along the mating edge of 1 cm to 10 cm, preferably 1.5 cm to 5 cm, most preferably 2 cm.

As shown in Fig. 10, the deeper cut-outs and the shallower cut-outs may be combined to form a stepped cut-out having a deeper central portion 76 and connected shallower cut-outs 75 on each side, although the respective deeper and shallower portions retain the dimensions noted above.

During assembly of the casement frame 22, the pieces of the glazing ledge 24 are welded to the pieces of the perimeter wall 23, and the welding channels provided by shallower cut-outs 75 are filled in with welding material, whilst the drainage holes 76 remain open to allow for the passage of water therethrough. Water which is drained through the drainage holes 76 runs into a drainage channel (not shown) or onto the base plate 17, which then acts as a drainage channel to carry the water away from the window assembly 1, which in this case is a roof light for installation in a pitched roof and so provides drainage towards its bottom end (the end opposite the hinges 12 in the illustrated embodiment).

In order to provide the perimeter wall pieces and the glazing ledge pieces having the necessary slots 74, tabs 73 and cutouts 75, 76, these pieces are preferably laser cut from sheet material. For window assemblies of the present type, the sheet material is preferably steel or aluminium. The pieces can then be joined and secured to one another by welding as noted above, although other materials and other joining and securing methods are well known and may be selected if preferred.

With reference next to Figs. 12 to 14, a constructional detail of the hinges 12 used to mount the casement 20 onto the base frame 10 will be described.

In the past, base frame 10 or casement 20 would simply have had hinge members welded on, or otherwise attached, at convenient locations along the hinged side of the window assembly 1, and the corresponding hinge members would then have been attached to the other of the casement 20 or base frame 10 to match. This process was essentially carried out manually, by eye.

However, the problem arose that when it became desirable to replace the casement 20 without having to remove the base frame 10 from the building in which it was installed, for example when a glazing unit 25 became cracked or the casement frame 22 suffered corrosion or other damage, the variations in position of the hinge members due to their manual placement meant that a replacement casement 20 could not be guaranteed to fit to the original base frame due to misalignment of the hinge members.

In the exemplary embodiment of Figs. 1 to 14, the base plate 17, as well as the casement perimeter wall 23 as described above, is preferably formed from a number of pieces that are laser cut from sheet material and then joined together. Preferably, the sheet material is steel or aluminium. The joining together may be done by welding.

When the sheet material is laser cut (or cut in another way) the pieces may be provided with accurately positioned alignment features, and this is used to advantage in the present example by providing slots 72 in the base plate 17 and slots 78 in the casement perimeter wall 23. Keyed base hinge members 13 are then provided, each having an alignment key 71 locatable in a slot 72 in the base plate 17. Similarly, keyed casement hinge members 15 are provided, each having an alignment key 77 locatable in a slot 78 in the casement perimeter wall 23.

After locating the hinge members in this way, they are preferably welded, or otherwise attached, securely in position. The corresponding base hinge members 13 and casement hinge members 15 each then align to form a hinge 12, when the casement 20 is mounted to the base frame 10, by passing hinge pins through the corresponding members (not shown). This acts to couple the casement 20 to the base frame 10 so as to be pivotably mounted thereto.

Accordingly, the casement 20 can move outwardly away from the base frame to open the window assembly 1, and close onto the base frame 10 to close the window assembly 1, by such pivoting.

In this way, the original casement 20 can be replaced, as the original design template can be used to manufacture a replacement casement frame 22 whose casement hinge members 15 will be guaranteed to align with the base hinge members 13 of the original base frame 10.

Although the foregoing description has been made with reference to a window assembly that is rectangular in plan view, viewed from the exterior side of the window assembly, the invention is not limited to window assemblies of this shape. The casement, in particular, may be any regular or irregular polygonal shape, such as triangular, square, rectangular or trapezoidal, or may be circular. Furthermore, the sides of the casement may be straight or they may be curved, in plan view, such that further shapes are possible including elliptical. The construction techniques described above for the casement frame are equally applicable, whether the casement frame is formed from single or multiple wall pieces and ledge pieces, and regardless of whether these pieces are straight or curved.

Claims

Claims: 1. A window assembly comprising: a casement comprising a glazing unit mounted in a casement frame, the glazing unit comprising a sealed unit having at least an inner pane and an outer pane, with the outer pane extending on one side beyond the end of the inner pane to form a projecting outer pane edge; wherein the casement is arranged to be mounted on a base frame to be installed in or on a building such that the base frame defines an opening in a wall or roof of the building, wherein the casement further comprises one or more window bars arranged at least on the external surface of the outer pane and integrated with the outside of the casement frame to demarcate adjacent panels of the glazing unit on opposite sides of each window bar, and wherein each window bar includes an inverted T-shaped member on the external surface of the outer pane extending at one end from one side of the casement frame and terminating at its opposite end in abutment with a window bar end piece, which end piece has a T-shaped section to align with the inverted T-shaped member and a generally U-shaped section arranged to hook over the projecting outer pane edge and connect on the underside thereof with another side of the casement frame opposite said one side.
2. The window assembly of Claim 1 wherein the T-shaped member and the window bar end piece are formed from the same material as the casement frame.
3. The window assembly of Claim 1 or 2 wherein the T-shaped member and the window bar end piece are formed from a material which is substantially more thermally conductive than the panes of the glazing unit.
4. The window assembly of Claim 1, 2 or 3 wherein the casement frame is formed from steel or aluminium.
5. The window assembly of Claim 1, 2, 3 or 4 wherein the T-shaped member and the window bar end piece are connected to said outer pane external surface by adhesive strips.
6. The window assembly of any preceding claim wherein a perimeter of each panel demarcated by the window bars and the casement frame is edged by a sealant to seal the gap between the glazing unit and the casement frame and along each side of each inverted T-shaped member, except along the projecting outer pane edge of the glazing unit.
7. The window assembly of any preceding claim wherein each window bar further includes a strip member on the internal surface of the inner pane, aligned with the inverted T-shaped member on the external surface of the outer pane, and extending from the one side of the casement frame to the other side of the casement frame.
8. The window assembly of Claim 7 wherein the strip member is connected to said inner pane internal surface by adhesive strips.
9. The window assembly of any preceding claim further comprising said base frame having said casement mounted thereon, wherein said base frame includes at least a base plate and a base wall extending outwardly from the base plate around said opening, the base plate and base wall being formed from the same material as the casement frame.
10. The window assembly of Claim 9 wherein the base plate and base wall are thermally isolated from the casement such that heat from the interior side of the window assembly heat will not conduct directly from said casement to said base plate or base wall.
11. The window assembly of Claim 9 or 10 wherein the casement is arranged to be mounted on the base frame to be moveable relative to the base frame for opening away from and closing onto the base frame.
12. A window assembly comprising: a casement comprising a glazing unit mounted in a casement frame; and a base frame for installation in or on a building to define an opening in a wall or roof of the building, wherein the casement is arranged to be mounted to the base frame to be xnoveable relative to the base frame for opening away from and closing onto the base frame, wherein said base frame includes a base plate and a base wall extending outwardly from the base plate around said opening, wherein the casement further includes a thermal insulation wall on the interior side of the casement extending inwardly, around the inside of the perimeter of the casement frame, such that, when the casement is closed onto the base frame, the thermal insulation wall is positioned inside the opening defined by said base wall, spaced from the base wall, to act as a barrier to conduction of heat between the space on the interior side of the window assembly and the base wall, and wherein the window assembly further includes an actuation bracket for opening and closing the casement, the actuation bracket being mounted on the interior side of the thermal insulation wall and structurally connected to the casement frame by a connecting member that passes through the thermal insulation wall, the connection member being enclosed along a section of its length by a thermal insulator, in the region between the actuation bracket and the casement frame.
13. The window assembly of claim 12 wherein the thermal insulation wall is formed from a material or combination of materials which is less thermally conductive than the material or materials from which the casement frame and the connection member are formed.
14. The window assembly of claim 12 or 13 wherein the thermal insulator is formed from a material or combination of materials which is less thermally conductive than the material or materials from which the casement frame and the connection member are formed.
15. The window assembly of Claim 12, 13 or 14 wherein the connection member is a bolt or screw threadedly connected to said casement frame.
16. The window assembly of Claim 12, 13, 14 or 15 wherein the casement frame and/or the connection member are steel or aluminium.
17. The window assembly of any one of Claims 12 to 16 wherein the thermal insulator is a nylon sleeve.
18. The window assembly of any one of Claims 12 to 17 wherein the thermal insulation wall is formed from
19. The window assembly of any one of claims 12 to 18 wherein the base frame is steel or aluminium.
20. The window assembly of any one of Claims 12 to 19 wherein the casement is mounted to the base frame by a hinge which allows the casement to pivot relative to the base frame for opening away from and closing onto the base frame.
21. The window assembly of Claim 20 wherein the hinge is provided on the opposite side of the window assembly to the actuation bracket.
22. The window assembly of any one of claims 12 to 21 wherein the glazing unit comprises a sealed unit having at least an inner pane and an outer pane.
23. The window assembly of claim 22 wherein the outer pane extends on one side beyond the end of the inner pane to form a projecting outer pane edge, wherein the casement further comprises one or more window bars arranged at least on the external surface of the outer pane and integrated with the outside of the casement frame to demarcate adjacent panels of the glazing unit on opposite sides of each window bar, and wherein each window bar includes an inverted T-shaped member on the external surface of the outer pane extending at one end from one side of the casement frame and terminating at its opposite end in abutment with a window bar end piece, which end piece has a T-shaped section to align with the inverted T-shaped member and a generally U-shaped section arranged to hook over the projecting outer pane edge and connect on the underside thereof with another side of the casement frame opposite said one side.
24. A building comprising a window assembly according to any one of Claims 1 to 11 installed in or on the building.
25. A building comprising a window assembly according to any one of Claims 12 to 23 installed in or on the building.
26. A method of glazing a building comprising installing a window assembly according to any one of Claims 1 to 11 in or on the building.
27. A method of glazing a building comprising installing a window assembly according to any one of Claims 12 to 23 in or on the building.
28. A window assembly substantially in accordance with any one of the embodiments as described hereinbefore with reference to the accompanying drawings.