GB2541646A

GB2541646A - Window assembly

Info

Publication number: GB2541646A
Application number: GB1514318.3A
Authority: GB
Inventors: Shalaby Amr
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-08-12
Filing date: 2015-08-12
Publication date: 2017-03-01
Anticipated expiration: 2035-08-12
Also published as: GB2541646B; GB201514318D0; WO2017025736A1

Abstract

A window assembly 10 suitable for installation into listed, heritage or period buildings is provided, which comprises a first pane of glass 30, a second sheet of glass 28 spaced apart from the first pane of glass so as to define a cavity 36 between them, and a window frame 12 within which the first and second panes of glass are mounted. To substantially match the appearance of a single glazed window, the second pane has a lower reflectance than the first sheet of glass. The second pane may be coated with an anti-reflective coating. The window assembly may include a spacer separating the two glass panes. The first glass pane may be made from crown, crown reproduction, float or laminated float glass. A method of preparing a window assembly for installation into a listed or heritage building is also provided.

Description

Window Assembly

The present invention relates to a window assembly, in particular a double-glazed window assembly, suitable for use in listed or heritage buildings to complement or match the existing aesthetic appeal thereof. The invention further relates to a method of preparing a window assembly for installation into a listed or heritage building.

Many old buildings are poorly insulated from heat loss, particularly via their windows. Often such buildings predate the widespread use of double or triple glazing in their windows, which acts as a thermal barrier. Single glazing offers relatively little barrier to heat loss, and therefore such buildings cool rapidly, particularly during the wintertime.

Many countries, in an effort to preserve their architectural heritage, have made legal provisions to prevent obtrusive features being installed to buildings of a certain age. In the United Kingdom, these are referred to as ‘listed’ buildings, of which there are hundreds of thousands of examples. The installation of standard double or multi glazed windows or window units into listed buildings is closely monitored by local authorities, since such windows or units can change the overall aesthetic appearance of the building once installed. This makes it difficult for the owners of listed buildings from adequately heating and insulating their properties without incurring excess energy bills.

In particular, there are two main obstacles to the permissibility of double glazed windows being installed into listed buildings. Firstly, the spacer bars between the panes of glass in the window are often thick and ungainly, diminishing the overall appeal of the window, and negatively affecting the character of the listed building.

Secondly, the overall reflectivity of a double glazed window greatly exceeds that of a single pane, since there is a greater number of glass panes installed therein. This means that the newly installed windows have a shiny appearance which appears to be out of chaiacter with contextually appropriate single glazed windows.

There have been various attempts to produce a slimline double glazed window which effectively hides the spacer bars; however, such windows have generally not met the relevant conservation requirements with regards to the shininess or reflectivity created by modem double glazing, and therefore such windows still cannot be installed into listed buildings.

Another alternative is to install what is known as secondary glazing, wherein a second window is installed adjacent to or slightly spaced apart from the primary single glazed window. This retains the exterior character of the building whilst improving the heat retention and sound damping effects associated with double glazing. However, there remains the problem that there are, in effect, two separate windows which cannot be opened as one, which is inconvenient for a user; in particular, dust, dirt and even insects can readily accumulate between the primary and secondary glazing which cannot easily be removed.

Secondary glazing is also controversial in that the two glazing panes are clearly not in keeping with the original character of the building, even if they appear to meet the approval of local authorities. It is also possible to achieve double reflections as light reflects off both panes of glass or plastics if used internally, which similarly can diminish the overall appearance of the window.

It is therefore an object of the present invention to provide a window assembly which simultaneously overcomes the problem of the reflectance of the window and the problem of bulky and/or unsightly spacer bars.

According to a first aspect of the invention, there is provided a window assembly suitable for installation into listed, heritage or period buildings, the window assembly comprising: a first pane of glass; a second pane of glass spaced apart from the first pane of glass and defining a cavity therebetween, the second pane of glass having a lower reflectance than the first pane of glass; and a window frame within which the first and second panes of glass are mounted.

By providing two panes of glass in a double glazed window assembly allows the reflectance of the two panes to be selected by the installer such that the total reflectance of the window assembly as a whole matches or substantially matches that of a single glazed window assembly. This beneficially improves the probability that the window assembly will be deemed permissible by local planning authorities if, for example. installed into a listed or heritage building, as the second pane of glass is rendered near-invisible when viewed from an exterior of the building. As such, the window assembly appears single glazed, when it is, in fact, double or multi glazed.

Preferably, the first pane of glass may be an external pane of glass, following installation of the window assembly into a building.

By making the pane of glass having a higher reflectance as the external pane of glass in the window assembly, the aesthetic appearance of the window assembly will advantageously better match that of a single glazed window assembly. This is because the appearance of double images, that is, accentuated reflection from the inner pane of the window assembly, is minimised when viewed from the outside of the building, which is the more important direction from a planning perspective, the exterior of the building typically having the more protected appearance.

Optionally, the second pane of glass may be coated with an anti-reflective coating. The first pane of glass may be formed from an extra clear float glass, an extra clear crown reproduction glass, or from two discrete laminated layers of extra clear float glass.

Various types and forms of glass may beneficially be utilised in conjunction with the present invention in order to best match the appearance of the building into which the window assembly is to be installed.

The window assembly may further comprise a spacer positionable between the first and second panes of glass to define the cavity. Said spacer may have a thickness of no greater than 4mm.

By providing a slimline spacer between the said first and second panes of glass, the appearance of the window assembly is improved, since said spacers are generally anachronistic when installed into historic and/or listed buildings which predate the use of double glazed window assemblies.

The first pane of glass may have a thickness of less than 7mm, and more preferably have a thickness of 3mm or 4mm. The second pane of glass may have a thickness of less than 5mm, and ideally may have a thickness of 3mm or 4mm.

The thickness of the panes of glass may have an effect on the reflectance and/or light transmission loss of the window assembly, and therefore the similarity of the window assembly to that previously installed in the building can be best matched by careful selection of the glazing.

Preferably, the sum of the reflectance of the first and second panes of glass may be between 8% and 12%, ideally 10%. Furthermore, the total light transmission loss of the first and second panes of glass may be between 8% and 12%, most preferably 10%. A single glazed window assembly typically has reflectance and light transmission loss factors of 8% and 11% respectively. By closely matching these factors in the newly installed double glazed window assembly, the aesthetic appearance of the window assembly can be matched or substantially matched to complement the building into which the window assembly is to be installed.

The reflectance of the first pane of glass may be between 6% and 10%, preferably 8%, and the light transmission loss of the first pane of glass may be between 6% and 10%, ideally 8%. The reflectance of the second pane of glass may be between 0% and 4%, preferably 2%. The light transmission loss of the second pane of glass may be between 0% and 4%, ideally 2%.

The individual panes of glass within the window assembly can be fine-tuned by the installer in order to best provide a complementary aesthetic appearance for the finished window assembly for installation into the relevant building. A window assembly having two panes of standard extra clear float glass would be too reflective, and two panes of treated, low-reflectance glass would be too clear. In either case, it would be simple for even the lay person to distinguish between the original windows in the building, and those which had been newly-installed.

According to a second aspect of the invention, there is provided a method of preparing a window assembly for installation into a listed or heritage building, the method comprising the steps of: determining a reflectance of a window to be replaced in the building; and providing a window assembly preferably in accordance with the first aspect of the invention having a reflectance which matches or substantially matches the reflectance of the window to be replaced.

By providing a means of matching the reflectance of a new window assembly to that of a historic building, it becomes easier for an installer to tailor their window assembly to match or substantially match the original windows of the assembly. This significantly reduces the risk of planning permission for the installation of the windows being rejected by the local planning authorities.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

Figure la shows a front view of one embodiment of a window assembly in accordance with the first aspect of the invention; and

Figure lb shows an enlarged cross-sectional representation through the circled portion of the window assembly of Figure la, when viewed from the side.

Referring firstly to Figures la and lb, there is shown a window assembly, indicated globally at 10 and which is intended for used in a listed, heritage or period building. The term listed building, in the United Kingdom, refers to a building which has been placed on the Statutory List of Buildings of Special Architectural or Historic Interest, which prevents such a building from being altered or demolished without governmental permission. The term ‘listed’ therefore used herein and throughout is intended to meet this definition or the equivalent definition in other territories outside of the United Kingdom. The window assembly 10 is intended to comply with local planning regulations for listed buildings, but it will be apparent that such a window assembly 10 could be installed into any type of building as desired.

The window assembly 10 is here formed as a sash window, a common construction of window for older buildings in the United Kingdom, and comprises a preferably elongate window frame 12 having upper and lower sashes 14, 16 mounted therein. The upper and lower sashes 14, 16 are slidable along a vertical axis of the window frame 12 in order to permit opening and closing of the window assembly 10.

Whilst a sash window is shown for illustrative purposes, it will be appreciated that a wide variety of different window styles are present in listed buildings, and as the intention of the invention is to better match the appearance of the original windows of the building, then the type of window construction used in the window assembly 10 will be chosen with this in mind.

Each of the upper and lower sashes 14, 16 includes a sash frame 18 formed as a rectangle made from a pair of horizontal rails 20 and a pair of vertical stiles 22 which are interconnected. Within the sash frame 18 is bounded at least one glazing assembly 24; in the depicted embodiment, there are six glazing assemblies 24 in each of the upper and lower sashes 14, 16, which are held in place relative to one another using a plurality of sash bars 26.

As can be best seen in Figure lb, each glazing assembly 24 is formed as a double glazing unit, having inner and outer panes of glass 28, 30, relative to the inside of the building. The inner and outer panes of glass 28, 30 are receivable within the sash frame 18 and the sash bars 26 with which they contact, thereby providing structural support to the glazing assembly 20. A receiving recess 32 of a sash bar 26 is shown in detail in Figure lb.

The inner and outer panes of glass 28, 30 are spaced apart from one another by providing a spacer bar 34 therebetween. This will preferably be a slimline spacer bar 34 which has a depth which is less than that of the receiving recess 32 of the sash bar 26, such that the spacer bar 34 is hidden or substantially hidden to a viewer of the window assembly 10. Preferably, this spacer bar 34 will have a thickness or depth which is no greater than 4mm. The spacing of the inner and outer panes of glass 28, 30 from one another therefore forms a cavity 36 in the glazing assembly 20, which will preferably be filled with an inert gas, such as Krypton, which can reduce the thermal efficiency of the window assembly 10.

In the depicted embodiment, the inner pane of glass 28 is ideally formed from a pane of glass having a low reflectance. In the depicted embodiment, this is a 4mm thickness pane of extra-clear, non-reflective float glass; however, other thicknesses and forms of glass are known. 3mm thickness glass is common, and any pane of glass which has a thickness of less than around 5mm should display the necessary aesthetic appeal.

Extra clear float glass is a specific type of melted glass, which is formed so as to have minimal iron content in the glass, thereby in turn minimising the reflectance of the window. Float glass is formed by allowing the glass mixture to solidify on top of a layer of molten metal, ensuring a very smooth surface.

The low reflectance of the inner pane of glass 28 will typically be achieved by application of an anti-reflective coating onto the surface of the pane of glass 28, and this will typically reduce the reflectance to 2% and the light transmission loss to 2%. However, other coatings or treatments may be available which may reduce the reflectance to anywhere in the range of 0% to 4% and the light transmission loss to 0% to 4%.

The illustrated outer pane of glass 30 is formed from extra clear float glass which is also 4mm thickness. 3mm glass is also known, and any glass having a thickness of less than around 7mm should be suitable. There is a greater scope for alteration of the outer pane of glass 30 than with the inner pane of glass 28 to permit the installer to best match the visual appeal of the listed building into which the window assembly 10 is to be installed.

Potential alternative embodiments for the outer pane of glass 30 might include the provision of extra clear crown reproduction glass instead of float glass; such glass has historically met with greater approval from local planning authorities in the UK for installation into listed buildings. Alternatively, two thin panes of glass, each of approximately 3mm thickness, could be provided adjacent to one another, which does not diminish the overall light transmission characteristics of the window assembly 10 but does increase the acoustic attenuation of the window assembly 10.

Crown reproduction glass is designed to mimic original crown glass as much as possible, wherein glass was blown into a globe-shape before being flattened under the application of heat and centrifugal force. Such glass is typically thicker in the centre of the plate as a result of the centrifugal flattening process.

The outer pane of glass 30 will, in the depicted embodiment, have a reflectance of 8% and a light transmission loss of 8%, though, depending upon the construction of the window assembly 10, this may be anywhere in the range of 6% to 10% for the reflectance and 6% to 10% for the light transmission loss.

Bearing this in mind, the total sum of the reflectance of the window assembly 10 will be 10%, and the total sum of the light transmission loss will also be 10%, though again, depending on construction, this could feasibly be anywhere in the range of 8% to 12% for the reflectance and the range 8% to 12% for light transmission loss.

For a single glazed window assembly, the reflectance is typically 8%, with the light transmission loss being around 11%. For a typical double glazed window assembly, the reflectance is therefore 16%, with the light transmission loss being 22%. The corresponding values for the present invention being 10% and 10% for reflectance and light transmission loss respectively mean that the appearance of the window assembly 10 is practically indistinguishable from a single glazed window assembly to the untrained eye. The shininess or reflectance associated with traditional double glazing assemblies is therefore avoided using the present invention, which should therefore overcome the objections which are often raised by local planning authorities.

It is therefore possible to provide a window assembly which is double glazed and can be installed into heritage or listed buildings to meet or overcome local planning regulations, the window assembly including first and second panes of glass which are spaced apart from one another. The second pane of glass is provided so as to have a lower reflectance than that of the first pane of glass, such that the total sum of the reflectances matches or substantially matches that of a window to be replaced, thereby limiting the shininess or reflectivity typically associated with double glazing.

The words ‘comprises/comprising’ and the words ‘having/including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity. described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention herein described and defined.

Claims

1. A window assembly suitable for installation into listed, heritage or period buildings, the window assembly comprising: a first pane of glass; a second pane of glass spaced apart from the first pane of glass and defining a cavity therebetween, the second pane of glass having a lower reflectance than the first pane of glass; and a window frame within which the first and second panes of glass are mounted.

2. A window assembly as claimed in claim 1, wherein the first pane of glass is an external pane of glass, following installation of the window assembly into a building.

3. A window assembly as claimed in claim 1 or claim 2, wherein the second pane of glass is coated with an anti-reflective coating.

4. A window assembly as claimed in any one of claims 1 to 3, wherein the first pane of glass is formed from an extra clear float glass.

5. A window assembly as claimed in any one of claims 1 to 3, wherein the first pane of glass is formed from an extra clear crown reproduction glass.

6. A window assembly as claimed in any one of claims 1 to 3, wherein the first pane of glass is formed from two discrete laminated layers of extra clear float glass.

7. A window assembly as claimed in any one of the preceding claims, further comprising a spacer positionable between the first and second panes of glass to define the cavity.

8. A window assembly as claimed in claim 7, wherein the spacer has a thickness of no greater than 4mm.

9. A window assembly as claimed in any one of the preceding claims, wherein the first pane of glass has a thickness of less than 7mm.

10. A window assembly as claimed in claim 9, wherein the first pane of glass has a thickness of 3mm or 4mm.

11. A window assembly as claimed in any one of the preceding claims, wherein the second pane of glass has a thickness of less than 5mm.

12. A window assembly as claimed in claim 11, wherein the second pane of glass has a thickness of 3mm or 4mm.

13. A window assembly as claimed in any one of the preceding claims, wherein the sum of the reflectances of the first and second panes of glass is between 8% and 12%.

14. A window assembly as claimed in claim 13, wherein the sum of the reflectances of the first and second panes of glass is 10%.

15. A window assembly as claimed in any one of the preceding claims, wherein the total light transmission loss of the first and second panes of glass is hetween 8% and 12%.

16. A window assembly as claimed in claim 15, wherein the total light transmission loss of the first and second panes of glass is 10%.

17. A window assembly as claimed in any one of the preceding claims, wherein the reflectance of the first pane of glass is between 6% and 10%.

18. A window assembly as claimed in claim 17, wherein the reflectance of the first pane of glass is 8%.

19. A window assembly as claimed in any one of the preceding claims, wherein the light transmission loss of the first pane of glass is between 6% and 10%.

20. A window assembly as claimed in claim 19, wherein the light transmission loss of the first pane of glass is 8%.

21. A window assembly as claimed in any one of the preceding claims, wherein the reflectance of the second pane of glass is between 0% and 4%.

22. A window assembly as claimed in claim 21, wherein the reflectance of the second pane of glass is 2%.

23. A window assembly as claimed in any one of the preceding claims, wherein the light transmission loss of the second pane of glass is between 0% and 4%.

24. A window assembly as claimed in claim 23, wherein the light transmission loss of the second pane of glass is 2%.

25. A window assembly substantially as hereinbefore described, with reference to the accompanying drawings.

26. A method of preparing a window assembly for installation into a listed or heritage building, the method comprising the steps of: determining a reflectance of a window to be replaced in the building; and providing a window assembly as claimed in any one of the preceding claims having a reflectance which matches or substantially matches the reflectance of the window to be replaced, the window assembly comprising: a first pane of glass; a second pane of glass spaced apart from the first pane of glass and defining a cavity therebetween, the second pane of glass being treated to have a lower reflectance than the first pane of glass; and a window frame within which the first and second panes of glass aremounted.

26. A method of preparing a window assembly for installation into a listed or heritage building, the method comprising the steps of: determining a reflectance of a window to be replaced in the building; and providing a window assembly as claimed in any one of the preceding claims having a reflectance which matches or substantially matches the reflectance of the window to be replaced. AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS Claims

1. A window assembly suitable for installation into listed, heritage or period buildings, the window assembly comprising: a first pane of glass; a second pane of glass spaced apart from the first pane of glass and defining a cavity therebetween, the second pane of glass being treated to have a lower reflectance than the first pane of glass; and a window frame within which the first and second panes of glass are mounted, wherein a total reflectance of the first and second panes is selected to match or substantially match that of a window to be replaced of the listed, heritage or period building.

11. A window assembly as claimed in any one of the preceding claims, wherein the light transmission loss of the second pane of glass is between 0% and 4%.

24. A window assembly as claimed in claim 23, wherein the light transnhssion loss of the second pane of glass is 2%.