GB2543742A

GB2543742A - Secondary glazing unit

Info

Publication number: GB2543742A
Application number: GB1517748.8A
Authority: GB
Inventors: Booyse Pieter
Original assignee: Fortis & Hooke Decorators Ltd
Current assignee: Fortis & Hooke Decorators Ltd
Priority date: 2015-10-07
Filing date: 2015-10-07
Publication date: 2017-05-03
Anticipated expiration: 2035-10-07
Also published as: GB2543742B; GB201517748D0

Abstract

A secondary glazing unit for a sash window, comprising a first part (1a, Figure 2) for positioning in alignment with a top sash 2a of a window 2 and a second part 1b for positioning in alignment with a bottom sash 2b of a window. The second part comprises a frame 3b, a transparent sheet 4b slideable within the frame and a securing mechanism (5, Figure 2) for releasably securing the transparent sheet into engagement with a bottom sash of a window. Also disclosed is a sash window comprising the secondary glazing. The transparent sheet may be secured to the bottom sash so that upward movement of the transparent sheet causes upward movement of the bottom sash. The second part may hingedly secure to the sash window. The releasable securing means may comprise one or more bolts and may comprise one or more handles..

Description

SECONDARY GLAZING UNIT

The present invention relates to secondary glazing units, in particular to secondary glazing units for use with sash windows.

Whilst sash windows are a desirable feature of many properties, they suffer from drawbacks; most notably in relation to their thermal performance.

Traditionally, sash windows include a pair of single glazed panels, or sashes, which are held in a frame and arranged to slide past one another allowing the top and/or bottom of the window to be opened. However, due to the presence of single glazing and gaps formed between the sashes and the frame, sash windows are often draughty and the cause of much heat loss from a building.

Whilst various efforts have been attempted to improve sash windows in this regard, there is a need for an improved solution to these problems.

Sash windows are known to be modified to include double glazing and/or secondary glazing units. Whilst double glazing may initially appear desirable, the installation of double-glazed units into existing sashes is not straightforward and is often not practical, for example due to the existing dimensions of the sashes. In addition, whilst various secondary glazing units have been proposed, they suffer from various drawbacks including only permitting restricted access to the sashes for cleaning and opening.

It is, therefore, an object of the present invention to seek to alleviate the above identified problems.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a secondary glazing unit for a sash window, the secondary glazing unit comprising:- a first part for positioning in alignment with a top sash of a window; and a second part for positioning in alignment with a bottom sash of a window; wherein the second part comprises: (i) a frame; (ii) a transparent sheet slideable within the frame; and (iii) a securing means for releasably securing the transparent sheet into engagement with a bottom sash of a window.

Remarkably, the present invention combines ease and simplicity of use of a secondary glazing unit with the benefits of a sash window.

As a result of the transparent sheet being slideable within the frame, when the frame is secured against a sash window and the transparent sheet is secured into engagement with a bottom sash of the window, upward movement of the transparent sheet causes upward movement of the bottom sash. This means that the bottom sash can be opened without removing the secondary glazing unit. At the same time, because the transparent sheet is releasably securable to the bottom sash by the securing means, the transparent sheet can be released and moved independently of the bottom sash to allow the bottom sash and the transparent sheet to be cleaned.

Preferably, the transparent sheet of the second part is slideable within the frame of the second part such that when the frame is secured against a sash window and the transparent sheet is secured into engagement with a bottom sash of the window, upward movement of the transparent sheet causes upward movement of the bottom sash.

Preferably, the frame comprises one or more channels for accommodating the transparent sheet.

Preferably, the transparent sheet is slideable within the one or more channels.

Preferably, the one or more channels comprise one or more spacers for allowing the transparent sheet to slide smoothly along the channel.

Preferably, the spacers comprise one or more brushes. These assist with smooth movement of the transparent sheet within the one or more channels and also provide for draught exclusion.

Preferably, the secondary glazing unit comprises one or more draught excluders.

Preferably, the securing means comprises one or more bolts, for example hex bolts.

Preferably, the securing means comprises one or more handles, for example one or more sash lifts. A handle may be provided in combination with one or more bolts. The handle is provided to assist with sliding the transparent sheet and bottom sash up and down.

Preferably, the transparent sheet is provided with one or more apertures through which the securing means can be provided.

Preferably, the securing means is engageable with the bottom sash of a sash window.

Preferably, the securing means is engageable with one or more screw threads in the bottom sash of a sash window.

Preferably, the second part is hingedly securable to a sash window, preferably to the frame of a sash window. A second part that is hingedly securable is particularly advantageous because it means that when the transparent sheet is released from engagement with a bottom sash of the window, the second part can be pivoted away from the window, from an engaged position to a maintenance position to allow cleaning of the bottom sash and the transparent sheet of the second part.

Preferably, the second part is hingedly securable to a sash window such that when the transparent sheet of the second part is released from engagement with a bottom sash of the window, the second part can be pivoted away from the window from an engaged position to a maintenance position to allow cleaning of the bottom sash and the transparent sheet of the second part.

Preferably, the frame of the second part is releasably securable into engagement with a sash window, preferably the frame of a sash window. This is particularly advantageous in combination with hinged attachment of the second part to a sash window because it allows the second part to remain securely in an engaged position during normal use and to then be released into a maintenance position for cleaning.

Preferably, the second part is releasably securable into engagement with a sash window, preferably the frame of a sash window, via one or more securing means, preferably one or more magnets, latches and/or bolts.

Preferably, the second part comprises one or more securing means for releasably securing the second part in engagement with a sash window; preferably, one or more magnets, latches and/or bolts.

Preferably, the second part is connectable to a window, preferably the frame of a sash window, by one or more hinges. Preferably, the hinges are positioned at or near the bottom of the second part for connection at or near the bottom of a window.

Preferably, the first part is hingedly securable to a sash window, preferably the frame of a sash window.

This is particularly advantageous because it means that the first part can be pivoted away from the window from an engaged position to a maintenance position to allow cleaning of the top sash and the transparent sheet of the first part.

Preferably, the frame of the first part is releasably securable into engagement with a sash window, preferably the frame of a sash window. This is particularly advantageous in combination with hinged attachment of the first part to a sash window because it allows the first part to remain securely in an engaged position during normal use and to then be released into a maintenance position for cleaning.

Preferably, the first part is releasably securable into engagement with a sash window, preferably the frame of a sash window, via one or more securing means, preferably one or more magnets, latches and/or bolts.

Preferably, the first part comprises one or more securing means for releasably securing the first part in engagement with a sash window, preferably one or more magnets, latches and/or bolts.

Preferably, the first part is connectable to a window, preferably the frame of a sash window, by one or more hinges. Preferably, the hinges are positioned at or near the top of the first part for connection at or near the top of a window.

Preferably, the first part comprises a transparent sheet held within a frame.

Preferably, the first part comprises a transparent sheet fixed within a frame.

Preferably, the first part comprises: (i) a frame; (ii) a transparent sheet slideable within the frame; and (iii) a securing means for releasably securing the transparent sheet into engagement with a top sash of a window.

As a result of the transparent sheet of the first part being slideable within the frame, when the frame is secured against a sash window and the transparent sheet is secured into engagement with a top sash of the window, downward movement of the transparent sheet causes downward movement of the top sash. This means that the top sash can also be opened without removing the secondary glazing unit. At the same time, because the transparent sheet is releasably securable to the top sash by the securing means, the transparent sheet can be released and moved independently of the top sash to allow the top sash and the transparent sheet to be cleaned.

Preferably, the transparent sheet of the first part is slideable within the frame of the first part such that when the frame is secured against a sash window and the transparent sheet is secured into engagement with a top sash of the window, downward movement of the transparent sheet causes downward movement of the top sash.

Preferably, the transparent sheet is slideable within the one or more channels.

Preferably, the transparent sheet of the second part is slideable past the transparent sheet of the first part. As such, when the secondary glazing unit is installed against a window, the transparent sheet of the second part is slideable between the transparent sheet of the first part and a top sash of a sash window to which the first part is secured.

Preferably, the first part comprises one or more channels for accommodating the transparent sheet of the second part.

Preferably, the first part comprises a pair of channels for accommodating the transparent sheet of the second part.

Preferably, the transparent sheet of the first part is slideable past the transparent sheet of the second part. As such, when the secondary glazing unit is installed against a window, the transparent sheet of the first part is slideable between the transparent sheet of the second part and a bottom sash of a sash window to which the second part is secured.

Preferably, the second part comprises one or more channels for accommodating the transparent sheet of the first part.

Preferably, the second part comprises a pair of channels for accommodating the transparent sheet of the first part.

Preferably, the spacers comprise one or more brushes.

Preferably, the secondary glazing unit comprises one or more apertures for permitting access to one or more locks of a sash window.

Preferably, the secondary glazing unit comprises one or more apertures for one or more locks of a sash window to pass through. For example, in a preferred embodiment, the locks are cable or chain locks provided on a sash window, the cable or chain locks are insertable through the one or more apertures and are securable to the frame of said sash window.

Preferably, one or more apertures are provided in the second part and/or the first part.

For example, in a particularly preferred embodiment of the present invention, the secondary glazing unit is for attachment to a sash window comprising locks positioned for preventing movement of a bottom sash of the window past a top sash of the window.

This provides a particular advantage in relation to the present invention due to the additional weight placed on the bottom sash of a window when the transparent sheet is secured to the bottom sash. In this respect, in embodiments wherein the transparent sheet comprises a sheet of glass, attachment of the transparent sheet to the bottom sash via the securing means results in a bottom sash of increased weight. In order to remedy this, the weights associated with the bottom sash are increased in order to restore ease of movement of the bottom sash. However, when the transparent sheet is released from the bottom sash to allow movement of the second part from an engaged position to a maintenance position, the bottom sash is urged upwards by the weights. This can be prevented by moving the locks into position before the transparent sheet is released from the bottom sash.

Preferably, the one or more locks comprise one or more sash stops.

Preferably, the one or more locks are positioned on the top sash above the bottom sash.

In one example, the locks are positioned in the uprights of the bottom and/or top sash of a sash window.

Preferably, the locks are positioned in the uprights of the top sash of a sash window.

Preferably, the one or more locks comprise one or more barrel locks.

Preferably, the one or more locks pass through both the top sash and the bottom sash.

Preferably, the one or more locks pass through the secondary glazing unit and the bottom sash.

Preferably, the one or more locks pass through the secondary glazing unit, the bottom sash and the top sash.

Preferably, the one or more locks comprise one or more cables and/or hooks for preventing movement of the bottom sash and/or the top sash.

Preferably, the one or more locks comprise one or more cables and/or chains provided on a sash of a sash window, wherein the one or more cables and/or chains are insertable through an aperture in the secondary glazing unit and securable to the secondary glazing unit and/or the window frame and/or a wall.

Preferably, the window comprises one or more anchors, locks, security cables and/or hooks for preventing movement of the bottom sash and/or the top sash.

Preferably, the secondary glazing unit comprises one or more locks for preventing movement of a bottom sash of a window relative to the secondary glazing unit.

Preferably, the secondary glazing unit comprises one or more locks for preventing opening of the secondary glazing unit.

Preferably, the secondary glazing unit comprises one or more locks for securing the secondary glazing unit to a sash window, preferably the frame of a sash window. This is advantageous in embodiments wherein the sash window itself is not provided with a lock, or in embodiments wherein the sash window is provided with a lock, but additional security is required.

Preferably, the frame of the second part is releasable securable to the first part. This is also particularly advantageous in combination with hinged attachment of the second part and/or the first part to a sash window, because it also allows the second part and/or first part to remain securely in an engaged position during normal use.

In another aspect of the present invention, there is provided a sash window comprising a secondary glazing unit as described herein.

In another aspect of the present invention, there is provided a sash window comprising a secondary glazing unit, the secondary glazing unit comprising:-a first part positioned in alignment with a top sash of the window; and a second part positioned in alignment with a bottom sash of the window; wherein the second part comprises: (i) a frame; (ii) a transparent sheet slideable within the frame; and (iii) a securing means for releasably securing the transparent sheet into engagement with the bottom sash of the window.

Preferably, the transparent sheet of the second part is slideable within the frame of the second part such that when the transparent sheet is secured into engagement with the bottom sash of the window, upward movement of the transparent sheet causes upward movement of the bottom sash.

Preferably, the transparent sheet is slideable within the one or more channels.

Preferably, the spacers comprise one or more brushes.

Preferably, the secondary glazing unit comprises one or more draught excluders.

Preferably, the securing means is engageable with the bottom sash of the sash window.

Preferably, the securing means is engageable with one or more screw threads in the bottom sash of the sash window.

Preferably, the second part is hingedly secured to the sash window, preferably to the frame of the sash window.

Preferably, the second part is hingedly secured to the sash window such that when the transparent sheet of the second part is released from engagement with the bottom sash of the window, the second part can be pivoted away from the window from an engaged position to a maintenance position to allow cleaning of the bottom sash and the transparent sheet of the second part.

Preferably, the frame of the second part is releasably secured into engagement with the sash window, preferably the frame of the sash window.

Preferably, the second part is releasably secured into engagement with the sash window, preferably the frame of a sash window, via one or more securing means, preferably one or more magnets, latches and/or bolts.

Preferably, the second part comprises one or more securing means for releasably securing the second part in engagement with the sash window; preferably, one or more magnets, latches and/or bolts.

Preferably, the second part is connected to the window, preferably the frame of the sash window, by one or more hinges. Preferably, the hinges are positioned at or near the bottom of the second part and are connected at or near the bottom of the window.

Preferably, the first part is hingedly secured to the sash window, preferably to the frame of the sash window.

Preferably, the frame of the first part is releasably secured into engagement with the sash window, preferably the frame of the sash window.

Preferably, the first part is releasably secured into engagement with the sash window, preferably the frame of the sash window, via one or more securing means, preferably one or more magnets, latches and/or bolts.

Preferably, the first part comprises one or more securing means for releasably securing the first part in engagement with the sash window, preferably one or more magnets, latches and/or bolts.

Preferably, the first part is connected to the window, preferably the frame of the sash window, by one or more hinges. Preferably, the hinges are positioned at or near the top of the first part and are connected at or near the top of the window.

Preferably, the first part comprises a transparent sheet held within a frame.

Preferably, the first part comprises a transparent sheet fixed within a frame.

Preferably, the transparent sheet is slideable within the one or more channels.

Preferably, the transparent sheet of the first part is slideable past the transparent sheet of the second part. As such, the transparent sheet of the first part is slideable between the transparent sheet of the second part and a bottom sash of a sash window to which the second part is secured.

Preferably, the spacers comprise one or more brushes.

Preferably, the transparent sheet of the second part is slideable past the transparent sheet of the first part. As such, the transparent sheet of the second part is slideable between the transparent sheet of the first part and the top sash of the sash window.

Preferably, the spacers comprise one or more brushes.

Preferably, the secondary glazing unit comprises one or more apertures for permitting access to one or more locks of the sash window.

Preferably, the secondary glazing unit comprises one or more apertures for one or more locks of the sash window to pass through. For example, in a preferred embodiment, the locks are cable or chain locks provided on the sash window, the cable or chain locks are insertable through the one or more apertures and are securable to the frame of said sash window.

For example, in a particularly preferred embodiment of the present invention, the secondary glazing unit is attached to a sash window comprising locks positioned for preventing movement of the bottom sash of the window past the top sash of the window.

Preferably, the one or more locks comprise one or more sash stops.

In one example, the locks are positioned in the uprights of the bottom and/or top sash of the sash window.

Preferably, the locks are positioned in the uprights of the top sash of the sash window.

Preferably, the one or more locks comprise one or more barrel locks.

Preferably, the one or more locks comprise one or more cables and/or chains provided on a sash of the sash window, wherein the one or more cables and/or chains are insertable through an aperture in the secondary glazing unit and securable to the secondary glazing unit and/or the window frame and/or a wall.

Preferably, the secondary glazing unit comprises one or more locks for preventing movement of the bottom sash of the window relative to the secondary glazing unit.

Preferably, the secondary glazing unit comprises one or more locks for securing the secondary glazing unit to the sash window, preferably the frame of the sash window.

Preferably, the frame of the second part is releasable secured to the first part.

Within this specification embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein and vice versa.

DETAILED DESCRIPTION

Example embodiments of the present invention will now be described with reference to the accompanying Figures, in which

Figure 1 shows a perspective view of a sash window comprising a secondary glazing unit in a maintenance position;

Figure 2 shows a perspective view of a sash window comprising a secondary glazing unit in an engaged position with the bottom sash in a closed position; Figure 3 shows a perspective view of a sash window comprising a secondary glazing unit in an engaged position with the bottom sash in an open position; Figures 4A, 4B and 4C show cross-sectional views through the uprights of the secondary glazing unit;

Figure 5 show a cross-sectional view through the frame and bottom sash of a sash window and through the second part of the secondary glazing unit in an engaged position;

Figures 6A and 6B show different positions of locks for restricting movement of the sashes of a sash window;

Figures 7A and 7B show alternative methods for restricting movement of the sashes of a sash window.

The present invention relates to a secondary glazing unit for a sash window.

It will be appreciated that reference to "one or more" includes reference to "a plurality".

With reference to Figures 1 to 3, a secondary glazing unit 1 is installed on the inside of a sash window 2. The secondary glazing unit 1 comprises a first part la positioned in alignment with the top sash 2a of the sash window, and a second part lb positioned in alignment with the bottom sash 2b of the sash window. As shown in Figure 1, the second part lb is moveable into a maintenance position for cleaning.

The first (top) part la of the secondary glazing unit 1 includes a transparent sheet 4a fixed and held within a frame 3a.

The second (bottom) part lb of the secondary glazing unit 1 includes a transparent sheet 4b slideable within a frame 3b, and bolts 5 for releasably securing the transparent sheet 4b into engagement with the bottom sash 2b.

In the example shown, the transparent sheets 4a and 4b are sheets of glass; however, it will be appreciated that these could also be plastic.

Because the transparent sheet 4b is slideable within the frame 3b, when the transparent sheet 4b is secured into engagement with the bottom sash 2b by bolts 5, upward movement of the transparent sheet 4b causes substantially simultaneous upward movement of the bottom sash 2b. This means that the bottom sash 2b can be opened into the position shown in Figure 3 without removing the secondary glazing unit 1. At the same time, because the transparent sheet 4b is releasably securable to the bottom sash 2b by the bolts 5, the transparent sheet 4b can be released and moved independently of the bottom sash 2b to allow the bottom sash 2b and transparent sheet 4b to be cleaned.

Whilst not specifically shown in the Figures, the bolts 5 could be provided through handles, for example sash lifts, to allow the transparent sheet 4b and bottom sash 2b to be lifted with ease in a single upward movement.

Holes 5a are provided for the bolts 5 in the transparent sheet 4b and the bottom sash 2b. The holes 5a in the bottom sash 2b are threaded for engagement with a screw thread on each bolt 5.

The second part lb is secured to the frame 8 of the sash window 2 by hinges 9. This means that when the bolts 5 are unscrewed and transparent sheet 4b is released from engagement with the bottom sash 2b, the second part lb can be pivoted away from the window, and so from an engaged position (as shown in Figure 2) to a maintenance position (as shown in Figure 1) to allow cleaning of the bottom sash 2b and the movable transparent sheet 4b of the second part lb.

When in an engaged position, the second part lb is additionally releasably secured into engagement with the frame 8 of the sash window 2 by magnets 10. This is particularly advantageous because it allows the second part lb to remain securely in an engaged position during normal use and to then be released into a maintenance position for cleaning, with ease.

Whilst not shown in the Figures, it will be appreciated that the first part la could also be attached to the frame via hinges and magnets to allow movement from an engaged position to a maintenance position. However, in the embodiment shown, the first part la is secured to the frame 8 in the position shown.

As shown in greater detail in Figures 4A to 4C, the frames 3a and 3b include channels 6b within which the transparent sheet 4b can slide. The channels 6b are provided with brushes 7 for allowing the transparent sheet 4b to slide easily within the channels 7, whilst excluding draughts in use.

Figures 4A and 4B show a first embodiment; Figure 4C shows a second embodiment with a slightly different profile.

Figure 5 shows a third embodiment with a different profile from those in Figures 4A to 4C. Also shown in Figure 5 are the sash window frame 8 and sashes 2a, 2b and the relative positions of the first and second transparent sheets 4a, 4b. Further shown in Figure 5 is the position of a shutter hinge/connection point 16 and the position of existing or replacement architrave 17 on the inside of the window frame 8.

Referring to Figures 4A, 4B, 4C and 5, the transparent sheet 4a of the first part la is held within the channels 6a of the first part la and is not moveable.

Alternatively, it will be appreciated that the transparent sheet 4a of the first part la could be slideable within the channels 6a and the first part la be provided with a securing means for releasably securing the transparent sheet 4a into engagement with the top sash 2a of the window. At the same time, the transparent sheet 4a of the first part could be slideable past the transparent sheet 4b of the second part lb between the transparent sheet 4b of the second part and the bottom sash 2b of the sash window. In such an embodiment, the channels 6a of the second part lb would accommodate the transparent sheet of the first part la.

The channels 6b are provided in the frames 3a, 3b of both the first and second parts la, lb. This allows the transparent sheet 4b of the second part lb to slide upwards into the channels 6b of the first part la and between the transparent sheet 4a of the first part and the top sash 2a of the sash window.

As shown in Figures 1 to 3 and 6A, the secondary glazing unit 1 includes apertures 11 for permitting access to sash locks 12 provided on the sash window 2. The sash locks 12 can take the form of a retractable bolt moveable between a locked position protruding from the sash and an unlocked position flush with the sash.

In the example shown, the apertures 11 are provide in the frame 3a of the first part la; however, it will be appreciated that the apertures could be provided elsewhere if desired. For example, as shown in Figure 6B, a lock 12 in the form of a barrel lock could be provided through both sashes 2a, 2b and the second part lb. In this embodiment, an aperture 11 could be provided within the frame 3b of the second part lb to allow the bolt to pass therethrough.

It will be appreciated that other methods of securing the sashes 2a, 2b in place could be used. For example, as shown in Figures 7A and 7B, hooks 13 and chains or cables 14 could be used to secure the sashes 2a, 2b in place. In particular, and with regard to the embodiment shown in Figure 7B, chains or cables 14 could be provided on the sashes 2a, 2b, fed through apertures 11 in the frames 3a, 3b, and secured to the inside of the window frame 8 and/or the secondary glazing unit and/or a wall.

In addition to locks 12 on the sashes, as shown in Figures 1 to 3, a lock 15 can be provided to secure the secondary glazing to the frame 8 of the sash window 2.

It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications are covered by the appended claims.

Claims

1. A secondary glazing unit for a sash window, the secondary glazing unit comprising:- a first part for positioning in alignment with a top sash of a window; and a second part for positioning in alignment with a bottom sash of a window; wherein the second part comprises: (i) a frame; (ii) a transparent sheet slideable within the frame; and (iii) a securing means for releasably securing the transparent sheet into engagement with a bottom sash of a window.

2. A secondary glazing unit according to claim 1, wherein the transparent sheet of the second part is slideable within the frame of the second part such that when the frame is secured against a sash window and the transparent sheet is secured into engagement with a bottom sash of the window, upward movement of the transparent sheet causes upward movement of the bottom sash.

3. A secondary glazing unit according to claim 1 or 2, wherein the frame comprises one or more channels for accommodating the transparent sheet.

4. A secondary glazing unit according to claim 3, wherein the transparent sheet is slideable within the one or more channels.

5. A secondary glazing unit according to any preceding claim, wherein the securing means comprises one or more bolts, for example hex bolts.

6. A secondary glazing unit according to any preceding claim, wherein the securing means comprises one or more handles.

7. A secondary glazing unit according to any preceding claim, wherein the second part is hingedly securable to a sash window.

8. A secondary glazing unit according to any preceding claim, wherein the second part is hingedly securable to a sash window such that when the transparent sheet of the second part is released from engagement with a bottom sash of the window, the second part can be pivoted away from the window from an engaged position to a maintenance position to allow cleaning of the bottom sash and the transparent sheet of the second part.

9. A secondary glazing unit according to any preceding claim, wherein the frame of the second part is releasably securable into engagement with a sash window.

10. A secondary glazing unit according to any preceding claim, wherein the frame of the first part is releasably securable into engagement with a sash window.

11. A secondary glazing unit according to any preceding claim, wherein the first part is connectable to a sash window by one or more hinges.

12. A secondary glazing unit according to any preceding claim, wherein the first part comprises a transparent sheet held within a frame.

13. A secondary glazing unit according to claim 12, wherein the transparent sheet of the second part is slideable past the transparent sheet of the first part.

14. A secondary glazing unit according to any preceding claim, wherein the first part comprises one or more channels for accommodating the transparent sheet of the second part.

15. A secondary glazing unit according to any preceding claim, which comprises one or more apertures for permitting access to one or more locks of a sash window.

16. A secondary glazing unit according to any preceding claim, wherein the secondary glazing unit comprises one or more apertures for one or more locks of a sash window to pass through.

17. A secondary glazing unit according to claim 15 or 16, wherein the one or more locks are for preventing movement of a bottom sash of the window past a top sash of the window.

18. A secondary glazing unit according to any of claims 15 to 17, wherein the one or more locks pass through the secondary glazing unit and the bottom sash.

19. A secondary glazing unit according to any of claims 15 to 18, wherein the one or more locks pass through the secondary glazing unit, the bottom sash and the top sash.

20. A secondary glazing unit according to any preceding claim, wherein the secondary glazing unit comprises one or more locks for preventing movement of a bottom sash of a window relative to the secondary glazing unit.

21. A secondary glazing unit according to any preceding claim, which comprises one or more locks for preventing opening of the secondary glazing unit.

22. A secondary glazing unit according to any preceding claim, wherein the frame of the second part is releasable securable to the first part.

23. A sash window comprising a secondary glazing unit according to any preceding claim.

24. A sash window comprising a secondary glazing unit, the secondary glazing unit comprising:- a first part positioned in alignment with a top sash of the window; and a second part positioned in alignment with a bottom sash of the window; wherein the second part comprises: (i) a frame; (ii) a transparent sheet slideable within the frame; and (iii) a securing means for releasably securing the transparent sheet into engagement with the bottom sash of the window.

25. A sash window according to claim 24, wherein the transparent sheet of the second part is slideable within the frame of the second part such that when the transparent sheet is secured into engagement with the bottom sash of the window, upward movement of the transparent sheet causes upward movement of the bottom sash.

26. A sash window according to claim 24 or 25, wherein the second part is hingedly secured to the sash window.

27. A sash window according to any of claims 24 to 26, wherein the second part is hingedly secured to the sash window such that when the transparent sheet of the second part is released from engagement with the bottom sash of the window, the second part can be pivoted away from the window from an engaged position to a maintenance position to allow cleaning of the bottom sash and the transparent sheet of the second part.

28. A secondary glazing unit substantially as hereinbefore described with reference to the accompanying Figures.

29. A sash window substantially as hereinbefore described with reference to the accompanying Figures.