This invention concerns improvements in and relating to window screens or blinds, especially but not exclusively, to window screens or blinds suitable for installation in conservatories.

Window blinds are commonly installed in conservatory roofs to provide a heat and light barrier. Such blinds are usually of pleated fabric that slide along cords fixed usually between top and bottom frame members of the roof. Fitting of window blinds to a conservatory roof can be difficult, firstly because of having to retrofit attachment means for ends of the cords, and secondly because many conservatory roofs have triangular panel sections where upper attachment of the cords has to be to side frame members.

Window blinds are, of course, also fitted to conventional windows. Different types of blinds are available, such as roller blinds and "Venetian blinds". A common problem with window and conservatory roof blinds is that gaps may be present between the edges of the blinds and the window frames between which they are mounted allowing light to penetrate, which can be irritating to persons close to the windows who may be dazzled by the light. Furthermore, penetration of light may cause damage, such as discolouration, over a period of weeks, months or years to soft furnishings.

An object of this invention is to provide an improved window blind or screen system suitable for use with windows and conservatory roofs.

According to the invention there is provided a screen system for a window, especially of a conservatory roof, comprising a screen, and means for securing the screen to a window frame, wherein the window frame and the screen have mutually engaging formations for the screen to be offered up to the window frame for retention thereon. The screen may be flexible, stretchable or rigid. It may be made from fabric, a plasties material, wooden slats or other suitable material, such as Pinoleum (wooden slats woven together to form a screen).

In a preferred screen system according to the invention the screen and window frames preferably have mutually engaging formations, whereby the one snap fits to the other. Preferably the screen may be provided with a male-type formation, e.g. a protrusion, whilst the window frame may be provided with a female-type formation, e.g. a recess or aperture; the protrusion and recess being cooperatively shaped so as to achieve retention of the screen in the frame. Of course the location of the male- and female- type formations may be reversed. Engagement of the mutually engaging formations is preferably disengagable as required to enable removal of the screen, e.g. for cleaning.

The window frame may have a slot therealong for retaining a formation of the screen. Where the window frame comprises a glazing bar having a stem and a cross bar, it may be convenient to provide the female-type formation, e.g. a slot, in the cross bar or a cover therefor. Typically aluminium glazing bars have on their cross bar a cover of plastics material. Sides of said cover may be formed as suitable slots. Preferably a slot is provided either side of a window frame, such that the slots are mutually opposing.

In preferred embodiments the slot has a narrower entrance, such as provided by a pair of facing lips, which are preferably flexible, whereby male-type formation screen parts can be push-fitted into the slots past the lips. The flexibility of the lips provides additional retentive means.

In one preferred embodiment of the invention the slot receives a fold of flexible screen and has a member associated therewith to retain the fold in the slot. The retaining member may be a rod or the like, which preferably exists separately from the slot, although it may be connected at at least one of its ends to the slot or otherwise to the window frame.

In some embodiments of the invention the screen may be self-supporting, i.e. no additional member such as a retaining member is required, and has formations, preferably male-type formations, that snap-fit into the slots of adjacent glazing bars to hold the screen to the window frame.

For a better understanding, the invention will now be further described by way of non- limiting example only, with reference to and as shown in the accompanying schematic drawings (not to scale), in which:

Figure 1 shows a first embodiment according to the invention; and Figure 2 shows a second embodiment according to the invention.

Referring to Figure 1 of the accompanying drawings, a conservatory roof comprises glazing bars 10 supporting glazing panels (not shown) therebetween. The glazing bars 10 have a stem 12 and a cross bar 14. The glazing bars 10 are typically of aluminium and their cross bars have plastics covers 16 thereon. The covers 16 have sides 18 that are turned inwards at their tops, whereby the covers can be slid onto the glazing bars and retained thereon.

On opposite sides of the covers 16 are downwardly (as shown) open slots 20. At or near the open ends of the slots 20 are inwardly-facing lips 22, to form narrower entrances to the slots. The nature of the plastics material used, e.g. polyvinyl chloride, means that the lips 22 have sufficient flexibility to receive formations, as will be described below. A screen 24, in the form of a fabric sheet, is fixed (preferably removably as required) at opposite edges to slots 20 of covers 16 of adjacent glazing bars 10 by firstly forming a fold 26 in the screen material in each slot 20 and secondly pressing in a retaining element 28, such as a bar or rod. The retaining elements could alternatively be T- shaped and the stems thereof pressed into the slots.

In Figure 2 of the accompanying drawings, an alternative to the screen system shown in Figure 1 is to have the screen 30 as a rigid or self-supporting item. The difference between this embodiment and the previous embodiment is that the screen 30 has on one face a pair of formations 32 near opposite edges thereof that press-fit (preferably removably as required) into the slots 20 of the glazing bar covers 16. These formations 32 may be continuous or discrete. All other features of the system shown in Figure 2 are identical to those shown in Figure 1 , and as such, like reference numerals have been used for like parts.