A frame for a window intended to serve either as a stationary frame or as a sash frame according to the invention comprises an insulating abutment list on a side surface of at least one of the top, bottom or side members intended to face a side surface of another frame of the window. The insulating abutment list is made from a material having a thermal conductivity of less than 0.08 W/(m·k), preferably less than 0.04 W/(m·K). Preferred materials for the insulating abutment list are expanded polystyrene (EPS) or extruded polystyrene (XPS). In a window with such a frame, an insulating abutment list on the sash frame preferably extends from hinge part to the bottom member of the sash frame and an insulating abutment list on the stationary frame preferably extends from a hinge part to the top member of the stationary frame.

BACKGROUND OF THE INVENTION 
     The present invention relates to a frame for a window, said frame being intended to serve either as a stationary frame or as a sash frame and comprising a top member, a bottom ember and two side members, each having a side surface intended to face a corresponding side surface of another frame of the window. It further relates to a window with such a frame and to a method of making a frame. 
     In this, whenever the term “frame” is used it is to be understood as including both sash frames carrying panes and stationary frames carrying sash frames. The terms “sash frame” and “stationary frame” are used when reference is made specifically to frames intended for one of these two purposes. 
     Frames for windows are traditionally made from wooden members, from moulded polyurethane members with a wooden core for reinforcement or from extruded members of aluminum or polyvinylchloride. Different components such as hinges, locking assemblies and gaskets are added to provide the needed functionality and when using extruded profiles, insulation material may be provided in hollows in the profile. 
     With these ways of making a frame, a limit on the thermal properties seems to have been reached, but the demand for still more energy efficient windows keeps rising. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to provide an alternative frame for a window and a method for making such a frame, which allows the construction of windows having even better thermal properties. 
     This is achieved with a frame, where at least one of the top, bottom or side members comprises an insulating abutment list on the side surface intended to face a corresponding side surface of another frame of the window, said insulating abutment list being made from a material having a thermal conductivity of less than 0.08 W/(m·K), preferably less than 0.04 W/(m·K). 
     Abutment lists are used where the sash frame comes into contact with the stationary frame during opening and closing of the window and closes the gap between the sash frame and the stationary frame formed to make room for hinges. For a centre-hung pivot window abutment lists are usually found at the lowermost half of the side members of the stationary frame and at the uppermost half of the side members of the sash frame. The abutment lists have hitherto been integrated in the frame member or made from the same material as a main body of the frame member, but now contributes to the insulation of the window. 
     It is noted that the terra pivot hinge is intended to cover hinges of the type originally described in DK70390 and the term pivot window to cover windows with this type of hinges, i.e. windows where the hinges are located between the side members of the sash frame and the stationary frame and where the axis of rotation is located at a distance from the plane of the frames. 
     The desired thermal conductivity may be achieved with numerous materials, including balsa wood, but polymers are presently preferred. Expanded polystyrene (EPS) or extruded polystyrene (XPS) is particularly well-suited since these materials are well tested, relatively cheap, non-toxic and durable. 
     The insulating abutment lists preferably cover the side surfaces of the parts of the side members extending from a hinge axis to the bottom or top member substantially entirely. This continuity provides for an uninterrupted surface, which makes it durable and easy to keep clean, but it is also possible to use discrete blocks of material. A continuous embodiment, however, allows the insulating abutment list to contribute to the tightening of the window and gives better insulating properties. Moreover, an abutment list on the stationary frame will also be visible from the inside, when the window is open, and a continuous surface is perceived as visually more appealing by most users. 
     The best possible continuity of the insulating abutment list is achieved when recesses are formed at the ends nearest to the hinge parts in the mounted state, said recesses conforming in shape to the shape of the hinge parts. 
     To improve the insulating properties even further it may be advantageous to use insulating abutments lists, which also cover at least a part of the exterior side of the frame members, i.e. the side intended to face the exterior of a building in the mounted state of the window. 
     Likewise it is noted that the frame member carrying the insulating abutment list may itself include insulating material, which may for example be provided in the interior of the frame member, and that the window may be arranged in one or more insulating frames during mounting in a load-bearing structure, such as a roof. 
     Insulating abutment lists may be attached to the main bodies of the frame members in any appropriate way including the use of screws, glue and/or an adhesive. The attachment must of course be sufficient to keep the insulating abutment list in place during use of the window, but it may be detachable to allow replacement of the insulating abutment list. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below by means of non-limiting examples and with reference to the schematic drawing, in which 
         FIG. 1  shows a perspective view of a window according to the invention in the assembled state seen from the interior, 
         FIG. 2  shows a perspective view of a window according to the invention in the assembled state seen from the exterior, 
         FIG. 3  shows a side sash frame ember in a perspective view, 
         FIG. 4  shows a stationary side frame member in a perspective view, 
         FIG. 5  shows a sketch of a cross-section along the line V-V in  FIG. 1  in the closed and mounted state of the window, 
         FIG. 6  shows a perspective view of the bottom ember of the stationary frame with insulation, strike plate and covering, 
         FIG. 7  shows a cross-section along the line VII-VII in  FIG. 6 , and 
         FIGS. 8 and 9  correspond to  FIGS. 1 and 2  showing a roof window according to the invention in from two different angles. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  show a preferred embodiment of a window  1  according to the invention comprising a pane  4 , a stationary frame  2  having a top member  5 , a bottom member  6  and two side members  7 ,  8  defining a stationary frame plane, and a sash frame  3  having a top member  9 , a bottom member  10  and two side members  11 ,  12  defining a sash frame plane. In the embodiment shown, the window is centre-hung in that the sash frame  3  is connected to the stationary frame  2  by a pivot hinge  19 ,  20  (see  FIGS. 3 and 4 ) provided between side members  7 ,  11 ;  8 ,  12  of the stationary frame  2  and sash frame  3 , respectively. The window is openable by tilting the sash frame  3  of the window  1  about the pivot hinge axis  21  defined by the pivot hinge. The pivot hinge comprises two parts, namely a stationary frame part  19  and a sash frame part  20 . 
     The hinges used are preferably of the type described in the applicant's earlier patent applications W09928581 and GB1 028251, where a curved member and a tap on one hinge parts  20  travels in a curved guide track in the other 19 during opening and closing of the window. The radius of curvature entails that when using such hinges, the hinge axis lies at a small distance above the actual hinge parts and as the sash frame is turned first the curved member and then the tap comes out of the track. In combination this provides a pattern of movement which allows easy operation of a centre-hung window and allows the sash frame to be turned substantially entirely around. 
     As used in this description, a closed position of the window  1  means a position in which the stationary frame plane and the sash frame plane coincide, that is form an angle of 0 degrees with each other. Similarly an open position of the window  1  as used herein generally means a position in which the sash frame  3  is tilted about the pivot hinge axis  21  such that the stationary frame plane and the sash frame plane no longer coincide. 
     As seen in  FIG. 1  a longitudinal axis  13  of the window  1  is defined as extending perpendicular to and between the stationary frame top member  5  and the stationary frame bottom member  6 , a transversal axis  14  of the window is defined as extending perpendicular to and between the respective stationary frame side members  7  and  8  and thereby perpendicular to the longitudinal axis  13  and a depth axis  15  of the window  1  is defined as extending perpendicular to both the longitudinal axis  13  and the transversal axis  14 . The pivot hinge axis  21  and the transversal axis  14  are parallel, and are shown as coinciding in the figures. 
     The window  1  furthermore comprises a locking assembly  17  of a type known per se for locking the stationary frame  2  and sash frame  3  to each other as well as a generally circumferentially extending sealing  18  provided on the sash frame  3  for sealing the gap between the sash frame  3  and the stationary frame  2  in the closed position of the window  1 . The sealing  18  comprises at least one, preferably at least two sealing strips. 
     Notwithstanding the centre-hung window  1  shown in  FIG. 1  the window according to the invention may in other embodiments be top-hung, with or without an intermediate frame structure, have the hinge axis somewhere between the top and the centre, be side-hung or for that matter even be bottom-hung. 
     The sash frame  3  and stationary frame  2  of the window according to the invention may for example be made of wooden members or members made of cast or extruded polyurethane (PUR). 
     Referring now to  FIGS. 3 and 4 , the window  1  further comprises at least one insulating abutment list  430   a ,  430   b . Here an insulating abutment list is provided on both of the opposing side members  8  and  12  of the sash frame and stationary frame respectively and each extending over approximately half the length of the side frame member. It is, however, also possible, though less preferred, to use an insulating abutment list only on one of the frame side members, possibly extending over its entire length. 
     Seen in the height direction, the insulating abutment lists  430   a ,  430   b  of this preferred embodiment covers the side frame members  8 ,  12  down to the sealing strip  18 ,  433 , which is arranged in a groove  18   a ,  433   a  in the main body of the side frame member. It is, however, also possible to use an insulating abutment list covering a bigger part of the side member, possibly the entire height, and the sealing strip  18 ,  433  may then shed attached to or integrated in the insulating abutment list. In this embodiment, each frame comprises only a single sealing strip, but particularly the stationary frame may advantageously comprise two sealing strips arranged one above the other. 
     For optimal insulation the insulating abutment lists preferably also covers at least a part of the exterior surface of the frame member, i.e. the side intended to face the exterior of a building in the mounted state of the window as may be seen most clearly in  FIG. 5 , but is also shown in  FIG. 4 . Here the insulating abutment list covers only a part of the exterior surface of the frame member and in  FIG. 4  a recess  83  is provided for receiving the part of the list projecting over the exterior side, but it may also cover a larger part or even the entire exterior surface. Likewise, the insulating abutment list may project over the exterior side in the height direction as in  FIGS. 3 and 5 . The design of the abutment list should, however, be made in accordance with the design of the covering and cladding members so as to allow a reliable attachment of these to the frame member and vice versa. 
     The insulating abutment lists  430   a ,  430   b  shown in  FIGS. 3-5  are attached to the side frame members  8 ,  12  by means of screws  431 , but other ways of attachment may in principle also be used. As an example the abutment strip may be glued to the main body of the side frame member  8 ,  12 . 
     The insulating abutment lists  430   a ,  430   b  each comprise a recess  432   a ,  432   b  conforming in shape with the respective part  19 ,  20  of the pivot hinge  200  connecting the stationary frame  2  and the sash frame  3 . This enables the insulating abutment list  430  to be mounted adjacent to possibly even abutting the pivot hinge. Due care should of course be taken to allow the intended movement of the hinge parts and the two frames in relation to each other. 
     Preferably, the insulating abutment list is made of expanded polystyrene (EPS) or extruded polystyrene (XPS) but may in principle be made of any suitable insulating material including any other type of styrene or polystyrene. 
     Prior art windows having no insulating abutment list  430  are provided with a sash frame  3  and/or stationary frame  2  having a wooden part or element corresponding to the insulating abutment list  430 . Providing the window  1  with insulating abutment lists  430  in lieu of the wooden part or element provides for a close fit and improved sealing of the gap between stationary frame  2  and sash frame  3  in the closed position of the window  1 . In addition, a frame  2 ,  3  build in this way has a smaller thermal conductivity and thus improved heat transfer properties. Thereby the provision of insulating abutment lists  430  provides for a window  1  having a smaller overall heat transfer coefficient, also known as U value or U factor. 
     The use of insulating abutment lists may be combined with the use of insulating materials at other positions in the window structure and/or with arranging the window in one or more insulating frames as described for example in EP1 061199. An example of such a combination of insulating materials is shown in  FIG. 5 , where the side member  8  of the stationary frame  2  is provided with an insulating abutment list  430   a , where the stationary frame  2  includes a strip  81  of an insulating material and where the window  1  is mounted in an insulating frame  82 . Here the insulating frame  82  covers only the lowermost corner of the stationary frame, but it is to be understood that it may cover a larger part of the frame and that two or more such insulating frames may be used in combination. Likewise the strip  81  of insulating material may be at a different position and/or of a different shape and/or be enveloped by the frame material, thus forming a core in the frame member. 
     The above embodiment is particularly preferred in case of a wooden window. In case of a PUR-window the insulating abutment list  430  and the side frame member  7 ,  8 ,  11 ,  12  may be made as a one piece integral side frame member, the insulating material of the insulating abutment list being attached to the wooden reinforcement typically used in such frames before moulding. 
     Depending on the type of window, it is furthermore possible to provide an insulating abutment list similar to the insulating abutment lists  430   a ,  430   b  described above, but attached to and covering substantially at least the half of the side sash frame member  11  nearest the top sash frame member  9  and vice versa for the stationary frame. Likewise, insulating abutment lists may be used in combination with traditional wooden or integrated abutment lists. 
       FIGS. 6 and 7  show an example of an insulating abutment list  434  on the top member  8  of the stationary frame  2 . As may be seen the insulating abutment list is profiled to give room for a strike plate  51  and the associated locking assembly  17  on the sash frame  3 . This insulating abutment list is furthermore provided with ventilation passages  435  allowing an air-exchange between the interior of a building and the space underneath the top frame covering  500  as indicated by the arrows A in  FIG. 7 . 
     Still referring to  FIG. 6  the insulating abutment list  434  is fastened to the top frame member  5  by means of plastic screws having relatively large heads. This of course minimizes thermal bridging and the risk of the screw heads damaging the insulating material, but more importantly it makes dismantling very easy for users of the window wishing to install accessories such as an awning or blinds. It is even possible to provide the screws with lugs or slots allowing them to be taken out without the use of a screwdriver or like tool, for example by hand or simply using a flat object such as a coin. 
     A window according to the invention is shown in an open state from two different angles in  FIGS. 8 and 9 . 
     In this a few embodiments of a roof window  1  with insulating abutment lists  430   a ,  430   b .  434  has been shown and described but it is to be understood that insulating abutment lists may also be used on other windows and that their shape and design may be varied accordingly. Likewise, different combinations of features mentioned as alternatives above are also covered by the invention as defined by the scope of the claims.