WO2007086734A1

WO2007086734A1 - Prefab element

Info

Publication number: WO2007086734A1
Application number: PCT/NL2007/000026
Authority: WO
Inventors: Jered Nijhof
Original assignee: Quick Drain Holding B.V.
Priority date: 2006-01-27
Filing date: 2007-01-26
Publication date: 2007-08-02
Also published as: EP1988807A1; NL1031013C1

Abstract

The invention relates to a prefab element (1) to be placed in a wet area, such as toilet/bathroom facilities, a kitchen or a scullery, comprising a water retaining surface (2), and a drainage channel (3) having a bottom wall (33) and upright side walls (31), wherein the drainage channel (3) has been provided with a waste to be connected to a waste pipe, and wherein the water retaining surface (2) and the drainage channel (3) have been integrally-formed.

Description

PREFAB ELEMENT

BACKGROUND OF THE INVENTION

The invention relates to a prefab element to be placed in a wet area, such as toilet/bathroom facilities, a kitchen or scullery. On the one hand the invention particularly relates to a floor element to form a water retaining layer in at least a part of a floor in a wet area and on the other hand to an element to form a washbasin or work surface, such as kitchen work top, in a wet area.

US patent 4,557,004 describes a watertight prefab element having an inner surface that can be tiled. The element can be placed on the floor of a bathroom in order to form a shower tray. The prefab shower element according to US 4,557,004 has typically been provided with a waste placed in the centre of the element. The bottom walls of the shower element have been placed at a pitch towards said waste.

A recent trend seems to be providing floors with ceramic or natural stone tiles of large dimensions. When placing such tiles in a shower element according to US 4,557,004 it will among others be necessary to cut the tiles diagonally and/or lay them in a pattern in order to achieve the pitch towards the centre of the shower element. On the one hand tiling the known shower element therefore is laborious, on the other hand the additional joints in the tiles floor disrupt the aesthetic look of the shower.

It is an object of the invention to improve on this.

SUMMARY OF THE INVENTION According to a first aspect the invention provides a prefab element comprising a water retaining surface, and a drainage channel having a bottom wall and upright side walls, wherein the drainage channel has been provided with a waste to be connected to a waste pipe, and wherein the water retaining surface and the drainage channel have been integrally formed.

Because the prefab element according to the invention comprises a drainage channel, only a pitch transverse to the channel and sloping in the direction of the channel will be necessary. Such a pitch in one direction can also easily and quickly be realised with large tiles and with natural stone slabs.

In order to be used in a floor of a wet area in a building, the prefab element has been provided with a water retaining surface which can be arranged at, in or underneath the finishing floor of the wet area in order to create a water retaining and/or vapour retaining layer, wherein penetration of water into the construction floor underneath can be prevented. As the drainage channel and the water retaining surface have been integrally formed, an adequate sealing between the water retaining surface and the drainage channel is achieved.

A further advantage of the prefab element according to the invention is that it will not be necessary to arrange a passage with sealings for the waste pipe in the water retaining surface while the element is being placed, as described in US patent specification 6,014,780. Arranging a passage with sealings namely has the drawbacks that its arrangement is laborious, requires skill and costs a lot of time, and that such a passage with sealings may be a source of leakage.

Although the prefab element is first of all intended to be placed in the floor in a wet area in a building, for instance for creating a shower location in a bathroom, the inventor realised that the device according to the invention is suitable for and advantageous to many further uses.

For instance the water retaining surface may also be adapted as surface "^'" of a washbasin, kitchen work top or work table. By placing the drainage channel along the rear side of the surface, that means at a side facing away from a user, only a pitch transverse to the channel and sloping in the direction of the channel will be necessary. A pitch in one direction is easy to realise with a water retaining surface, such as for instance a natural stone surface, as a result of which substantially the entire surface or a part thereof is able to drain naturally in the direction of the channel.

In a simple embodiment the water retaining surface and the drainage channel have been made of the same material. On the one hand the prefab element according to the invention is thus easy to produce, for instance on one working step. On the other hand an aesthetically attractive element can thus be achieved, particularly to be used as an element for a washbasin, kitchen work top or work table.

In one embodiment the water retaining surface connects near the sides of the upright side walls of the drainage channel, which sides face away from the bottom wall. When used the drainage channel sits substantially underneath the water retaining surface, wherein the drainage channel forms a collection tray for liquid. The liquid on the water retaining surface may flow over said surface into the drainage channel, and be discharged via the waste of the drainage channel.

In one embodiment the prefab element comprises a supporting structure for supporting the water retaining surface at a distance above a floor of the wet area. Such a supporting structure may comprise a number of supporting elements which have been placed at the side of the water retaining surface which faces the floor when the prefab element is being placed. The supporting structure is particularly advantageous when the drainage channel extends below the plane of the water retaining surface.

In one embodiment the height of the supporting structure substantially equals or exceeds a height of the upright side walls of the drainage channel. In that way the prefab element with the supporting structure can be placed directly on a basis without a recess having to be present or arranged in the basis for accommodating the drainage channel therein. In an advantageous embodiment the supporting structure and/or the supporting elements have been integrally formed with the water retaining surface, as a result of which the prefab element with supporting structure can be placed as one unity.

In one embodiment the water retaining surface and/or the supporting structure form a substantially shape retaining or solid body for offering a work surface, for instance for a washbasin, kitchen work top or work table, or for offering a supporting surface, for instance for supportingly bearing one or more persons in a shower.

In a further embodiment, particularly to be placed in the floor of a wet area in a building, the bottom wall of the channel has been placed substantially in the plane of the water retaining surface. When placing this embodiment the water retaining surface is placed on the construction floor or finishing floor, after which a filling material, such as for instance a mortar bed, is arranged on the water retaining surface. The filling material is placed such that it offers a supporting structure to ceramic or natural stone tiles arranged on or in the filling material, and that this tiled floor drains towards the drainage channel.

Particularly when placed in the floor, as described above, wherein the water retaining surface itself does not need to form a work surface or supporting surface, at least the water retaining surface may substantially have been made of a flexible material.

In one embodiment at least a part of the circumference of the water retaining surface comprises an upright edge, wherein the upright edge extends out of the plane of the water retaining surface. In one embodiment the upright edge is placed substantially perpendicular to the plane of the water retaining surface. Such an upright edge is substantially used to be placed against a wall in a wet area. In practice said upright edge may at least partially be covered by the wall tiles.

In one embodiment at least a part of the circumference of the water retaining surface comprises an edge that can be folded up. Said embodiment is particularly, though not exclusively, advantageous in combination with a water retaining surface of a flexible material. When installing the prefab element, the edge adjacent to a wall in the wet area can be folded up at that location to be placed against the lowermost part of the wall in order to realise a water retaining and/or vapour retaining layer, in which way penetration of water to the wall can at least be largely prevented.

In one embodiment the drainage channel extends substantially parallel to the edge of the water retaining surface, which edge is upright and/or can be folded up. In this way it can be achieved that the drainage channel is placed parallel to and near the wall of the wet area.

In one embodiment the water retaining surface comprises a folding seam substantially along the edge that can be folded up. In one embodiment the water retaining surface, at least at the location of the folding seam, has greater flexibility than the edge that can be folded up and/or a part of the water retaining surface substantially adjacent to the folding edge. In one embodiment the folding seam comprises one or more recesses, such as for instance corrugations, grooves or V- grooves, arranged in the water retaining surface, which recesses extend substantially along the folding seam.

In one embodiment at least a face of the water retaining surface has been provided with adhesion enhancers. In one embodiment the adhesion enhancers comprise a rough or profiled surface texture. Said embodiments are particularly advantageous when tiles, natural stone slabs or a filling material has to be arranged on the water retaining surface.

In one embodiment the drainage channel extends substantially along almost a full side of the water retaining surface. When the water retaining surface has been provided with an edge that can be folded up, the drainage channel extends substantially within said edge that can be folded up.

According to an advantageous embodiment the drainage channel comprises a stench-trap, wherein the stench-trap has been placed in between the upright longitudinal side walls and connects to the waste. As the drainage channel has been provided with a stench-trap a waste pipe can be directly connected to the waste of the drainage channel of the prefab element according to the invention. A stench-trap, such as for instance a siphon, placed in the pipe is not necessary.

According to a further aspect the invention provides a water retaining surface having a surface area comprising a number of walls extending away from the surface area, wherein the walls comprise two longitudinal side walls and two head side walls for forming a channel in between.

Preferably at least the two longitudinal side walls have been placed substantially parallel to and spaced apart from each other. On the one hand a through-opening may have been arranged in between the longitudinal side walls in the water retaining surface, on the other hand at least one of the side walls may have been provided with a through- opening for connecting a waste pipe.

In one embodiment a shape retaining drainage channel has been placed in between the longitudinal side walls of the channel, which drainage channel has been placed in the channel with its waste adjacent to the opening for connecting the waste pipe to the waste of the drainage channel.

The aspects and measures described in this description and claims of the application and/or shown in the drawings of this application may where possible also be used individually. Said individual aspects, such as a washbasin surface, a work top or kitchen work top including drainage channel, a water retaining element including edge that can be folded up, and other aspects may be the subject of divisional patent applications relating thereto. This particularly applies to the measures and aspects described per se in the sub claims.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will be elucidated on the basis of a number of exemplary embodiments shown in the attached drawings, in which: Figure 1 A shows a schematic top view of a first exemplary embodiment of a prefab element according to the invention;

Figure 1 B shows a view in cross-section along the line l-l of figure 1 A;

Figure 2 shows a view in cross-section of a detail of the exemplary embodiment of figure 1 A along the line H-Il;

Figure 3 shows a schematic view in cross-section of a floor in a wet area, wherein the exemplary embodiment of figure 1 has been placed in the floor;

Figure 4A shows a schematic top view of a second exemplary embodiment of a prefab element according to the invention;

Figure 4B shows a view in cross-section of the exemplary embodiment of figure 4A along the line IV-IV;

Figure 5A shows a view in perspective of a third exemplary embodiment of the prefab element according to the invention;

Figure 5B shows a view in cross-section of the exemplary embodiment of figure 5A;

Figure 6A shows a view in perspective of a fourth exemplary embodiment of a prefab element according to the invention;

Figure 6B shows a view in cross-section of the exemplary embodiment of figure 6A;

Figure 7A-C show views in perspective of further exemplary embodiments of a prefab element according to the invention;

Figure 8 shows a view in cross-section of an exemplary embodiment of the prefab element wherein a shape retaining drainage channel has been placed between the upright walls.

DETAILED DESCRIPTION OF THE DRAWINGS A first exemplary embodiment of a prefab element 1 according to the invention is shown in figure 1 . Said prefab element 1 is intended to be a bottom mat to be placed in a wet area, and particularly to be placed on or in the floor of a toilet/bathroom facility. The element 1 comprises a water retaining surface 2 and a drainage channel 3 that has been integrally formed with the water retaining surface 2.

The bottom mat 1 has been made of a water retaining and vapour retaining material. Both the water retaining surface 2, and the channel 3 may have been manufactured of a flexible material.

In the exemplary embodiment as shown in figure 1 , and in detail in figure 2, the bottom wall 33 of the channel 3 and the water retaining surface 2 have been integrally formed. The bottom wall 33 sits in the plane of the water retaining surface 2.

The drainage channel 3 has been provided with a waste which may have been placed in the bottom wall 33 of the drainage channel 3. In the exemplary embodiment of figure 1 , the waste 34 has been placed in an upright side wall 31 of the drainage channel 3. The drainage channel 3 may furthermore be provided with a stench-trap 35, wherein the stench-trap 35 has been placed between the upright longitudinal side walls 31 in the drainage channel 3 and connects to the waste 34. The waste 34 may furthermore be connected to a waste pipe 4. Due to the waste 34 being placed in an upright side wall 31 of the drainage channel 3, the waste pipe 4 will at least be partially placed above the water retaining surface 2, as a result of which a construction floor 5 situated underneath the bottom mat 1 , is also protected against leakages in this part of the waste pipe 4 and in the connection of the waste pipe 4 to the waste 34.

The prefab element 1 according to figure 1 is particularly suitable for creating a shower location in a bathroom. A shower is usually placed near a bathroom wall. The drainage channel 3 is usually placed near said wall. In order to achieve a proper watertight connection to the bathroom walls, the water retaining surface 2 at its circumference is provided with an edge 21 that can be folded up. If at least the water retaining surface 2 is sufficiently flexible, the circumference of the surface 2 can be folded up at any location in order to form a watertight connection to the wall. In order to facilitate said folding, also for a water retaining surface 2 manufactured of a rigid or stiff material, the exemplary embodiment of the bottom mat 1 has been provided with a folding area 22 between the edge 21 that can be folded up and the centre portion of the water retaining surface 2, which folding area comprises a number of adjacent folding seams 23. The folding seams 23 extend substantially parallel to the folding edge 21 of the bottom mat 1 . Due to said folding seams 23 the edge that can be folded up can easily be folded up in the direction of the arrow Q as shown in figure 2. By placing a number of folding seams 23 adjacently, the position where the edge 21 can be folded up is adjustable; that means that the position of the drainage channel 3 can be adjusted with respect to the wall, and be adapted to the actual situation.

In order to offer the channel 3 sufficient firmness, particularly when the prefab element 1 has been made of a flexible material, the upright side walls 31 may have been provided with strengthening means, such as for instance reinforcement 32.

In an alternative embodiment the walls 31 of the channel 3 may also have been manufactured of a less flexible material; if the bottom mat 1 has for instance been made of a rubber material, the walls of the channel 3 could have been vulcanised more strongly than the material of the water retaining surface 2. As a result the bottom mat 1 can be made of substantially the same material and the channel 3 is less flexible than the water retaining surface 2.

In an alternative embodiment the walls of the channel 3 may be designed thicker than the water retaining surface 2. Due to this greater thickness of the walls of the channel 3 said channel also acquires a greater stiffness.

In addition a known shape retaining drainage channel, such as for instance described in Dutch patent specification 1025765, may be placed in the channel 3, as shown in figure 8. Such a shape retaining drainage channel 100 may have been manufactured from a synthetic material or metal and comprises a bottom wall 101 and upright side walls 102. The bottom wall 101 and the side walls 102 are adjacent to the bottom wall 3 and the side walls 31 , respectively, of the channel 3. At a side facing away form the bottom wall 101 the side walls 102 have been provided with anchoring flanges 103. A cover grid 104 has furthermore been arranged in the drainage channel 100. The upper side of said cover grid 104 has been placed substantially in the plane of the tiled floor, as shown in figure 8, so that a substantially continuing surface is formed. To that end the cover grid 104 may have been provided with side walls 105 which in this example rest on the bottom wall 101 of the drainage channel 101 .

Figure 3 shows the bottom mat 1 of figure 1 , at least a detail thereof, which has been placed in a floor of a wet area 6. The water retaining surface 2 has been placed on a construction floor 5 wherein the edge 21 that can be folded up has been placed folded up against the wall 7 of the wet area, by folding up the edge 21 that can be folded up along one of the folding seams 23 in the folding area 22.

Optionally the water retaining surface 2 may have been fully or partially glued together with the construction floor 5 and/or the wall 7. In order to provide the drainage channel 3 with sufficient firmness, the embodiment as shown in figure 3 has been provided with a frame 35 that is substantially placed near a side of the upright side walls 31 facing away from the bottom wall 33. Preferably the upright walls 31 have been attached to the frame 35.

After the water retaining surface 2 has been placed on the construction floor 5, the waste pipe 4 can subsequently be placed and connected, as shown in figure 1 . Subsequently a filling layer, particularly a finishing layer or mortar layer 8, is arranged on top of the water retaining surface 2. The filling layer 8 is arranged such that the upper side of the frame 35 is substantially at the same level as the upper side of the filling layer 8. Said filling layer 8 preferably is also placed at a pitch so that the surface of said layer is able to drain in the direction of the drainage channel 3. Subsequently a tiled floor 9 can be arranged on top of this layer 8, and the wall 7 may be provided with wall tiles 10. Finally a cover grid 36 can be placed over the drainage channel 3, which cover grid has been provided with passage openings to let water flow from the tiled floor 9 into the drainage channel 3.

Figure 4 shows a second exemplary embodiment of a prefab element 41 according to the invention. The prefab element 41 comprises a water retaining surface 42 and a drainage channel 43. This exemplary embodiment as well is particularly intended for placement on the floor of a wet area, for instance at a shower location in a bathroom.

The water retaining surface 42 in this exemplary embodiment is formed like a rigid body for supportingly bearing one or more persons on the prefab element 41 . As shown in figure 4B the drainage channel 43 has been placed such that the water retaining surface 42 connects to the sides of the longitudinal side walls 45 that extend away from the bottom wall 44. Thus the drainage channel 34 projects from under the plane of the water retaining surface 42.

For support, the prefab element 41 has been provided with a supporting structure 46 with which the self-supporting water retaining surface 42 is able to support on a subfloor. The supporting elements 46 are substantially of equal height h as the drainage channel 43. As a result the drainage channel 43 will also support on the subfloor. Please note that in this exemplary embodiment a connection pipe will be placed under the water retaining surface 42.

The supporting structure as formed by the supporting elements 46 is designed such that the water retaining surface 42, if the device 41 is placed on a substantially flat surface, will drain in the direction of the drainage channel 43.

A side 48 of the water retaining surface 42 which side faces away from the supporting elements 46 may on the one hand be provided with a finishing layer which thus forms the floor of for instance a shower.

On the other hand said side 48 may comprise a rough or profiled surface texture. On the one hand such a rough or profiled surface texture may serve as an anti-slipping provision to prevent slipping in the shower. On the other hand, if the water retaining surface 42 is provided with a tiled floor at its upper side, such a rough or profiled surface texture may enhance adhesion between the tiles and the water retaining surface 42.

After the prefab element 41 has been placed, as shown in figure 4, on a construction floor, the upper side of the water retaining surface 42 may thus be provided with a tiled floor. Finally the drainage channel 43 may be provided with a cover grid 47 that can be placed such that the upper side of the grid 47 is substantially in the same plane as the upper side of the tiled floor on the water retaining surface 42.

Further exemplary embodiments show a number of prefab elements used as work surface or work table, for instance to be used as washbasin, sink and/or kitchen work top. Figures 5A, 6A, 7A, 7B and 7C show views in perspective of a number of exemplary embodiments of such a prefab element 51 , 61 , 71 , 81 and 91 . Each of said prefab elements 51 , 61 , 71 , 81 , 91 comprises a water retaining surface 52, 62, 72, 82, 92 and a drainage channel 53, 63, 73, 83, 93.

The water retaining surface 52, 62, 72, 82, 92 may have been made of natural stone, or have been moulded from a synthetic material or a natural stone-synthetic material combination, such as natural stone granulate in a synthetic resin. On the other hand the water retaining surface 52 may also have been made of a ceramic material or of a metal such as stainless steel.

The water retaining surface 52, 62, 72, 82, 92, at least a part 54, 64, 74, 84, 94 thereof, is adapted for receiving a liquid and guiding said liquid to the waste. The water retaining surface 52, 62, 72, 82, 92, at least the part 54, 64, 74, 84, 94 thereof, may have been provided with a substantially elongated waste for placing a drainage channel 53, 63, 73, 83, 93 therein. However, preferably the water retaining surface 52, 62, 72, 82, 92 and the drainage channel 53, 63, 73, 83, 93 have been integrally formed, and said drainage channel has been provided with a waste for connection to a waste pipe. The exemplary embodiment as shown in figure 5 has been provided with a substantially flat work top 55, that is placed at a slight pitch in the direction of the drainage channel 53. In figure 5B said pitch is shown in a slightly exaggerated manner in order to clearly show said pitch. In one embodiment the work top 55 may have been manufactured from another material than the water retaining surface

52. As a result the work top 55 may be adapted to the use made thereof. For instance the prefab element 51 may at least form a part of the kitchen work top having a drainage channel 53 placed in the kitchen work top and a work top 55 placed near the drainage channel

53. In the example of figure 5B the waste 56 has been placed in the bottom wall of the drainage channel 53.

In order to be used as washbasin or sink, the water retaining surface 62, 72, 82, 92 has been provided with a recessed part 64, 74, 84, 94 for receiving a liquid therein and guiding said liquid to the drainage channel 63, 73, 83, 93.

The exemplary embodiment as shown in figure 6 shows a prefab element 61 that is suitable to be used as washbasin. In the example of figure 6B the waste 66 has been placed in a side wall of the drainage channel 63, particularly in a side wall of the drainage channel 63 that faces the rear side of the element 61 . As a result the waste 66 can be connected to a waste pipe (not shown) that can be placed substantially directly under the washbasin out of sight. In a further development the waste pipe, at least partially, may have been placed in the water retaining surface 62. In a further development the part of the waste pipe placed in the water retaining surface 62 is integrated into the prefab element 62.

In a further development the rear side of the washbasin 71 may have been provided with an upright edge 75 as shown in figure 7A, for instance to be placed against the wall of the wet area. Said upright edge 75 may have been provided with a water supply device such as a tap with outflow part 76.

When used the drainage channel 53, 63, 73, 83, 93 may have been provided with a cover grid, such as schematically shown in figure 7A. In the exemplary embodiments as shown in figures 5A, 6A and 7A the drainage channel 53, 63, 73 is placed substantially near a rear side of the prefab element 51 , 61 , 71 , that means near a side of the prefab element 51 , 61 , 71 that faces away from the user.

In an alternative embodiment as shown in figure 7B the drainage channel 53 is placed substantially centrally in the prefab element. Such an embodiment has no explicit front or rear side and can be placed such that the prefab element 81 is accessible from several sides.

In an alternative embodiment as shown in figure 7C the drainage channel 93 is placed near a side of the prefab element 91 . Said embodiment offers the opportunity to combine the prefab element 91 with a second prefab element 91 placed adjacent thereto, wherein the sides of the prefab elements have been placed with the drainage channels facing each other. The wastes of both prefab elements can be connected to one and the same waste pipe.

Whereas the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be evident to the expert that various adaptations as regards shape and details can be made without deviating from the spirit and scope of protection of the invention as defined by the attached claims.

Claims

1 . Prefab element to be placed in a wet area, such as toilet/bathroom facilities, a kitchen or a scullery, comprising a water retaining surface, and a drainage channel comprising a bottom wall and upright side walls, wherein the drainage channel has been provided with a waste to be connected to a waste pipe, wherein the water retaining surface and the drainage channel have been integrally formed.

2. Prefab element according to claim 1 , wherein the water retaining surface and the drainage channel have been made of the same material.

3. Prefab element according to claim 1 or 2, wherein the water retaining surface connects near the sides of the upright side walls, which sides face away from the bottom wall.

4. Prefab element according to claim 3, wherein the prefab element comprises a supporting structure for supporting the water retaining surface at a distance above a floor of the wet area.

5. Prefab element according to claim 4, wherein the distance substantially equals a height of the upright side walls.

6. Prefab element according to claim 4 or 5, wherein the supporting structure has been integrally formed with the water retaining surface.

7. Prefab element according to claim 4, 5 or 6, wherein the water retaining surface and/or the supporting structure forms a substantially shape retaining body for offering a work surface or supporting surface.

8. Prefab element according to claim 1 or 2, wherein the bottom wall of the channel has been placed substantially in the plane of the water retaining surface.

9. Prefab element according to claim 8, wherein at least the water retaining surface has substantially been made of a flexible material.

10. Prefab element according to any one of the preceding claims, wherein at least a part of the circumference of the water retaining surface comprises an edge that can be folded up.

1 1 . Prefab element according to claim 10, wherein the water retaining surface comprises a folding seam substantially along the edge that can be folded up.

12. Prefab element according to claim 1 1 , wherein the water retaining surface at least at the location of the folding seam has greater flexibility than the edge that can be folded up and/or a part of the water retaining surface substantially adjacent to the folding edge.

13. Prefab element according to claim 1 1 or 12, wherein the folding seam comprises one or more recesses arranged in the water retaining surface, which recesses extend substantially along the folding seam.

14. Prefab element according to any one of the claims 1 -9, wherein at least a part of the circumference of the water retaining surface comprises an upright edge, wherein the upright edge extends out of the plane of the water retaining surface.

15. Prefab element according to claim 14, wherein the upright edge has been placed substantially perpendicular to the plane of the water retaining surface.

16. Prefab element according to any one of the preceding claims, wherein at least a face of the water retaining surface has been provided with adhesion enhancers.

17. Prefab element according to claim 1 6, wherein the adhesion enhancers comprise a rough or profiled surface texture.

18. Prefab element according to any one of the preceding claims, wherein the drainage channel comprises a stench-trap, wherein the stench-trap has been placed in between the upright longitudinal side walls and connects to the waste.

19. Prefab element to be placed in a wet area, such as toilet/bathroom facilities, a kitchen or a scullery, comprising a water retaining surface having a surface area comprising a number of walls extending away from the surface area, wherein the walls comprise two longitudinal side walls and two head side walls for forming a channel in between.

20. Prefab element according to claim 19, wherein at least the two longitudinal side walls have been placed substantially parallel to and spaced apart from each other.

21 . Prefab element according to claim 19 or 20, wherein a through- opening has been arranged between the longitudinal side walls in the water retaining surface.

22. Prefab element according to claim 19 or 20, wherein at least one of the side walls has been provided with a through-opening.

23. Prefab element according to any one of the claims 19-22, wherein the prefab element has furthermore been provided with a shape retaining drainage channel placed in between the longitudinal side walls of the channel, which drainage channel has been placed in the channel with its waste adjacent to the through-opening for connecting the waste pipe to the waste of the drainage channel.

24. Prefab element provided with one or more of the characterising measures described in the attached description and/or shown in the attached drawings.

25. Method comprising one or more of the characterising steps described in the related description and/or shown in the related drawings.