The present invention first of all relates to a system of elements for the assembly of a staircase.

More specifically, the present invention relates to a system of elements for the assembly of a staircase with steps, at least part of which are winders, whereby in other words a certain angular displacement is applied.

The present invention also relates to a staircase, more specifically a winding stair, composed with elements of such a system.

Many ways are already known for designing and installing a staircase, but they exhibit a large number of disadvantages .

Indeed, contrary to what many might think, designing and installing a staircase is a rather complicated matter.

A staircase is used, of course, to bridge a particular vertical distance, for example typically between different floors of a building.

When designing a staircase, many parameters must be taken into account . Firstly, there are the parameters which are dependent on the shape of the building and the place which is available for the staircase. Such parameters are for example the shape of the stairwell, the head (which is the total length which can be used to place the staircase) , the stair height and the passage height or headroom. Taking these parameters into account, a certain shape of staircase can be selected.

Here again there are plenty of options. The simplest stair shapes are for example the straight staircase or the so-called landing stairs, whereby several landings or platforms are provided in such a landing stair, for example to change direction or to serve as a resting place in the case of longer straight stairs.

In more complicated stair shapes, successive steps of the stair represent a certain angular deflection in relation to one another, such that the user, while climbing (or descending) , is simultaneously re-oriented on a portion concerned of said stair.

Thus, a greater height can be overcome in a much narrower place, be it by compromising somewhat on the ease of use. The most extreme example thereof is a spiral staircase or winding staircase. Other examples are the so-called quarter-turn staircase or double quarter-turn staircase and single or double leeward stairs . The design of a staircase with winders in particular is accompanied by many difficulties.

In order to achieve parts of stairs with successive steps exhibiting a certain angular deflection in relation to one another, a so-called angular displacement is usually applied, for which a number of well-known techniques exist as well, such as for example the harmonic displacement, the hoopnet method, the Leroi and Winkler method, and the infinite displacement.

All these known techniques are geometrical methods to determine the dimensions of winders.

The line on which a user is supposed to walk on the stairs, which line is called the walkline, is hereby divided into equal pieces .

These pieces are then reduced by a geometrical projection on the central stringer or central stringers of the staircase, so that also at these central stringers, the steps have a width which is not too small, which should contribute to the comfort when using the stairs.

Nonetheless, at the inner stringers of the staircase there is little space available. A major factor to be taken into account when designing a staircase is the stability and bearing power of the staircase . Distributing the available space more or less proportionally over the winders results in that, at the central stringers, the steps may turn out very narrow.

Such narrow portions of the steps are often unable to provide sufficient bearing power to carry the weight of persons on the staircase, resulting in very limited design possibilities .

Moreover, the steps are to be inserted between the outside stringers and the inner stringers and they must be fixed to the central stringer, which requires a certain manipulation of the steps for which the necessary space is not always available. Numerous techniques exist for coupling the steps of a staircase to the so-called stringers, which can have a great influence on the possible stair shapes which can actually be achieved in the end during the installation. For example, it is common to partially work in the steps of a staircase in the side stringers of the staircase at their far ends.

In order to make that possible, one must already verify during the design stage whether there is sufficient manoeuvring room to insert for example steps in stringers which have already been provided in a stairwell or to install for example a pre-assembled staircase in its entirety in a stairwell.

Thus a specific staircase shape may in principle offer a good comfort to a user, but turn out to be impossible to achieve in practice as the connection techniques are too weak or as certain dimensions of the materials used are too restricted to withstand the forces exerted on the staircase during its use or because the stairs cannot be mounted due to lack of space.

Further, there are numerous other parameters that need to be taken into account during the design of a staircase in order to obtain a safe and easily walkable staircase.

Such parameters are for example the rise angle, the size of the riser and the tread, the shape of the walkline and the useful width of the stairs. In many cases, safety arrangements must be provided as well in the form of banisters and handrails and the like.

These are other factors which severely restrict the architects' options and freedom of design.

All this implies that architects must usually take into account numerous factors and that the design options for architects are often very restricted because of possible installation problems with a particular shape of staircase or because of the staircase's stability, so that it is often impossible with the known techniques to achieve the desired shape of staircase in practice. In some cases, architects must even omit walls to allow for the installation of a staircase or they have to create entrance halls to be able to place stairs.

In other words, architects must often give up habitable space to address these problems.

Also, the present invention aims to remedy one or several of the aforesaid disadvantages and possibly also other disadvantages .

More specifically the invention aims to offer a new system of elements for the assembly of a winding stair, wherein said system of elements is such that a winding stair can be obtained which is very efficient from an ergonomic point of view and as far as stability is concerned, and this for any possible situation and available space in buildings .

Further, the invention aims to provide such a system of elements which allows architects, engineers and other designers to choose, as of the design stage, the most appropriate solution as far as user' s comfort and aesthetics of the staircase are concerned, wherein the available space or installation possibilities in the building must not or hardly be taken into account, and wherein the method and the system of elements are such that requirements regarding the stability or bearing power of the staircase no longer or hardly influence the exterior design of the staircase. Another aim of the invention consists in providing a solution which makes it possible to obtain a computerized system wherein the design and manufacture of a winding stair is automated or can be carried out semi- automatically.

The aim in particular thereby is to provide a solution or method which is such that an automated system can be achieved which calculates, draws and if necessary produces a fully-fledged winding stair and all of its components on the basis of a restricted number of input data provided by a designer.

In other words, the idea behind the new system of elements for the assembly of a winding stair aimed by the invention should allow to achieve a design program and production software which automatically apply the knowledge of a traditional stairs maker, such that any specific stair- making knowledge is no longer required from the user to guarantee a proper production and installation.

The input data may for example be parameters regarding the available space, the shape of the staircase, the available machines, the type of displacement one wishes to apply, etc.

Another aim of the invention is to provide a system of elements for the assembly of a winding stair with which the required design time, installation time, production time and finishing time can be strongly reduced compared to the corresponding times with the known methods and systems . More specifically, a reduction of the design time, installation time and production time of around 50% is aimed for, as compared with the known methods for designing, installing and producing a staircase.

Similarly, it is an object of the invention to reduce the finishing time with 25% to 50% as compared to the known methods .

Another aim of the invention is to reduce the installation and manufacturing costs of a staircase to a minimum.

To this end, the present invention concerns a system of elements for the assembly of a staircase with steps, at least a part of which are winders, whereby the system of elements comprises at least one or several outside stringers and inner stringers and possibly intermediate central stringers, as well as steps which can be provided on the stringers, whereby at least a part of the steps are winders which are partially widened such that, after they have been provided on the stringers so as to form a staircase, the portion of the rear edge of an underlying winder at the outside stringer or outside stringers of the staircase is vertically aligned with the front edge of a superjacent step, possibly save for an overlap of a vertical step placed or to be placed on top of it and/or for forming a nosing on the superjacent step, whereas on the inner stringer or inner stringers of the staircase, the aforesaid winders exhibit a widening on their rear edges which is such that underlying winders, seen from above, extend under the respective following step over a distance which is larger than the aforesaid possible overlap, at least as far as such an overlap is applied, whereby the steps would thus extend behind a possibly provided overlying vertical step, should such a vertical step be placed with its back at a distance corresponding to said overlap from the front edge of the superjacent step concerned.

A major advantage of a system of elements according to the invention is that its winders are widened near the side which is designed to be fixed on the inner stringers, whereby the widening of such a step extends under a superjacent step and behind a bottom plate which may have been provided.

In short, the space behind the vertical steps between successive winders is also used for designing the winders, thus creating many new opportunities. A positive result of a wider embodiment of the steps on the side which is designed to be fixed to an inner stringer is that the usually tapered end of such a winder can be made much wider and thus stronger than with the known systems or methods .

Another advantage of the widened embodiment of the steps on the side which is designed to be fixed to an inner stringer is that the winders can bear over a larger length or dimension on the inner stringer concerned, making the connection with the inner stringer or the support thereof on the inner stringer also stronger and less stressful to the materials from which both the steps and the inner stringers are made.

In the conventional designs of the steps of a stair, the steps can be fit together in such a manner that they cover the floor plan of the staircase to be formed, save for a possible overlap which is applied to compensate for the thickness of a vertical step or to create a nosing at the steps .

As a result, there are many limitations to the design of a staircase, since the steps at the inner stringers are often too narrow to have sufficient bearing power. Widening the bottom plates makes it possible to develop new forms of winding stairs which are impossible to realise with the known techniques.

According to a preferred embodiment of a system of elements in accordance with the invention, the stringers are provided with a phased upper section, whereby the steps can be mounted on horizontally extending parts of the phased upper sections on the placed stringers. A major advantage of this embodiment of a system of elements in accordance with the invention is that the shape of the stringers makes it possible to mount the steps on top of the latter, as opposed to the known systems wherein the steps are installed in between the stringers or are incorporated in the stringers. As a result, winders can be easily applied on the stringers, so that little or no space must be available for the manipulation of the steps during their installation on the stringers.

Another major advantage of this embodiment of a system of elements in accordance with the invention is that the steps can be laterally arranged on the stringers more or less independently from the exact position of the stringers themselves, so that errors in the alignment of walls and the finishing of walls of the stair well have little or no influence on the shape of the staircase.

Thus, it is possible to align the steps in relation to one another without having to take into account the lateral position of the stringers in the stair well.

As a result, it is possible to design and provide for a staircase which is fit for the given circumstances and which can also be easily installed in practice.

Thus, a system of elements in accordance with the invention once again offers more possibilities for designing winding stairs, since there are less restrictive criteria that such a design must meet than with the known systems .

According to a preferred embodiment of a system of elements in correspondence with the invention, a winder of such a system has an outer edge designed to be attached at the respective outside stringer, and the shape of this outer edge corresponds to the shape of a fraction of the contours formed by the installed outside stringers or of the stair well in which the latter are installed.

Another preferred characteristic of a system of elements in accordance with the invention consists in that a winder has an inner edge designed to be attached at the respective inner stringer and whose shape corresponds to the shape of a fraction of the contours formed by the installed inner stringers or of the stair well in which the latter are installed.

These embodiments of a system of elements in accordance with the invention are advantageous in that the winders fit within the contours of the building in which the staircase is to be installed, whereby a play can be provided for, however, which can compensate for possible misalignments in the shell of the building or the like or which promotes an easy installation. It is important to note, however, that the dimensions of the inner edge of such a winder of a system in accordance with the invention are substantially larger than would be the case if such a step would wind in a conventional manner, because a widening is provided on this side of the step.

This allows to lend more bearing power to such winders of a system of elements in accordance with the invention. Preferably, the inner stringer or inner stringers of a system of elements in accordance with the invention are made such that the broadened winders, after having been installed at the inner stringer or inner stringers, are fully supported over the width of their inner edges.

It is this combination of custom inner stringers and the broadening of the winders which result in a very strong whole, which moreover is very quick and easy to install.

In a preferred embodiment of a system of elements in correspondence with the invention, the system of elements is provided with basic elements consisting of the stringers, steps and possibly vertical steps, with which a basic staircase can be composed, and with additional elements for a superstructure with which a finishing layer can be provided on said basic staircase so as to form a finished staircase, and whereby these additional elements consist of finishing steps, finishing vertical steps and possibly intermediate elements, with which the riser of the finished staircase can be adjusted. A major advantage of such a system of elements in accordance with the invention is that, already in the initial stage of a building project, a basic staircase can be installed which may serve as scaffolding stairs and which will later serve as the substructure of the ultimate staircase.

Thus, it is possible to work safely, whereas moreover there is no need to break down the basic staircase or scaffolding stairs again at a later stage.

As the basic staircase will be finished at a later stage of the building project and will be covered by a superstructure, it is not terrible either if the scaffolding stairs are slightly damaged during the building phase. Typically, excessive use of scaffolding stairs and carrying heavy materials along such scaffolding stairs during the works leads to scratches and little holes in the scaffolding stairs, which would be unacceptable at the time of completion of the stairs.

In order to better explain the characteristics of the invention, the following preferred embodiments of a system of elements in accordance with the invention for the assembly of a winding stair, as well as a staircase in accordance with the invention which is composed with elements of such a system are described by way of example only without being limitative in any way, with reference to the accompanying drawings, in which: figures 1 to 3 are side-elevations of each time three stringers of a system of elements in accordance with the invention for forming a double quarter-turn staircase, more specifically the outside stringers, the central stringer and the inner stringers respectively;

figure 4 shows a plan view of steps which are part of the system of elements in accordance with the invention;

figure 5 shows a plan view according to arrow F5 of the result on a staircase in accordance with the invention which was made on the basis of the elements represented in figures 1 to 4 and elements which are not shown;

figures 6 to 8 show the steps from figure 4 as enlarged, indicated by F6 to F8 respectively;

figures 9 and 10 show the parts indicated respectively by the cross-cuts IX-IX and X-X in figure 5 as a section on a larger scale;

figures 11 and 12 represent a possible alternative embodiment in a similar manner as in figures 9 and 10;

figure 13 shows the scaffolding stairs from figure 5 according to arrow F13, seen in perspective;

figure 14 illustrates an alignment tool, seen in perspective, which can be used when installing a staircase according to a method in correspondence with the invention;

figure 15 is a side view which illustrates the use of the alignment tool from figure 14;

figures 16 and 17 illustrate the placing of stringers with the aid of a support tool, seen in perspective; figure 18 is a plan view of a possible embodiment of finishing steps of a more comprehensive system of elements in accordance with the invention; and, figure 19 shows a plan view of yet another staircase in accordance with the invention which was realised by covering the basic staircase from figures 5 and 13 with the finishing steps from figure 18 and any possible other elements. The elements 1 represented in figures 1 to 4 together form a system 2 of elements in accordance with the invention for the assembly of a winding stair 3 in accordance with the invention, which is represented in figures 5 and 13.

More specifically, the system 2 of elements 1, represented in the aforesaid figures, is designed for the assembly of a double quarter-turn staircase 4 which is provided in a tubular stair well 5 formed between an inner wall 6 and three outer walls 7, 8 and 9. The system 2 of elements 1 comprises a series of stringers 10, as well as steps 11.

More specifically, there are three outside stringers 12, 13 and 14 in this case, as represented in figure 1, and which are designed to be attached to the outer walls 7 to 9 respectively.

Similarly, there are three inner stringers, more specifically inner stringers 15, 16 and 17 as represented in figure 3, and which are designed to be attached to the sides 18, 19 and 20 of the inner wall 6 respectively.

Finally, there are three intermediate central stringers 21, 22 and 23, represented in figure 2, and these are meant to be mounted in between the corresponding inner stringers 15 to 17 and outside stringers 12 to 14.

More specifically, it is hereby intended that the heads 24 of the central stringer 21 and 22 are laterally mounted on the outside stringers 13 and 14 respectively, which is indicated in figure 1 by means of vertical stripes 25 and 26. Further, the feet 27 of the central stringers 22 and 23 must be mounted on the underlying central stringers, on the middle stringer 21 and middle stringer 22 respectively, which is indicated in figure 2 by means of vertical stripes 28 and 29.

All the stringers 10 from figures 1 to 3 are carried out with a phased upper section 30, whereby portions 31 which are horizontally oriented during the mounting and portions 32 which are vertically oriented during the mounting alternate .

The aim hereby is that steps 11 are provided on the portions 31 of these phased upper sections 30 which are horizontally oriented after having been mounted.

These steps 11 are represented in figure 4. First of all, there are a number of steps 11 which form straight steps 33.

There are the straight steps 33 on the bottom side of the staircase 3, more specifically the first step 34 and the second step 35 which are stepped on when the stairs 3 are mounted as of a lower floor 36.

These straight steps 33 have a length C, in correspondence with the width K of the staircase 4 to be formed, and a width D. Further, there is also a straight step 37 which serves to form the final step 37 of the double quarter-turn staircase 4 and which has slightly larger dimensions. At two opposite angles 38, the latter step 37 is also provided with a notch 39 designed to fit between standing portions 40 in the shape of a kind of ears 40 provided on the topmost outside stringer 14 and the topmost inner stringer 17.

When installing the staircase 4, these ears 40 protrude above the bearing floor 41 of the upper floor level 42.

Finally, there is also a welding piece 43 designed to lie on the horizontal portions 44 of the aforesaid ears 40 as soon as a connecting screed or slab and tile floor are provided on the bearing floor 41 of the upper floor level 42. Thus, these straight steps 33 are designed as straight portions of the double quarter-turn staircase 4 where no angular displacement is required.

All the other steps 11 are winders 45 designed for a winding portion of the double quarter-turn staircase 4, whereby a certain angular displacement is applied.

These winders 45 are special, since they are not designed as is usually the case.

According to the known methods, the available space for the staircase 3 on a floor plan of the stair well 5 is subdivided in a number of parts in correspondence with the number of steps 11 that will be used to overcome the difference in height between a lower floor 36 and a higher floor 42.

Such a floor plan or top view is represented for example in figure 5.

With the known techniques, the steps 11 are outlined on this floor plan whereby a certain angular displacement may be either or not applied.

In order to apply an angular displacement, the walkline is projected on the inner stringers 15 to 17 as well as on the outside stringers 12 to 14 or on the contours of the stair well 5 with the aid of a geometric method.

Such a geometric method may for example be the hoopnet method, the Leroi and Winkler method or a method whereby a harmonic displacement or an infinite displacement is applied .

These methods imply a whole lot more than simply outlining the steps 11 according to the radials of a circle towards a centre, but it would lead us too far to elaborate these known methods in greater detail.

Thus, according to the known displacement methods, the available space is better divided over the steps 11, such that the space to place one's feet on the steps 11 is optimised . In addition, an attempt is made to maintain the width of the steps 11 at the inner stringers 15 to 17 sufficiently large, both to increase the comfort of a user and to ensure the stability and bearing power of the staircase 3.

The winders 45, represented in figures 4, 6, 7 and 8, have a first portion 46 in the shape of a polygon whose contours correspond to the contours of steps as they are traditionally designed.

Such a first portion 46 is defined by an outer edge 47 whose shape corresponds to the shape of a fraction of the stair well 5 on the outer walls 6 to 8, the stair well 5 or the installed outside stringers 12 to 14.

On the opposite side 48, such a first portion 46 with contours in correspondence with a known design is defined by an inner edge 49 whose shape corresponds to the shape of a fraction of the stair well 5 on the inner wall 6 or the installed inner stringers 15 to 17.

Every first portion 46 is further defined by a front edge 50 in the shape of a straight line 50 extending between the outer edge 47 and the inner edge 49.

Finally, such a first portion 46 is defined on the rear side 51 by a line 52 consisting of an imaginary line portion 53 indicated by the dotted line 53 which constitutes the extension of a rectilinear portion 54 forming a portion 54 of the rear edge 55 of the winder 45. Figures 6 to 8 represent yet another dotted line 56 which is parallel to line 52 and at a distance S therefrom.

Said distance S is in this case equal to the thickness F of a vertical step 57 which may possibly be placed above a step 11 so as to form a closed staircase 3.

The vertical steps 57 are not all represented as separate in the figures, but they can be found for example in figures 9 to 13.

It is important to note that, according to the conventional design methods, the first portions 46 are such that they can be placed adjacent to one another on the floor plan, possibly with an overlap in correspondence with the aforesaid mentioned distance S to cover a vertical step 57 or to form a nosing 58 on a step 11, whereby the first portions 46 together assume the shape on this floor plan of the portion of the stair well 5 wherein the staircase 3 is to be installed.

However, the winders 45 according to the invention are specially made, whereby they are widened more specifically.

To this end, the winders 45 are provided with a widening 59 with which the first portion 46 is enlarged near the inner edge 49 and as of the rear edge 55 of the respective winder 45.

This widening 59 forms a sort of wing 59 on the first portion 46. This wing 59 is such that, on the inner edge 60 of such a winder 45, the shape correspond to the shape of a fraction of the stair well 5 on the inner wall 6 or the installed inner stringers 15 to 17.

This inner edge 60 of a winder 45 is in other words composed of an inner edge portion 49, belonging to the first portion 46 of the winder 45 which corresponds to the contours of a traditionally designed winder, and an inner edge portion 61 which forms an extension to the inner edge portion 49, although still according to the contours of the stair well 5 on the inner wall 6. The inner edge 60 of the winder 45 is designed to be attached at the respective inner stringer 15 to 17 and, thanks to its enlarged form, the step 45 there finds a better support. The widening 59 extends as of the point U where the rectilinear portion 54 of the rear edge 55 changes into the dotted line 53.

With certain winders 45, as is for example the case with the step 45 represented in figure 8, the portion 62 of the rear edge 55 of the winder 45 which defines the widening 59, is made rectilinear.

With other winders 45, as is for example the case with the steps 45 represented in figures 6 and 7, the portion 62 of the rear edge 55 of the winder 45 which defines the widening 59 forms a flowing line. This shape of the winders 45 is such that, after they have been placed on the stringers 10 so as to form the staircase 3, the portion 54 of the rear edge 55 of an underlying winder 45 at the outside stringer or outside stringers 12 to 14 of the staircase 4 will be vertically aligned with the front edge 50 of a superjacent step 45, possibly save for an overlap S for a vertical step 57 placed or to be placed on top of the latter and/or for forming a nosing 58 on the superjacent step 45.

On the other hand, the shape of such a winder 45 is such that, after it has been installed, at the inner stringer or inner stringers 15 to 17 of the staircase 4, the aforesaid winders 45 will be provided with a widening 59 on their rear edges 55 which is such that underlying winders 45, seen from above, extend under the respective subsequent step 45 over a distance V which is larger than the above-mentioned possible overlap S, at least in so far as such an overlap S is applied.

The winders 45 would thus protrude behind a possibly provided overlying vertical step 57 should such a vertical step 57 be placed with its back 63 at a distance Z corresponding to the above-mentioned overlap S from the front edge 50 of the respective superjacent step 45.

This situation is clearly illustrated in figures 9 and 10. More specifically, figure 9 represents a view on a section on the side of the outside stringer 12. The portion 54 of the rear edge 55 of an underlying winder 45 is hereby vertically aligned with the front edge 50 of an overlying winder 45, save for an overlap S however, which in this case is equal to the thickness F of a vertical step 57.

In other words, the rectilinear portion 54, which extends as of the outer edge 47 up to the intermediate point U, after the winders 45 have been installed on the stringers 10, will be directed parallel to the front edge 50 of a superjacent step 45.

Thus, the step 45 does not protrude from behind the vertical step 57 on the side of the outside stringer 12.

Figure 10 represents a section of the same winders 45, this time at the inner stringer 15.

At this inner stringer 15, the winders 45 have been enlarged with a widening 59, and the underlying step 45 protrudes over a distance V which is larger than the overlap S under the overlying winder 45, such that in this situation, the bottom winder 45 protrudes from behind the vertical step 57.

Figures 11 and 12 represent a similar situation, whereby this time a larger overlap S is applied, however, so as to form a nosing 58 having a width Y on the steps 45. This does not change anything essential, since once more the widening 59 protrudes from behind the vertical step 57 on the side of the inner stringer 15, whereby this widening 59 can be used to better support the winder 45.

According to the invention, the inner stringers 15 to 17 are made such that the broadened winders 45, after having been installed on their inner stringers 15 to 17, are fully supported over the width of their inner edges 60.

Due to the special shape of the winders 45 with widening 59, this requires some adjustment of the inner stringers 15 to 17.

The major advantage, however, is that the design and installation options give more freedom to architects and designers.

According to the invention, the winders 45, while being installed on the stringers 10, are aligned in relation to one another, which makes their installation very easy and as a result of which the installation can be carried out by one person.

In order to facilitate the alignment, a number of alignment holes 64 are provided in the steps 11, in the winders 45 as well as in the straight steps 33.

In the case of the figures, each time three such alignment holes 64 are provided, more specifically two holes 65 on the rear edge 55 of said step 11 and, in the middle between them, a hole 66 close to the front edge 50 of said step 11. These holes 64 are designed to cooperate with an alignment tool 67, a possible example of which is shown in perspective in figure 14, whereas its use is illustrated in figure 15, albeit in a straight portion of a possible staircase 3.

This alignment tool 67 forms a kind of rack with a rectangular bottom 68, whereby three upright sections 70 are provided at an edge 69 of the bottom 68, which are perpendicular to the bottom 68 and which serve as a stop against which a step 11 can rest during the alignment.

These standing sections 70 are mutually connected by a connecting rod 71 and diagonally supported in relation to the bottom 68 by diagonal sections 72.

On the middle standing section 70 is provided a protrusion 73 which can be applied in a fitting manner in a centre hole 66 at the front edge 50 of a step 11.

In a similar manner, a pair of protrusions 74 are provided under the bottom 68 of the alignment tool 67 which can be applied in a fitting manner in the holes 65 at the rear edge 55 of a step 11.

The alignment tool 67 can engage with an underlying step 11 by means of the protrusions 74 on the lower side of the bottom 68 thereof, more specifically in holes 65 of such a step 11.

For a proper placement of an upper step 11, the protrusion 73 is inserted in the hole 66 of the respective upper step 11, and the front edge 50 of that step 11 may rest against the stops formed by the sections 70.

Preferably, according to the invention, one starts by placing the first step 34, and the subsequent steps 11 are placed from bottom to top by making the alignment tool 67 engage with an underlying step 11, making the superjacent step 11 rest against the stops 70 of the alignment tool 67 and fixing them on the stringers 10.

These actions are further repeated each time until all the steps 11 are in place.

The alignment tool 67 and the holes 64 are such that, when aligning the steps 11, at least a portion of the rear side 55 of an underlying step 11 is each time vertically aligned with the front side 50 of a subsequent superjacent step 11, in the given example save for a thickness F of a vertical step 57 of the staircase 4 to be placed, however.

It should be noted that the steps 11 and vertical steps 57 are not provided up against the vertical portions 32 of the stair-shaped sections 30 of the stringers 10 but that, on the contrary, a certain space L is left.

A major advantage of this assembly method consists in that the steps 11 are mounted as it were almost independently from the stringers 10, so that a staircase in any shape whatsoever can be installed without any further complications, for example resulting from errors in the shell of the building or the like, and this in a very precise manner. In a preferred method according to the invention, for the installation of the stringers 10 and the first step 34, use is made of a supporting tool 75, a possible embodiment of which is illustrated in figures 16 and 17.

The supporting tool 75 is provided with a frame 76 with legs 77 which are adjustable in height, and on the frame 76 are provided holders 78 wherein a foot of the stringers 10 can rest.

The intermediate distance I between the holders 78 on the frame 76 is hereby adjustable, making it possible to mount stringers 10 for staircases 3 with a varying width K.

The supporting tool 75 is further provided with a number of stops 79 designed for the alignment of the first step 34 on the lower horizontally extending portions 31 of the stringers 10 when they are placed in the holders 78.

The stops 79 are in this case formed of vertically extending portions 80 provided on either side of the frame 76. The first step 34 is not provided with a hole 66 on the front edge 50, since the aim is not to align this first step 34 with the alignment tool 67 represented in figure 14, which would be impossible indeed as another underlying step 11 is required to that end.

The stringers 12, 15 and 21 are mounted with the supporting tool 75 as follows. First, the supporting tool 75 is placed on a bearing floor 12. Then, the frame 76 is put level with the holders 78 by means of the adjustable legs 77 at a certain height above the bearing floor 81 in correspondence with a pre-set floor level W to be achieved later. The holders 78 are further adjusted widthwise by setting the intermediate distance I in correspondence with the stair width K.

Next, the bottom sides 27 of the stringers 10 are put in the holders 78 on the frame 76.

Finally, the first step 34 can be provided against the stops 79 of the supporting tool 75 and fixed to the respective lower horizontal portions 31 of the stringers 10.

This situation is represented in figure 17.

In this manner, placing the stringers 10 and the first step 34 can be done very precisely, which offers the advantage that the staircase 3 can already be installed in its final position before a screed or slab and a tile floor or the like are provided on the bearing floors 41 and 81.

In a special embodiment of a system 1 of elements 2 in accordance with the invention, the system 2 is not only provided with basic elements 82, as represented in figures 1 to 4 and which consist of the stringers 10, steps 11 and possibly vertical steps 57 and with which a basic staircase 3 can be assembled, as is represented in figures 5 and 13.

In such a special embodiment of a system 2 of elements 1, additional elements 83 are provided for applying a superstructure 84 in the form of a finishing layer 84 on such a basic staircase 3 so as to form a finished staircase 85, more specifically in this case a finished double quarter-turn staircase 85.

These additional elements 83 consist of finishing steps 86, finishing vertical steps and possibly intermediate elements, with which the riser of the finished staircase 85 can be adjusted.

Figure 18 is a plan view of such finishing steps 86, and they are such that they can be mounted in a fitting manner on top of the steps 11 of the basic staircase 3 represented in figure 13.

The alignment is done in this case by bringing the finishing steps 86 up against the vertical steps 57, but other methods may be used in other embodiments.

In between successive finishing steps 86 are preferably also provided finishing vertical steps, which are not represented in detail in the figures. The result is a double quarter-turn staircase 85, as shown in the plan view in figure 19.

In the given example of figure 19 was also applied a certain overlap W between successive finishing steps 86.

The basic staircase 3 may serve as scaffolding stairs during the structural works, after which these scaffolding stairs 3 are then embellished to a finished staircase 85 later on by covering them with the additional elements 83.

Thus, it is possible to work with a final staircase 3 as of the initial phase of the works, whereby any slight damages to this basic staircase 3 will be covered later by the finishing layer 84.

It is clear that a staircase 3 and a system 2 of elements 1 in accordance with the invention offer many advantages compared to the known methods and systems.

First of all, the installation of a staircase 3 in accordance with the invention can be done much faster and can be performed by a single person. Compared to the known methods in which concrete must be poured, a method according to the invention offers the advantage that the works may continue immediately after the assembly of a staircase 6. Nor is there any obstruction in stairwells as is the case for example when casting concrete, whereby a curing cycle must be observed. No secondary material such as concrete and material for a formwork is used. In addition, there is no form removal.

Further, a better displacement is possible, which contributes to the safety of the method and simplifies the subsequent finishing process.

The finished steps 61 can be mounted directly on the scaffolding stairs 6 without any separate slab or special positioning techniques being required, which is the case indeed when finishing concrete scaffolding stairs.

All sorts of step/ ertical step configurations can still be determined after the substructure has been placed.

When renovating, the method is also very user-friendly in terms of customisation.

The speed at which a staircase 3 can be placed according to the method of the invention and the limited number of workmen required to do so also greatly contributes to reducing the cost price.

Another advantage of a method in accordance with the invention is that, after the scaffolding stairs 6 have been put in place, the surrounding walls 69 to 72, slabs or screeds 57 and tile floors 58 can be finished first, and only afterwards the superstructure is applied on the scaffolding stairs 6. Damage to the final staircase 3 caused by plastering, demolition works or other conditions which are very demanding for a staircase 3 can thus be avoided.

The bottom plates 29 or 89 are hereby designed such that they can resist prolonged periods of heavy use.

The invention is by no means restricted to the embodiments of a staircase 3 according to the invention and a system 1 of elements 2 for manufacturing a staircase 3 according to the invention described by way of example and illustrated in the figures; on the contrary, such staircases 3 and systems 1 of elements 2 can be achieved in many other ways while still remaining within the scope of the invention.

Nor is the invention restricted to the described examples of methods in accordance with the invention for installing a staircase 3; also other methods can be applied while still remaining within the scope of the invention.