Such a wall is known from EP-A-0 801 190.

In this prior art wall the density of the layer of mineral wool is constant over the whole cross-section of the wall. The choice of the density of this insulating layer is therefore determined by the thermal insulation value in combination with the lowest possible cost price.

It is herein noted that thermal insulation value is understood to mean not only the normal measurable insulation value, but that the fire- retardation is also very important. It is of course of the greatest importance to ensure that the construction is as fire-resistant as possible.

Fire-retardation is often also very important in respect of legal regulations.

Experience has shown that this prior art wall construction collapses more quickly under wind load than is desirable. Research has shown that this is a result of the fact that the rigidity of the construction in lateral direction, i. e. the ability to absorb shear forces between the outer skin and inner skin, is not optimal.

The object of the present invention is to provide such a construction wherein the resistance to wind load is much greater without the noses having to be placed considerably closer together or the pointed connections having a greater closeness or having to have excessively heavy dimensions.

These two latter measures would after all result in a sharp fall in the thermal insulation value and particularly in a reduction of the fire-retarding time, which is highly undesirable.

This objective is achieved in that the insulating layer has a greater density on the outside than on the inside and in that the pointed connections are adapted to absorb forces in the direction parallel to the plane of the wall.

As a consequence of these measures a greater lateral rigidity of the wall construction is obtained.

The combination of measures achieves that lateral forces are at least partially absorbed by the pointed connections without the pointed connections having to be embodied in excessively heavy form. The pressure forces are absorbed by the mineral wool with a high density and transmitted on the one hand to the layer of mineral wool of a lower density located therebehind and on the other hand to the noses.

It is noted here that it is of course possible to fill the whole wall construction with mineral wool with a high density. This will of course result in a sturdier construction. However, increasing the density results in higher cost.

A construction is known from EP-A-0 849 420 wherein mineral wool with a higher density is applied on the outside, albeit in combination with a screw connection which is not suitable for absorbing lateral forces. This is an attempt to obtain a combination of a thick layer of mineral wool on the inside with an acceptable thermal insulation and low cost, and a thinner layer of mineral wool with a greater density located on

the outside with the purpose of obtaining a sturdier construction and an optimal thermal insulation.

Although these measures result in an improved result, these results are not found to be optimal; because the pointed connections cannot absorb lateral forces, or hardly so, the lateral pressure is transferred with no appreciable reduction to the underlying layer of wool of lower density. In the present invention there is found to be a surprisingly large reduction in these forces which are absorbed largely by the pointed connections. They herein absorb these forces because they can be loaded in lateral direction.

An optimum result is however still not obtained, since the transition between the layer of high density and the layer of low density cannot be mechanically loaded in optimal manner. There is after all a discontinuity here.

The problems associated herewith are obviated by the measure according to a first preferred embodiment of the invention, wherein the density of the layer of mineral wool progresses smoothly from a low density on the inner skin to a high density on the outer skin.

Discontinuities and the associated uneven loading are hereby avoided.

The forces perpendicularly to the plane of the wall are herein transmitted without discontinuity due to the uniform progression of the density. A good distribution over the surface of the wall herein takes place.

According to a first preferred embodiment the density on the inner side of the wall is practically constant over a considerable part of the total distance toward the outer side.

This results in optimization of the thermal insulation and in material-saving.

According to a further preferred embodiment the part with the practically constant density extends at least as far as the noses.

Thus is achieved that during construction the introduction and fixation of the insulation layer in the inner skin with the noses mounted thereon takes place more easily; the noses can after all engage in the mineral wool where it still has a low density.

Further achieved is that the whole space in the cassette is filled. The occurrence of channels extending in lengthwise direction, which can result in convection, is hereby prevented.

According to a yet another preferred embodiment the low density lies between 30 and 40 kg/m3. Experience has shown that combination with an insulating layer with a greater wall thickness results in an optimal thermal insulation.

Optimization on the other side, i. e. a sufficiently high density to obtain the mechanical strength necessary there while still making a contribution toward the thermal insulation, is obtained when the high density lies in the range between 55 and 85 kg/m3.

An optimization of this value is obtained when the high density lies in the range between 65 and 75 kg/m3.

According to a final preferred embodiment the specific fibre direction of the mineral wool extends transversely of the main plane of the wall.

A greater mechanical load-absorbing capacity is hereby obtained; with the above stated densities of the mineral wool this fibre direction results in a maximum strength and a high resistance to lateral loads, i. e. shearing in the directions of the plane of the wall construction.

The present invention will be elucidated hereinbelow with reference to the annexed drawings, in which: figure 1 shows a partly broken-away perspective view of a wall construction according to the present invention; and

figure 2 shows a graph of the density curve of the mineral wool by way of elucidating the present invention.

Shown in figure 1 is a wall construction designated as a whole with"1", which is fixed to vertically extending profiles 2. On vertical profiles 2 is mounted an inner skin 3 which is formed by cassettes extending in substantially horizontal direction. The cassettes are provided with a wall fixed against the profiles and with bent noses designated as a whole with "4". Arranged on the outside is an outer skin 6 which is formed by a metal plate. This is preferably corrugated.

Outer plate 6 is connected to the noses by means of screw connections 7.

Up to this point the construction corresponds with the construction described in EP-A-0 801 190.

A block of mineral wool 8 is arranged in the space between inner skin 3 and outer skin 6. According to the present invention the density of the block of mineral wool progresses in the direction transversely of the direction of the wall construction from a low value of about 35 kg/m3 on the inner side to a high value of about 65 kg/m3 on the outer side. This progression is smooth so as to avoid discontinuities, particularly in the path of forces. In addition, the density from the inner side as far as the length of noses 4 is substantially constant at the low value in this configuration.

It is hereby possible to place the plate of mineral wool easily behind the noses into the cassettes.

Figure 2 shows the density graphically. This shows that the density is practically constant over a total length of roughly 90 mm, this being the thickness of noses 4. The density then increases in a smooth curve to the recommended value of 65 kg/m3.

The advantages elucidated in the preamble are thus obtained.