As is known these panels have a composite structure, also called"sandwich"structure, wherein at least one insulating layer is arranged between two faces, one of which is at sight when the panel is in the installed position on a building, while the other remains on the inner side of the roof.

The insulating material is generally foamed polyurethane or similar (but it might also be rock wool or other insulating substance), while the external faces in most cases are steel sheets (coated, galvanized or treated in some other way), copper or aluminium sheets and the like.

The latter are profiled so that the sheet intended to form the face at sight of the roof, has a desired external appearance while the inner sheet, usually thinner, serves as a base resting on the understructure of the roof.

For this purpose, the face at sight may be shaped with a profile which is undulated, corrugated or reproduces the components (for example the bent tiles) of a roof, while the inner face is mainly flat and reinforced by light ribbing.

Fixing of these panels is currently carried out, using special self-threading or self-boring screws, which penetrate from above and pass through the whole thickness of the panels until they engage in the underlying beams of the structure supporting the roof;

examples of insulating panels which are fixed using this system can be seen in European patent application No. 967,343 and in international patent application No.

WO 96/35028.

Fixing performed in this way has essentially two drawbacks.

The first one is that the screw hole forms a point where water, dust, mould, etc. may infiltrate, since the screw is applied into the panel from above, namely on its side which is exposed to atmospheric agents.

The second drawback is that the heads of the screws are visible from the outside when laying of the roof has been completed; this situation may in certain cases be unacceptable from an aesthetic point of view, for example in the case of panels which reproduce the appearance of the bent tiles of roofs.

In order to overcome these drawbacks it is known to use sealing washers or caps for the screws or to arrange them in joining zones of the panels, ensuring that they are"hidden"by mating edges of the panels which for this reason are suitably configured.

It is obvious that the first solution does not solve the aesthetic problem associated with the visibility of the screws, while the second solution is applicable only along the joining edges of the panels so that if the latter have to be fixed also in intermediate points, screws must again be applied thereby resulting in the same problems before.

The present invention aims to remedy this state of the art, namely it has the object of providing a panel for roofs of buildings and structures in general, having structural and functional features as to allow

installation thereof without the drawbacks mentioned above.

This object is achieved by a panel whose features are stated in the claims accompanying the present description, which will emerge fully from the non- limiting example provided hereinbelow and illustrated in the accompanying drawings wherein: Fig. 1 shows a perspective view of a panel according to the invention; - Fig. 2 shows a cross-sectional view of a detail of the fixing system for the panel of Fig. 1; - Fig. 3 is an enlarged view of a detail of Fig.

2; - Figs. 4 and 5 show a cross-section, similar to that of Fig. 2, of respective constructional variants of the panel according to the invention.

With reference to the first of these figures, therein a panel denoted in its entirety by 1, is shown, comprising an external or upper face 2 formed by a profiled and pressed metal sheet having a surface finish reproducing the appearance of the bent tiles on a roof.

This metal sheet may be made of copper, steel or other metal, likewise the opposed sheet which forms the inner or bottom face 3 of the panel, whose thickness is less than that of the first face; the bottom face 3 is essentially flat even though reinforced by a series of micro-ribs 4 with a flat profile.

An insulating layer 5 formed by expanded polyurethane is present between the faces 2 and 3 of the panel; the edges of said layer and of the top and bottom faces are configured so as to allow longitudinal

connection of the panels for fixing thereof, as will be explained below.

Figures 2 and 3 show the joined edges of two panels 1 and 1'which are fixed to a beam 7 of the roof understructure by means of screws 8, 8' ; the panels 1, 1'are identical and therefore the components of the second panel will have the same numbering as those of the first one, with the addition of a prime.

The screws 8, 8'are of the type commonly used for these applications (i. e. self-threading or self- boring), but have a smaller length than the known type since they do not have to pass through the thickness of the panels as occurs in the prior art; moreover, if they are of the self-boring type, they do not require preliminary boring of the panels or the beams because with the thicknesses which are usually employed, they are able to penetrate them.

The bottom face 3 of the panel. has a projecting longitudinal edge 9 obtained by folding the sheet metal from which it is made, while the other edge of this face terminates in one of the ribs 4; in this way the projecting edge 9 of one panel may be inserted underneath the rib of an adjacent panel, for installation thereof.

Similarly, in the roof the insulating panels 5 and 5'of two adjacent panels abut with each other longitudinally, while the end edge of the upper face 2 of a panel is superimposed on the face 2'of the adjacent panel.

For their fixing to the beam 7, the panels are provided internally with reinforcing elements 10; in the example shown in Figs. 2 and 3, these elements are

formed by metal strips with a thickness not less than that of the pressed sheet which forms the upper face 2 of the panel.

The elements 10 are positioned on the ribbing 4 along the edge of the panels and are engaged by fixing screws 8; in this way the latter penetrate into an underlayer of suitable thickness providing the connection between the panels and the beam 7.

Indeed the inner face 3 of the panels is too thin for having a suitable strength to stand the action of the screws.

The reinforcing elements 10, which obviously can also be arranged in other zones of the panel and not only along the longitudinal edges thereof, may be metal sections like those shown in Figures 4 and 5, where for the sake of simplicity the same numbering of the previous example has been retained.

These sections have a flat portion so that they can be applied on the ribs 4 of the bottom face 3 of the panel, inside which the screws 8 engage; compared to reinforcing elements formed by simple strips, the sections have the advantage of ensuring a better grip within the foam.

In this connection it is necessary to point out that in accordance with a preferred embodiment of the invention, the reinforcing elements are kept in position only by the pressure exerted on them by the expanded polyurethane.

However there would be no bar to prevent fixing the elements, be they in the form of strips or profiled sections, using an adhesive or by means of (spot or continuous) welding.

From what has been explained hitherto it is possible to understand how the panel 1 considered in the foregoing achieves the object put forward initially for the invention.

Indeed, since the panel is fixed using screws applied from below which do not pass beyond the insulating layer 5, outside of the panel there are no holes which can give rise to infiltrations, as occurs in the prior art; as a logical consequence thereof, it is also obvious that the panel 2 does not have an unaesthetic appearance due to the visible nature of the screws on its outer face.

It is also important to point out that in the case of panels where the external metal sheet has transverse impressions (such as for example that which reproduces the profile of bent tiles shown in Fig. 1), there is a further advantage with respect to the prior art: the possibility of positioning the screws in the longitudinal direction of the panel, independently of the position of the transverse impression on the external metal sheet and hence with an interaxial space between the support points which is free.

These important results are obtained without having to modify the original structure of the panel since it is sufficient to provide for its manufacturing, the metal profiled sections or strips 10 as additional components.

In other words the present invention has the advantage that it may be easily applied to pre-existing panels, so that from the manufacturing point of view it is not necessary to make any modification to moulds, rolls and other apparatus, it being only necessary to

provide means for mounting the metal sections or strips 10.

This mounting operation may moreover be performed both manually or in an automated manner, before casting the polyurethane; it should nevertheless be pointed out that the invention can be used advantageously also with panels wherein the insulating layer is formed by rock wool or glass.

These and other equivalent variants fall within the scope of the following claims.