As-is known, the use of sheet metal for the above-mentioned applications is quite widespread since it allows to make low cost roofs that can be fitted relatively easily and quickly ; furthermore, since they are also light, the sheet metal roofings do not require particularly strong support structures so that the constructions where they are used, are also simple and economical to build.

However the sheet metal, even if it is suitably ribbed, does not have per se good insulating properties and therefore the range of applications of the roofings produced with sheet metal alone, is limited to cases in which there are no particular requirements in terms of temperature and/or energy saving to be complied with.

When this is not the case, use is made of a layer of insulating material (such as mineral wool) fitted underneath the ribbed sheet metal which forms the roofing, or composite panel, also known as sandwich panels are used, which have an insulating core of polymer foam (polyurethane, phenolic or the like) interposed between two outer sheet metal faces.

However, neither of these alternatives is advantageous as the elements of profiled sheet metal alone, from the point of view of the costs of the roofing components or of their weight.

The present invention aims at overcoming this situation.

That is to say, it aims at providing a prefabricated insulating element of sheet metal for roofs and coverings in general, which has improved thermal insulation properties compared to known elements of ribbed sheet metal alone, and which is at the same time light, economical and simpler to install than insulations of mineral wool or composite panels.

This object is achieved by a prefabricated element for coverings, which comprises a profiled metal sheet with longitudinal ribs that give it a degree of load-bearing capacity, the element being characterised in that it has a thin foil applied to the metal sheet itself so that the ribs thereof are closed, thereby defining channels wherein air can flow.

A roofing element of this type achieves three important results.

The first one is that when the element is mounted in an inclined position to form the inclined surfaces of a roof, or of a canopy or any other covering in general, air can circulate in the above-mentioned channels according to an ascending direction by effect of convection: the heat absorbed by the sheet metal because of solar radiation, is therefore partially taken away by convection with the circulating of air.

It just matters to point out that through-openings for the air flowing to and from the outside, are provided in the roofing (for example, in the region of the eaves and/or the ridge).

The second result is that the foil applied to the profiled metal sheet is also a barrier to the transmission of radiant heat into the surrounding atmosphere when the metal sheet reaches elevated temperatures, as can occur at given times of the year or in zones having hot climates.

This effect can be further enhanced by using appropriate materials for the foil or by coating it with paints or varnishes which reflect infrared rays; to this end the foil is preferably made from aluminium or another light metal, optionally surface- plated, but it is also possible to use plastics or non-metallic films treated with the above-mentioned paints or varnishes (for example, based on aluminised compounds, or the like).

According to a preferred embodiment of the invention, the surface of the foil not facing the profiled metal sheet, is also painted, varnished, veneered or coated, with a protective film of plastics material, silicone and the like.

The third result is that, if the foil is made of a plastics film, the roofing element has improved sound-insulating performance in relation to impact noises (rain and hail), than a non-coated ribbed sheet metal.

All of these features and further ones, as well, are set out in the claims appended to this description; they will be better appreciated from the explanation given below in connection with a preferred and non-limiting embodiment of the invention, illustrated in the appended drawings, wherein: Figure 1 shows schematically a covering with a prefabricated element according to the invention; Figure 2 is a cross-section of the element in Figure 1.

In the drawings reference numeral 1 generally designates an element for coverings according to this invention, made from a profiled metal sheet 2 under which a thin foi 3 is applied.

The foil 3 is fixed to the metal sheet 2 at the horizontal zones 5 thereof; the fixing is preferably achieved by adhesive bonding, since it is easy to do in a continuous production line for manufacturing the elements 1 and is effective for the various materials with which the foil 3 can be produced and assembled (at most, it is a matter of selecting the most appropriate adhesive).

However it is possible to provide fixing systems alternative to adhesives by making use, if necessary, of the properties of the materials connected; for example, if the foil 3 is of metal, such as aluminium or the like, it is possible to carry out the fixing by welding (spot-welding or continuous-seam welding).

It should further be noted that if the foil 3 is made of plastics film, it is also possible to carry out the fixing by heat-sealing the film to the metal sheet.

The element 1 thus produced is used with other elements identical thereto to form a roof, by installing it in an inclined condition with the channels 6 of the various elements 1, defined by the trapezoidal ribs of the sheet metal 2 and by the foil 3, aligned longitudinally; naturally, the channels 6 are inclined according to the slope of the covering, as schematically shown in Figure 1 with reference to the sloping faces of a roof (one of which is outlined in broken line), each of which is formed by a single element 1.

This allows the circulation of air inside the channels by means convective effect, as already explained before.

It will be appreciated that the prefabricated element 1 fulfils the initial object set out for the invention and indicated above.

Indeed it is evident that the circulation of air in the channels 6 of the profiled metal sheet 2, obtained by applying the foil 3 thereto, allows a heat-exchange by convection which cools down the sheet metal; furthermore, the radiant heat emitted by the sheet metal is screened by the foil 3 which, to this end, can be of a material suitably reflective in the range of infrared rays, or which is coated with paints or varnishes having such properties.

With regard to the material of the foil, reference has already been made to the use of metals such as aluminium, or plastics films (based on polyolefins, such as high- density or low-density polyethylene HDPE or LDPE, polypropylene and other polymers of different types), whilst the paints, the varnishes or the reflective coatings can contain metallic compounds or the like.

Moreover, it should be pointed out that the surface of the foil 3 not facing the metal sheet 2, can be subjected to finishing in order to protect it against external agents, to colour it or to make it more suitable to the uses for which the element is intended.

For this purpose that surface of the foil 3, whether produced from metal or plastics material, can be painted, varnished, veneered or coated in the most appropriate manner and with the most appropriate materials.

The element for roofings according to the invention is suitable for being produced industrially in a continuous manner with plants wherein, downstream to the normal profiling machines used to form the ribs on the sheet metal, there is also provided a station for applying the foil.

The latter can be unrolled from a coil and adhesively bonded to the metal strip which advances through the plant downstream of the profiling machine, by applying adhesive thereto (by spraying, with a roller or in another manner).

It will be appreciated that it is possible in this manner to produce an element for roofings at low cost, less than that of composite insulation panels or than it is necessary for providing mineral wool under the metal sheets of existing roofings.

The element so produced is also light since in practice its weight is increased, with reference to that of the ribbed metal sheet alone, by the weight of the foil 3; however the foil 3 is barely relevant, given that the thickness thereof is less than that of the ribbed metal sheet and is preferably a few tenths of millimetre.

Furthermore, the materials forming it such as aluminium or plastics films, are light materials.

Naturally, variants of the invention are possible relative to the above-mentioned embodiment.

Firstly, it is evident that the profile of the ribs of the metal sheet 2 can be different from the trapezoidal profile; the latter profile has the advantage of having flat zones, at which it is readily possible to fix the foil 3 on the metal sheet 2 but, as mentioned above, the same effect can also be achieved with the typical ondulated profile of the metal sheets, or with other profiles.

Furthermore, the dimensions of the channels 6 formed by the ribs and the distance between each of them can be greater than that shown in the drawings; in other words, depending on the convection heat exchange which is required to obtain, the number of channels 6 (and therefore of ribs) per unit of surface area of the metal sheet 2, and the dimensions thereof, can vary from one case to another.

Therefore, there will be cases in which the metal sheet has ribs which are less closely arranged, others in which they are more numerous and/or smaller, and so on.

Finally, it should not be excluded that the metal sheet be replaced by non-metallic material.

All of these variants fall within the scope of the appended claims.