Such a sub-structure for a roof is known from European application no. EP- 0685612-A1, where the support structure is typically formed by an old roof under repair or renovation, e. g. a trapezoidal sheet roof structure or a wooden structure with for example wooden barriers. On top of the support structure there is provided a thin barrier layer against moisture and air, typically formed by a foil or the like, and on this thin barrier layer there is provided a relatively thick layer of tread-proof fibre heat insulating layer. In order to allow the subsequent mounting of retaining elements for holding building sheets forming the new outside of the roof or the facade, load bearing elongate spacer sections are provided on top of the insulating layer for mounting such retaining elements. According to EP-0685612-A1 these load bearing elongated spacer sections are formed by longitudinal U-shaped profiles of metal, the web of which forms the securing base or mounting base for the retaining elements and further having two arms extending substantially perpendicular to the web into the heat insulating layer. To achieve a reliable and durable positioning of the elongate spacer sections with respect to the support structure, the elongate spacer sections are secured by means of spaced-apart long connecting elements, e. g. thread screws made of stainless steel, which pass through the web of the elongate spacer sections, through the tread-proof heat-insulating layer and into the support structure. Prior to mounting the retaining elements onto the elongate spacers sections, the elongate spacer sections need to be carefully located with respect to the support structure, and furthermore the elongate spacer sections need to be sunk into the tread-proof thermal insulating layer. For the latter purpose by using a special device, tracks for the two arms of the U-shaped elongate spacer sections are being milled into the tread-proof heat-insulating layer.

Thereafter the U-shaped spacer sections are located into these milled tracks and connected to the support structure by means of long threaded screws.

A disadvantage of this sub-structure is that it requires the cutting or milling of the

tracks for the U-shaped elongate spacer sections, which cutting or milling requires in turn dedicated equipment and skilled labour force. A further disadvantage is the difficulty of the cutting or milling of the tracks in the event of roof structure having a steep inclination or on a facade structure. Yet another disadvantage is the limited thermal insulation of the known sub-structure.

It is an object of the invention to provide a sub-structure for a roof or a facade for a building and which sub-structure is easier to construct.

It is another object of the invention to provide a sub-structure having an improved thermal insulation while being easier to construct.

According to one aspect of the invention, there is provided a sub-structure for mounting on a support structure, whereby the sub-structure and support structure together form part of a roof or a facade structure of a building, the sub-structure comprising a heat insulating arranged on the support structure, and further elongate spacer sections on the heat insulating layer and whereby the elongate spacer sections are for connecting to the support structure usually by means of spaced connection elements, such as screws, securing the spacer sections to the support structure and in addition for holding or mounting retaining elements or mounting brackets for engagement with the building sheets, usually the free ends of the building sheets are flanged over the head part of the retaining element. The sub-structure is characterised in that the elongate spacer sections are formed by a profile having, as seen in cross- section perpendicular to its direction of elongation, a channel-shaped recess to receive the retaining elements, formed by upstanding flanges which overhang the base surface of the recess to provide parallel opposed lateral grooves, and wherein on top of the heat insulating layer and between the space formed by the building sheets and the retaining elements there is arranged a further layer of heat insulating material of lower stiffness, usually obtained by a lower density, than said first heat insulating layer.

This achieves the effect that the elongate spacer elements formed by the rigid sheets or strips can be positioned in a very easy manner just by placing the rigid sheet or strip on top of the underlying heat insulating layer. There is no need for anchoring points or anchoring lines. The elongate spacer elements can be connected to the support structure using long connection elements, such as screws. Consequently, the sub-structure enables much flexibility during the construction of the sub-structure and is much easier to construct as compared to the prior art. For example, the need for a special device for milling tracks into the underlying heat insulating layer has been

overcome. Another advantage is that it allows installing a well-know roof construction, such as the Kalzip (trade mark) construction, on a rigid thermal insulation layer.

The use of two heat insulation layers of different densities in the present arrangement achieves the effect of a cheaper roof or facade structure, while simultaneously achieving significantly improved thermal insulation efficiency. Tread- proof thermal insulating material, usually formed by a high-density mineral wool, are relatively expensive and have a lower thermal isolation capacity compared to more conventional heat insulating material of lesser density. It is now possible to keep the first underlying layer of tread-proof material relatively thin and thereby keeping costs relatively low, while the second layer can be made thicker than the first layer, thereby further improving the thermal isolation capacity of the whole sub-structure. The material selected for the second insulating layer is much more flexible and more easy to handle than the more rigid first underlying heat insulating layer material. The application of such a second thermal insulation layer achieves the effect that the elongate spacer sections themselves are isolated thermally also and thereby act much lesser as a undesirable thermal bridge compared to spacer sections according to the prior art sub-structure laying directly underneath the outer metal building sheets.

In an embodiment of the sub-structure according to the invention the retaining elements are slidable mounted in the grooves of the elongate spacer sections.

In an embodiment of the sub-structure according to the invention the retaining elements are rotatable mounted in the grooves of the elongate spacer sections. The retaining elements can be positioned at the latest moment during construction and the positioning of the elongate spacer elements with respect to the overlying support structure, the elongate spacer element and the building sheets is less stringent, because the relative movement of the retaining elements provides the required flexibility. It allows that the roof sheeting to adjust themselves in and on the retaining element. The flexibility of the retaining elements result also in less noise, which noise usually results from or is due to friction between sliding metal contacts in case both the building sheet and the retaining element are made of a metal.

According to the invention in another aspect, there is provided an assembly of at least such a sub-structure mounted on at least one support structure, thereby forming part of a roof or a facade structure of a building.

The invention will now be illustrated by discussing the prior art and several non- limitative embodiments, with reference to the accompanying drawings, in which:-

Fig. 1 shows a schematic perspective view of a sub-structure according to the prior art; Fig. 2 shows a schematic view of a sub-structure in accordance with the invention; Fig. 3 shows a schematic perspective view of the elongate spacer section used in the sub-structure according to the invention in combination with a retaining element; Fig. 4 shows a schematic perspective view of the retaining element used in the sub-structure according to the invention; Fig. 5 shows a schematic perspective view of the sub-structure according to the invention.

Fig. 1 shows schematically a sub-structure according to the prior art as known from European patent application EP-0685612-A1, comprising a support structure 1 formed by a trapezoidal sheet roof structure or the like, such as a timber structure, a thin moisture and air barrier layer 8, a relatively thick layer 2 of tread-proof high- density mineral wool for heat insulating purposes, and two load bearing elongate spacer sections 3,4 which are formed by U-shaped elongate metal profiles with a web having a width of about 60 mm. The two arms of the U-shaped profiles extend substantially perpendicular to the web into the heat-insulating layer 2 and fixate the U- shaped profiles 3,4 with respect to the insulating layer. The U-shaped profiles 3,4 are secured to the support structure 1 by means of long countersunk thread screws located at spaced intervals along the centreline of the web of the U-shape. On top of the web of the U-profiles there may be mounted retaining elements for engagement with building sheets forming e. g. a standing-seam roof structure or alternatively a trapezoidal sheet roof 9 may be connected to the spacer sections.

Fig. 2 shows a schematic cross-sectional view of the sub-structure in accordance with the invention and which has been arranged on a support structure 1 formed by an existing trapezoidal sheet roof structure. On top of a spacer section 3 formed by a rigid sheet (shown in more detail in Fig. 3) there are provided mounting brackets or retaining elements 5 for holding building sheets 9. The rigid sheet 3 is arranged on top of an underlying heat insulating layer 2, typically a tread-proof high- density mineral wool material, which in turn is arranged on top of a thin barrier layer 8, the rigid sheet being connected to the support structure using connection elements such as long screws. On top of the first underlying insulating layer 2 and between the space formed by the building sheets 9 and the retaining elements 5 mounted on the rigid sheet 3 there is provided a second layer 11 of heat insulating material having a

lower density then the first insulating layer 2, and thereby providing an improved heat insulating efficiency of the whole sub-structure. Further advantages have been set out above.

Fig. 3 shows a perspective view of an elongate spacer element 3 engaging a retaining element 5. The spacer element 3 is in a preferred embodiment made of an extruded metal profile, such as an aluminium alloy or magnesium extruded profile.

Alternatively the spacer element can be made of a plastic material or a reinforced plastic material. Suitable plastic materials are, but not limited to, nylon or thermoplastic material such as PVC, PA, PE, PUR, PP, PDFE or cellulose polymers. Suitable reinforcement could be of, but not limited to, metal, e. g. aluminium or steel, another plastic, glass fibres, ceramic fibres and the like to provide amongst others further mechanical stability. As seen in cross-section perpendicular to its direction of elongation, there is a base surface 6 and a channel-shaped recess to receive the retaining element 5. The channel-shaped recess is formed by upstanding flanges 7 which overhang the base surface of the recess to provide parallel opposed lateral slots or grooves, which receive the corresponding lateral portions of the foot-section of the elongate retaining element. The upstanding flanges could also have an essentially T- shape, such as shown in Fig. 3B. The shape of the elongate spacer element provides sufficient bending and torsion stiffness or can be designed to do so. The elongate spacer element 3 is connected to the support structure using elongate connection elements, such as screws. The connection elements are preferably located through holes in the base surface arranged outside the channel-shaped recess. This achieves the advantage that there is no need to use countersunk screws, resulting in cheaper and easier construction. The location of the connection elements outside the channel- shaped recess allows a much greater flexibility for the location of the elongate retaining elements, since it is usually not advisable the locate a retaining element directly above the head part of a screw. Preferably the connection elements are at leaped positions with respect to each other along the direction of elongation of the elongate spacer element. In this way the resistance against torsion of the spacer element is being further improved. The elongate retaining element 5 can be provided with a square and rectangular foot-section. During construction of the sub-structure according to the invention such foot-section is slide at the beginning of the elongate spacer element 3 under the overhanging flanges 7 and the retaining element 5 is broad to its desired location. Optionally, at the desired location it can be connected to the elongate spacer element 3 using for example connection elements such as screws

or rivets. In another embodiment the foot-section of the elongate retaining element 5 is provided with a shape where the edge sections have been rounded-off or have semicircular ends or have an elliptical periphery. Such retaining element 5 can the inserted into the lateral grooves of the elongate spacer elements at or close to their final position. There they can be rotated into their desired direction or orientation. This allows for a large flexibility of positioning of the direction of the retaining element 5 with respect to the direction of elongation of the spacer element 3 joined to a support structure 1. At the desired location is can be connected to the elongate spacer element 3 using for example connection elements such as screws or rivets.

Fig. 4 shows a schematic perspective view of the elongate retaining element 5 used in an embodiment of the sub-structure according to the invention. The retaining element 5 is provided with a head-part 12, a foot-section 10 and a connecting flange or web 13. The retaining element can be made of a metal, in particular of an extruded aluminium alloy, or of a plastic material reinforced with a core of a different material, for example with a metal core as known from EP-A-1236840 (incorporated herein by reference), or of a fully plastic material. Suitable plastic materials are, but not limited to, nylon or thermoplastic material such as PVC, PA, PE, PUR, PP, PDFE or cellulose polymers. In this particular embodiment the foot-section is provided with two straight opposite sides essentially parallel to the elongation direction of the head-part and semicircular ends as to allow inserting into the channel-shaped recess and rotation to the desired orientation.

Fig. 5 shows a perspective view of the sub-structure according to the invention as shown in Fig. 3 above and which has been arranged on a support structure 1 formed by an existing trapezoidal sheet roof structure, and which could also have a different structure. On top of the elongate spacer section 3 formed by a rigid sheet (shown in more detail in Fig. 3 and 3B) there is provided a rotatable retaining element 5 for holding building sheets 9 allowing for improved ease of construction. The rigid sheet 3 is arranged on top of an underlying heat insulating layer 2, typically a tread- proof high-density mineral wool material, which in turn is arranged on top of a thin barrier layer 8. The elongate spacer section 3 being connected to the support structure using connection elements such as long screws, preferably in a leaped arrangement. On top of the first underlying insulating layer 2 and between the building sheets 9 and the retaining elements 5 mounted on the elongate spacer section 3 there is provided a second layer 11 of heat insulating material having a lower stiffness obtained by a lower density then the first insulating layer 2, and thereby providing an

improved heat insulating efficiency of the whole sub-structure. Further advantages of the rotatable arrangement of the retaining element 5 have been set out above.

Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made without departing from the scope of the invention as hereon described.