This invention relates to a method of cladding a base surface, such as a roof or a building side wall, with sheet metal, comprising the steps of preforming sheet metal strips with upstanding flanges along both longitudinal edges, mounting the strips side by side on the base surface and joining them together by seaming the preformed longitudinal edges to form a double-fold standing seam. The invention is applicable not only to so-called strip cladding in the conventional sense using continuous strips, but also to so-called panel cladding, using "strips" formed by a number of sheet metal panels joined together by seaming. As used in this specification, the term strip is to be construed as embracing both types of strips.

The predominant technique for strip cladding comprises a preforming step consisting in folding up the longitu¬ dinal strip edges perpendicularly or almost perpendicu¬ larly to the plane of the strip so that the strip is formed with an upstanding flange along both longitudial edges. One of the flanges, the "high flange" is approxi¬ mately 1 cm higher than the other flange, the "low flange", the height of which is about 2.5 cm. The preformed strips are mounted side by side on the base surface with the high flange of one strip abutting the low flange of the con¬ tiguous strip, whereupon the portion of the high flange extending above the low flange is folded down over the low flange so that a so-called single-fold standing seam is formed. Then the upper portion of that seam is folded 180 about the lower edge of the previously folded down portion of the high flange so that a double-fold standing seam is formed.

Clips are used to anchor the strips to the base surface. Such strips are secured to the base surface by means of screws or nails and include an upstanding sheet metal tongue which is interleaved between the high flange and the low flange and ^' folded together with these flanges as the double-fold seam is formed.

To render the standing seams waterproof it is cgiaπtSS ^"

practice to apply a seam sealant before the high flange and the low flange are folded.

A problem with the prior art technique of strip cladding as discussed above is that it is difficult to ensure uniformity and tightness of the standing seams, especially if the base surface is uneven. This problem is often attributable to nonuniform width of the portion of the high flange which is folded down over the low flange.

The reason for the nonuniform width may be that the base surface is uneven in the vicinity of the seam or that the strips are not properly positioned when the high flange is turned down over the low flange.

The object of the invention is to improve the strip cladding method referred to initially by facilitating the forming of the standing seam and eliminating or at least substantially reducing the ris of the standing seam becoming nonuniform and thus leaky.

According to the invention this object is achieved in that the preforming of the strip comprises forming flanges of a shape different from that of the flanges previously used and in that the mounting of the strips on the base surface and the subsequent seaming of the flanges are effected in a special way which is specified in the characterizing part of the claim along with the shape of the flanges.

In addition to the achievement of the above object, the invention accomplishes a further advantage in that a rainproof cladding is obtained as soon as the strips are mounted on the base surface, i.e., before the flanges are seamed. Thus, the seaming need not be effected immediately after the strips have been mounted on the base surface but may be put off for a shorter or longer time.

Another advantage achieved through the invention is that the seaming may be affected in a manner that saves the sheet metal so that the protective coating, if any, of the sheet metal is not damaged.

The invention will be explained in greater detail hereinafter, reference being had to the accompanying drawing.

Fig. 1 is a diagrammatic perspective view of a sheet metal cladding of the type to which the invention relates;

Fig. 2 is a diagrammetical cross-sectional view of a sheet metal strip showing the shape of the strip after it has been subjected to the preforming step according to the invention;

Fig. 3 is -a cross-sectional view divided into four sub-figures I, II, III and IV and showing the mounting of the strips on the base surface and successive steps of the seaming of the strip flanges.

The sheet metal roof cladding of which Fig. 1 is a diagrammatic and fragmentary illustration is a strip cladding in the true sense, because it is made up of a member of continuous strips 10A, 1OB,IOC, 10D, 10E laid out side by side and joined together along contiguous longtudinal edges through standing seams 10AB, 10BC, 10CD, 10DE. Fig. 1 does not reveal the details of the standing seams but these are here assumed to be so-called double-fold standing seams. Fig. 2 illustrates the cross-sectional shape of the strips 10 as it appears after the preforming step but before the strips are joined together by seaming. Along one of its longitudinal edges the strip is provided with a flange 10F having a flat inner portion 10FA standing substantially perpendicularly to the web 10G of the strip and a likewise flat terminal portion 10FB which is sub¬ stantially parallell to the strip web 10G and extends in cantilever fashion from the upper end of the inner portion towards the other longitudinal strip edge. The height or width of the inner portion 10FA suitably is about 25 mm, and a suitable width of the terminal portion 10FB is 9-10 mm. Suitably, the radius of curvature at the juncture of the strip web and the inner portion of the flange and at the juncture of the inner portion and the terminal portion is a few millimetres.

Along its other longitudinal edge the strip is pro¬ vided with a flange 10H having a flat inner portion 10HA standing substantially perpendicularly to the strip web 10G, a likewise flat intermediate portion 10HB which ij

substantially parallell to the strip web and extends from the upper end of the inner portion in the same direction as the terminal portion 10FB of the flange 10F, and a flat terminal portion 10HC extending in cantilever fashion from the outer end of the intermediate portion 10HB and down¬ wardly towards the strip web 10G at an acute angle to the intermediate portion 10HB.

The width of the intermediate portion 10HB of the second flange 10H is a few millimetres larger than that of the terminal portion 10FB of the first flange 10F, e.g.

12-13 mm. The width of the terminal portion 10HC is a few millimetres smaller than the width of the intermediate portion, e.g. 9-10 mm. The angle is 20-30°. The height of the inner portion 10HA is equal to or slightly larger than the height of the inner portion 10FA. The radii of curvature at the junctures of the web 10G and the inner portion 10HA and of the inner portion 10HA and the inter¬ mediate portion 10HB suitably are a few millimetres. The radius of curvature at the juncture of the intermediate portion 10HB and the outer portion 10HC suitably is 1-2 mm.

The dimensions given above are only illustrative examples. It is important, however, that the flanges 10F and 10H are dimensioned such that the gap 10J between the intermediate portion 10HA of the flange 10H and the free end of the its terminal portion 10HC is a few millimetres narrower than the terminal portion 10FB of the flange 10F. Moreover, the terminal portion 10HC of the flange 10H should be slightly narrower than the intermediate portion 10HB.

The cross-sectional shape of the strip 10 may vary somewhat from that shown in Fig. 2 without departing from the scope of the invention. For example, the inner portions of the flanges may be inclined outwardly from the strip web by a few degrees, and, moreover, the terminal portion 10FB and the intermediate portion 10HB need not be accurately parallel to the strip web 10G. Besides, the strip web need not be absolutely smooth and straight as shown in Fig.2 but may be provided with profile forrj^adriuirfr-

Fig. 3 is a diagrammatic cross-sectional view showing a sheet metal cladding according to the invention at different successive stages following the preforming step, the earliest stage being shown to the left and the finished cladding being shown to the right.

Subfigure I of Fig. 3 thus shows the preformed strip 10A which at this stage is held to the base surface 11 by a clip 12 of the sliding type nailed to the base surface (the clip is disclosed in greater detail in Swedish Patent Specification No. 7802914-9 with publication No. 420,008). The original shape of the clip 12 is shown in phantom lines. The mounting of the strip 10A on the base surface 12 is accomplished by laying out the strip in the proper position, hooking the sliding member 12A of the clip 12 onto the free edge of the flange terminal portion 10FB and folding it down towards the base surface and then naling the anchoring member 12B of the clip to the base surface. The hooking of the sliding member 12A onto the flange and subsequent folding down of the same ensures that the strip is reliably anchored at an early stage and drawn into firm engagement with the base surface.

The strip is secured in the above-described manner at suitable intervals throughout the length of the strip. When the seaming of the flanges is subsequently effected, the clips are folded into the seams, although this is not shown in the drawings.

After the strip 10A has been secured by means of the clips, the next strip 10B is engaged by its flange 10H over the flange 10F of the strip 10A. This is shown in Subfigure II of Fig. 3. Then the flange 10F of the strip 10B is secured by means of clips in the above-described manner. (This is not shown in Subfigure I) .

The terminal portion 10HC of the flange 10H of the strip 10B then is folded up towards the underside of the terminal portion 10FB of the flange 10F of the strip 10A as is shown in Subfigure III of Fig. 3. This folding suitably is accomplished by means of a power-driven so-called roof seamer.

Finally, the flange portions 10HB, 10FB and 10HC thus

folded together are jointly folded down towards the inner portion 10FA of the strip 10A so that the double-fold standing seam 10AB shown in Subfigure IV of Fig.3 is obtained. Suitably, this step is also carried out by means of a roof sea er. Although for clarity of illustration

Subfigure III shows a gap between the flange portions 10FA and 10HC, it will be understood that these flange portions are actually brought into engagement with each other.

In connection with the preforming of the strip 10 it is advisable to apply a semi-solid sealant to the inner side of the flange 10H as shown at P in Fig. 2. During the seaming operation the sealant is squeezed out between adjacent flange portions to waterproof the finished standing seams. Moreover, it is advisable immediately after adjacent strips have been hooked together to fold up the flange portion 10HC locally to the position shown in Subfigure III of Fig. 3 at suitable intervals in order to lock the strips ^' together more securely until the seaming of the flanges by power-driven means can be carried out.

As is evident from the foregoing, the terminal portion 10HC of the flange 10H is an important part of the preforme strip. By virtue of the acute angleα it includes with the intermediate portion 10HB, the terminal portion 10HC ensures a proper folding up of the entire terminal portion towards the terminal portion 10FB as shown in Subfigure III of Fig. 3. Moreover, it ensures a positive locking together of contiguous strips prior to the actual seaming operation. From Subfigure III of Fig. 3 it is also apparent that the final folding to the position shown in Subfigure IV can be effected reliably and uniformly thanks to the fold-locating bend at the juncture of the inner portion 10FA or 10HA and the respective adjacent flange portion, that is, the terminal portion 10FB or the intermediate portion 10HB.

Subfigure II also shows that the sheet metal cladding is made rainproof already in connection with the laying out of the strips. The entire base surface may thus very

rapidly be provided with a rainproof cladding; the steps shown in Subfigures III and IV need not be carried out until the entire base surface has been covered.