Bratex modular roof tiles part 2
Correct construction
A roof covered with modular metal tiles consists of even several hundred sheets. Assuming that the covering area of one sheet is 0,8 sq m, it can be easily calculated that a medium-sized roof of 250 sq m consists of 250 sheets that are screwed to the substructure and interconnected. In the case of using a conventional roofing sheet, i.e. the one cut to length, the number of sheets is several times smaller. That is why many investors decide to buy conventional metal roof tiles. Unfortunately, the list of advantages of conventional metal roof tiles ends only with a smaller number of sheets.
With such a large number of sheets and joints, doubts arise about the quality of the joints and whether the sheets will be installed straight. The issue of durability related to the outflow of rainwater with impurities and the ventilation of the transverse overlaps of modular metal roof tiles was explained in previous article. In the aspect of joining sheets, their correct design is equally important, which takes into account the joining of many sheets.
Despite the fact that the thickness of a metal roof tile sheet is only 0,5-0,6 mm, the fact remains that the joints where 3-4 sheets meet become crucial for the geometry of the entire roof. In the places where several sheets meet, we are talking about distances (shifts) of 1,5-2,5mm (3-4 sheets), which are repeated every column and every sheet joining. The shifts affect how the next sheets will be arranged, i.e. whether the construction of the next sheet superimposed on the existing sheets takes into account that it will be moved by a certain distance, which will then be duplicated further and accumulated.
In order to make it easier to understand the problem of connecting many sheets, we present a photo of a connection of four sheets of metal roof tiles called "modular", which has nothing to do with the system modular roofing sheet.
The problem presented in the photo is a consequence of poor production quality and the lack of appropriate construction solutions for a modular product. We discussed the problem of the suction gap in the previous article. The Anti-Cap solution was used in the Bratex modular metal roof tiles. The fitting of the metal roof tile, i.e. the application of the sheets so that they fit perfectly and do not fall down in relation to the reference line (eaves line), is the result of a high-quality production process and technical solutions.
All Bratex system metal roof tiles are manufactured on the highest quality machines of the Finnish company Samesor, which can be seen in the films presenting the company's facilities on our channel YouTube.
However, the basic issue for which the laying of metal roof tiles ends with a great effect is their construction. Ordinary conventional metal roofing tiles or metal roofing tiles called "modular" do not have special solutions that compensate for the thickness of the sheets placed on top of each other.
Each successively applied sheet falls by the thickness of the sheet plus the elasticity resulting from the fitting, we assume that it is about 0,8mm. Thus, on twelve sheets, the slope on the eaves is already one centimeter, which as a result, after applying the next top sheets, would look like sheathing laid on the roof at an angle. The presented problem of the lack of compensation, i.e. the lack of taking into account the distance of the material thickness in the construction of a sheet of metal roof tiles, is cleverly swept under the carpet by roofers. In order to save the situation on the roof and avoid the problem of the sheets falling on the eaves, roofers make a deliberate maneuver of mowing the first sheet relative to the eaves line so that the subsequent sheets form a line parallel to the eaves.
Unfortunately, just leveling the jump of the sheets relative to the eaves line does not solve the most important problem related to the imposition of subsequent, higher rows of sheets.
The sheets in the upper rows will be arranged unevenly in relation to the lower row of sheets, according to the principle - what kind of substrate, in this case what "hook", such a layout. This is how the arrangement of four sheets of metal roof tiles looks like without solving the problem of overlapping the thickness of the sheets.
Recommendations are made to mitigate the problem of joining four sheets, which are based on the instruction to start covering the second row from half a sheet. In this way, three sheets, not four, meet each other at common joints (at the corners of the sheets).
Unfortunately, such a recommendation does not lead to solving the problem, it requires additional cutting of the sheets, which are anyway placed on the sheets of the lower row already mowed in relation to the eaves line.
Compensation pocket - what is it?
All Bratex modular metal roof tiles have a unique design feature, the so-called a two-segment compensation pocket, which fully solves the presented problem with the parallel arrangement of sheets and the compensation of accumulating sheet thicknesses.
The compensation pocket consists of two segments:
- back-stamping of the covered wave;
- congestion on the surface of the covered wave.
Back pressing of the covered wave (the one located underneath, on the left side of the sheet) is a shift in the process of pressing this wave backwards by the distance necessary to accommodate the excess thickness of the covered sheets. This is not visible to the naked eye, but can be checked with measuring instruments. Depending on the model of the metal roof tile, the back embossing is of different depth, and even in some models, for technical reasons, it covers the entire segment of the metal roof tile.
The crowding with the depth of the sheet thickness occurs on top of the capped corrugation and forms a kind of pocket for the tongue of the bottom sheet. Thanks to this, after applying the top sheet, it does not stick out because the tongue of the bottom sheet "sits down" in the crowded recess.
The graphic below schematically shows the layout of the system sheets Bratex modular metal roof tiles.
It is worth noting that the Bratex modular metal roof tiles cover the so-called column coverage. This way of arranging the sheets, apart from adapting the function of the compensation pocket to the assumptions, brings additional benefits for the contractor and the investor. It is not required to set the scaffolding across the entire width of the eaves, and additionally, laying the sheets in columns does not require stepping on the sheet surface - just fit the sheets, tilt the screwdriver and apply the screw.
When discussing in this article the aspect of the correct construction of a metal roof tile, one should also pay attention to the issue of the so-called symmetry. There are phrases that "a metal roof tile is symmetrical, so its left and right waves can be on top". This feature supposedly makes the sheet flexible and can be covered with it.
Unfortunately, this is a bunch of false information misleading investors. Such a thing as a "symmetrical metal roofing tile" in covering does not exist in the area of design. There are two reasons why this is not possible:
- the radii of the top wave must be different from the bottom wave;
- the sheet in the coil always has a variable width.
From the basics of geometry, it becomes impossible to superimpose a circle on a circle of the same diameter. The outer circle, in this case, is the wave of the top sheet, which must be of a larger diameter than the wave of the bottom sheet.
Forming elements for machines producing metal roof tiles are designed in such a way as to profile the sheet with specific radii. It is assumed that the outer arc radius of the top sheet must be increased by the sheet thickness in relation to the outer radius of the lower sheet arc. For example, for a wave radius of the bottom sheet of 26 mm, the wave radius of the top sheet is 26,5 mm. Such profiling allows the sheets to fit perfectly, horizontally and vertically (on the ribs). If there is a change in the overlap, i.e. the alleged "symmetrical overlap", the result of shifting the top (green) sheet under the bottom sheet (gray) will be a lack of fitting, a gap will be created and the tightness will be compromised.
There remains one problem related to the size of the input material, whose nominal width is 1250 mm. In accordance with the applicable standards, coils for the production of roofing sheets are manufactured in steelworks with width tolerances and in fact the width of the coil is even 1255mm. This excess width of the plate is useless, so it is always hidden underneath. Thus, the capped edge of the sheet is variable in width. This argument contradicts the use of "symmetrical opacity". It would be incorrect when at some point, e.g. in the middle of the slope, sheets from a new pallet, which was made of a coil of a different width, are used. The result will be a complete lack of proper sheet fitting and aesthetics.
To sum up, the sheet of the modular metal roofing tile has two longitudinal sides, covered and covered, which do not have a double function.
Read the article Bratex modular roof tiles part 1