Trapezoidal sheet metal roof - the substructure is decisive for the service life

Both the sheet length and the sheet thickness are important for a trapezoidal roof. But at least as important is the substructure of the trapezoidal sheet metal roof for a long service life. Here we show what to look for in the substructure.

Design Distances

Each type of trapezoidal sheet has precise specifications for the different sheet thicknesses as to how far apart the beams or walls on which the sheet rests. These must also be apparent from the installation plans, which must be on the construction site.

In addition, the trapezoidal sheet should not project too far beyond the last beam at the front and at the lower end. Again, one must check which supernatants are still acceptable. Concern should be the attachment of the eaves at the bottom, for which there is still room.


The type of screws and supports must also match the selected trapezoidal sheet metal. The particular profile could sag or deform if, for example, the wrong semi-trailer is selected.

These semi-trailers are usually made of solid plastic. They are available in the building materials trade exactly matching the profile of the sheet metal.

Beams and rafters

In addition to the distances in which beams must be attached, the strength of the respective semi-trailers is crucial and depends in part on the thickness of the sheet. The thicker the sheet metal, the heavier it is, of course.

Important points for the substructure

  • Clearances of the beams
  • Connecting material
  • Thickness of the construction elements
  • Overhangs
Tips & TricksWhen laying the trapezoidal sheet metal panels on a wooden structure, you should place a strip of roofing felt on the beams. In sheds and garages, where the tin roof is not insulated, moisture is constantly dripping on the wooden structure. This would soon start to rot.
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