The durability of trapezoidal sheeting depends on the specific conditions on the roof, not on a single universal number of years. To realistically assess the expected service life, check the type and condition of the protective coating, the local environment (e.g. salinity or industrial pollution) and the quality of installation. Roof geometry and access for cleaning also matter, as areas that trap moisture age faster. Rather than relying on the profile name alone, analyse this set of factors – they determine the durability of the covering.

The thickness of trapezoidal steel sheet for a roof is selected to suit the specific profile, loads and support spacing. There is no single value suitable for every garage, house or hall. T18 and T35 come in various versions, and thickness alone does not describe the full load-bearing capacity. The steel grade, geometry and the relevant tables must be checked. The protective coating is a separate parameter and does not replace the required thickness of the steel core. Two sheets of the same thickness can have different rib heights and widths. This changes the stiffness and the way they perform. The steel grade also matters. It should not be assumed that every product described as T18 or T35 has an identical cross-section.