The spacing of battens under T18 or T35 sheeting depends primarily on the load-bearing capacity of the specific sheet within the adopted support arrangement, not on a single universal rule. To determine it, you need the profile, steel thickness and grade, the loads and the support layout. It is also worth checking the bearing width and the method of fixing the battens. A deeper trapezoidal profile may offer different possibilities, but it does not justify arbitrarily thinning out the substructure. The starting point is structural selection and measurement of the roof slope, not cutting timber alone.

For a carport, trapezoidal steel sheet T18 or T35 can be considered, but the choice requires checking the support spacing and loads. A higher profile does not mean an arbitrarily larger span. The steel thickness, geometry, building location and method of fixing all matter. In an open carport, wind acting from underneath must also be taken into account. Limiting condensation under the covering is a separate decision. A carport roof is exposed from various sides. Wind can act on both the upper and lower surfaces of the covering. Fixings from a closed garage should therefore not be copied without checking the conditions. Location, height, surroundings and degree of wall openness are important. These data influence the selection of the sheet, fasteners and the entire structure.

Structural trapezoidal steel sheet can form the load-bearing substrate of a roof or work in another arrangement specified by the design. Deep ribs allow steel to be used efficiently, but the profile height alone does not determine the permissible span. The choice is governed by thickness, steel grade, supports and loads. The price must be compared for the same structural task, taking into account fixings and the other roof layers. A low profile used as an external covering sheet and a high load-bearing profile may look similar in a small sample. Their tasks, however, are different. Structural sheet is part of the load-transferring system. It can support the roof insulation and waterproofing. In such an application, tightness is provided by a separate layer designed above it.