Comparing T18 and T35 trapezoidal steel sheet prices by thickness, cover width and anti-condensation fleece

In the example trapezoidal roof sheet T18, the overall width is 1137 mm and the effective width is 1100 mm. For the specified T35, the values are 1082 and 1035 mm. These figures relate to the stated geometries. They cannot be treated as universal dimensions for every sheet with that name.

A higher profile may have different load-bearing capacities, but the permissible support spacing depends on the data for the specific sheet. Steel thickness, material grade and span arrangement also matter. The number 35 alone does not replace verification of load capacity.

For the aforementioned T35, the ratio of overall width to coverage is 1082/1035, i.e. approximately 1.0454. If, for the example calculation, we take €8.80 net per m² of overall area, we obtain approximately €9.20 net per m² of effective area. This is the same sheet shown on two bases.

Only after such a conversion can you compare an offer that states the coverage price from the outset. A lower figure in the overall square metre column does not automatically mean a cheaper roof. In the factory, part of the sheet does not increase the finished roof area.

The unit conversion does not yet include cutting waste. With hips, roof valleys and many openings, the purchase quantity may be greater than the roof area. Therefore the final cost results from the number and length of sheets, not solely from multiplying the building footprint by the rate.

Compare the same steel thickness and the corresponding scope of surface protection. Different organic or metallic coatings may be offered. A similar colour does not guarantee identical properties. The selection should match the operating conditions and the required durability.

A thicker sheet usually contains more steel, but the decision should not be based on price alone. A variant that is too thin may not suit the loads and support spacing. Conversely, increasing the thickness unnecessarily does not replace correct fastening and roof geometry.

When replacing part of the covering, check profile compatibility. Two T18 trapezoidal sheets may not fit at the overlap. In such a renovation, the seemingly cheaper sheet may require a larger scope of replacement. It is worth establishing the fit before ordering the whole batch.

Anti-condensation felt periodically absorbs moisture that forms on the underside of the sheet. It later needs conditions to dry out. It is neither thermal insulation nor roof waterproofing. Its suitability depends on ventilation and the actual way the building is used.

The surcharge can be stated on the same basis as the sheet price. If, in our example, we additionally assume €2.08 net per square metre of total sheet area, this corresponds to approximately €2.17 net/m² of coverage for the given T35. Together with the assumed sheet metal, this gives approximately €11.37 net/m² effective, excluding the other costs.

Check the preparation of the felt at the eaves and overlaps according to the product solution. The absorbent layer cannot be treated as an arbitrary addition whose edges are always left unchanged. Compare the cost with the full scope of preparation and installation.

Add flashings, fastenings, seals and transport. Determine sheet lengths and the method of unloading. For larger dimensions, access to the work site matters. Long sheet metal can reduce the number of joints but make handling more difficult and increase the risk of deformation.

Check minimum order conditions and logistics surcharges. In a small renovation, these can significantly change the unit cost. The example rates used above show the calculation; they are not a current offer for every colour and quantity.

Finally, compare the cost of a complete covering with the required parameters. If one offer omits felt, flashings or part of the transport, note this clearly. Only such a result allows you to assess which profile and purchase variant are advantageous for a specific construction.