How much does T18 or T35 trapezoidal steel sheet weigh, and how do you calculate an order?

Profiles with the same family name can differ in sheet width, rib spacing and steel thickness. These differences change the amount of steel per square metre of cover. Check roof and wall versions separately, even if they share a profile designation.

T18 and T35 identify profile families. To compare weight or permissible span, use the full product reference, cross-section and thickness. If a supplier quotes kilograms per square metre without defining the area, ask which width was used in the calculation.

For an estimate, take steel density as about 7,850 kg/m³. One square metre of flat steel 0.50 mm thick then weighs about 3.925 kg. This uses the steel core thickness and the developed area of the material before profiling. The installed roof area is a different basis.

The developed width, measured along the folds, exceeds the projected width of the profiled sheet. Coatings add weight, and overlaps reduce cover area. Use the declared weight for the exact product in structural calculations, since the flat-steel estimate leaves these factors out.

Overall width spans the whole sheet. Cover width is the usable width once the specified side lap is made. Dividing the weight of a sheet by its smaller cover area gives a higher figure in kg/m². The sheet itself still weighs the same.

Suppose a 20 kg sheet has an overall area of 5 m² and covers 4.8 m². Its weight is 4.00 kg/m² of overall area or about 4.17 kg/m² of cover. Both figures describe the same sheet. These example dimensions illustrate the calculation only.

For a value in kg per linear metre, multiply by sheet length and quantity, grouping equal lengths together. For a value in kg/m², use the area defined in the data sheet. Combining cover width with a weight based on overall area understates the sheet weight.

Include flashings, fasteners and packaging when calculating the transport load. The gross bundle weight on the lorry serves a different purpose from the permanent load of the covering on the roof. Before delivery, confirm each bundle’s weight and the points where it must be supported.

Greater thickness can improve load capacity. Rib height and shape, steel grade, support arrangement and fixings also govern behaviour. T35 sheets of different thicknesses and spans have different capacities. Weight alone cannot determine which one to specify.

Structural trapezoidal steel decking requires the relevant load tables or calculations. Check strength and deflection separately. Which face of the profile is in compression also matters. Use a table for the exact model, thickness and span arrangement.

A lighter covering can reduce part of the permanent load. Existing timber damage, weak joints and changes made during earlier alterations still need assessment before reroofing. Include new roof layers and equipment as well as wind and snow loads.

A long, lightweight sheet can bend if supported incorrectly during handling. Its large surface also catches the wind. Plan unloading and lifting according to sheet dimensions and the handling instructions as well as weight.

Provide the profile family, full product designation, thickness, steel grade and cross-section drawing. Include sheet lengths and details of the supports. For the delivery team, provide the bundle weights and unloading method. Each team then has the data it needs for its part of the work.

Mark on the quotation whether each weight and price refers to a square metre of overall area, a square metre of cover or a linear metre of sheet. This can explain apparent differences between offers. Give the designer the exact product documentation for the load check.

Use the declared mass for the chosen thickness and the stated reference area. Knowing the order weight helps with transport, estimating and identifying permanent loads. Use structural design data to establish the roof’s capacity.