What does the price per square metre of trapezoidal steel sheet actually cover?

The overall width covers the full width of the sheet. The effective width results from the cover width after the side joint is made. The cover width is used to determine the number of runs on the roof. The unit stated in the specific offer is used for settling the purchase.

Ask for the overall and effective widths if they are not given next to the price. Do not guess from the T18 or T35 designation alone. The dimensions depend on the profile family. A difference of a few centimetres repeated across many sheets can clearly change the result.

Consider profile T18 with an overall width of 1137 mm and an effective width of 1100 mm. At a unit price of €8.10 net/m² of overall area, the covering price is €8.10 × 1137 ÷ 1100. The result is approximately €8.37 net/m² of effective area.

This calculation accounts for the width difference. It does not yet include cuts and lengthwise overlaps. If shorter sections cut from full sheets are needed for the covering, the cost of the metre used may increase. The final quantity therefore results from the cutting plan.

Do not add the side overlap a second time to a price already converted to cover width. Separate the individual sources of difference: profile width, length division and waste. Such a breakdown allows an error to be found without recalculating the entire order.

Galvanised steel sheet and steel sheet with an organic coating are not identical variants. They differ in finish and in the range of surface properties. To compare prices, the requirements for the given environment must be assumed. The colour alone also does not describe the type of coating.

The steel thickness matters. For the specific profile T35 with widths of 1082 and 1035 mm, the rate of €11.11 net/m² of overall area gives approximately €11.61 net/m² of covering. If it applies to a 0.6 mm sheet with a polyester coating, it is not equivalent to the price of 0.5 mm galvanised sheet.

So don’t judge the difference in amounts as just a difference in margin. First establish whether both items have the same profile, thickness and protection. For an alternative variant, also check the mechanical parameters and compatibility with the supports. A cheaper sheet must still meet the roof requirements.

Anti-condensation felt is sometimes a separate item. Its price must also be related to the correct area. If the surcharge is calculated per gross metre, it must not be added to the effective metre price without conversion. The simplest approach is to keep the whole calculation in one unit.

Beyond the sheet, there are flashings, fasteners, sealants and transport. A small order may have a high delivery cost per metre. With long sheets, unloading arrangements are also added. All these items should be visible before the purchase is approved.

Also check whether the offer includes cutting to the specified lengths and any additional material preparation. Don’t assume that every service is free of charge. If the cutting plan changes, ask for the current total. Not only the area but also the delivery arrangements may change.

First add up the cost of the entire order for the defined scope. Then divide it by the actual area of the covered roof. This gives you an indicator that takes the cutting plan and extras into account. It must be clearly stated whether it also includes installation.

For example, €2,221.92 net for the cost of materials including delivery for 160 m² of finished roof surface gives €13.89 net/m². This is a hypothetical calculation, without indicating a market price. If installation costs an additional €1,203.54 net, the total rises to €3,425.46, that is €21.41 net/m².

Keep both pieces of information: the unit price of the sheet and the cost of the defined task. The first helps you check the offer, the second allows you to plan the budget. If the profile or dimensions change later, recalculate both results. This way, a lower number in the price list will not obscure a higher order total.