How much will you pay for 100 metres of steel sheet and what area will it cover?

One hundred linear metres can mean, for example, 20 sheets of 5 m. It can also mean a different combination of lengths. The same total does not, however, guarantee the same suitability for a roof. Short sections may require joints that a longer sheet does not need.

Do not equate the length of the eaves with the number of linear metres of steel sheet either. The eaves run across the strips, while the sheet length usually runs down the slope. A roof with 20 m of eaves may need many different totals of lengths, depending on the dimension of the roof slope and the way the covering is divided.

Let us take a specific T18 variant with 1100 mm coverage and 1137 mm overall width. For 100 linear metres, the coverage area is 110 m². The area calculated from the full width gives 113.7 m². The difference results from the geometry of the side laps.

The coverage result does not take into account additional losses for fitting to the roof slope or transverse laps. If sheets have to be joined along their length, the effective coverage will decrease. The width used in the calculation must correspond to the actual profile variant, not to any T18 sheet.

At an agreed net price of €9.72 per m² of coverage, one linear metre of the described sheet metal costs €9.72 × 1.10 = €10.69 net. One hundred linear metres comes to €1,069.20 net. This is a calculation example. It is not a price list binding on any particular supplier.

If the price of €9.72 related to a m² of the total, the result would be €9.72 × 113.7 = €1,105.16 net. The difference is €35.96. Both offers may show a similar figure, but the basis of settlement changes the cost. The unit must be checked before comparing.

Assume a simple roof slope 20 m wide and 5 m long down the slope. It has 100 m². With a cover width of 1.10 m, 19 sheets 5 m long are needed. Eighteen strips give only 19.8 m of width. The order will therefore be 95 linear metres and 104.5 m² according to cover width.

At the same agreed rate of €9.72 net, the material costs €1,015.74 net. This is not €972.00 resulting from a simple multiplication of 100 × €9.72. The final sheet requires adjustment. The calculation relates solely to the assumed geometry and does not specify the support spacing.

A sheet spanning the full length of the slope can reduce the number of joints. However, the production range, transportability and safe handling must be checked. A long, thin element is prone to deformation during improper lifting.

Shorter sheets require planning of the laps and proper support. Fixings and working time are added. Do not choose the division solely according to the available vehicle. Savings on delivery may be eaten up by additional material and jointing work.

The sheet quantity alone does not include flashings, fasteners, seals and rainwater goods. Transport, unloading and installation are priced separately. In a heated building, further layers of the section are needed. Anti-condensation felt also has its own price and a specific function.

In a small structure, the edge length relative to the area may be large. For this reason, the cost of accessories does not have to grow proportionally to the m². Count the ridge, eaves, sides and penetrations. A quantity schedule is more accurate than a single general markup.

Provide the profile, steel thickness, coating and colour. Add the number of sheets and the length of each group. Indicate the method of calculating the area. If you expect a quote for a complete roof, include the roof slope drawing and the scope of work. A message simply saying “please quote for 100 m” leaves too much room for guesswork.

After receiving the quote, recalculate the quantities using one method. Check whether full pieces and laps have been included. Keep the linear metres of sheet and flashings separate. They are written similarly but mean different elements. This order also makes delivery checking easier.