Metal sheets and roofing
What does a square metre of roofing sheet cost once it is on the roof?
A price per square metre of metal roofing is useful only if you know which area it buys. Some suppliers charge for the full sheet width, including the side lap. Others use the effective cover width, which is the width each sheet adds to the finished roof. A price per linear metre refers to a length of sheet of a specified width. Convert quotations to a common unit and compare the specifications. Then work out how many whole sheets your roof needs. Delivery, cutting waste, flashings, fasteners and installation all affect the cost per square metre of finished roof.
In this guide
Which unit is the supplier charging for?
Check whether the price includes VAT and which extras it covers. Put both quotations on the same tax basis. The supplier may list materials and services separately, so ask for an itemised breakdown. This lets you identify an actual saving rather than an apparent difference caused by the way the bill is presented.
How do you convert a price based on overall width to a price based on cover width?
Take a T35 sheet with a cover width of 1.05 m and an overall width of 1.09 m. Multiply the price per square metre of overall sheet area by 1.09 and divide by 1.05. An illustrative net price of about €8.33 per m² of sheet becomes about €8.65 per m² of cover. This conversion allows for the side lap. End laps and cutting losses are still to be added where applicable.
The ratio of the two widths varies by profile. A fixed percentage allowance will not work for every trapezoidal sheet. If the quotation says only T35, ask for the exact cross-section and both widths. Sheets of the same nominal profile depth are available in different widths, which changes the calculation.
Which offer costs less once delivery is included?
Suppose you buy ten 4 m sheets of this profile. They give 42 m² of effective cover from 43.6 m² of overall sheet area. Supplier A charges about €8.33 per m² of overall area. Supplier B charges about €8.80 per m² of effective cover. These are hypothetical net prices. The table uses unrounded unit rates for the material costs and adds the displayed amounts for delivery.
| Item | Quotation A | Quotation B |
|---|---|---|
| Sheets | 43.6 m² overall: €363.28 | 42 m² effective cover: €369.39 |
| Illustrative delivery charge | €92.58 | €57.86 |
| Total excluding VAT | €455.86 | €427.25 |
The sheets alone cost €6.11 less from supplier A. With the delivery charges shown, supplier B costs €28.61 less overall, excluding VAT. Check that both quotations specify the same steel thickness, coating and material condition before choosing.
Which material specifications need to match?
List the profile, steel grade, nominal steel thickness, surface protection and colour. Include any fleece backing and sheet preparation. Similar photographs do not establish equivalent specifications. Two coatings of the same shade can be intended for different exposure conditions, so check suitability before choosing the cheaper one.
Check the commercial quality grade and the condition of the batch. A cosmetic defect and a damaged sheet edge call for different assessments. A discount cannot compensate for inadequate load capacity or a joint that will not keep out water. If a new profile does not fit an existing roof, adjoining components may need costly replacement.
Why does a square metre of finished roof cost more than a square metre of sheet?
A completed roof also needs flashings, fasteners, the specified layers below the covering and installation labour. The cutting list includes whole sheet runs and pieces that need trimming. You cannot order the exact geometric area of a slope as arbitrary fractions of sheets. Calculate the available effective cover first, then check it against the actual layout.
Allow for unloading and, where needed, lifting the sheets onto the roof. On a small order a fixed delivery charge can add substantially to the price per square metre. On a refurbishment, include removal of the old covering and the work required by the condition of the structure. Compare totals for the same scope of work and use unit prices to investigate the differences.
How can you keep track of costs when ordering extra sheets?
Keep the quantity and length of each sheet on record, with its intended position on the roof. If more material is needed, those notes help distinguish a design change from damage or an overlooked cut. Work from the dimensions and profile of the missing piece. Its area alone will not tell you which replacement fits.
Check the cost of a second delivery and whether the shade may vary between batches. The invoice for a few extra sheets can be only part of the cost of putting a shortage right. An accurate cutting list helps avoid these expenses. An itemised quotation also shows which costs arise from the sheet specification and which from delivery or work on site.
Frequently asked questions
Is a price based on overall sheet area less transparent than one based on cover area?
Both are valid ways of pricing the same batch if the unit is clearly stated. Convert the prices to the same basis before comparing them.
Does the biggest percentage discount give the best price?
Check the starting price, specification, unit and scope first. A larger percentage reduction from a different starting point can still leave a higher total for the order you actually need.
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