How to specify trapezoidal steel sheet in a single order

Measure an existing frame before ordering. Do not estimate purlin spacing by eye. On a refurbishment, check purlin condition and connections. New sheeting cannot correct an inadequate supporting structure. Resolve capacity questions before comparing profile prices.

T18 and T35 identify profile families, not complete sections. Rib pitch, cover width and section properties vary. Specify the precise configuration that was checked for capacity; similar rib height alone is not grounds for substitution.

Assess steel thickness together with profile and support conditions. Roofing sheets may be 0.50, 0.60 or 0.70 mm thick, among other options. No one gauge suits every building. Check loads, deflection and fasteners, and confirm permitted use of the sheets during installation.

Specify the metallic protective layer, organic coating type, colour and gloss. Match them to the surroundings: a residential site differs from exposure to aggressive fumes or frequent wetting. Paint thickness alone does not establish suitability.

Match flashings to the sheet finish and identify the outside face. Roof and façade sheets with similar designations may have different side laps. Confirm the profile orientation and the side carrying the decorative coating.

Fleece on the underside can temporarily retain some condensate. It must then be able to dry. It can help in certain uninsulated buildings, but it provides neither thermal insulation nor an airtight enclosure. Do not specify it as a universal moisture remedy.

Agree on treatment at eaves and laps to prevent the absorbent layer from drawing water in. The method depends on the product. A heated or very humid building needs a complete roof design; paying extra for fleece cannot correct an unsuitable layer sequence.

List sheet lengths and quantities, with both effective cover width and overall width. Ask which area is billed. Price flashings, fasteners, seals and freight separately. Similar rates can otherwise represent different scopes.

For an overall width of 1.142 m and a cover width of 1.100 m, about €9.27 per m² of overall sheet equates to about €9.62 per m² of cover, excluding VAT. These are illustrative rates, not an offer. Allow for edge cuts and any end laps before calculating the roof cost.

Give each length group a code linked to the drawing and delivery list. This helps stack packs in erection order and spot a missing length. A correct total length can still conceal the wrong assortment of sheets.

Bring the drawing, material specification, cutting list and accessories into one order version. Include unloading, delivery date and storage area. Identify who submits changes and signs off final lengths. Scattered messages make it easy to use the wrong revision.

Use that document at delivery. Count packs, check labels and coating condition, and measure selected sheets. Record discrepancies before installation. This is more reliable than trying to remember what “standard roof sheet” meant.