When is thinner steel roofing a false economy?

One T18 range, for example, comes in thicknesses from 0.5 to 0.7 mm. The thinnest sheet in that range will not suit every roof slope. Use the data for the exact cross-section. Assigning 0.5 mm to garages and 0.7 mm to industrial buildings overlooks differences in their supporting structures.

Forming a flat sheet into a profile changes its stiffness. A shallow profile and a deeper one of the same steel thickness can therefore carry different loads. Flange widths and the shape of the stiffening ribs also matter. Consult the load tables for the specific profile. Even profiles with similar names can have different capacities.

Increasing the nominal thickness from 0.5 to 0.7 mm adds 40%. You cannot increase the distance between supports by the same percentage on that basis. Load capacity and deflection depend on the entire cross-section and the support and loading conditions. Compare the relevant design data before changing the spacing.

When reroofing, measure the actual spans and bearing widths. Check metalwork for corrosion and inspect the timber and connections. The previous covering may have had different support requirements. Assess the layout again, even if the old roof survived several winters. Its past performance does not establish that every replacement sheet will work.

Thicker steel cannot repair a rotten batten or a weak purlin connection. The supports may need alteration, or a different profile may be more economical. Compare the installed cost. Extra framing and the labour to fit it can use up the saving on a thinner sheet.

Ask whether the quoted figure is the steel core thickness or the finished thickness including the protective layers. These layers protect the steel and do not count towards its load-bearing thickness. Request a precise product designation and the specification for the batch to be delivered. “About half a millimetre” is too vague.

A thickness check needs a suitable instrument, a suitable measuring point and a clear definition of the dimension being checked. A rib can be harder to measure than a flat section. A single calliper reading across the coating does not verify conformity. Use the tolerances and method specified for the product.

A long, thin sheet can kink permanently if carried incorrectly. Provide suitable support, enough people or appropriate lifting equipment. Even a thicker sheet can be damaged if lifted by one end. Plan transport and installation around the dimensions and weight of each sheet.

Plan a safe route to chimneys and rooftop equipment for maintenance. Treating the covering as a general working platform can damage sheets of any thickness. A misplaced foot, a dropped tool or an unsuitable fixing can all leave damage. Provide compatible access equipment and plan how inspections will take place.

First rule out sheets that fail the technical requirements. For the remaining options, add the cost of supports, fixings and transport to the sheet price. Where two systems meet the design requirements, ease of installation and future maintenance may decide which is better value.

Keep the thickness, steel grade, profile and coating on file. Years later, you may need all four to replace a damaged section. Matching the colour alone is insufficient. The most economical specification meets the roof requirements while avoiding unnecessary work.