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Roll Curving

Pre-curved corrugated roof cladding is used for bull-nosed verandah roofs, ridges, or for roofs where the radius is less than the minimum required for sprung or draped curved roofs.
Corrugated (symmetrical sinusoidal) G300 roof cladding is easily curved or bull-nosed. The sheets are passed through matching curving rolls, which progressively form curves in a wide range of radii. If G300 and G550 steel sheets are to be used together, because these two materials will not have matching profiles, adjustment of the roll-forming machine setting is necessary.

Circular barns have been successfully cladded with 0.4 mm steel for many years, but 0.55 mm steel or 0.9 mm aluminium should be used for roll-curved roofs subject to foot traffic. G300 coated steel of 0.4 mm and 0.7 mm aluminium are only suitable for roofs without access or for wall cladding.

G300 steel can be curved to a radius as small as 300 mm using pyramid curving rolls. There is, however, a straight portion of about 80 mm at the end of the sheet which may need to be trimmed off if a true curve is required.
If the edge of the sheet is too flat or long, rippled edges may result, and these should be dressed out using a dressing tool or trimmed off before the sheet is installed.
 

Dressing Tool

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A curve can be rolled on one end of a straight length of roof cladding to provide an over or cranked ridge, but for ease of fitting and transport, a lap is usually made at the first purlin down from the ridge. This should be sealed in the same manner as is required for any transverse lap.
An alternative ridge detail can be used with straight sheets, without any lap, by roll curving or draping the cladding over the ridge, where the ridge purlins are extended their maximum span.
For safety, roofs which are often used as a means of access to or onto a verandah should be provided with an intermediate support. Simply supported roofs cannot withstand foot traffic to the same degree as continuously supported sheeting.
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