Many factories now need their gutters re-lined. The roof is in excellent condition but the box gutters have corroded despite being galvanised steel. On the example above the Permadeck has been taken ~75mm up behind the parapet coping and, on the opposite side, behind the L-shaped flashing trim, which is part of the corrugated roof. The ends were fitted with large bore overflows and the existing outlets moulded down into. This is a cost effective solution to what would otherwise be a very expensive re-build with considerable disruption.
And if someone says they can ‘coat’ your gutter with some sticky plasticy rubbery stuff chase them. Water will easily get below it and soon disintegrate, making it more expensive to do properly and even choking your underground drains.