Flat Metal Roof Rusting. How do I repair?

[rambunctious]

corrupted profile would not be suitable not enough fall if you use corrupted roofing t will leak where it goes into the gutter.

Been meaning to reply to this for a while now. Actually all you need is a flashing from on top of the gutter batten and a drop of probably 20mm at 30 degrees into the gutter for any water wicking back to drop into the gutter. I had to do it here when we moved in because previous owners had sheeted an almost flat pergola with custom orb, and all I used was a sheet of colour fencing which had a perfect profile for what I needed, and once I cut it length ways with the shears I got I think about 9 metres of flashing from the one fence sheet.. Custom orb/corrugated roofing has a recommendation for 5 degrees fall/pitch but it will not give problems provided the battens are no more than about 650 apart so the sheets don's dip down when walked on. Of course if the structure/roof is being approved then the inspector/certifyer will knock it back for incorrect profile, but if not being approved, then no worries.

[Stuckster]

Is any part of the surface pitted?
If it's simply dusty then it's only surface rust.

Our Kliplok roof is exactly the same. Was considering repairing/painting it 8 years ago but decided not to. We are now replacing it with an extension, but I reckon it would have lasted another 5 without touching it.

Depends how quickly the rust is worsening. Its a pretty invovled process to treat and paint and would only consider it if you're not going to be replacing the roof in the next 5-8 years. Something to also think about is that recoating or painting can often make the issue worse by sealing up all the places where the water was previously able to get out!

If the roofing sheets have been installed correctly water shouldn't penetrate the building envelope. Problems start to arise when you try to silicone up every little gap. On our roof the installers siliconed the crap out of the transition flashing. Water would find a way in behind the flashing, but couldn't flow back out again due to the silicone. So it pooled at the back of the sheets (under the flashing) and eventually rusted though. It would have been much better off without the silicone. Let the flashing and turned up sheet ends do their job.

In short, unless the metal is pitted or flaking I'd grab yourself a roll of Flashtac (foil backed butyl tape) stick it over the holes/leaks and not worry about the rust. I've got patches of tape still going strong 5 years later!