Can you get condensation from overlapping corrugated iron roof?

Question

HI.

While making a roof with corrugated iron, there will be an overlap of two sheets. My question is: Could condensation be formed in the overlap. The roof exist of Sips (metal - foam - metal) with 40mm purlins on top, insulation on top of the Sips between the purlins and corrugated iron on top of the purlins.

A sheet overlap ends at my chimney outlet and I have leakage on that spot. Where is the water coming from.

I hosed the whole area and no leakage.

The angle of the roof is smaller than 5 degrees.

Maybe there is someone with the same problem?

lebobo

MitchellMc · Answer

Hi @lebobo,

https://www.bunnings.com.au/selleys-sealant-remover-375g_p0828840

would help soften what's there and then a sharp-bladed scraper will cut it away. Once the bulk is removed, you can then clean up the surfaces with the silicone remover and then wipe done with degreaser.

Mitchell

lebobo · Answer

Hi MitchellMC. Thanks for your reply. How do you remove lots of old sealant on those spot, probably by a lot of elbow grease.

At some point I was thinking to take of the whole rubber flashing and Strat again from scratch but that wouldn't be easy either..

I will have a good look again.

Cheers

MitchellMc · Answer

Hi @lebobo,

The simple answer as to why it’s leaking at the flue is that there is almost certainly a breach in the seal at the flashing or cowling, even if it’s not immediately obvious. While you’ve done the right thing trying to seal the area, repeatedly applying sealant over the top of existing sealant rarely fixes the root problem. Once sealant begins to fail, it loses adhesion, and anything applied over it tends to be only a temporary fix rather than a long-term solution.

The best approach is to remove all the existing sealant around the flue, thoroughly clean the surfaces, and then reapply fresh sealant directly to clean metal and rubber. Leaving the old sealant in place and layering over it might reduce the leak temporarily, but it won’t address the underlying issue of failing sealant.

Based on your description, it’s also very likely the leak is occurring on the uphill side of the flue, where water is pooling in the corrugations. With such a low roof pitch, water doesn’t shed quickly and can sit in those areas, and pooled water will eventually find its way through even very small gaps or imperfections in the seal.

So while the low pitch and overlaps do make the situation more challenging, the most likely cause is still a failing seal around the flashing under pooled water conditions, rather than condensation.

Mitchell