Roof rusting below chimney

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New Member
Aug 18, 2023
Hey folks, I’m Max, new to the forum.

So a quick backstory, I live in SE Alaska and we bought this house last year, just before winter. At the time we bought it, below the chimney you could see the metal roof had oxidation. Didn’t really get to inspect it too closely. That’s on me.

Today I got up on the roof to replace roofing screws and as I made my way to the chimney I took a closer look and saw that the there were actually a few small spots that actually had holes rusted into it— talking pinhole and slightly larger.

This past winter was pretty miserable as the wood we had was not fully seasoned, fires didn’t stay hot etc. This year I’ve added a proper woodshed and have dry wood and plenty of room to cycle what isn’t dry yet.

My question to you guys is if any of you have had this experience and may know what is causing it. The rust is localized to just the roof panel at and below the chimney.

No idea when the roof was last replaced, I was told it had 10-20 years left, starting to have my doubts.

I’m wondering if the creosote and/or smoke is speeding up the oxidation, or if perhaps the oxidation From the brace above the chimney is trickling down.

My plan is to remove and replace that panel but I’d like to fix the problem if possible.

For reference my stove appears to be an Englander, model no. 13-nc-clp however mine doesn’t appear to match the ones online.

Thanks for any advice

Roof rusting below chimney Roof rusting below chimney Roof rusting below chimney Roof rusting below chimney
Creosote when combined with water is corrosive. Burning dry wood and will help.

Is the chimney tall enough to satisfy the 10-3-2 rule?

Is the top end of the flashing slipped under the metal roofing or is it just sitting on top of it?
I don’t know about the 10-3-2 rule but I will look into it and get a measurement when I get back home. The flashing is just sitting right on top…It looks like they just slapped a bunch of silicone around the edges.
Sounds like it might have been a DIY install. Go over everything inside and out to look for other potential or real issues.

Here's a graphic showing the 10-3-2 rule requirements.

Roof rusting below chimney
Pyroligneous acid is a component of creosote and it will eat a galvanized roof. The zinc tries to self-heal, buy eventually it disappears. My guess is the prior owner burned green wood with a low efficiency stove creating creosote that ran over the roof. The other possible aspect is that cheap silicone sealant uses acetic acid to catalyze the silicon. Silicone 2 uses alcohol and is less corrosive.
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You may be able to extend the roof life a bit by painting it after fixing the holes.
The good news is that it is exceptionally easy to replace a single panel with that exposed-fastener roofing, if you don't mind a slight difference in sheen for the first few years of a new panel amongst the old. I'd be pulling that panel and flashing, and re-doing it. Ditch the DIY snow shield, which is also rusting and staining everything below it, and install some proper snow guard system.