Mold on the roof sheathing

Ok, I saw this yesterday and am a little puzzled. It looked like mold, but was in a specific area. Initially I thought maybe it was some sort of roofing construction material, but I saw it at a place that showed signs of prior moisture. The photo shows the “mold” and when I tested the area it showed signs of moisture. I’m thinking that the mold is present due to moisture leaking through to the sheathing, maybe an errant roofing nail, and that’s why its localized and not throughout the attic. But if this is the case, is there something in the sheathing itself that is allowing the mold to grow when it gets wet? I haven’t seen growth localized like this before. Again, I’ve seen it in another area of the attic that showed prior moisture but I’ve also seen areas of the attic that showed prior moisture and didn’t have any mold. The first two photos show the mold with moisture, the third photo shows the mold without moisture. Any input would be greatly appreciated! Thanks!

Mold 101: wood is food for mold. Moisture is needed to sustain mold’s life, just like that of a human. Mold will consume and help break down the wood back into its basic elements.

Keep it simple, a roofer is needed to fix the leak :slight_smile:

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Hey Simon, Thanks for the feedback, I always keep it simple for my clients. The information is more for my own edification. I like to know why things are doing the the things they are doing.

Picture #3 looks like a flashing issue, to me.


Like @lkage said…Image 3 looks like a flashing fail at a transition from a wood framed chimney box to the roof. OSB will look like that and degrade with long term exposure to moisture. The heat in the attic is also a catalyst for mold growth. I would not officially call it mold in the report unless you have tested it, but it is mold and water damage and needs to be fixed, with up to some sheathing replaced and possibly some framing.

Where do you see a chimney chase?

Wood rot in sheathing.

@srechkin - It was a guess on looking internally and to the right of image 3. To me, looked like a chimney box (wood built) that would surround a metallic flue pipe. Full on guess though and really not a worry for this. The wood rot is enough to be a concern!

Hey Jordan, you are correct, picture #3 is the roof sheathing on the lower side of a chimney chase. Good call and thanks for the feedback.

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