black spots on one part ...: "I have a 40 squares tin roof. On one of ..." - Guest User (8/11/2016) | I Have An Existing Metal Roof and Have A Question

I have a 40 squares tin roof. On one of the slope has black spots that the others don't have. There are no trees anywhere close to the roof. Any ideas what it can be?	Guest User 8/11/2016	Share Or copy this URL: https://www.metalroofing.com/spirit/comment/21418/find/
It the roof steel or aluminum?	Eric Novotny An informed customer is the Best Customer! 8/11/2016	Share Or copy this URL: https://www.metalroofing.com/spirit/comment/21419/find/
I believe it is aluminum. Notice that the other slope doesn't have any spots.	Guest User 8/11/2016	Share Or copy this URL: https://www.metalroofing.com/spirit/comment/21420/find/
Could just be an airborne mold, but it looks a bit to clearly defined to be that. We would need to see a picture close up.	Eric Novotny An informed customer is the Best Customer! 8/11/2016	Share Or copy this URL: https://www.metalroofing.com/spirit/comment/21421/find/
It's funny because it also happened the last time I cleaned it, also in the same location. Did you try magnifying the picture? Thanks for all your help.jNTr5K	Guest User 8/11/2016	Share Or copy this URL: https://www.metalroofing.com/spirit/comment/21422/find/
I am sorry to hear this. This is unusual but not unheard of especially in certain climates -- usually tropical or sub tropical. If I had to guess, I'd guess this is happening on a roof slope that tends to hold dew during the mornings? I also wonder a tiny bit about the possibility that this is a ridge vent and for some reason a lot of moisture exiting the house in that area. Unfortunately, once this starts, it usually continues despite cleanings. There are some biological products out there like RoofWash and Wet and Forget which I have heard of favorable results with. I would be curious of the chemistry of the paint system on the roof. Also, it's unusual, but there are some possible paint system defects that could lead to this. Since it is limited to one roof slope, though, I doubt that is happening. You may wish to reach out to the roofing manufacturer.	Todd Miller Isaiah Industries, Inc. 8/12/2016	Share Or copy this URL: https://www.metalroofing.com/spirit/comment/21423/find/
If the roof surface is North facing, it is most likely and airborne algae/mold that is growing on the roof as a result of the dew formation. Still need a close up of the spots though to rule out a finish issue.	Eric Novotny An informed customer is the Best Customer! 8/13/2016	Share Or copy this URL: https://www.metalroofing.com/spirit/comment/21424/find/

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black spots on one part of the tin roof