Why exterior roof mildew along lines

It's where the aluminum frame is. It sweats in the morning in the high humidity. Ever notice vertical sweat lines on your sides in the morning?

My roof has the same black lines. It's telling me to step here.

flguppie wrote:
Thanks. You don't think It's creating a mold on the inside somewhere is it?

Nope. Mold needs three things to propagate--The correct surface to adhere to, a source of food, and the correct temperature and humidity conditions. The last is actually a fairly narrow band of conditions and is the easiest to change. If you have a dehumidifier inside the cabin, you're removing the humidity and interrupting the growth.

I know nobody likes mold and mildew, myself included. I don't fear it like some folks, though. Ever since the Texas mold litigation, mold has become big business and marketing loves fear. I do some mold/mildew remediation and I've come to believe that it's impossible to remove it forever and we shouldn't worry so much about it. Not that you have to live with it constantly but there are very few varieties that are injurious to health or cause a financial loss. YMMV and I know Florida has a lot of it.

Hi neighbor.....What you are seeing is normal here on the coast. I looked at mine last week while on the ladder waxing the sides, and mine has a red tinge of mildew that I need to take care of. There is just no keeping this stuff off the roof for long.

Looks more like a simple dirt line from where the sheeting underneath is. Every RV with rubber roif I have seen has it.

Thanks. You don't think It's creating a mold on the inside somewhere is it?

The mold is probably growing there because you've created a thermal band where a roof sheathing seam exists. The colder air inside the cabin is seeping out at that seam and creating the perfect temperature for the mold to exist. I wouldn't be too concerned as a quick wash of that area would probably cause the mold to disappear for most of the time. There are mildewcides that you could apply if it bothers you a lot. Original Listerine mouthwash is one and wouldn't be injurious to the rubber roof.