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Blakem713 wrote:

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I think its because the clean spots represent where water does not flow.

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!/2 correct, the other 1/2 is the natural fungicide from the metals in the vent pipes.

The Zinc Strip Rip Off artists down here actually use the clean areas under vent pipes to "prove" Zinc Strips actually "work".

I have seen houses with zinc strips installed every 5 rows of shingles!
Not only does that look like chit, it don't work either, at least here in Tampa.

I THINK that the reason a vent pipe keeps the area under it clean is more then just the Zinc in the metal.

I believe it blocks the water from running down a roof.

Yes, it is true that when it rains, all the roof is wet, pipe or no pipe.

But overall, the area of roof right under the vent pipe receives less TOTAL water.

Any plant that receives less total water then it's "neighbors" will be not grow as good, nor as fast.

 

Unbelievable! I just got my first ever call from a potential customer. He is a real estate broker and he asked me about this very subject. I told him that I believed it had to do with zinc in the flashing which is what he kind of hinted at. Now I'll be able to send him an email that shows him I looked into the subject and got back to him with a definitive answer kinda like a true professional. As soon as he gets some $$ sent my way I will immediately forward 100 of them to RCIA.

This is great info to know Chris, thanks. It makes perfect sense too - I can actually picture a roof we treated recently and the dark area of the roof mirrored exactly how the water ran down the roof.

I also had a customer that said her roof was only dirty were the gutter was emptying out onto the lower roof. Her shingles were very dark to begin with, but there was a major difference between the front and back half of her roof. She didn't believe me till I had her take a look. As of yesterday, her roof is all the same color. Amazing how easy it can be to show others the obvious visual difference. If only they knew how/where to look!