White Stains on roof

This one is in Florida. I see this quite a bit, where I see white staining (or is it a lack of dirt/fungal growth?) on older asphalt roof coverings, immediately under all penetrations. Can anyone tell me what it is from, and if it tells us anything about the roof condition I should be reporting? Thanks in advance for your expertise!

Zinc from the lead boots.

Well, that was easy! Thanks much

Actually, the roof has black algae (Gloeocapsa magma) on it and rain washes the zinc down killing the algae. So the light-colored stain is actually the original shingle color. Copper will also kill the algae. You can actually buy shingles now with copper mixed in with the granules to prevent the algae.

It’s the rest of the roof that’s stained. Those jacks are improperly installed by the way. The flanges should be interleaved with the shingles.

FYI, for retrofit on existing roofs there are a number of products from zinc strips to spray on algae killers.

Don Hawley CPI
Hawley Home Inspections LLC

Home Inspection Services, Termite, Radon & Sewer Scope
Licensed Radon Professional
Licensed Home Inspector

Thanks much. What do you mean by the “jacks?” The bottom flange of the lead boots? I see them both interlaced with shingles, and not in the photo I believe.

Ah nevermind, I’m just not used to them being called jacks in these parts. I got it now, lol. Too early!

Yep, we call them vent boots in these parts. I hope you read up on black algae and AR shingles vs non-AR shingles.

The lower flange should terminate on top of the shingle in the course below. One is correct, the others are wrong.

Thanks Kenton. Yes, that’s what I like to see also with that flange hanging out. I see them fully buried under the shingles all the time unfortunately!