What is the white staining on these roof tiles?

Dear Roofing Experts,

Can someone please take an educated guess as to the likely cause of the white staining on these roof tiles please? Sorry about the poor quality photograph.

I’ve read that white staining around a chimney could signal serious structural issues but I have also read that this could the a simple stain from a poor job done when completing the flashing work.

Thank you all in advance.


It seems to be all around the chimney and not zinc leaching from galvanized flashings. I’m going to guess it’s a wood fireplace and the soot has stained the surrounding area over the years. Or maybe it’s a popular pigeon hangout?

Never seen white soot so I’m pretty sure it’s not that but birdshit is a possibility. Need a picture that isn’t blurry. I see a patina on part of the flashing and that could be relevant

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Thanks for the response, Ivoman.

The fireplace at the bottom of the chimney looks like its never been used - there isn’t even a fire grate, it’s basically used to hold a plant pot.

Also, I’ve not seen any birds in the vicinity, never mind pigeons.

I’m suspicious that this is not due to the lead flashing - due to the spread around the chimney and the fact that none of of other chimneys on the roof have any issue(s).

Does this look like efflorescence to you?

Thanks for the response, Tileman.

In what way to you think the patina would be relevant? And would you not expect that same pattern to appear on all chimneys on the house? This seems to be the only chimney with this issue and only on this side of the roof.

If it tastes salty, you may be right. Puzzling that it appears only around the chimney and not on the chimney itself? If it is the roof tile, why only on an area surrounding the chimney? The roof on the lower right of the image does not show this residue.

If it tastes birdy, I may be right. :wink:

I’ve seen pigeons congregate on roofs for a short while and then never again. Maybe, at one time, someone in the area was a pigeon keeper and has since shut down their coop? Bird droppings excrete uric acid which is known to corrode roof tiles over time. This may be their enduring legacy!

Efflorescence: Cause and Control
Bird dog problem

Thank you for the attached document, Ivoman.

I’ve added an additional picture of the other chimneys on the property.

I’m wondering if it’s significant that this is the only chimney that has had a satellite dish mounted on it - could this have penetrated the chimney cavity perhaps? But, to challenge myself, why has this staining not occurred on the back side of the roof, if that were indeed the case.

That was one nimble dog by the way :slight_smile:

Roof Full Front

Rear of roof.

Again, in the lower left corner of your image, the chimney flashing shows a similar residue. The satellite dish, if the culprit, would produce localized staining and not staining surrounding the whole area would it not?

I’m still in the “once upon a bird” camp …

Is this on the leeward side of the prevailing winds?

Good spot on the left corner, however it’s not quite staining the roof tiles at all - just above the tiles.

I had to Google “leeward” to find out what it meant :). I’m not sure about the winds, but I’ve attached a satellite image to show you North and South facing.

Interestingly, there is an identical (same blueprint, same age, same structure) house in close proximity facing the same directions and there are no issues on that corresponding chimney. I’ve highlighted in the picture the two roof top views. I would have thought birds would have found the same chimney location on a different house just as appealing :slight_smile:

Seems specific to this one chimney area, on one side of the roof.

Thank you for your engagement on this by the way - I’m finding this useful just bouncing ideas off someone who knows about this stuff.

I asked about the winds as birds prefer to find shelter out of the wind. As to why they might like one roof over the other could be a combination of proximity, additional shelter from nearby trees and access to food … who the heck knows? As far a being someone who knows about this stuff, you might be too generous with your kind assumption surrounding this particular dilemma. Good luck on your mysterious staining inquiry as I’ll now step back eager to learn of other hypotheses.


Thank you for the help.

Underneath the chimneys where the metal keeps the roof clean…

Everything else needs to be cleaned and it will look the original color.

Its not a stain.
Its the original color which you will enjoy if you clean the roof.


Hi roof_lover, I’m not sure I follow you. Are you saying this is not a stain?

Its not a stain.
The entire rest of your roof is stained.
Have the roof cleaned and it will look all the same.

The chimney flashing keeps the roofing under it
(5 feet or less) clean by stopping the algae and streaking from happening.

You will see the same directly under any lead plumbing flashing( one to two feet)

10 percent of Atlas shingle granules are coated with copper which does the same thing.

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I’m either being incredibly thick or perhaps that’s a tongue-in-cheek response from you roof_lover - if it’s the former, I apologise, but I’m not following.

If I too interpret correctly, the tile under the existing flashings will reveal the “true” tile color. The rest of the roof is discolored due to weathering.

A roof over 6-7 years old starts to stain.
Many times it stains all over by year 10.
But, Just under your metal accesories, chimney flashings, plumbing flashings, galvanized exhaust vents these things will keep the shingles clean just under them.
The shingles do not want to stain directly under these things.
But only for a short distance.

That is why the old product with metal algae resistant strips installed under ridge caps never worked
Because it only cleaned a couple of feet below it.

What are the ‘tiles’ made of? Asphalt-cement/asbestos-clay?

I think they are cement roof tiles.