Black stains on roofs: here is our catalog listing the types of black stains that are found on roofs, using asphalt shingle roofs as the prime example.

This article series tells readers how to identify & explain the most-common causes of black, brown, red, gray, green, or white stains appearing on roof shingles and on other building surfaces.

Roof shingle stains are often caused by black algae, bleed-through or extractive bleeding of asphalt, dirt, soot, or organic debris.

Catalog of Causes of Black Stains on Roofs

Aesthetic or Cosmetic Roofing Issues - Black Stains on Asphalt Shingles

Some consumers have concerns with how their shingles look on the roof as much as with how long the roof will last. Roofing manufacturers offer a wide variety of products which give different "looks" and shadings.

It's possible that in addition to site and installation conditions, variations in manufacturing process (granule adhesion, bleed-through) can affect how the roof looks from the ground.

We've also investigated client concerns with shadows appearing in early morning or late afternoon which show variations in the roof surface.

Some shadows which are only of cosmetic nature may be caused by slight buckling or unevenness in the roof decking and may not indicate a structural or durability concern.

If you have particular concerns about roof appearance ask your roofer if s/he can direct you to a house where the product which interests you is already installed.

Remember that site differences (orientation to sun, shade trees, height above ground, roof pitch, and probably other factors) may make shingles look a bit different on your house.

Bleed-Through Shingle Stains

Black Bleed-Through or Extractive Bleeding Black Stains on Asphalt Shingles

Extractive bleeding - bleed-through

asphalt shingle stains may be mistaken for but are not black algae or black "fungus", nor are they soot. Extractive bleeding stains on asphalt shingles are caused by loss of black pigment in the asphalt mix intended to impregnate the shingle mat itself.

Extractive bleeding or "bleed through" stains

leaving black streaks running down an asphalt shingle roof is an indication of a defective roofing product.

Typically bleed-through on asphalt shingles appears as black streaks running down shingles.

You'll see black streaks of varying length and width (photo at left).

Really? Some experts claim that extractive bleeding of roof shingles is a fantasy - that it never occurs, and that all black roof stains are due to algae growth or other causes. Having found some expert citations describing extractive bleeding of asphalt roof shingles as a product defect, while we agree that it's not common, we don't agree that it's a fantasly.

See EXTRACTIVE BLEEDING on SHINGLES for our full discussion of extractive bleeding stains on asphalt shingles.

Black Algae Roof Staining

Black Algae Stains on Asphalt Shingles, Roll Roofing & Many Other Kinds of Roof Surfaces

Black algae stains on roofs is in many areas the most common explanation for black blotches, streaks, or discoloration on asphalt roofing products as well as on some other roofing materials.

Misnamed as "mildew" or "fungus" by some writers, algae staining on asphalt shingles usually in shaded areas or on the more-shaded roof slopes (photo at left) characterized by black staining fairly uniform over shingles, but appearing specifically in areas of the roof shaded by nearby trees.

See BLACK or GREEN ALGAE on ROOFS for our full discussion of this topic.

The black stains on the roof at above left are probably an algal growth.

Debris-Staining on Roofs

Black Debris Can Cause Stains on Asphalt Shingle Roofs & Other Roof Materials Too

Debris staining on roofs produces fairly uniform black or brown staining in areas where due to low-slope or presence of overhanging trees, organic debris collects on the roof slope.

Decaying debris may encourage fungal or algal growth (cited above). Debris staining often incorporates fungal or algal growth in the shaded, longer-wet areas of a roof as well as staining caused by the actual roof debris itself.

Please see DEBRIS STAINING for our full article on this topic.

Soot Staining on Roofs

Black Soot Stains on Roof Surfaces Around & Below Chimneys

Soot from fireplace flues washing down onto the roof - characterized by staining appearing below and in line with the chimney, as Roger Hankey is demonstrating above.

See CHMNEY-CAUSED ROOF STAINS for the full article on this topic as well as some important fire and flue gas safety warnings.

The photograph of a soot-stained roof top was provided courtesy of Roger Hankey a Minnesota home inspector. Thanks again Roger.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Could roofing felt have caused these black stains on our slate roof and brick exterior walls?

Do you have reports of tar paper failure when the tarpaper would discolor both the slate and walls of the building? Black staining.

The black stain ran down the brick and limestone staining it.  It would not clean off the brick or stone and the storm door had to be refinished because of the black stains

Would appreciate hearing back from you at your earliest convenience. - Anonymous by private email Mar 11, 2026,

Reply by (mod) - No, those black stains are not caused by roofing felt and are more likely an algae

I'm too experienced to say that the stains in your photos could not possibly be from asphalt bleed-out from "tar paper" (i.e. "roofing felt") under the slates, and I'd need more information to be more confident, but my guess/opinion is that we're seeing a black algae rather than asphalt bleed-out.

Notice that in your first photo that the facing roof slope has stains, but the slope to its left (that left hand gable roof) shows no staining.

Now tell me which roof slopes get the most sun. (More sun = less algal growth).

There's often a correlation between shade and sun exposure vs. biological stains such as from algae.

Also, that extensive black staining on the white stone archway over your entry door (red arrows) is highly unlikely to be related to roof wash-down - it's on a gable end that does not receive roof runoff, even if your roof gutters were clogged.

That's more argument for an environmental contaminant.

You could also do some tests: If the staining were from the roofing felt, it's basically an asphalt compound that would be soluble in a mineral based solvent like odorless paint thinner.

When I did field work on stains like this I collected tape samples of the staining material to examine in my forensic lab: it's easy to identify algae and also to test for soluble asphalt. (I'd offer to look at a sample from your home but in fact am currently working out of the U.S. ) I

have several articles that I'd like you to look-over.

BLACK ROOF STAIN CAUSES  - I will include your photos and an anonymous version of this discussion on this page - it's the only consulting compensation I request.

ALGAE STAIN TEST METHODS

STAIN DIAGNOSIS on ROOFS  - more general 

BLACK or GREEN ALGAE STAINS on ROOFS 

and BLACK or GREEN ALGAE STAIN REMOVE / PREVENT

Watch out: On the roof itself I very much advise against power washing - likely to cause much more damage than good.

But if you want to try some of the cleaners I discuss in the removal article (the last one), try working first on a small inconspicuous area.

Why do some parts of my roof look more wet or black-stained than others?

Just trying to get a handle on what causes part of my roof to look "wetter" than other parts.

See attached photo. The photo was taken several hours after a rainfall.

The tree out front doesn't seem close enough to cause Algae or moss. The roof has not been power washed.

So, not sure what would cause one section to look wetter than other sections.

I believe when the roof is dry the sections appear uniform. I will have to double check that.
Appreciate any insight. On 2022-05-17 by Sam G.

by Friedmandaniel911 (mod) - slow drying wet areas - not stains on the roof?

@Sam G.,

Thank you for the photo and the "dark roof areas - looking wet" area question.

Frankly, I don't know the cause of those dark areas for sure but a reasonable guess is that the darker areas of the roof are simply those that take longer to dry out after a rain-storm.

Notice that the dark areas are on the lower slope and lower edges of the roof, where there would be more water, slower water run-off, and so perhaps where the roof surface takes longer to dry out after a rainstorm.

That variation in dry-out area time for different roof sections would in turn be caused by variation in air movement over the roof or variations in sun exposure.

In turn the underlying causes would be shade + tree patterns + other site features that affect air flow and sun exposure.

Furthermore - gilding the lily of my guess - the lower roof areas

- are wetter at the end of a brief rainstorm because during rain there is more water (it's cumulative) at the lower roof sections as those receive both the water that falls on to that section plus the water that runs-down from above

- will often dry out at a different rate over an un-heated porch or carport than over the occupied portion of the home

Other factors (and more lily-gilding) include roof slope and, less likely, (and ususally less-significant), variations in the shingle material themselves from different bundles or in exposure of some bundles during storage.

Finally, I see that your roof includes a ridge vent but I can't see whether or not there is intake venting along the soffits.

Is that intake venting present and un-blocked?

Have you inspected the attic side of the roof decking for moisture, condensation, mold?

Followup by Sam G.

@Friedmandaniel911,
Appreciate the quick response. I will look at again today. Both inside and outside to compare now that it has been dry the past few days. I'll let you know.
Thanks.

 

What would cause black stains on a gray shingled roof?

What is the cause of black stains on grey c!adding roof. A roof , 20 years old. Started small and spread to both sides On 2021-04-30 by James murphy

Reply by danjoefriedman (mod)

@James murphy, most likely one of the roof stain sources discussed in the article above; please take a look and let me know what you think.

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Continue reading at BLACK or GREEN ALGAE STAINS on ROOFS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Roof Stain Diagnosis, Repair, Prevention Articles

• STAIN DIAGNOSIS on ROOFS - home
  • ALGAE, FUNGUS, LICHENS, MOSS on ROOFS
  • BLACK ROOF STAIN CAUSES
  • BLACK or GREEN ALGAE STAINS on ROOFS
  • BLACK or GREEN ALGAE STAIN REMOVE / PREVENT
  • CHIMNEYS, STAINS on / near
  • DEBRIS STAINS on ROOFS
  • EXTRACTIVE BLEEDING on SHINGLES
  • LICHENS on ROOFS
  • MOSS on ROOFS
  • POWER WASHING ROOFS
  • RUST STAINS on ROOFS
  • SOOT STAINS on ROOFS
  • TARRY BLEED on ROOFS
  • TOBACCO JUICING SHINGLE STAINS
  • WHITE STAINS on ROOFS
• TEST LABS - ROOF SHINGLE

Suggested citation for this web page

BLACK ROOF STAIN CAUSES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING ROOFING

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