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Extractive bleeding roof stains (C) Daniel Friedman Catalog of Black Stains on Building Roof Surfaces

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.

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Catalog of Causes of Black Stains on Roofs

Photograph of black algae growth on roof shingles

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

Photograph of possible asphalt shingle bleed-through or extractive bleeding on asphalt roof shingles (C) Daniel Friedman

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

Photograph of black algae growth on roof shingles (C) Daniel Friedman

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

Roof stain or lichens or moss caused by trees (C) Daniel Friedman

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

Photograph of chimney soot stains on a roof.

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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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

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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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