Catalog of Black Stains on Building Roof Surfaces InspectAPedia® -
Online guide to black, brown, green, and other stains on building roof surfaces
Diagnostic Guide to Types of Stains and Staining Materials Found on Roof Surfaces
Causes, cure, and prevention of black stains on roof shingles
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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 BLACK ROOF STAINS - 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 - 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).
Please see Bleed-Through for our full discussion of extractive bleeding stains on asphalt shingles.
BLACK ALGAE - Black Algae Stains on Asphalt Shingles
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.
Please see Black Algae for our full discussion of this topic.
The black stains on the roof at above left are probably an algal growth.
DEBRIS STAINING - Black Debris Stains on Asphalt Shingle Roofs
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).
Please see Debris Staining for our full article on this topic.
SOOT STAINING - Black Soot Stains on Roof Shingles Around Chimneys
Soot from fireplace flues washing down onto the roof - characterized by staining appearing below
and in line with the chimney
Please see Chimney-Caused Roof Stains for the full article on this topic as well as some important fire and flue gas safety warnings.
Photograph of a soot-stained roof top was provided courtesy of Roger
Hankey a Minnesota home inspector.
List of Stains on Building Roofs, Surfaces, Walls
In the following guide we list types of stains by stain color & appearance, by building location or material, and by stain cause. We distinguish among the following stuff that may stain or be found growing building roofs, walls, or other surfaces, with extra focus on asphalt shingle roofs as well as other roofing materials such as wood shingles, wood shakes, roll roofing, and even slate or tile roofs. Some of these types of roof stains or discoloration are only cosmetic in nature, while others may indicate growths that are likely to reduce the roof covering life. A more detailed, illustrated version of the list below is given at Stain Diagnosis on Building Exteriors.
Black stains on asphalt roofing products such as asphalt shingles or roll roofing, caused by extractive bleeding (product defects) - see Bleed-Through and see Roofing material defect / environmentally-caused roof shingle stains.
Black, brown, or gray stains on roofing products due to debris left on the roof surface, such as piles of leaves and organic waste from nearby trees. See Debris Staining and see Proximate cause roof shingle stains
Black or other colored stains on roof surfaces may be caused by soot from chimneys, both wood-fired and oil-fired devices. Black or other colored stains may also appear on roof surfaces from nearby industrial activities. See Soot Staining.
Brown or red stains on roof surfaces are often caused by rust from wearing steel flashing or other on-roof metal products. See Rust Stains on Shingles.
Lichens growing on roof surfaces - Lichens are not the same growths as moss or algae, and are difficult to remove without damaging the roof surface. See Lichens on Roofs for details about how lichens can cause roof damage, see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES for a guide to preventing these roof growths and stains. Also see ALGAE, FUNGUS, LICHENS, MOSS COMPARED.
Moss on roof surfaces - see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES. Green or other colored mosses are a bit easier to remove than lichens on roofing surfaces, but both can carry away mineral granules and damage the roof surface. Moss tends to hold more water and moisture on the roof surface. So in our opinion moss is more likely to damage a roof surface than lichens or algae. Also see ALGAE, FUNGUS, LICHENS, MOSS COMPARED.
Rust Stains on buildings - see Rust Staining - Red or Brown Rust Stains (on shingles)
Soot or Creosote black or brown stains on roof surfaces near or below chimneys - see SOOT STAINING - Black Soot Stains on Roof Shingles Around Chimneys and see Proximate cause roof shingle stains
White stains on roof surfaces may be from wash-down of pigments in paint on surfaces above the roof such as a gable end or dormer wall; white or less-black roof surfaces may also be found below copper or aluminum flashing whose salts run down the roof surface in wet weather, preventing algae or moss growth and leaving a white area on an otherwise stained roof surface. Our article at ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES includes a photograph of this condition on a wood shingle roof.
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7/07: thanks to Roger Hankey & Cheryll Brown, ASHI home inspectors in
Minnesota, for the rooftop soot staining photograph. Mr. Hankey is a past chairman of the ASHI Technical Committee, serves as co-chairmain of ASHI legislative committee, and has served in other ASHI professional and leadership roles.
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