Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
ROOFING INSPECTION & REPAIR
AGE OF ROOFING
AMERICAN CEMWOOD ROOFING
ARCHITECTURE & BUILDING COMPONENT ID
ASBESTOS IDENTIFICATION IN BUILDINGS
ASBESTOS & FIBER CEMENT ROOFING
ASBESTOS MATERIAL REGULATIONS
ASPHALT ROOF SHINGLES
ATTIC CONDENSATION CAUSE & CURE
BEST CONSTRUCTION PRACTICES GUIDE
BEST ROOFING PRACTICES
BUILDING SAFETY HAZARDS GUIDE
BUILT UP ROOFS
CERTIFICATIONS for ROOFING CONTRACTORS
CHIMNEY INSPECTION & REPAIRS
CHIMNEY FLASHING Mistakes & Leaks
CHOOSING A ROOFING CONTRACTOR
CLAY TILE ROOFING
CLAY, CONCRETE, FIBER CEMENT TILE INSTALLATION
COOLING LOAD REDUCTION by ROOF VENTS
DEBRIS STAINING on ROOFS
DECKS, ROOFTOP CONSTRUCTION
DEFINITIONS of ENGINEERED WOOD OSB LVL etc
DISASTERS: BUILDING INSPECTION & REPAIR
DISPUTE RESOLUTION on ROOF JOB PROBLEMS
ENERGY SAVINGS in buildings
EPDM, RUBBER, PVC ROOFING
EPDM ROOF LEAK REPAIRS
EXTRACTIVE BLEEDING on SHINGLES
FELT UNDERLAYMENT REQUIREMENTS
FIBER-WOOD & FIBERBOARD ROOFING
FIRE RATINGS for ROOF SURFACES
FIRE RETARDANT PLYWOOD
FLASHING on BUILDINGS
FLASHING, ASPHALT SHINGLE VALLEYS
FLASHING, CHIMNEY Mistakes & Leaks
FLASHING, CLAY TILE ROOFS
FLASHING MEMBRANES PEEL & STICK
FLASHING for METAL ROOFS
FLASHING ROOF WALL DETAILS
FLASHING ROOF-WALL SNAFU
FLASHING SIDING DETAILS
FLASHING WALL DETAILS
FLASHING WINDOW DETAILS
FLASHING WOOD ROOF DETAILS
FLAT ROOF MOISTURE & CONDENSATION
GALVANIC SCALE & METAL CORROSION
GREEENHOUSE / SOLARIUM ROOF LEAKS
GUTTERS & DOWNSPOUTS
HAIL DAMAGED SHINGLES
HEAT TAPES & CABLES for ROOF ICE DAMS
HOT ROOF DESIGNS: UN-VENTED ROOF SOLUTIONS
HOUSEWRAP INSTALLATION DETAILS
HUMIDITY LEVEL TARGET
ROOF ICE DAM LEAKS
INSECT INFESTATION / DAMAGE
INSULATION IDENTIFICATION GUIDE
INSULATION INSPECTION & IMPROVEMENT
LEAD POISONING HAZARDS GUIDE
LEAKY ROOF DIAGNOSIS & REPAIR
LEED GREEN BUILDING CERTIFICATION
LOW SLOPE ROOFING
MODIFIED BITUMEN ROOFING
NOISE / SOUND DIAGNOSIS & CURE
NOISE CONTROL for ROOFS
PLASTIC ROOFING TYPES
PVC, EPDM, RUBBER ROOFING
ROLL ROOFING, ASPHALT
ROOF ARCHITECTURAL STYLES - PHOTO GUIDE
ROOF CLEANING RECOMMENDATIONS
ROOF COLOR RECOMMENDATIONS
ROOF DORMER TYPES - PHOTO GUIDE
ROOF INSPECTION SAFETY & LIMITS
ROOF SLOPE DEFINITIONS
ROOF NOISE TRANSMISSION
ROOF REPLACEMENT SNAFUs
ROOF SLOPE DEFINITIONS
ROOF VENTILATION SPECIFICATIONS
ROOF VENTILATION ENERGY SAVING DETAILS
ROOFING FELT UNDERLAYMENT REQUIREMENTS
ROOFING MATERIALS, Age, Types
ROOFING TILE SHAPES & PROFILES
ROOFING UNDERLAYMENT BEST PRACTICES
RUBBER, EPDM, PVC ROOFING
SADDLE CONSTRUCTION at CHIMNEYS
SLATE ROOF INSPECTION & REPAIR
SNOW GUARDS & SNOW BRAKES
SOUND CONTROL in buildings
STAIN & BIODETERIORATION AGENT CATALOG
STAINS on & in BUILDINGS, CAUSES & CURES
STAINS on CONCRETE
STAIN DIAGNOSIS on BUILDING EXTERIORS
STAIN DIAGNOSIS on BUILDING INTERIORS
STAINS on INDOOR SURFACES, PHOTO GUIDE
STAINS & Thermal Tracking
STAIN DIAGNOSIS on ROOFS
STAINS on STONE, DIAGNOSE & CURE
STONE SURFACE CLEANING METHODS
STRESS SKIN INSULATED PANELS
TEST LABS - ROOF SHINGLE
WALK-ON ROOF SURFACES
WARRANTIES for ROOF SHINGLES
WIND DAMAGE to ROOFS
WOOD SHAKE & SHINGLE ROOFING
WORKMANSHIP & ROOF DAMAGE
ZINC METAL ROOFING
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.
Green links show where you are. © Copyright 2015 InspectApedia.com, All Rights Reserved.
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.
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.
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.
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 from fireplace flues washing down onto the roof - characterized by staining appearing below and in line with the chimney
See CHMNEY-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.
Continue reading at BLACK or GREEN ALGAE STAINS on ROOFS or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
No FAQs have been posted for this page. Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References