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ROOFING INSPECTION & REPAIR
CERTIFICATIONS for ROOFING CONTRACTORS
CHOOSING A ROOFING CONTRACTOR
ASBESTOS CEMENT ROOFING
ASPHALT ROOF SHINGLES
  ASPHALT SHINGLE DEFINITIONS
  ASPHALT SHINGLE FAILURE TYPES
  ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES
  ALGAE, FUNGUS, LICHENS, MOSS COMPARED
  ALGAE STAINS ON ASPHALT ROOF SHINGLES
  ALGAE STAIN TEST METHODS
  BLACK STAIN REMOVAL & PREVENTION
  BLISTERS on ASPHALT SHINGLES
  CRACKS in FIBERGLASS SHINGLES
  CUPPING ASPHALT SHINGLES
  CURLING ASPHALT SHINGLES
  FISHMOUTHING ASPHALT SHINGLES
  GRANULE LOSS from SHINGLES
  HAIL DAMAGED SHINGLES
  LADDERING & STAIR STEPPING SHINGLES
  LIFE / WEAR FACTORS in SHINGLES
  MECHANICAL DAMAGE of SHINGLES
  MOSS & LICHENS on SHINGLES
  ORGANIC FELT SHINGLE DEFECTS
  SPLICE DEFECTS on ASPHALT SHINGLES
  STAINS on ROOF SHINGLES
ATTIC CONDENSATION CAUSE & CURE
BUILT UP ROOFS
CERTIFICATIONS for ROOFING CONTRACTORS
CHIMNEY INSPECTION & REPAIRS
CHOOSING A ROOFING CONTRACTOR
CLAY TILE ROOFING
FIRE RETARDANT PLYWOOD
HEAT TAPES & CABLES on Roofs for Ice Dams
LOW SLOPE ROOFING MATERIALS
MASONITE WOODRUF FIBERBOARD ROOFING
MEMBRANE & SINGLE PLY ROOFS
METAL ROOFING TYPES
MODIFIED BITUMEN ROOFING
ROOF INSPECTION SAFETY & LIMITS
ROOF VENTILATION SPECIFICATIONS
ROOF VENTING ENERGY SAVING DETAILS
SLATE ROOF INSPECTION & REPAIR
  SLATE ROOF DURABILITY
  SLATE ROOF REPAIRS
  SLATE ROOF SOURCES
  SLATE ROOF TYPES
  SLATE ROOF PHOTO LIBRARY
  SLATE ROOF INSPECTIONS
  SLATE ROOF INSPECTION CLASS
SIDING WOOD
STAIN DIAGNOSIS on Building Exteriors
STAIN DIAGNOSIS on Indoor Surfaces
STAIN DIAGNOSIS on Roofs
  Causes of Roof Stains
  Catalog of All Roof Stains
  Catalog of Black Roof Stains
  Black Algae
  ALGAE STAIN TEST METHODS
  Black Stain Removal & Prevention
  Bleed-Through
  Chimney-Caused Roof Stains
  Debris Staining on Roofs
  Lichens on Roofs
  Moss on Roofs
  Rust Stains on Shingles
  Soot Staining on Roofs
SOD ROOFING
SIDING WOOD
STAIN DIAGNOSIS on Building Exteriors
STAIN DIAGNOSIS on Roofs
STANDARDS for ROOFING
STONE ROOFING
THATCH ROOFING
THERMAL EXPANSION of MATERIALS
THERMAL MASS in BUILDINGS
THERMAL MASS in UPSTAIRS
TILE ROOFING
WARRANTIES for ROOF SHINGLES
  CLASS ACTION SHINGLE LAWSUITS
  REPORTING SHINGLE FAILURES
  ROOF FAILURE REPORT FORM
WOOD SHAKE & SHINGLE ROOFING
WORKMANSHIP & WIND DAMAGE

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Photograph of mossy growth on asphalt roof shingles

Guide to Identifying, Removing, Preventing Algae, Fungus, Lichens, Moss on Roof Shingles
InspectAPedia®  -    

  • Algae, moss, lichens, or fungal growth on roof shingles: causes, effects on roof life, cure & prevention
  • Types & photographs of organic felt asphalt roof shingle defects & failures
Our site offers impartial, unbiased advice without conflicts of interest. We will block advertisements which we discover or readers inform us are associated with bad business practices, false-advertising, or junk science. Our contact info is at InspectAPedia.com/appointment.htm.

Here we discuss the causes of algae, moss, lichens, or fungal growth on roof shingles, the effects of these conditions, and how to cure or prevent them.

Also see STAINS on ROOF SHINGLES. This website tells readers how to identify & explain the most-common asphalt roof shingle failures and how to obtain asphalt roofing shingle failure claims assistance.

These defects occur on organic-mat or fiberglass-mat asphalt roof shingles. Readers are also invited contribute roof failure information to the web author for research purposes. web author for research purposes.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

Algae, Fungus, Lichens, Moss Effects on Asphalt Shingle Roofs

Causes of moss or lichens growth on roofs

Moss growing on any roof surface will be more severe on roof sections that area shaded and exposed to periodically damp cool weather conditions.

The presence or absence of much sunlight on a roof surface is often a determining factor in the amount of moss or lichens growth (more sun, less moss and lichens.

Mossy roof shingles (C) Daniel Friedman Mossy roof (C) Daniel Friedman

Moss and lichens are more than a cosmetic issue on many kinds of roofing materials - asphalt shingles, roll roofing, wood shingle roofs, wood shake roofs. By holding moisture against the roof surface lichens but more so moss speed the wear of the asphalt shingle surface in freezing climates by increasing frost damage to the mineral granule coating on the shingles.

Sometimes there is so much moss and crud on a roof that we're not sure what roofing material was used. The photo at right is actually of a wood shingle roof, though it may make more sense to call this a moss roof in Rhinebeck, New York.

But on an asphalt or possibly some (treated) wood shingle roofs, shingle chemistry is also involved - some roof shingle materials contain algaecides or fungicides which will also retard moss growth on the roof surface. You'll also notice that moss, lichens, and usually algae and fungus will be conspicuously absent from a roof surface down-roof from areas where galvanized metal, copper, or even aluminum flashing are installed. Mineral salts washing off of these metals will retard moss or algae growth on the shingles.

Moss on a wood shingle roof (C) Daniel Friedman

New asphalt roof shingles are available with an inclusion of chemicals that resist moss, lichens, algae, and even fungal growth. Resist does not mean moss-proof or lichens proof however for shingles subject to difficult conditions such as extensive shade under trees and lots of organic debris left on the roof surface.

We have observed that the chemical or mineral salt wash-off from some building materials like aluminum flashing and copper flashing and even some paints which appear to kill of moss, lichens, algae, and fungus, as their extracts are washed over the roof surface. It's particularly easy to spot this effect by noticing where there are moss-free areas on an otherwise mossy roof surface.

One of our most obvious photos of rain wash off of copper flashing keeping moss off of a roof happens to be on a wood shingle roof, But we see this effect below copper flashing (and often aluminum flashing) on asphalt shingle roofs as well.

What are the effects of moss growth on roofs?

Because moss or lichens growing on a roof surface will hold moisture on the roof longer than other areas, these growths can reduce the life of the roof covering.

Particularly where the roofing materials are asphalt shingles or wood shingles, holding water on the roof surface by any means (leaves, debris, moss, or lichens) speeds up wear on these shingles. In freezing climates there may be faster frost damage, cracking, and wear of the shingles under the moss or lichens. Even in non-freezing climates, the roots or growth structures of moss or lichens eventually penetrate and separate the roof shingle materials, speeding their demise.

Is lichens on a roof as much of a problem as moss?

Photograph of lichens growth on asphalt shingles

Because lichens growing on a roof surface does not have as much thickness of body as moss, it will hold less water on the roof surface and is less of a wear factor than moss.

Therefore if we have only lichens growing on a roof surface we would be less quick to try to clean it off since lichens not only has a tighter "grip" on the roof surface but the cleaning process for lichens risks doing more harm than good to the roof surface.

At ALGAE, FUNGUS, LICHENS, MOSS COMPARED we show photographs of lichens damage to asphalt shingle roofs.

Is green or black algae on roof shingles as much of a problem as moss or lichens?

Algae on a roof surface appears as a thin green coating which is mostly a cosmetic concern. The presence of algae on the roof is an indicator that this roof area is in a shaded spot where you may want to be alert for development of moss or other roof problems, but the level of damage from algae is probably low, even less than that caused by lichens. Avoid any aggressive cleaning methods that might damage the roof surface.

Black algae stains on asphalt singles

Photograph of ...

Some black stains on asphalt roof shingles are caused by a black algae (sometimes misnamed as a black fungus or even a "mildew") such as that shown in the photograph here. Black algae stains may be mistaken for but are not "extractive bleeding" - a product cosmetic defect.

When the staining or bleeding appears to run down the roof from individual small points or "spots" we think this is extractive bleeding or "bleed through" on shingles. (See ALGAE STAINS ON ASPHALT ROOF SHINGLES and also STAINS on ROOF SHINGLES for a more detailed discussion of bleed through or extractive bleeding as well as black algae stains on roof shingles.

When black stains on the roof surface are more uniform and cover a wide area that does not originate at one or more single pinpoints in the shingles, this may be a black algae growing on the shingle surface.

As we said about green algae on roofs, the presence of these black fungal or algal stains on the roof is an indicator that this roof area is in a shaded spot where you may want to be alert for development of moss or other roof problems, but the level of damage from the black fungus or algae is probably low, even less than that caused by lichens and certainly less than that caused by moss. Avoid any aggressive cleaning methods that might damage the roof surface.

How to clean off mossy or lichens-covered roofs

Photograph of mossy growth on a worn out asphalt shingle roof

Do not try to clean a roof like the one shown in this photograph. The shingles are worn out and fragile. It will be impossible to clean the roof without damaging it. A new roof is needed.

Power washing or brushing: it is possible to remove moss from a roof surface by gentle cleaning using a soft brush or a power washer.

But be careful: power washing or even brushing or sweeping an asphalt shingle roof (or a wood shingle roof in old, worn, fragile condition) is itself a process that can damage the roof by breaking shingles or by loosening the protective mineral granules from the shingle surface.

Chemicals that "kill" the moss or lichens risk also damaging the shingles or contaminating the environment, and have the further disadvantage that they still leave the moss or lichens in place where it holds water on the roof surface.

How to prevent moss or lichens growth on roof surfaces

Wood shingle roof in Key West FL

Notice the clear area below the turret on top of this wood-shingled pyramid shaped roof located in Key West Florida. Chemicals from the metal cap atop the turret and from flashing at the turret base appear to be washing down the wood shingles in a path which prevents or even kills off moss, algae, and lichens on this roof (which we viewed from the Key West lighthouse museum.)

Installing copper or other metal strips along the ridge of an existing roof will slowly kill off moss or lichens as rainwater washes over the metal and down the roof surface. This method is suitable for both prevention of future or further moss or lichens growth on the roof and for gently treating an otherwise fragile old roof.

 

Trim back trees whose branches overshadow the roof surface. Keep the roof clean of organic debris like leaves or pine needles which may collect in valleys or at other roof locations.

Chemically treated roof shingles are available from several asphalt roofing manufacturers who offer these products which are resistant to moss, lichens, or algae growth on roofs. Discuss this option with your roofer when it's time to replace the roof.

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ASPHALT ROOF SHINGLES
  ASPHALT SHINGLE DEFINITIONS
  ASPHALT SHINGLE FAILURE TYPES
  ALGAE, FUNGUS, LICHENS, MOSS COMPARED
  ALGAE STAINS ON ASPHALT ROOF SHINGLES
  ALGAE STAIN TEST METHODS
  BLACK STAIN REMOVAL & PREVENTION
  ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES
  BLISTERS on ASPHALT SHINGLES
  CRACKS in FIBERGLASS SHINGLES
  CUPPING ASPHALT SHINGLES
  CURLING ASPHALT SHINGLES
  FISHMOUTHING ASPHALT SHINGLES
  GRANULE LOSS from SHINGLES
  HAIL DAMAGED SHINGLES
  LADDERING & STAIR STEPPING SHINGLES
  LIFE / WEAR FACTORS in SHINGLES
  MOSS & LICHENS on SHINGLES
  ORGANIC FELT SHINGLE DEFECTS
  SPLICE DEFECTS on ASPHALT SHINGLES
  STAINS on ROOF SHINGLES
ATTIC CONDENSATION CAUSE & CURE
BUILT UP ROOFS
CERTIFICATIONS for ROOFING CONTRACTORS
CHIMNEY INSPECTION & REPAIRS
CHOOSING A ROOFING CONTRACTOR
CLAY TILE ROOFING
FIRE RETARDANT PLYWOOD
HEAT TAPES & CABLES on Roofs for Ice Dams
LOW SLOPE ROOFING MATERIALS
MASONITE WOODRUF FIBERBOARD ROOFING
MEMBRANE & SINGLE PLY ROOFS
METAL ROOFING TYPES
MODIFIED BITUMEN ROOFING
ROOF INSPECTION SAFETY & LIMITS
ROOF VENTILATION SPECIFICATIONS
ROOF VENTING ENERGY SAVING DETAILS
SLATE ROOF INSPECTION & REPAIR
  SLATE ROOF DURABILITY
  SLATE ROOF REPAIRS
  SLATE ROOF SOURCES
  SLATE ROOF TYPES
  SLATE ROOF PHOTO LIBRARY
  SLATE ROOF INSPECTIONS
  SLATE ROOF INSPECTION CLASS
SIDING WOOD
STAIN DIAGNOSIS on Building Exteriors
STAIN DIAGNOSIS on Indoor Surfaces
STAIN DIAGNOSIS on Roofs
  Causes of Roof Stains
  Catalog of All Roof Stains
  Catalog of Black Roof Stains
  Black Algae
  ALGAE STAIN TEST METHODS
  Black Stain Removal & Prevention
  Bleed-Through
  Chimney-Caused Roof Stains
  Debris Staining on Roofs
  Lichens on Roofs
  Moss on Roofs
  Rust Stains on Shingles
  Soot Staining

Online Guide to Types 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.

ROOFING INSPECTION & REPAIR

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