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Cleaning & Prevention of Black Algae Stains, Moss, Lichens on Asphalt Roof Shingles InspectAPedia®  -     How to clean off & then prevent black algae growth and stains on roof surfaces Caution advised before trying to remove lichens growth from roofs Caution advised before trying to remove moss growth from roofs How to identify & prevent black algae growth and stains on roof surfaces Algae stains and black marks on asphalt roof shingles: causes, effects on roof life, cure & prevention

Here we discuss methods for cleaning off and preventing future roof stains due to algae or "black fungal growth" on roof shingles, the effects of these conditions, and how to cure or prevent them. We provide a list of type of stains and colors that appear on roof shingles and on other roofing materials. Also see Black Algae for more photos of black algae stains on roofs. And see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES and 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.

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How to clean off algae, mossy or lichens-covered roofs

Regardless of the cause of a roof stain, moss, or lichens, avoid aggressive roof cleaning methods (like scrubbing with a stiff brush or power washing) that might damage the roof surface. Before deciding to remove a roof stain, you should

First Step of shingle stain removal: Assure that the roof shingles are sound and thus not likely to be damaged by any cleaning procedure. 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.

Second Step of Shingle Stain Removal: Test the roof stain as well as your stain cleaning method on a small area of the roof.

Identify what the roof problem or stain or material is: algae staining, debris staining (probably can be removed or cleaned gently) versus moss or lichens growth (probably will damage the roof during removal).

How to identify algae staining on roofs: there is a simple test of applying a light spray of a diluted mixture of trisodium phosphate [use a TSP substitute, not TSP which is an environmental contaminant] and chlorine (with water) in the proper proportion will determine weather or not this is algae quite readily. If it is asphalt pigment, it will not lighten.

While we have not confirmed its presence, some black stains on roofs and roof gutters might be due to black molds or sooty molds, for which the USDA has published How to Recognize & Control Sooty Molds. Black mold growth on leaves, on roof debris that has fallen from a tree overhead, or on an aluminum roof gutter, is not a predictor that any of the species discussed in the USDA article will appear as black "sooty mold" growth on a roof shingle.

Step Three of Shingle Stain or Debris Removal: clean the roof using the gentlest possible method

Power washing or brushing??: it is possible to remove moss or lichens from a roof surface by gentle cleaning using a soft brush or a garden hose. Power washing risks damaging shingles by blowing mineral granules off of the shingle surface (as does unnecessary foot traffic on a roof).

Furthermore, unlike the simple removal of black algae stains or debris stains from a roof, trying to mechanically remove moss or lichens is likely to also remove roof surface materials, damaging the roof and reducing its life. Where mineral granules are lost from an asphalt roof surface, such as due to lichens damage shown at ALGAE, FUNGUS, LICHENS, MOSS COMPARED, there is a real risk of increased deterioration rate or reduced roof life because of loss of the protection of the mineral surface coating. In some cases the result may be actual holes in the roof shingles and leaks that can damage the structure below.

Be very 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.

That's why we prefer to use the most gentle method possible to remove moss, algae, lichens, or stains from roofs, and usually we leave moss and lichens alone except to take steps to reduce further growth of these organisms - discussed below at Remedies.

Some Roof Cleaning Chemicals may reduce or remove roof stains from algae or other causes. Be cautious: sone chemicals intended "kill" the moss or lichens risk also damaging the shingles, staining building siding (such as using bleach) 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. Some deck cleaning sprays such as StainhandleR roof and deck cleaner are also sold for use as cleaning solutions for stained roofs .

Remedies for & prevention of black algae staining on shingles

Black stains on asphalt shingles caused by algae is avoided by some of the new roof shingle products which include chemicals to retard algal growth.

Cutting back overhanging tree branches for more sun can also help reduce this problem.

Zinc or copper strips tacked along the ridge will produce (in rain) metal salts which will kill algae, lichens, and moss as the zinc salts wash down the roof. New shingles offered by some manufacturers include algae resistant chemicals in their mineral granule coating.

Shingle Shield™ and StainhandleR and Z-stop™ are example of a zinc strip products intended for use in reducing roof growth of moss, lichens, algae.

Whatever cleaning is done on a roof surface, make sure the process does not cause more harm than good to the roof and to the environment around the building.

See  Causes of Roof Stains and  Catalog of All Roof Stains for the causes and types of stains that occur on building roofs. Our complete list of types of black stains on building roofs is at Catalog of Black Roof Stains.

Removing Sooty Black Molds on Plastic or Painted Surfaces (not specifically roofs)

The USDA publication we cited above includes suggestions for removing sooty black molds (the author considers Cladosporium sp. and Aureobasidium sp. as sooty black molds though they may in fact be brown or black and may not easily wipe off as "sooty" molds). Quoting:

Sooty molds can be indirectly controlled by reducing populations of sucking insects that excrete honeydew. Outdoor furniture can be hosed down with water during periods of honeydew excretion, particularly during drought. The growth of sooty mold fungi is inhibited by preservatives used in treated wood in rustic outdoor furniture. Here is the recipe for a good cleaning solution for removing sooty molds from plastic or painted surfaces:

Be sure to wear rubber gloves when cleaning with this solution. [Note that trisodium phosphate is no longer used as a cleaning agent because it is an environmental contaminant. However substitute products may be available. Be careful not to add a cleaning agent to bleach that can cause production of toxic chlorine gas.

How to prevent algae or fungal growth on roof surfaces

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.

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.

Our photo, left, shows an absence of moss or lichens on this wood shingle roof found in Key West, Florida - notice that the "clean" wooden shingles aer all below the cupola and its flashing?

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.

List of All 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.

• Algae caused black stains on roof surfaces - Some photos of black algae stains are at Black Algae Stains on Asphalt Shingles. For details see ALGAE STAINS ON ASPHALT ROOF SHINGLES. Algae can produce black stains on asphalt roofing products. Also see  ALGAE, FUNGUS, LICHENS, MOSS COMPARED.
  
• 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.
• Black stains on building interiors: such as on carpets, drywall, or trim: see STAIN DIAGNOSIS on Indoor Surfaces and then STAIN DIAGNOSIS on Indoor Surfaces and also see STAINS on Indoor Surfaces: PHOTO GUIDE
  
• 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.
• Chimney stains on roofs - see see SOOT STAINING - Black Soot Stains on Roof Shingles Around Chimneys and see Proximate cause roof shingle stains
• Debris stains on roof shingles - see Debris Staining - Black Debris Stains on Asphalt Shingle Roofs
• Extractive bleeding stains on asphalt roofs - see Bleed-Through and see Roofing material defect
• 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.
• Mold or fungus growing on roof surfaces or on other building surfaces - see ALGAE STAINS ON ASPHALT ROOF SHINGLES. See FIND MOLD in BUILDINGS, HOW TO for a guide to looking for mold contamination in or on buildings, and see WHAT MOLD LOOKS LIKE for a guide to just what mold looks like on building surfaces. Be sure also to see Stuff that is Mistaken for Mold to avoid becoming excited about harmless substances that people think are toxic mold. If you know your building has a mold problem, see ACTION GUIDE - WHAT TO DO ABOUT INDOOR MOLD.
• 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
• Tree-caused stains on roofs - 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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ASPHALT ROOF SHINGLES
  ASPHALT SHINGLE DEFINITIONS
  ASPHALT SHINGLE FAILURE TYPES
  ALGAE STAINS ON ASPHALT ROOF SHINGLES
  ALGAE STAIN TEST METHODS
  ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES
  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

• Shingle Shield™ are zinc strips that are inserted under the shingle tabs of individual shingles to reduce moss, lichens, and algae growth on asphalt roofing - see shingleshield.com
• StainhandleR are zinc strips that are inserted under the shingle tabs of individual shingles to reduce moss, lichens, and algae growth on asphalt roofing- see stainhandler.com
• Zinc-Shield® - zincshield.com and Z-stop™ zinc roofing strips - z-stop.com, are roll-out zinc strips intended for installation near the ridge of a roof to reduce moss, lichens, and algae growth on roofs
• 04/09: thanks to William M. Norman, P.E., S.E., Keeler-Webb Associates, 486 Gradle Drive, Carmel, IN 46032 for opening discussion regarding the legitimacy of extractive bleeding as a term to apply to asphalt roofing material. Mr. Norman suggests that many (not all) black stains on asphalt roofing may be due to algal growth. We will report progress in this discussion as updates to this web article.
• How to Recognize & Control Sooty Molds, USDA publication on the recognition and control of black sooty molds, including on buildings. This publication is also available in printed form from the U.S. Government Printing Office, 1992 657-152 HT-69 1992. The original article was authored by Kenneth K.Kessler, Jr., Principal Plant Pathologist, U.S. Forest Service, in the Department of Agriculture of the United States. Copies are also available from North Central Distribution Center, Forest Products Laboratory, One Gifford Pinchot Dr., Madison WI 53705-2398.

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