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This article describes and provide photographs of lichens growth that occurs on buildings and in nature and we provide advice about handling lichens growth on roofing surfaces. We include links to references useful in the identification of algae, moss, lichens, and mold. Our photo at page top shows moss on an asphalt shingle roof.

This website tells readers how to identify, evaluate, remove or prevent stains on building surfaces. Also see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES where we describe not only moss and lichens but black fungal stains on asphalt shingles and on other building surfaces. Also see Lichens on Stone Surfaces. For the diagnosis and cure of other building stains, see STAIN DIAGNOSIS on BUILDING EXTERIORS and STAIN DIAGNOSIS on BUILDING INTERIORS. Also see Red or Other Colors on Stone. See STAIN DIAGNOSIS on STONE for additional examples of diagnosing, cleaning, and preventing stains on building materials and artifacts.

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What does Lichens look like on buildings, in nature, and in the microscope?

What does lichens growth look like on an asphalt shingle roof and how do we distinguish this material and its effects from algae, moss, or other roof problems?

Lichens, one of the most hardy growth organisms found in nature, can grow in harsh conditions. Lichens is often found growing on roof shingles, especially asphalt and wood shingles as we show here. Our photo (left) shows blue-green lichens covering a significant portion of the roof surface, and below we provide closeup photographs showing just what lichens does to the roof surface if you try to remove it. Is lichens on a roof as much of a problem as moss? Yes and no, as we discuss below.

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.

Our photographs (above) show lichens growing on an asphalt roof shingle in situ (above left). In the photo where our pen is inserted for scale (above right) we had "picked" the spot of lichens gently and flipped it over. Our pen points to the hole left in the asphalt shingle as the lichens had such a good grip on the mineral granules that when removing the lichens it brought some of the roof protective coating along with itself. If you click to enlarge the photo at above right you'll see the actual mineral granules from the shingle adhered in the "roots" of the lichens.

Moss Damage Compared with Lichens Damage to Roofs

Our photographs below show a Two Harbors Minnesota asphalt shingle roof with heavy moss and lichens growing on the same surface. You can see that comparing the loss of mineral granules where we have gently lifted off moss (below left) and where we used a knife blade to gently lift off lichens from the shingle surface (below right), both growths have loosened the mineral granule coating and exposed the organic shingle substrate in a similar fashion.

Notice that both roof photos show that both moss and lichens are happy to co-exist on the same shingle surface. Our photo at left shows testing where moss was lifted off of the shingle, and at right, cup lichens was pried off of the roof using the tip of a knife blade.

Because moss is a thicker growth on roof surfaces, we suspect that its ability to hold water and moisture on the roof surface is greater than that of lichens. So in some circumstances and climates, moss damage may be as severe or even more severe than lichens damage to a building roof, and we suspect that the degree of moss or lichens damage also varies by roofing material, with still more severe moss and water damage on wood shingle roofing.

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. Removing the protective granules from an asphalt shingle or mineral-granule coated roll roofing surface is going to reduce the future life of that roof covering.

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.

Online Guide to Types of Stains on Building Surfaces:

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 or green stains on roof or other building surfaces - Some photos of black algae stains are at Black Algae Stains on Asphalt Shingles. For details on roof algae see ALGAE STAINS ON ASPHALT ROOF SHINGLES, and ALGAE STAIN TEST METHODS. Algae can produce black stains on asphalt roofing products. Also see  ALGAE, FUNGUS, LICHENS, MOSS COMPARED. And see STAIN DIAGNOSIS on STONE for examples of algae staining on other building surfaces.
• 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 BUILDING INTERIORS and then STAIN DIAGNOSIS on BUILDING INTERIORS 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.
• Catalog of Biological Substances that Alter Stone or Other Inorganic Materials lists the causes and types of damage that raise aesthetic and conservation issues on cultural artifacts, buildings, and art works.
• 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, and see Proximate cause roof shingle stains (types of roof stain by color, location, probable cause)
• Green roof stains on roof shingles, clay tiles, cement tiles, and asbestos cement roof shingles or newer fiber cement roof shingles are often caused by algae. For details see ALGAE STAINS ON ASPHALT ROOF SHINGLES. Moss on roofs is also often green and should be unmistakable in appearance. See ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES.
• Lichens growing on building surfaces - Lichens are not the same growths as moss or algae, and are difficult to remove without damaging the roof surface. See Lichens on Stone Surfaces, and also see Lichens on Roofs for details about how lichens can cause roof damage. See Methods for Cleaning Stone Surfaces and ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES for a guide to preventing lichen growth and stains. Also see ALGAE, FUNGUS, LICHENS, MOSS COMPARED for an explanation of the difference among these.
• 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 roofs and other building surfaces: see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES, and Green Stains on Stone. 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
• Stains on stone or masonry surfaces - see STONE CLEANING METHODS for cause, cure, and prevention
• 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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ROOFING INSPECTION & REPAIR
  ALGAE STAINS ON ASPHALT ROOF SHINGLES
  ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES
  STAINS on ROOF SHINGLES
  WHAT ARE ASPHALT SHINGLES
  WIND DAMAGE to ROOFS

ALGAE, FUNGUS, LICHENS, MOSS COMPARED

STAIN DIAGNOSIS on ROOFS
  Causes of Roof Stains
  Catalog of All Roof Stains
  ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES
  ALGAE STAIN TEST METHODS
  ALGAE STAINS ON ASPHALT ROOF SHINGLES
  Catalog of Black Roof Stains
  Black or Green Algae
  Black Stain Removal & Prevention
  Bleed-Through
  Chimney-Caused Roof Stains
  Debris Staining on Roofs
  EXTRACTIVE BLEEDING on SHINGLES
  Lichens on Roofs
  Moss on Roofs
  Power Washing Roofs
  Rust Stains on Shingles
  Soot Staining on Roofs
STAIN DIAGNOSIS on STONE

• Guides to identifying mosses:
  Graphic Guide Ontario Mosses (some of which appear widely dispersed by climate and geographic area, not just in Ontario) which offers a graphic guide to mosses. worldofmosses.com/ggom/index.html
• Also see the sources listed at worldofmosses.com/ggom/ggomBibliography.html
• Also see the Journal Folia Geobotanica, Springer, Netherlands ISSN1211-9520 (Print) 1874-9348 (Online) IssueVolume 11, Number 2 / June, 1976 DOI10.1007/BF02854759 Pages217-22

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

• Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
• Asphalt Roofing Residential Manual,
• Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF] ISBN-10: 0471331724 ISBN-13: 978-0471331728
• Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008) ISBN-10: 1405161035 ISBN-13: 978-1405161039
• Built-Up Roof Systems, Manual, C.W. Griffin, Mcgraw-Hill (Tx); 2nd edition (July 1982), ISBN-10: 0070247838, ISBN-13: 978-0070247833
• Green Roof Plants: A Resource and Planting Guide, Edmund C. Snodgrass, Lucie L. Snodgrass, Timber Press, Incorporated, 2006, ISBN-10: 0881927872, ISBN-13: 978-0881927870. The text covers moisture needs, heat tolerance, hardiness, bloom color, foliage characteristics, and height of 350 species and cultivars.
• Green Roof Construction and Maintenance, Kelley Luckett, McGraw-Hill Professional, 2009, ISBN-10: 007160880X, ISBN-13: 978-0071608800, quoting: Key questions to ask at each stage of the green building process Tested tips and techniques for successful structural design Construction methods for new and existing buildings Information on insulation, drainage, detailing, irrigation, and plant selection Details on optimal soil formulation Illustrations featuring various stages of construction Best practices for green roof maintenance A survey of environmental benefits, including evapo-transpiration, storm-water management, habitat restoration, and improvement of air quality Tips on the LEED design and certification process Considerations for assessing return on investment Color photographs of successfully installed green roofs Useful checklists, tables, and charts
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