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Algae growth on vinyl siding (C) Daniel Friedman

Online Guide to Diagnosing Stains on Building Exteriors
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Online guide to diagnosing, removing, or preventing stains on building exterior surfaces: roofs, walls, siding, trim, walks, drive, stone, wood stains, moss, algae, mold, etc.

Photographs of Algae, lichens, moss, mold help identify these substances in nature and on buildings

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 describe and provide photographs and microscopic photographs of algae, moss, lichens, or fungal growth that occurs on buildings and in nature. 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. Our page top photo shows algae growing on the shaded side of a vinyl-clad building. Readers should see Stain Diagnosis on Roofs and see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES where we discuss not only moss and lichens but black fungal stains on asphalt shingles and on other building surfaces. For identifying and diagnosing stains on indoor building surfaces see Stain Diagnosis on Indoor Surfaces.

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

A Detailed Online Guide to Types of Stains or Marks on Building Exterior Surfaces: roofs, walls, decks, siding, trim

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.

Animal stains in buildings may be caused by animals brushing against walls or trim of the inside or outside of a building, or may be due to more odious causes such as pet urine staining.

Our photo shows an indoor black stain on walls caused by a dog who slept against this part of the room.

See Black stains from animals for details about pet stains on building floors (urine) and for black or other pet stains on walls see Pet Stains on Walls for diagnosing stains such as the black marks in our photo at left.

For indoor surface stains and markings in general, see Stain Diagnosis on Indoor Surfaces

Algae stains on concrete (C) Daniel Friedman

Green Algae stains on siding (C) Daniel Friedman

Algae causes black stains on roof surfaces and green stains on other building exterior surfaces such as concrete (photo above left), decks, and building siding (above right).

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. Algae very often appears as a flat green coating or stain on building siding and even on sidewalks and concrete (photo at left). See ALGAE, FUNGUS, LICHENS, MOSS COMPARED for additional photos (including algae in the microscope) and details.

Photograph of possible asphalt shingle bleed-through or extractive bleeding on asphalt roof shingles (C) Daniel Friedman

Black mold growth on building exterior wall siding (C) Daniel Friedman

Black stains on asphalt roofing products such as asphalt shingles or roll roofing, caused by extractive bleeding (product defects) shown at above left. - see Bleed-Through and see Roofing material defect / environmentally-caused roof shingle stains.
Black stains on vinyl or painted building exterior wall siding may also be mold, as our photo shows at above right.

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.
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 and also see STAINS on Indoor Surfaces: PHOTO GUIDE

Black mold in buildings: often is mistaken as being the only or most severe mold problem - be sure to look for other molds that are perhaps equally or more toxic but are harder to spot. Our photo (left) shows cosmetic black mold on building framing. See MOLD APPEARANCE - WHAT MOLD LOOKS LIKE for complete details, and see Black Mold for specifics about black mold growth in buildings.

Mold on a building exterior surface indicates damp or shaded conditions, is not normally itself a hazard to building occupants, but it might indicate conditions that have also produced an indoor mold hazard.

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. Debris stains on building walls, including stains from animals may appear as black smudges that may be mistaken for mold.

Extractive bleeding stains on asphalt roofs - see Bleed-Through and see Roofing material defect

Lichens growing on roof surfaces, often a blue-green material - see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES. Lichens are not the same growths as moss or algae, and are difficult to remove without damaging the roof surface. 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.

For complete information about recognizing and dealing with mold growth in or on building surfaces

see FIND MOLD in BUILDINGS, HOW TO for a guide to looking for mold contamination in or on buildings,
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

Thermal tracking snow melt on a roof (C) Daniel Friedman

Thermal tracking stains (C) Daniel Friedman

Thermal tracking stains or marks on buildings: Thermal tracking stains will not normally be visible on a building exterior, but we might see similar tracking of wall studs or roof rafters (photo, above left) where temperature differences in a building or points of heat conductivity and heat loss cause variations in snow-melt (on roofs) or moisture condensation (on walls).

Black stains on building interior surfaces may follow a similar pattern (photo, above right) due to deposits of house dust on cool or damp building surfaces often follow building wall framing or ceiling framing studs or joists. See THERMAL TRACKING & THERMAL BRIDGING for details.

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.

White stains on masonry walls (powdery or crystalline marks on the wall in our photo at above-left) and on some plaster walls (white-yellow bubbly) are usually mineral salts - efflorescence left by evaporating water and are a sign of wet or damp conditions. See Efflorescence & white or brown deposits

Yellow stains in buildings - crystalline or round shiny stains on wood framing may be sap that exuded from building framing as it was heated, such as on an attic rafter. Yellow stains indoors may also be due to mold or pets.

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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) Issue Volume 11, Number 2 / June, 1976 DOI10.1007/BF02854759 Pages217-224

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

STAIN DIAGNOSIS on Building Exteriors
STAIN DIAGNOSIS on Indoor Surfaces
STAINS on Indoor Surfaces: PHOTO GUIDE
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
  Bleed-Through
  Chimney-Caused Roof Stains
  Debris Staining on Roofs
  Lichens on Roofs
  Moss on Roofs
  Rust Stains on Shingles
  Soot Staining

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