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This document 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. But there are other sources of roof staining and they vary in significance, from cosmetic to harmful to the roof. Here we give an index of all sorts of roof stains and what causes them. For the diagnosis and cure of other building stains, see STAIN DIAGNOSIS on Building Exteriors and STAIN DIAGNOSIS on Indoor Surfaces.

The remedies for and means of preventing stains on roof shingles are discussed as well. In the photo shown here, the black stains on the lower roofs are bleed-through or extractive bleeding. The upper roof, shaded by the large tree in the photo, was also moss covered. Notice the streak of "clean" roof shingles that lack the stains on the upper roof near its left edge? Those shingles were installed down-roof from an aluminum attic vent fan cover. The aluminum salts washing off of the fan cover prevented moss, lichens, and algae from growing on those shingles.

Also see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES where we discuss not only moss and lichens but black fungal stains on asphalt shingles and other roof types.

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How to Distinguish Roof Stain by Type of Cause

As for distinguishing between an algae growing on shingles and a fungus growing on roof shingles, building or environmentally-caused roof staining, or other causes, here are several approaches:

Visual Roof Inspection & Roof Stain Area Context Help Diagnose Cause of Roof Stains

Proximate cause roof shingle stains

If you see a roof stain that develops only in limited areas of a single roof slope look for a relation between the stained area and a proximate cause such as a sooty chimney top or a tree that shades that section of the roof or drops organic debris onto it.

These include tree shade caused moss, tree-shade caused lichens growth on a roof, or dark stains on roof coverings caused by organic debris such as leaves and sticks that fall onto and collect on the roof surface (photo at left). Our photo at above right shows brown stains below a metal roof chimney. Probably more important, this chimney has lost its cap, risking damage to and unsafe conditions at the building heating equipment.

See Debris Staining (trees), see ALGAE STAINS ON ASPHALT ROOF SHINGLES (algae) and Soot Staining(chimneys).

Roofing material defect / environmentally-caused roof shingle stains.

Our stained asphalt roof shingle photo at above lefty show black extractive bleeding stains on roof shingles colored other than white. Even on darker shingles these effects may occur. See Black Bleed-Through or Extractive Bleeding Black Stains on Asphalt Shingles. Click to enlarge our stained shingles photo at above left and you may also notice vertical cracks running up through shingles to the left of the dormer. This roof may also have a defective roof product causing splitting shingles (see CRACKS in FIBERGLASS SHINGLES). We're not certain about the cause of the staining at above right. It is probably extractive bleeding but a second candidate might be roof algae. We need a closer look.

If the stain pattern on a roof surface occurs across the entire field of the roof and independent of proximate causes like chimneys or trees, it is more likely due either to the roofing material itself (possibly extractive bleeding), the overall environment (downwind from a chemical plant or incinerator or factory), or due to the slope' orientation (North slope, cooler, East or West roof slope -more sunlight). See SHINGLE LIFE / WEAR FACTORS for a discussion of sunlight effect on roof life.

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.

The chemistry of roof shingles, their granule coverings, and substrates is quite different from other organic substances that are home to many molds. Further, many newer shingle products include chemicals to retard black algae growth that may also retard mold growth. Specific mold genera/species like to grow on particular surfaces - it's their food, and while
some molds are more choosy than others (for example mildews grow only on living plants), you'll need to look carefully at a roof and the conditions around it (such as trees, and areas of sun or shade) and perhaps even sample the black debris to determine if it is mold and if so what is its species.

The roof cleaning methods to remove black algae will probably work well for black mold growth on a roof as well.

Roofing material defect / installation / structurally-caused roof shingle stains

If you see roof staining or defects that occur on all roof slopes regardless of slope orientation or presence/absence of proximate causes (chimneys, trees) then the condition may be due to roofing material, its installation, or the building itself (inadequate under roof venting).

Forensic sampling of Roof Stain Material

A simple collection of the stained material using clear adhesive tape followed by a laboratory analysis by an experienced microscopist is conclusive. We don't recommend lab sampling of shingle stains in most cases but if you want to sample a stain material for analysis in our forensic laboratory, instructions are at Six Easy Steps to Get and Mail a Mold Test Kit. Don't bother worrying about mildew on your roof. Mildew is an obligate parasite which grows only on living plants. Unless your roof is covered with grapes it is not likely to have much mildew there.

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.

• 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 (roof debris), and see Proximate cause roof shingle stains (types of roof stain by color, location, probable cause), and see Black Bleed-Through (black bleeding stains from asphalt shingles - extractive bleeding).
• Black or other colored chimney soot 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, and see Proximate cause roof shingle stains (types of roof stain by color, location, probable cause)
• 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. Also see the USDA recommendations at How to Recognize & Control Sooty Molds.
• 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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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.

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
  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
  WHAT ARE ASPHALT SHINGLES
BUILT UP ROOFS
CERTIFICATIONS for ROOFING CONTRACTORS
CHIMNEY INSPECTION & REPAIRS
CHOOSING A ROOFING CONTRACTOR
CLAY TILE ROOFING
FIRE RETARDANT PLYWOOD
LOW SLOPE ROOFING MATERIALS
MEMBRANE ROOFS
METAL ROOFING TYPES
MODIFIED BITUMEN ROOFING
ROOF INSPECTION SAFETY & LIMITS
ROOF VENTILATION SPECIFICATIONS
ROOF VENTING ENERGY SAVING DETAILS
SLATE ROOF INSPECTION & REPAIR
SOD ROOFING
SIDING WOOD
STAIN DIAGNOSIS on Building Exteriors
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

• Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Technical Committee and the ASHI Standards Committee. Mr. Hankey serves as co-chairmain of ASHI legislative committee, and has served in other ASHI professional and leadership roles. Contact: 952 829-0044 - hankeybrown@comcast.net
• 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.

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

• Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
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More Information on Building Diagnostic Inspections and Repairs

• Roofing
• ASPHALT ROOF SHINGLES

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