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ROOFING INSPECTION & REPAIR
AMERICAN CEMWOOD ROOFING
BEST ROOFING PRACTICES
BUILT UP ROOFS
CATHEDRAL CEILING VENTILATION
CERTIFICATIONS for ROOFING CONTRACTORS
CHIMNEY FLASHING Mistakes & Leaks
COLD WEATHER ROOF TROUBLE
DECKS, ROOFTOP CONSTRUCTION
EPDM, RUBBER, PVC ROOFING
EXTRACTIVE BLEEDING on SHINGLES
FIRE RETARDANT PLYWOOD
FLASHING on BUILDINGS
FLAT ROOF MOISTURE & CONDENSATION
GREEENHOUSE / SOLARIUM ROOF LEAKS
HEAT TAPES & CABLES for ROOF ICE DAMS
ROOF ICE DAM LEAKS
MASONITE WOODRUF FIBERBOARD ROOFING
NOISE CONTROL for ROOFS
PLASTIC ROOFING TYPES
PVC, EPDM, RUBBER ROOFING
ROOF ARCHITECTURAL STYLES - PHOTO GUIDE
ROOF CLEANING RECOMMENDATIONS
ROOF COLOR RECOMMENDATIONS
ROOF INSPECTION SAFETY & LIMITS
ROOF LEAK DIAGNOSIS & REPAIR
ROOF NOISE TRANSMISSION
ROOF REPLACEMENT SNAFUs
ROOFING FELT UNDERLAYMENT REQUIREMENTS
ROOFING MATERIALS, Age, Types
SADDLE CONSTRUCTION at CHIMNEYS
SNOW GUARDS & SNOW BRAKES
STANDARDS for ROOFING
STRESS SKIN INSULATED PANELS
TEST LABS - ROOF SHINGLE
TREES & SHRUBS, TRIM OFF BUILDING
TRUSSES, FLOOR & ROOF
UNDERLAYMENT REQUIREMENTS on ROOFS
VENTILATION in BUILDINGS
WALK-ON ROOF SURFACES
WARRANTIES for ROOF SHINGLES
WORKMANSHIP & ROOF DAMAGE
Roof discoloration & stain diagnosis, cure, prevention:
Stains on roofs have a variety of causes, but noticing the stain color, its location, and the relation of he roof stain color and location to roof components such as chimneys, flashings, and the stain relation to roof conditions (pitch, shading, nearby trees, debris, roofing materials) will usually lead to a quick reliable diagnosis of the cause of the staining.
Knowing the cause guides us to knowing the cure for unsightly black, brown, green, red, rust, or other colored stains on building roofs. 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.
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Dark black or brown 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 roof stain colors and causes. The remedies for and means of preventing stains on roof shingles are discussed as well.
[Click to enlarge any image]
The red stains on the roof shown at left are discussed and diagnosed
In the photo shown at page top, the black stains on the lower roofs are bleed-through or extractive bleeding. The upper roof, shaded by the large tree in the page top photo, was also moss covered.
Notice the streak of "clean" roof shingles that lack the stains on the [page top photo] 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.
As stated in Best Practices Guide to Residential Construction:
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 ROOFS (algae)
and Soot Staining(chimneys).
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. 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 ASPHALT 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
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.
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).
A simple collection of the
stained roof surface 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
Also see TEST LABS - ROOF SHINGLE for chemical and durability tests on roofing materials.
While most home inspectors will agree that we ought to keep shrubs at least 24" off of building walls, and that trees within five feet of a building wall risk damaging the structure by root pressure or impact, we don't think that there is an arbitrary correct distance for trimming trees back around a roof.
Our photo (left) shows the dramatic measures that a building owner followed to avoid removing a tree that was really too close to the building - in this case in Tupper Lake, NY.
For tree trimming advice, it is more useful to explain the objects of trimming trees away from a building so that the homeowner or maintenance worker can determine what is needed to meet those objectives at a particular site. Here are some objectives to meet when trimming trees that may be close to a building:
Watch out: you should hesitate to remove beautiful, large, old trees at a property. Consult with a tree expert and think twice before drastic cutting or removal of trees.
For roofing material testing services and shingle testing
As we discuss at Power Washing Roofs we do not recommend power-washing asbestos-cement nor any other roofing. See Black Stain Removal & Prevention for advice on diagnosing, cleaning, and preventing stains on roofing.
Also see ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES where we describe not only moss and lichens but black fungal stains on asphalt shingles and other roof types.
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
Continue reading at ALGAE STAINS on ROOFS or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: white stains on roof
(Aug 15, 2014) Deborah said:
I have a new roof with architectural shingles that has a white discoloration on it for the moment it was installed. The roofer said it was back surfacing mineral and would wash away. It has been months now. It has faded, but not completely. It is most noticeable when the sun goes behind the house in the afternoon. In the morning, ( house faces east) it is barely noticeable. He said it will weather off. Is this true?
I don't know, Deborah as I don't know what's on the shingles. Please take a look at WHITE STAINS on ROOFS
Question: roof wear or stains above windows
9/1/14 Hodge said:
We have a 4 yr old roof in great shape except for sign of early wear above two windows. The areas of wear are the same width of the windows and extend up and gradually fade . Any ideas ?
If the windows are a source of drafts, temperature variations in the roof above, or moisture sources, or if construction details obstructed roof venting over those areas those might explain variation in roof shingle wear. Use our CONTACT link email to send me some photos and I can comment more usefully.
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