Does Your Roof Look Like it Has Stains?

Here are some of the types of stains that are found on roofs, focusing on asphalt shingle roofs as the main example. This post should help you to identify the most-common causes of black, brown, red, gray, green, or white stains appearing on roof shingles and on other building surfaces. Stains on your roof are usually caused by black algae, bleed-through or extractive bleeding of asphalt, dirt, soot, or organic debris.

Likely Causes of Black Stains on Roofs

Some home owners have specific expectations on how their shingles look on the roof as much as with how long the roof will last. Roofing manufacturers offer a variety of products which give many different options on colour and styles.

Site and installation conditions, variations in the manufacturing process (granule adhesion, bleed-through) can affect how the roof looks from the ground.

Shadows appearing in early morning or late afternoon will show variations in the roof surface. Some shadows which are only of cosmetic nature may be caused by slight buckling or unevenness in the roof decking and may not indicate a structural or life expectancy concern.

Concerns about how a roof might appear could be addressed by a roofing specialist so that they can direct you to a house where the product that interests you is already installed. Remember the variables that can affect the roof appearance, site differences (orientation to sun, shade trees, height above ground, roof pitch, and probably other factors) may make shingles look a bit different on your home.

Black Bleed-Through or Extractive Bleeding Black Stains on Asphalt Shingles

Extractive Bleeding – bleed-through asphalt shingle stains may be mistaken for but are not black algae or black “fungus”, nor are they soot. Extractive bleeding stains on asphalt shingles are caused by loss of black pigment in the asphalt mix intended to impregnate the shingle mat itself. Extractive bleeding or “bleed through” stains leaving black streaks running down an asphalt shingle roof is an indication of a defective roofing product. Typically bleed-through on asphalt shingles appears as black streaks running down shingles. You’ll see black streaks of varying length and width

Really? Some experts claim that extractive bleeding of roof shingles is a fantasy – that it never occurs, and that all black roof stains are due to algae growth or other causes. Having found some expert citations describing extractive bleeding of asphalt roof shingles as a product defect, while we agree that it’s not common, we don’t agree that it’s a fantasly.

Black Algae Stains on Asphalt Shingles, Roll Roofing & Many Other Kinds of Roof Surfaces

Black algae stains on roofs is in many areas the most common explanation for black blotches, streaks, or discoloration on asphalt roofing products as well as on some other roofing materials. Misnamed as “mildew” or “fungus” by some writers, algae staining on asphalt shingles usually in shaded areas or on the more-shaded roof slopes (photo at left) characterized by black staining fairly uniform over shingles, but appearing specifically in areas of the roof shaded by nearby trees. The black stains on the roof at above left are probably an algal growth.

Black Debris Can Cause Stains on Asphalt Shingle Roofs & Other Roof Materials Too

Debris staining on roofs produces fairly uniform black or brown staining in areas where due to low-slope or presence of overhanging trees, organic debris collects on the roof slope. Decaying debris may encourage fungal or algal growth (cited above). Debris staining often incorporates fungal or algal growth in the shaded, longer-wet areas of a roof as well as staining caused by the actual roof debris itself.

Soot Staining on Roofs

Black Soot Stains on Roof Surfaces Around & Below Chimneys. Soot from fireplace flues washing down onto the roof – characterized by staining appearing below and in line with the chimney,