On a light colored roof, what causes periodic streaking running down the roof? Like a stain…


the most common cause is actually air polution.



It’s most likely an algae called “Gloeocapsa”. It has no bad effects on the roof other than appearance. It can be professionaly removed with chemicals. I wouldn’t advise a client to do it himself–he could easily remove protective granules of sand as well. Recommend a roofing contractor.

Identifies the causes and provides a cure. Enjoy


This is a company that I have worked with. They produce incredible results and are also located in your market area…

Contact person is Jim Robertson.

There is a company in town that will pressure wash that stain right off the roof…along with the shingles and anything else that gets in their way of making a quick dollar. I have seen their work and they have been busy.


The company that I posted uses a chemical application that is non-toxic to plants and animals. Chemical is applied and hosed off with a garden hose (Low Pressure).

No pressure or damage occurs.

I still don’t understand, what exactly do I say when a cleint asks me what causes the streaking. Thank you for the ways to clean it but I need information on what causes it, because people think that the streaking compromizes the shingle life span (true?). You said air polution causes this? How does it cause this? There is no trees close to roof and the home is in the country farming area.

Jae’s right, it’s a form of algae.

Check out the “did you know” section on page 4

Hope this helps explain the cause.


Sorry that is old school telling you to use bleach.
The findings now say Bleach does not touch mold .
If you are putting up a new roof then have them install a zinc strip at the last ( top row of shingles ).
When it rains a small amount of zinc is washed down the shingles and Moss, mold will not grow .
Where this started from was under the first zinc vents no moss grew and now it is commin in damp areas that get a lot of moss to install zinc strip.
If your roofer has no idea what you are talking about get another roofer .
Roy Cooke

Bleach will not kill growths–it just turns it white for awhile–then it returns to its original color. Durashield and Accubright are products designed to remove this type of growth, but it is always best to recommend professional help. If the client wants to do it himself, that’s O.K.–but you still want to protect yopurself by recommending a pro.

If you tell the client to do it, and something goes wrong…he’s got you where you don’t want to be.

Describe the possible the cause (ALGAE)…
state the concern (NOT A DEFECT–JUST UNSIGHTLY)…
and make the recommendation (CALL A PRO).

If you go the Durashield website it has all the information you seek including the causes of shingle staining. These stains do not just affect roofs. It is the same algaes that stains driveways, siding, etc. It is on their website, you just have to dig a “little”.

Let it be know that I was only suggesting this link for the cause.
Bleach definately is not a good solution.

The discoloration is due to algae and you will notice that this growth will generally appear on the north and.or easterly sides of the home, in other words, the UV radiation doesn’t kill the growth as it does on the westerly and southerly sides. Short of changing the house’s orientation, eradication is the only solution (excus the pun)

Recommend a higher quality shingle (of course more expensive) next replacement.