Replies

1. 
   Mooney | Nov 16, 2003 12:43am | #1

   If its a steep pitch its the same as the north side of a tree. If its a shallow roof the debri from the trees can land and set on it . Any way its pretty common for north slopes in high humidity areas.

   Tim Mooney

2. 
   MojoMan | Nov 16, 2003 01:25am | #2

   It's very possible that mold, algae and/or fungi are growing up there. It happens on many roofs, it's just that it is much more visible on a white roof. This is a good argument for a dark roof. A temporary, bothersome and potentially risky fix might be to spray it with a bleach solution. Some people have tried tucking pieces of copper under the top course of shingles with a bit sticking out. The leaching metal seems toxic to many forms of plant life. This effect can sometimes be seen below a chimney with copper flashing.

   Al Mollitor, Sharon MA

3. 
   WayneL5 | Nov 16, 2003 03:22am | #3

   Like Al said, it's algae or mold.  After cleaning it off, you can tuck strips of zinc under the top row of shingles, with the zinc exposed to the weather.  The zinc oxide will inhibit new growth of mold.  They also make shigles with the inhibitor in them, but it won't help you, of course, since your roof is so new.

   I can't do a search on this computer, but I've searched the internet in the past and found a few good articles on dealing with algae and mold on roofs.

4. 
   FrankB89 | Nov 16, 2003 04:12am | #4

   I've seen the symptoms you describe on the roofs of young houses here on the South Oregon Coast.  I don't know if this is your situation, but in the situations I've seen, it's been weather and water eroding the white sand off the roof.  Specifically, black streaks appear where water flow is higher, such as around roof obstructions like stack vents and attic vents.

   In every case, the black has shown up on 3-tab roofs....mostly tract homes and manufactured units.

   My inlaws had such a POS roof and I replaced it with some better quality 40 yr. laminated.  Their neighbors are still playing with Moss remover and zinc strips with no improvement.  There are no large trees in the neighborhood.

   I don't know if this reflects your case; just adding to the "possible" list.

   Good luck!

    

5. 
   rjw | Nov 16, 2003 06:49am | #5

   As noted, it's likely a form of mold.

   Two things to try: spray with bleach and water 50%/50% - giving it a good soaking, or spray with Roundup or another vegetation killer.

   I've used Roundup with good success and longer term results than bleach, but I don't know if it'll remove the staining.

   Do NOT physically scrub or powerwash or otherwise abrade the shingles.

   Zinc strips can have limited effect, with the most effect closest to the strip, but staining appearing lower on the roof.

   _______________________

   Albert Einstein said it best:

   “Problems,” he said, “cannot be solved at the same level of consciousness that created them.”

   Your mileage may vary ....

6. 
   SonnyLykos | Nov 16, 2003 06:51am | #6

   It's a fungus, of which all algae and mold are members. Plural is called "fungi."

   Home Depot sells two items that can help you. One is the aforementioned zinc strips except HD carries them in a coil. Not cheap - about $50 for I think is 50 feet. Another is a solution to be applied with either a paint sprayer of garden type pump sprayer. It kills the fungi and eliminates what's there.

   Also, if you use a search engine and type in "roof algae" you'll get other items on the market. Here's one that even has photos of what you have:

   http://www.roofraider.com/