Asphalt Shingle Roof Cleaning: Use bleach to clean mold from roofs

Tom Kraeutler asks,

I noticed unsightly black stains on my shingle roof a few months ago. I’m guessing they are the fungus/mold that grows on the North side of buildings and spreads from rooftop to rooftop. What can I use to get rid of these unsightly black stains and clean my roof?

Our Answer

The best thing to do is to clean the roof with 10% bleach to 90% water solution. Rinse it with a pressure washer on a low setting. Cleaning the roof on a sunny day is best; the sun actually helps the bleach to work more thoroughly.
After you get the mold off, you can install a copper or nickel piece of flashing along the peak of your roof. Every time it rains, the rain will cause some of the flashing to wash down along your roof, effectively self-cleaning the shingles and fighting mold spores before they have a chance to make themselves at home.