On The Level: There are solutions for stains on your asphalt roof

What causes those black stains that appear to streak down asphalt shingle roofs? Is there anything that can get rid of them?

If I took all the letters and e-mails I've received and stacked them in piles by category, the pile with questions about roof stains would be the tallest, edging out wet basements. I've discussed them before but due to the greater than average amount of warm and wet weather we've had over the past few years, conditions have been right for these roof stains to occur.

The simple answer is it's an algae. The spores are always floating around in the air and if you looked at the surface of a...