Q:I have noticed my roof is stained black, making it look horrible and perhaps damaging it. Is there something I could do to remove this marking?

A: This question appears almost as often as algae on roofs. The black stuff is an algae called Gloeocapsa magma, and it thrives on asphalt shingles on the shady roofs of houses, where it has constant moisture.

When roofing manufacturers began making fiberglass shingles as older materials disappeared from the market, they added ground-up limestone to make the shingles heavier. The algae appear to thrive on limestone. Manufacturers are changing the mix. Some add copper filings to counteract algae growth.

You can clean the algae off with oxygen bleach; chlorine bleach will damage the shingles.

Roofers are now nailing copper or zinc strips at the highest points of roofs so that rain washes copper and zinc down on the algae, killing it.

Q: I have an older house with bathroom wainscoting covered by lead paint partly covered by tile. What I would like to do is remove the rest of the tile, smooth the combination of paint and adhesive, and paint it.

My concern is the lead dust when I pull off the tiles, and my idea is to wet around and behind each tile as much as possible before pulling one off, wear a mask, and keep the window open and the door closed. I’ve discussed this with a plumber and also with a contractor who was in the house for other reasons. Both say I worry too much and that the amount of lead is insignificant.

I suspect that they prefer to believe this, but that it’s not true. I would value your opinion, as well as any suggestions you might have.

A: I always err on the side of caution. Take every precaution you’re planning to take, and check the Web site of state and federal environmental agencies for their advice as well.

It may even be wise to have one of the tiles tested for lead, especially if you have children younger than age 6—the most vulnerable to lead poisoning.

Finally, there is probably not very much lead dust, as the plumber and contractor told you, but there is enough to track it around the house on the soles of your shoes.

Have questions for Alan J. Heavens? E-mail him at

aheavens@phillynews.com

or write him at The Inquirer, Box 8263, Philadelphia PA 19101.