Keep Mold From Taking Hold

By: Jeanne Huber, This Old House magazine (Page 2 of 4)

interior of a flood damaged house with level marks for mold line, flood repair recommendation and actual flood line

Enlarge this image Photo: Katherine Slingluff

Rashida Ferdinand exposed the studs—added in a 2005 renovation—on her New Orleans house by removing the drywall to a foot above the flood line.

Norm taking a hammer and chisel to a mold-damaged wall

Photo: Katherine Slingluff

TOH master carpenter Norm Abram tears away at the original wall in search of overlooked mold

mold covering wall about a moldy bed and bedspread

Photo: Katherine Slingluff

A bedroom in St. Bernard Parish in New Orleans in November 2005, two months after Hurricane Katrina. Floodwater-soaked houses were an ideal environment for mold to flourish on walls, floors, and fabrics.

diagram of mold-resistant wall construction

Photo: Katherine Slingluff

When contaminated floodwaters are a possibility, the best way to build walls is to line the stud bays with 2 inches of closed-cell foam insulation, then cover it with paperless drywall, leaving an air pocket between the two. Gaps at the top and bottom, hidden by crown and baseboard—as well as one in the middle that can be filled with a rubber gasket—allow the wall cavity to be rinsed out and dried after a flood. Electrical wires go above the first gap.

image of the leakage break to leave in wallboard to help prevent mold

Photo: Katherine Slingluff

A cruder defense against rampant mold involves putting a single break in the wallboard so water can’t wick all the way to the top. This preserves the upper pieces of drywall. Chair rail hides the gap.

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The U.S. Environmental Protection Agency suggests that homeowners might need help from a professional if they find mold on an area more than 10 square feet in size, but after big floods, that's not always possible. So the EPA has published guidelines that even inexperienced homeowners can follow.

Once Norm discovered the mold, on went the respirators and out came the pry bars. People can be sensitized to mold through the skin as well as the lungs, so rubber gloves, goggles, and a respirator—the EPA recommends a double-elastic disposable labeled "N-95"—are all important.

Careful mold removal begins by sealing off the area with plastic over the doorway. Then all absorbent materials (including carpet, drywall, and paper items) have to go. "Take walls down to the studs," says Rebecca Morley, director of the National Center for Healthy Housing in Columbia, Maryland. Even though most guidelines say material a foot above the floodwater mark can remain, "you actually do need to go further," Morley says. Researchers measured mold levels before and after cleanup in four demonstration homes and found that spore counts dropped to a background level in the three where crews removed all the drywall, but stayed alarmingly high in the one where they only took away the bottom pieces.

No one knows how dangerous it is to leave mold trapped in inaccessible places, such as inside walls or behind cabinets. "With lead and asbestos, you can manage it in place," Morley says. "But mold is a growing organism. Even behind a cabinet, I'd be leery about whether it is truly contained."

For Rashida, the decision was easy. The demolition phase was the time to get rid of questionable materials, including the old drywall and burlap covering the barge boards. She didn't want to worry later about shortcuts she took.