By Matthew Power Why the sudden panic about mold in new homes? Hasn't mold been around forever?

"Two things have happened," says Nisus researcher Jeff Lloyd. "People now take a shower every day or do stupid things like venting their dryers into the basement. At the same time homes have become tighter."

"Mold has been around forever, and has always been dangerous," he adds. "Many molds are completely harmless fungi that become toxic in certain situations. They're not usually cause for concern. Molds give off spores (little packets of biochemicals) and mycotoxins (volatile chemicals) when they grow on certain materials."

In new homes, that material tends to be drywall. "It has cellulose, starch, and a big open surface where mold can grow," Lloyd says. Then what happens is that if a person is sensitive to allergens, their body launches an immune response to the mycotoxins or the spores.

In a damp house, he says, spore counts can reach up to 7,000 per cubic yard, versus 1 spore per cubic yard in a normal home. "Probably 70 percent to 100 percent of people are irritated by mold spores at some time each year, and they don't even know it. The problem is actually addressed to some degree in the building code: Prevent rising damp, penetrating damp (by way of overhangs and gutters), and condensation (from inside moisture)."

Propane Blues

During construction in cold climates, subcontractors often use "salamander" type propane heaters indoors. These heaters produce 7 to 8 pints of moisture for every gallon of fuel they use. That moisture may end up stored in drywall, which absorbs water easily. Be sure to let cold, dry air move through the home before closing it up.

Wet Enough to Worry?

Material Dry range Wet range
Plaster and Drywall Below 1% 1%-3%
Brick* 1%-3% 1%-15%
Cement Mortar and Concrete Below 2% 2%-20%
Lime Mortar 2%-5% 5%-20%
Wood and Wood Products 8%-18% 20%-30%

*depends on type of brick

Note: Under the right conditions, most materials can be "wet" enough to grow mold, even with moisture content in the "dry" range. Source: Nisus Corp.

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