It takes two to three days for mold to begin growing in a flooded building. It can take years to get rid of it. For most houses and buildings damaged by Hurricane Katrina, it already is too late to stop the mold invasion, say sources. And the longer there is no power in New Orleans to dry out buildings, the worse the situation will get. That means many buildings will have to be stripped to the bone to rid them of mold.

"It is too late already," says consulting engineer Joseph Lstiburek, a principal with Building Science Corp., Westford, Mass. "If drying does not start...within days, you can expect a complete gut job."

Powerless buildings are acting as "mold incubators," agrees Terry Townsend, principal of the consulting engineering firm that bears his name, in Chattanooga and Panama City, Fla., which was hit by Katrina.

For mold to form, there has to be moisture, a food source and certain temperature and humidity (ENR 5/3/99 p. 32). Almost every single building in New Orleans has all three ingredients.

Saturation. Many buildings will have to be gutted to rid them of mold growth, say sources. (Photo by Reuters/Lee Celano)

Buildings fitted out with gypsum board offer the best mold breeding ground, say sources. But even plaster has a food source because of how it is applied. New buildings with light frames of steel, concrete or wood; cavity wall construction; and steel or wood studs will be "completely trashed," says Lstiburek.

Older buildings, especially bearing wall structures built a century ago from nonporous brick, are expected to do much better. If the heating, ventilating and air conditioning equipment has not been submerged, turning it back on is not likely to be a problem. But "so what?" says Lstiburek. "The enclosures will all be trashed by then anyway."

Lawrence Spielvogel, a consulting engineer in King of Prussia, Pa., agrees it will be necessary to replace any drywall, carpeting, furniture or wood that’s water-saturated or moldy. Without electricity, "you can’t run a fan or a dehumidifier, much less air conditioning, to remove the moisture," he says.

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Like Sponges

But Bill Estes, a Townsend project engineer, says "it may be impossible to dry out a building, because the interior cavities of walls act like sponges."

Estes says that if there were resources and intent, buildings could be designed and built to resist mold growth, even in floods. "There are materials available that are far more water-resistant than those being used," he says. "But these materials were not available when many of these structures were originally constructed."

Before air conditioning, facilities were built so they were well-ventilated, water would drain and buildings had operable windows. "Our buildings today are made tighter so that they are more energy-efficient," says Townsend. That means that many are ill-equipped to self-remediate when the power is out.

Townsend advises owners to get assessments of conditions before trying to salvage any of the interiors. A lot of people will add dehumidifiers, which is no assurance of a proper fix. "If you don’t get all the moisture and mold out, it will come out by itself," later, after the clean-up is done, he says. "That’s just nature."

In some cases, it may only be necessary to strip the walls to a couple of feet above the floodline, says Estes. Other than relays and controls, most electrical components, which are plastic, can be returned to service.

Ductwork and insulation, if saturated, should be completely scrapped. "If there is moisture, ductboard can also provide opportunity for mold growth," says Townsend. The material, made of compressed insulation with aluminum foil backing, is not as expensive as sheet metal and has been widely used in residential construction for 20 years. Flexible ductwork, because of unsealed joints, also can be a breeding ground for mold.

Sources say the cost of remediation is tough to nail down. Much depends on the size of the job and the level of contractors available. "You need to have contractors certified by recognized organizations," says Townsend. An unqualified contractor can cause more damage down the road, he warns.

"Mold growth cannot be taken in a light manner," says Townsend. "It doesn’t go away by itself."