A growth industry: architects clear the air in their fight against mold

Residential Architect, April, 2004 by Nigel F. Maynard

policy Holders of America, a consumer advocacy group, counted 129 first-party mold claims in 1998. By 2001, the number had soared to an astonishing 9,563. Although claims dropped to 2,563 last year, mold remains an unwelcome newsmaker and a trouble spot for residential architects and their clients.

"Mold does seem to be a big problem these days," says Ken Miller of Kenneth Miller Architects in Hobe Sound, Fla. "It seems that whenever the AIA holds an education seminar, mold is always a topic that's well attended." Indeed, Miller's coastal community is no stranger to mold, nor are other humid climates homeowners flock to.

The fact is that harmless mold spores exist all around us. But they can turn harmful when construction defects cause them to proliferate. Leaky windows or roofs, inadequate flashing, leaky pipes, and cracks in the siding all provide entry points for moisture, which then combines with warm indoor air and protection from sunlight to form molds. Those molds are certainly an aesthetic problem, and they're a potential health concern as well.

tight quarters

"Tight houses are part of the problem," says Rob Harrison, AIA, of Robert Harrison Architects in Seattle. "A house with inadequate insulation dries out quickly, but the houses we see having mold problems are those that were built tight but had bad ventilation."

Of course we can't turn back the hands of time and build drafty houses again. We expect and need the efficiencies and comfort that well-insulated houses provide. That's why architects experienced in controlling mold are sticking to designing tight houses, but have found ways to introduce more fresh air and to deter mold from taking hold in the first place.

Most architects and builders agree that moisture control is the most effective weapon against mold. "Keeping the water away from the house is a big issue," says Christopher Rose, principal of Christopher Rose Architects in very humid Johns Island, S.C. One way Rose achieves a moisture-resistant building envelope is with closed-cell sprayed foam insulation. Typically sprayed into stud cavities, foam expands to fill all voids and is unaffected by moisture. It's more expensive than fiberglass, but it creates such a tight house that a client can recapture the investment by reducing the size of the HVAC system, Rose says.

"I have been to these seminars where they say that no matter what you do, some moisture will still get into the house," Rose says. So, as an added measure of protection, he uses a wall slicker behind the siding to channel water down to the bottom of the exterior wall. He also applies 30-pound felt paper over the sheathing because it allows the house to breathe and "performs better than housewrap." When he specs foam insulation, he includes a humidistat and an air exchange system to ventilate the house with fresh air. Architect Ellen Bailey Dickson says moisture is a problem in the Chicago area where she practices as well, so her firm takes preventative measures as a matter of course. Fresh air is her focus. "Houses are so tight these days that there aren't enough natural places for fresh air to get into the house," says the principal of Bailey Edward Design. "So we have been trying to create points through the ductwork where we're actually bringing in fresh air at a ratio of about 5 percent to 8 percent of the total air." She continues, "We bring it through a separate mixing box before it gets to the furnace so that you are not taking minus 5-degree air and mixing it with 72-degree air." The box warms the outdoor air before it gets to the furnace. Dickson also specs "green board" for all the walls in the intense wet areas to help resist moisture, and she uses concrete board as a tile backer.

"Moisture control has always been an issue for us," says Harrison of his invariably cloudy climate. That's why he strives to make exterior walls as tight as possible, and it's why he's adopted a systemic approach to fighting mold in every house he designs. A cross section of a typical Harrison house would reveal fiber cement siding, furring strips, builder paper, plywood sheathing, blow-in cellulose insulation, and gypsum board. All of his houses have a whole-house ventilation system. "We also work with an air tightening specialist who does blow tests and works with the contractor to seal air gaps," he says.

Florida's Miller says he has not made any major changes in his career-long battle against mold, but he has tweaked his specifications list a bit over the years. "I try to avoid oil-base paint on the exterior," he says. "It helps avoid mold buildup. I also try to avoid wood on the exterior." Both approaches may require a little "client education" to implement.

product support

While there are no substitutes for good building techniques, manufacturers have come up with products they claim add an extra measure of protection. For example, Florprufe by Grace Specialty Building Materials in Cambridge, Mass., is a high-performance vapor barrier for use below slabs on grade. When the foundation is poured, the concrete forms a full adhesion, incorporating the vapor barrier and helping prevent moisture intrusion.