Everyone's on pins and needles down here," reports custom builder Luis Jauregui of Austin, Texas. "We recently got a callback for a minor window leak, and immediately the homeowners are talking about toxic mold."

Heightened concerns about toxic mold have been spreading across Austin and the rest of Texas since last summer, when a jury awarded Melinda Ballard of nearby Dripping Springs $32 million in a suit against Farmer's Insurance Group for the mishandling of a policy claim.

According to Ballard, the 22-room house was built by a custom home builder for himself and his family, and he "took no short cuts." The cause of the mansion's demise, Ballard reports, was high iron content in the domestic water, which gradually corroded copper water lines.

Eventually, water trapped in the walls and subfloor caused mold to grow to such an extent that the 11,000-square-foot house was rendered uninhabitable, and the Ballards and their son became seriously ill. While Ballard urges, "This is a case of insurance failure, not a construction failure," the mold damage and the court ruling were of such immense proportions that they have spawned a wave of mold-related lawsuits in the area.

A pervasive problem

According to the Texas Department of Insurance, the number of claims filed in Austin make it the second-most mold-plagued city in Texas, behind Corpus Christi. Many of the claims reference plumbing or flood damage, and growing numbers of builders have been sued for construction oversights. In an effort to stem a flood of payments that could cripple insurance companies, Texas insurance commissioner Jose Montemayor is considering whether insurance companies can place a $5,000 cap on residential mold claims. If that happens, it seems likely that homeowners will seek restitution increasingly at the expense of builders.

As a legal matter, the issue is hardly confined to Texas. In California an estimated 2,000 plaintiffs are currently involved in pending toxic mold cases involving school buildings, hospitals, and a courthouse, as well as single-family homes, apartments, and condominiums. While Texas and California are the epicenters of legal action on mold, there have been cases filed throughout the United States, and the incidence of lawsuits will undoubtedly increase as the occurrence of the mold itself increases. "Mold grows everywhere," says Dr. David Strauss, a microbiologist with Texas Tech University. "We have found mold in every climate zone in the country; it's not a problem that's likely to go away."

The U.S. Centers for Disease Control and Prevention identifies six varieties of mold common in houses and other buildings. Strachybotrys atra--the culprit in the Ballard house--is one of three varieties that produce airborne toxins, causing health effects that can include breathing difficulty, hearing loss, dizziness, and bleeding in the lungs. More common are three less-toxic molds--cladosporiums, penicillium, and aleraria--especially in damp regions of Texas, Louisiana, Florida, and the Pacific Northwest. But even these mild molds are often associated with such health problems as chronic sinus and respiratory infections and asthma.

There are no practical ways to eliminate mold spores in an indoor environment. "The best we can do is prevent them from growing," Strauss contends. Mold grows at temperatures between 50 and 100 degrees F, in dark areas--inside walls, attics, crawlspaces, and HVAC ducts--and feeds on the nutrients in cellulose-based building materials, such as drywall, carpet backing, ceiling tiles, particleboard, and OSB. Mold can even feed on adhesives, paints, dust, and lint. "Homes provide ideal growing conditions for mold," says Strauss. "Just add water, and it will flourish."

Mold has always been with us, but it has surfaced as a problem in houses recently for two reasons, says building scientist Terry Brennan of Camroden Associates, an indoor air quality specialist in Syracuse, N.Y. For starters, houses are built tighter. Poly vapor retarders and vinyl wallpaper tend to trap any moisture that infiltrates a wall. The other chief reason is that modern building materials are more mold-friendly, Brennan reports. Molds metabolize the adhesives used in wood products like OSB, hardboard, and engineered lumber more easily than the cellulose in solid wood. Also, the starches and sugars in cellulose that molds depend on for nutrients are more accessible from pulverized wood than solid wood or even continuous laminates of plywood. "In today's wetter houses, mold simply has more to feed on," Brennan concludes.

Prevention is the cure

According to Brennan, Strauss, and others, the most practical way to control indoor mold growth is to control moisture. Technically, mold will grow in environments where relative humidity exceeds 70%, but most experts agree that humidity becomes a factor only if moisture condenses out of the air. "It's important to remember that all of the sensational mold cases have involved lots of water--from plumbing leaks and flood damage," cautions Joe Lstiburek, a principal with the Massachusetts-based Building Science Corporation. "This doesn't mean a builder can ignore indoor humidity conditions, but the issue should be kept in perspective." The focus, he says, should be on eliminating liquid water from infiltrating homes.

Lstiburek and other building experts point to a broad group of strategies to prevent problems--proper flashing and other water-shedding details on roofs, walls, windows, and doors; foundation drainage to prevent ground water from seeping inside; and proper detailing of the thermal envelope to prevent water condensing on building surfaces. Here are some of the most common problems and their solutions:

Roof flashing. Every roof detail -- hips, valleys, ridges, rakes, or eaves -- is a potential leak. Leaks at penetrations such as vents and chimneys are most common. Make sure roofing felt is always extended well over the top of the base flashing, in "weatherboard" fashion. Avoid relying on roofing mastic to hold base flashings. Mastic will never last as long as the rest of the roof and often fails soon after installation. Install drip edge along rakes and eaves and overlap it with roofing felt. If you just cut the felt at the sheathing edge, wind-driven rain will find its way under the roofing.

Wide overhangs. "The days of the diminutive overhang are over," says Peter Pfeiffer, AIA, an Austin-based architect who frequently consults with builders on residential indoor air quality and energy concerns. Particularly in the South, houses must have deep overhangs to shield walls from rain, which can soak the siding and be driven inward by outdoor warmth.

Insulation. To prevent extreme temperatures from creating cold spots (or hot spots in some climates) inside the wall, pay close attention to insulation details, particularly at problem areas -- exterior corners, the juncture between roof and wall framing, and rim joists -- where framing often makes access difficult when applying insulation. Framing techniques such as "California corners," raised trusses, and let-in foam at rim joists can usually solve these problems.

Insulate cold water pipes and seal HVAC ducts. In hot, humid climates, it is often necessary to insulate cold water pipes to prevent surface condensation. This has become particularly important in the past 15 to 20 years, notes Pfieffer, as homeowners now tend to cool houses much more than they used to. Leaky HVAC ducts can overcool spots in wall cavities, attics, and crawlspaces where moisture will condense. Ducts should be sealed with mastic, not just duct tape.

Window and door flashing. In addition to cap flashing above the head trim of windows and doors, flashing should be installed beneath the trim and housewrap. "This is rarely done," says Pfeiffer. Typically a house is wrapped, window and door openings are X-cut, window and door units are installed, and the cap flashing is applied directly over the housewrap. This method, while efficient, invites water into the wall cavity. Windows with flanges should be set over flashing "splines" installed first at the sill, then along the sides, and last across the head. Most important, the housewrap must lap over the window flange and flashing.

Drainage plane for stucco and brick. Every exterior wall should have a continuous drainage plane between siding and sheathing. This is especially important with porous materials such as stucco and brick, which absorb water and draw it inside. A drainage plane can be as simple as building paper or felt properly installed over the exterior sheathing and (in the case of stucco) under the metal lath. Avoid synthetic stucco systems that manufacturers claim do not need a drainage plane.

Rain screen for wood siding. Wood siding should always be back-primed with a water-repellent preservative (best choice) or an oil-based primer. Just as important, wood siding should always be installed over an airspace, using vertical strapping or wedges between siding courses. This is critical over foam sheathing. But even over plywood sheathing and housewrap, the airspace provides the only way to dry the back side of the siding, which will inevitably get wet.

Foundation drainage. Water will always take the path of least resistance, so a foundation barrier combined with gravel backfill and perimeter drains will further protect against groundwater infiltration. To keep water outside the foundation, the top of the interior slab should always be above the top of the drain tile. In areas with high seasonal water tables, use both exterior and interior perimeter drains or a stay-in-place footing form such as CertainTeed's Form-A-Drain. In addition to the drains, treat the foundation with a barrier--a standard asphalt-based foundation coating or a dimpled drain panel--to resist the flow of water through the foundation, and always use gravel backfill, even with drainage panels.

Promising products

While eliminating moisture is the first and best line of defense against mold, a promising product may offer back-up security. Strauss reports that he and colleagues at Texas Tech have devised a mold-proofing treatment for drywall, plywood, and other building materials. Tests on samples soaked in water and left in the Ballard house (which has become a veritable laboratory for testing mold remediation strategies) grew no mold, while samples of untreated drywall, and samples treated with an anti-microbial used in shower curtains and other mold-resistant products, supported mold growth. Strauss says the best way to use the new product would be to add it to drywall and other sheet goods during manufacture. The product has been handed over to a technology transfer company, which reports it is currently negotiating with several building product manufacturers.

Some mold-proof products are available already. For example, Denglass--a gypsum-based panel with a silicon-treated core and a fiberglass facing--is much less likely to support mold than drywall, and Foster's 14-40, an acrylic paint that won't support mold, is sometimes used by mold remediation specialists when a building owner won't pay for a permanent fix to a moisture problem. Clearly, such mold-proof products represent a last resort, employed behind a front-line strategy of sound building practices. However, in a building environment that grows ever more litigious, such final remedies may someday offer the only firm protection against a monster lawsuit. --Clayton DeKorne is a freelance writer specializing in technology and training for the building trades. This article originally appeared in Custom Home, a sister publication of REMODELING.


APA The Engineered Wood Association offers training publications on building moisture-resistant building envelopes. www.buildabetterhome.org.

Building Science Corporation offers seminars on mold-growth prevention, moisture-control fact sheets, and region-specific information for builders and homeowners. www.buildingscience.com.

Environmental Protection Agency publications address mold-related issues for builders and homeowners. www.epa.gov/iaq/pubs

The New York City Department of Health offers guidelines for assessing mold problems and outlines current remediation procedures. Search for "toxic mold" on www.nyc.gov.