Where there's mold, there's misery

Hunting down the health culprits in leaky buildings

You've just settled into your new condominium. Every-thing's great. Then you notice that the carpeting near the sliding door to the deck seems to get wet after heavy rains. You mention it at an association meeting, and soon you find out that you're not the only one with the problem. A year or two passes while the association talks with the contractor. The problem seems to be getting worse, and owners of other units are have observed dark lines at floor level on the wood molding. You begin to notice a musty odor that doesn't go away. Oh oh.

You find out that the exterior skin of your building is leaking water. The water is accumulating inside the walls, rotting structural timbers and wetting the back side of the gypsum wallboard in your unit. The contractor's insurance company will cover the costs of repairs, but there will be consultants, architects, industrial hygienists, and others evaluating the problem over the next six to nine months. Groan.

Then the really bad news hits. Those black lines are mold. You surf the Internet, looking for answers. And you find them. In sufficient quantities in water-damaged buildings, mold spores can result in airborne exposures to occupants, possibly resulting in allergic, irritant and maybe even additional health symptoms. Sneeze.

Your building's beautiful, modern exterior is not doing a very good job keeping Seattle's weather outside, where it belongs. Your experience is shared by many people in this corner of the continent, where rapid development meets heavy rains.

Harboring the enemy

Where there's water leakage, there will eventually be mold.

Buildings with traditional stucco, brick or other exteriors can and do experience water leakage. But recently, the most urgent cases of leakage seem to be in buildings clad with synthetic stucco material, known as EIFS (external insulation and finish system). Vancouver, B.C., has a very big problem with mold in construction, most of it related to EIFS. Seattle has a much smaller one, but a substantial one nonetheless.

How does mold growth within walls affect occupants indoors, especially if the mold isn't visible on the interior of the building? The answer begins with understanding the types of building materials commonly used in construction.

Gypsum wallboard is present on the interior side of most residential construction. Consist-ing of a hygroscopic material (a sponge) surrounding two layers of paper (food for mold), the wallboard is an ideal environment to support mold growth following significant moisture infiltration. Some EIFS construction systems also use gypsum wallboard in a semi-waterproofed state, to provide external sheathing as well as interior sheathing. Such systems are even more vulnerable to moisture and mold problems. It's the paper on the surface of the wallboard that is the problem.

Most fungi are unable to grow well in the alkaline medium created by the gypsum. With only paper as food, certain filamentous fungi such as penicillium aurantiogriseum, aspergillus versicolor, stachybotrys chartarum, and others not only tolerate alkaline conditions but also out-compete other organisms. They become dominant, and the wallboard becomes covered with these molds.

Normally, we are exposed to mold spores in significant quantities outdoors. Many of these molds are leaf-decomposing fungi. The mold species indoors in water-damaged buildings are often soil fungi, different from those prevalent outdoors. When the levels of exposure to the spores of molds growing on building materials reach a certain level - likely to be different for each individual - the risk of health symptoms emerges. Health studies conducted in many countries over the last 20 years have indicated that symptoms such as cough are more prevalent in homes with water infiltration.

Knowing which mold species grow, and how they grow on the interior of building materials is half the answer. The other part is how occupants become exposed to the spores of those molds.

In any building, small movements of air occur through the walls. These movements are enhanced by exhaust ventilation indoors which creates negative pressure, drawing moisture and mold inward to occupied areas. If water damage exists in the walls, the resulting molds can produce massive quantities of spores and release them within the wall cavities. The amounts of mold spores coming into the building with air currents may not be very high, but if the process continues for an extended period of time (typically years) the dust deposited on upholstery, carpeting, or other indoor surfaces becomes skewed in composition. Instead of containing mostly outdoor molds derived from decomposing leaves, an increasing percentage of the dust is composed of the spores from the molds growing on the water-damaged building materials. Then, when the children jump up and down on the couch, their activities release clouds of dust, creating an atypical mold exposure to occupants.

Getting answers

There are three test methods, typically used together as a suite, to determine whether mold accumulation and exposures are occurring. One way is to sample the vacuumed dust from surfaces. The sample is then either microscopically scanned looking for mold spores, or is cultured in appropriate growth media to determine its mold population. Comparing the ratio of outdoor leaf-decomposing molds to those known to grow in building materials indicates if the composition of the dust is normal or skewed, indicating potential exposure and health issues. A second, complementary method is to conduct air sampling, injecting the particles in indoor air onto a petri dish with appropriate growth media, in order to determine what types of mold are growing. Interpretation is similar to the settled dust sample. The types of mold are compared with what should normally be present.

In essence, the settled dust technique paints a picture over time of what typical exposures may have existed over the last few months, while the direct air sampling method gives a snapshot of the exposure levels at a moment in time. Doing only the latter test and omitting the settled dust sampling can often result in what industrial hygienists call "false negatives," e.g. the testing suggests that a problem doesn't exist when it really does. Nobody likes false negatives, especially professionals with errors and omissions insurance, given that unknown and potentially harmful exposures could result to people.

The third test method is to conduct a thorough physical inspection of the building, focusing on the areas behind walls where moisture may be present. Thorough visual examination for moisture and mold, the quantity of mold present within the building can be estimated. This provides information on the degree of risk and in choosing appropriate remediation practices. Inspection is accomplished using boroscopes with bright fiber optic light sources and hand-held mirrors, accessing the wall through small openings in the wall board. These holes are patched immediately upon completion. Industrial hygienists, teamed with specialty architects and engineers who understand why buildings leak and where to look for water can accomplish this task. These professionals often need to open walls to inspect construction details. By combining our efforts, we make fewer inspection holes and save the client time and money. By using special work practices as walls are opened, spores previously enclosed behind walls will notbe released.

All three of these methods are typically used together in understanding the degree of potential risk from mold growing in water-damaged building materials, and in choosing appropriate remediation technology to prevent release of spores which could impact the health of remediation workers or occupants.

Water intrusion into a building can result in structural damage as well as health concerns due to growth of mold. Mold growing in walls may, over time, release spores which accumulate in living areas. These spores are different from the spores we are exposed to ordinarily outdoors, and may result in exposures which elicit allergic or irritant symptoms in occupants. Testing methods including direct observation of the areas within the walls, surface sampling, and/or air sampling can indicate the presence of spores indoors and provide some estimate of the potential health risk. When mold is discovered, remediation methods must not scatter the spores, resulting in further exposures.

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