HOW OLD IS THE WATER DAMAGE? USING FUNGI AS FORENSIC TOOLS IN WATER DAMAGE INVESTIGATIONS
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How Old is this Water Damage?
One question we often receive is whether the water damage is sudden or accidental or whether can be attributed to a long-term event or a single past event. Another question we receive from building owners and insurers is what is the cause and origin of the mold and fungi growth in the building.
There are a number of ways that these questions can be answered. First of all, molds are fungi. Fungi can be used as forensic tools to determine the location of water intrusion into the building and to determine the history of water or fungi damage. This is more effectively done in conjunction with accompanying observations, such as the type of wood damage, the color and pattern of the damage, the extent and type of the fungal growth, the humidity levels, and so on.
Fungi and Mold Epidemic?
During the last twenty years or so we have seen an explosion in mold- and fungal-related building repairs and insurance claims. Current estimates show that replacement materials needed to repair damage caused by rot alone account for nearly 10 percent of the annual wood production in the United States. Our opinion is that the changes we had to make in construction materials (such as the invention of medium density fiberboard (MDF), particleboard and oriented strand board (OSB)), along with changes in building designs, construction methods and negligent construction and maintenance have led to such a phenomenon.
Earlier structures built with wood such as red oak, chestnut, hickory, and other hardwoods as well as wood cut from the heartwood of softwood species did not evidence as much mold or wood-decaying fungal growth. Builders have had to replace these hardwoods with framing material made out of yellow pine, spruce, Douglas fir, aspen; they are also making use of the above-referenced engineered products that are made out of softwood, sawdust, nitrogen, etc. Mold can attack the sapwood and engineered-wood surface, including the paper of the drywall faces, but it has hard time living of the hardwood that is common in older buildings.
In addition, newer designed homes implement more organic material than old homes. New homes use more insulation which can trap moisture behind walls. EIFS (fake stucco) is also prone to mold attack, especially when wet. Additionally, tight building structures and poorly monitored HVAC systems found in newer buildings have contributed to mold growth. Leaky HVAC produces mold and disperses it throughout a building via ventilation.
The result is that, in combination with “more energy efficient designs”, today’s structures can more easily attacked by mold and wood decaying fungi. Even “small” modifications to the ventilation of a home can lead into major fungal outbreak. In a recent case, an insured had reduced his central air conditioning flow of air, resulting in reduced ventilation; this led to significant condensation and the growth of mold and fungi inside his home. The insured initially claimed that recent storms have caused the “water leaks”, but we conclusively established that it was simple condensation. The insured was asking for tens and tens of thousands of home repairs.
Most buildings have experienced some type of water intrusion: high humidity, leak, flooding, wind-driven rain, moisture intrusion from the crawl space or the sump pump, and so on. We often find mold growth in bathrooms, kitchens, basements and other high moisture areas. Careful inspection of buildings will usually find areas of fungal growth where the conditions are favorable: moisture, organic material, fungal spores and to a lesser extent temperature and light conditions. If all these factors are at play at a certain building for months or years, then there is high probability that a fungal growth has been developing over the long-term and it was not a sudden or brand-new growth. Often times, the lack of weather protection of the building components during construction has caused rapid degradation of the framing members even at subsequently moderate moisture levels.
Wood Decaying Fungi
Wood decay by fungi is typically classified into three types: soft rot, brown rot and white rot. Brown rot fungi are the most prevalent with regard to attack on coniferous, structural wood products in North America. The wood decayed by brown rot fungi is typically brown and crumbly and it is degraded via both non-enzymatic and enzymatic systems. Brown rots usually cause wood to lighten in color prior to becoming dark brown, and to crack along and across the grain. When dry, very decayed timber will crumble to dust.
White rot fungi are typically associated with hardwood decay and their wood decay patterns can take on different forms. White rotted wood normally has a bleached appearance and this may either occur uniformly, leaving the wood a spongy or stringy mass, or it may appear as a selective decay or a pocket rot. The fungi producing these rots can produce airborne spores and influence air quality. However, they are primarily of concern because of their capacity to destroy the structural integrity of wood.
The soft rot fungi can degrade all three of the structural wood components, although the major food sources are cellulose and hemicellulose. A wide variety of fungi can cause soft rot, including the ubiquitous Chaetomium. For soft rot to occur, liquid water must be continuously present. Wood with soft rot is spongy. The most common sites for soft rot in buildings are wooden windowsills and areas where roof drips continually wet wood materials.
White and brown rot fungi can form fruiting bodies on the surface of colonized wood, and can produce massive numbers of basidiospores. If basidiospores are higher indoors than out on air samples, the possibility of wood rot should be considered, and the type of basidiospores explored more carefully.
Because water flows downward under the influence of gravity, looking at the uppermost area of rot could help determine the origin of the rot. The pattern of the rot is the best clue to the water entry mechanism. Figure 1, 2 and 3 present some examples of cases where we were able to use the knowledge of fungi growth to determine the timing of the water release.
Figure 1: Mushroom of a brown rot fungus (a Basidiomycete) growing in the attic. This is just the fruiting body (the spore-producing body) of the fungus. There is a much larger fungal body inside the wood. This fungal growth and associated wood damage started in areas of the roof sheathing weakened by nail and other penetrations, took a lot time to develop and was not caused by a recent sudden or accidental moisture release. The recent storm did not cause the water damage.
Figure 2: Fungi (Peziza domiciliana) growing on the basement exterior foundation wall and feeding on the organic and inorganic matter present on the wall. Note the mycelium (net-like structure). Constant moisture coming through the cement block or leaking pipes/equipment in the basement, to name a few causes, will increase the humidity in the building. This will in turn cause this fungal growth. By knowing the growth rate of Peziza, we determined that this fungal growth took several weeks to develop. Many homes in high moisture areas exhibit these types of growth that are not necessarily caused by a single sudden or accidental event.
Figure 3. The wood above is not only moldy, a closer examination shows that it has rotted. The rotted condition of the wood indicates long-term exposure to water and makes it less likely that the mold on the wood is due only to the single recent leak event occurred few days prior to the inspection. In combination with other construction defects that we observed, we opined that faulty construction caused the rotted wood and mold and not the leaked pipe.
In many cases we see both dry desiccated fungal growth and more recent growth, suggesting multiple water damage events. Depending on the pattern of the fungal growth and the speciation, we may be able to distinguish between old and new water impacts.
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