Defining whether a water loss is from a single intrusion event or is from chronic moisture is a key element in a building investigation. EFI Global frequently uses wood decay testing to assist insurance assessment investigations in residential and commercial structures. Wood decay information can scientifically define relative times during which water exposure occurred. This allows the investigator and claims adjuster to understand whether a water loss occurred from a recent single event or is a result of a chronic water intrusion.
Evidence for dating a water intrusion event can include observations such as rust on metal (nails), the presence of fungal reproductive structures, the lack of moisture on the substrate, mold on mold growth, mold caused by condensation on the underside of sheathing of an un-insulated roof in the cold season, and condensation related mold on air conditioning ducts in humid locations in the cooling season. Although they may be useful clues in determining water intrusion, these observations are less conclusive than wood decay evaluation.
Microscopic Analysis
Wood decay analysis consists of a microscopic evaluation of the fungal types present, and the extent of their penetration into the wood or wood product surface and the strength of the substrate. According to the USDA Forest Products Laboratory, different wood types are more susceptible to water intrusion than other types. Under controlled conditions, wood decay can create loss of wood mass in as little as five weeks. “Soft rot” wood decay, however, requires a minimum of one year and typically requires 3 to 7 years. Alternatively, exterior grade plywood and oriented strand board (OSB) exposed to exterior conditions become mold infested within seven years, and “Aspen based OSB” retains virtually none of its mechanical property values after 11.5 years. In summary, soft woods are more resistant to water intrusion than hardwoods.
In addition to different wood types, temperature, and moisture conditions will have a determinant impact on the rate of decay. One can safely state that a single short term water exposure should not result in moderate to late stage wood decay. For example, a single exposure of solid wood framing (two-by-four studs) to moisture will not lead to wood decay. Only chronic exposure to moisture will break down the complex carbohydrates (Lignin, hemicellulose and cellulose) that compose woods, whereas cellulose found on gypsum board is relatively quick to begin fungal decay. Wood also contains tanins (in hardwood) and phenolics (in softwoods), Thujaplicins (in cedars) that are fungitoxic compounds and inhibit fungal decay to various degrees.
Different types of fungi present in the substrate can also affect the rate of wood decay. Slow-growing fungi such as Stachybotrys chartarum, requires chronic moisture, whereas Cladosporium, a rapidly growing fungi, can become established in just a few days. Furthermore, the presence of mite infestation and mite feces in a mold sample indicates that the mold has been present long enough for the mold to become established and for it to attract insects who will feed on the mold. To help identify the specific areas and extent of mold present in walls, thermal imaging and moisture meters are often used.
A recent case study resulting from Hurricane Sandy illustrates the value of a wood decay analysis in determining the extent of water intrusion. A New Jersey building claimed that wind driven rain had impacted the entire two story building. Thermal imaging and moisture mapping of the walls indicated that the wall cavities along the base of the building had late stage wood decay from what appeared to be surface runoff impacting a slab on grade floor. However, the presence of the fungi Stachybotrys with all water damage that was tested, along with the presence of mites and their fecal matter, confirmed that the water damage had been ongoing prior to the storm.
The roof was in poor condition with ponding present throughout, and maintenance on building envelope had rarely been performed.. These observations along with the wood decay and fungi present confirmed that that water intrusion in this building had been present prior to the hurricane, and worsened as a result of the chronic water intrusion occurring during and after the storm.
Mark Goldman, CMC, CEICS, is a senior air quality scientist at EFI Global, Inc. For more information, visit www.efiglobal.com.
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