Defining whether a water loss is from a single intrusion eventor is from chronic moisture is a key element in a buildinginvestigation. EFI Global frequently uses wood decay testing toassist insurance assessment investigations in residential andcommercial structures. Wood decay information can scientificallydefine relative times during which water exposure occurred. Thisallows the investigator and claims adjuster to understand whether awater loss occurred from a recent single event or is a result of achronic water intrusion. 

Evidence for dating a water intrusion event can includeobservations such as rust on metal (nails), the presence of fungalreproductive structures, the lack of moisture on the substrate,mold on mold growth, mold caused by condensation on the undersideof sheathing of an un-insulated roof in the cold season, andcondensation related mold on air conditioning ducts in humidlocations in the cooling season. Although they may be useful cluesin determining water intrusion, these observations are lessconclusive than wood decay evaluation.

Microscopic Analysis

Wood decay analysis consists of a microscopic evaluation of thefungal types present, and the extent of their penetration into thewood or wood product surface and the strength of the substrate.According to the USDA Forest Products Laboratory, different woodtypes are more susceptible to water intrusion than other types.Under controlled conditions, wood decay can create loss of woodmass 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 withinseven years, and “Aspen based OSB” retains virtually none of itsmechanical property values after 11.5 years. In summary, soft woodsare more resistant to water intrusion than hardwoods.

In addition to different wood types, temperature, and moistureconditions will have a determinant impact on the rate of decay. Onecan safely state that a single short term water exposure should notresult in moderate to late stage wood decay. For example,a single exposure of solid wood framing (two-by-four studs) tomoisture will not lead to wood decay. Only chronic exposure tomoisture will break down the complex carbohydrates (Lignin,hemicellulose and cellulose) that compose woods, whereas cellulosefound on gypsum board is relatively quick to begin fungaldecay.  Wood also contains tanins (in hardwood) andphenolics (in softwoods), Thujaplicins (in cedars) that arefungitoxic compounds and inhibit fungal decay to variousdegrees.

Different types of fungi present in the substrate can alsoaffect the rate of wood decay. Slow-growing fungi such asStachybotrys chartarum, requires chronic moisture, whereasCladosporium, a rapidly growing fungi,  can becomeestablished in just a few days. Furthermore, the presence of miteinfestation and mite feces in a mold sample indicates that the moldhas been present long enough for the mold to become established andfor it to attract insects who will feed on the mold. To helpidentify the specific areas and extent of mold present in walls,thermal imaging and moisture meters are oftenused.  

A recent case study resulting from Hurricane Sandy illustratesthe value of a wood decay analysis in determining the extent ofwater intrusion. A New Jersey building claimed that wind drivenrain had impacted the entire two story building. Thermal imagingand moisture mapping of the walls indicated that  the wallcavities along the base of the building had late stage wood decayfrom what appeared to be surface runoff impacting a slab on gradefloor. However, the presence of the fungi Stachybotrys with allwater damage that was tested, along with the presence of mites andtheir fecal matter, confirmed that the water damage had beenongoing 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 presentconfirmed that that water intrusion in this building had beenpresent prior to the hurricane, and worsened as a result of thechronic water intrusion occurring during and after thestorm. 

Mark Goldman, CMC, CEICS, is a senior air qualityscientist at EFI Global, Inc. For more information, visit www.efiglobal.com.