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. Perithecia,
Cleistothecia, or similar fungal bodies are fungal fruiting bodies
formed to store and protect fungal spores, for example when moisture conditions
or lack of food create hostile growing conditions. The most common perithecia
we find in buildings is for Chaetomium.
Chaetomium is a cellulolytic mould commonly found in
soil, air, and decaying plant material. There are about 80 species of Chaetomium. The most common ones
are Chaetomium atrobrunneum,
C. funicola, C. globosum, and C. murorum. In indoor
environments the most common species of Chaetomium
is Chaetomium globosum. C. globosum is frequently
isolated in water-damaged buildings and produces two mycotoxins called
chaetoglobosins A and C when cultured on building material. Presence of Chaetomium species in indoor
environment is a sign of serious water problem.
Chaetomium may occur together with other water-loving
moulds such as Fusarium, Stachybotrys and Ulocladium. Species of Chaetomium are known to produce
mycotoxins but to what extent these toxins contribute to poor indoor air
quality or affect human health is not documented. However, injection of
chaetoglobosin A in rodents has been shown to be fatal at relatively low doses.
In medical literature some species have been reported to cause disease in
immuno-compromised individuals. Species that have been reported to cause
invasive human disease grow well at 35 to 37oC, and those with a
predilection for the central nervous system often display growth at up to 42 to
45oC.
Spores of Chaetomium are produced within
structures (asci) contained in a flask-shaped fruiting body known as
perithecium. Once the spores are mature, the walls of the asci dissolve
releasing mucilaginous spores within the perithecium. The spores ooze out of
the perithecium (plural perithecia) and get trapped by coiled or dichotomously
branched hairs that grow around the neck of the perithecium. Since the spores
are cemented together by mucilage and also trapped by hairs, few become
airborne until the mould has completely dried out or disturbed, say during
renovations or mould remediation. It is therefore not uncommon to find low Chaetomium spore counts in
pre-remediation samples and relatively higher counts in post-remediation
samples
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. The presence of
mold spores (such as Pen/Asp) in chains suggests that there is some active mold
growth in this building. These chains are so fragile that if mold were only
entering from outdoors it is more likely that I would only see single spores or
very small fragments.
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. Figures 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.
Metropolitan Engineering, Consulting & Forensics (MECF)
Providing Competent, Expert and Objective Investigative Engineering and
Consulting Services
P.O. Box 520
Tenafly, NJ 07670-0520
Tel.: (973) 897-8162
Fax: (973) 810-0440
E-mail: metroforensics@gmail.com
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