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Getting to Know the Enemy

May 15, 2002

28 • Interface February 2002
ndoor air quality is gaining momentum both as a matter of
public acknowledgment and an insurance company liability. But
buildings may have been infested with colonies of mold and
mildew long before the onset of weather that inflicts physical
damage. Questions to ask include:
• Which types of mold and mildew are now present?
• Were any colonies present prior to the storm?
• Was the condition exacerbated by the storm?
• How can the distinction be proven?
• Which fungal colonies are traceable to housekeeping
practices, deferred maintenance, and sanitation habits
versus those stemming from insurable storm damage?
A building science consultant is likely to encounter these
questions. Hopefully, the team of professionals (often called
litigants) will build arguments within the sciences of building
construction and microbiology.
Meet the Molds
Molds discussed below are among those found during a
storm investigation or other event of water leakage into a
building. The varieties reviewed are certainly not inclusive of
all that may be encountered. They are commonly revealed in
building components, but they may be found elsewhere in the
environment. Indeed, some are found virtually everywhere.
Stachybotrys (Figure 1) has gained considerable notoriety for
compromising indoor air quality due to its production of potent
toxins; however, this species rarely causes disease in humans. It is
usually associated with cellulose-containing matter where water
has been present for some time. It is thought to already be present
in two to five percent of American homes.1
Cladosporium is dark green to black and is a slow-growing
form of mold, an aspect that can be helpful in determining when
the colonies were fostered. The slightest movement will disrupt
the branched chains, greatly complicating preparation of microscopic
Aspergillus is a common household mold that excretes digestive
enzymes that enable growth on virtually any substance containing
organic matter, including a number of building materials
and foods. This genus of fungi is considered as both the most
useful and most harmful to humans. Some produce industrially
useful enzymes while others produce carcinogenic toxins.
Penicillium (not penicillin) can be found in locations as innocent
as a mulch garden. It can begin to produce spores in as little
By Lyle D. Hogan, P.E.
Figure 1: Stachybotrys has gained considerable notoriety for compromising indoor
air quality due to its production of potent toxins; however, the species is rarely
pathogenic for man.
February 2002 Interface • 29
as a day after being given a fresh culture medium.
The spores (some brilliantly colored) are
consumed by the millions when humans eat
blue cheese. This species tends to favor
cooler temperatures.
Wet Basements and Crawl Spaces
When the same residential walls repeatedly
have mildew stains, a damp crawl space is the
likely culprit. This moisture may also cause
problems in the attic, but it originates in the
basement. There may be leaking pipes, surface
water entering through basement vents, downspouts
that do not adequately divert water away
from the foundation, or other sources. And,
even without these conditions, a bare earth floor
can generate large amounts of moisture.
There is no way to completely eliminate
indoor mold spores, but moisture can be controlled
to keep growth to a minimum.2 For moisture
in a crawl space, the remedy is simple.
Naturally, it’s important to address the source of
unwanted moisture, but an easy solution is to place
polyethylene sheeting on the bare earth floor. This can
sharply curtail the moisture that would otherwise permeate
into the occupied spaces above.
Poorly Vented Attics
Proper attic ventilation is crucial for the roof as well
as the rest of the building.3 Many investigations identify
substandard attic ventilation as the culprit in premature
steep roofing failures. Figure 2 depicts severe mold/mildew
in a humid Southern climate that was hot and dry at the
time of the study.
Mold/mildew colonies develop in the winter from
condensation, which then dries to a powder during the
hot season. This condition alone may create pervasive
indoor air problems, and poor attic ventilation is largely
to blame.
Long-Term Leakage in Flat Roofing
If roof repairs are not implemented quickly, insulation
becomes wet and prompts deterioration of the deck, which
can sharply increase the cost of re-roofing. Figure 3 depicts an
example of fungal colonies discovered during roof removal.
Colonies had spread widely below the rubber roof membrane.
When entrapped water reached the underside of the roof deck
and framing members, fungal colonies grew on those surfaces
as well.
Even ceiling materials can harbor mold and mildew. When
ceiling tiles repeatedly become wet, the moisture invites numerous
types of fungal growth. Figure 4 depicts form boards of a poured
gypsum deck that repeatedly became wet from roof leaks.
Concerns about indoor air quality can often be traced to this
condition, particularly in a return air plenum (an air-filled space
in a structure that receives air from a blower for distribution).
HVAC Ducts, Chases, and
Condensate Pans
Dehumidification is a beneficial side effect of air conditioning,
providing a pleasant escape in hot, humid climates. The
summer months at coastal retreats may bring huge cooling loads
where air conditioning systems are running at warp speed. Sheet
metal surfaces in the HVAC devices are sure to sweat and, in the
concealed chases, the equipment becomes a breeding ground for
mold. Then, when the contaminated air is released into occupied
spaces, it can create a number of health maladies.
Moisture from any source will condense on surfaces that
become cooler than the dewpoint. HVAC devices create con-
Figure 2: Fungus and spores and mold — Oh my! Mold/mildew accumulation in a humid
southern attic. The colonies were fostered from a wintertime condensation scenario, drying
during the hot season to the formation shown. Note that attic insulation must be held back in
order for the soffit to serve as the intake port. A pre-manufactured baffle can be used to keep
blown-in insulation from becoming a ventilation impediment.
Figure 3: Fungal colonies found during a roof tear-off. Colonies had spread widely
below the roof covering. When entrapped water reaches the building interior,
the same fungal colonies can grow on roof decks and framing members.
30 • Interface February 2002
densation that must be collected and removed from the
occupied space. Placing a condensate pan beneath air conditioning
devices ordinarily takes care of this. The pan
works well when there is:
1. adequate slope,
2. a functional outlet or port for drainage, and
3. a place for the water to go.
When any of these elements is missing, molds will harbor
in the standing water. Figure 5 shows a condensate pan
where a curious mix of molds was fostered. Note also the
dead rat in the water, a condition also found elsewhere in
this upscale hotel. The storm prompting this investigation
did not produce these conditions; however, at the
outset, the mold remediation was included in this
damage claim.
Water, water everywhere…
Hurricanes are common in many coastal
regions. High-rise, oceanfront hotels are routinely
exposed to torrential rains and high winds. Oceanfacing
doors let in water that saturates carpets and
sometimes invades the floors below. Power outages
are also common after a hurricane. Put all those
factors together and perfect conditions for growing
mold are present. Wet carpet left for several days
in a hot, humid, dark setting is a known breeding
ground for fungal colonies. Hotel owners know
that the first order of business after a storm is to
dry out the building. For good reason, then, drying
contractors are among the first on the scene in hurricane-
ravaged areas.
During the clean-up period, wall coverings may
be peeled back. To the building owner’s astonishment,
the back surface of vinyl wall coverings is
often covered with mold colonies. But most buildings
don’t need a hurricane to foster mold and
mildew. Since moist air will condense on any building
surface colder than the dewpoint, the wall covering
may be the first such component. Figure 6
illustrates severe accumulation of mold colonies
thriving on the paper facing of the gypsum drywall
and kept wet by the low permeability of the vinylbacked
wall covering. The condition is quite likely
to occur near window openings, bathroom ventila-
Figure 6: Severe accumulation of mold colonies, thriving on
the paper facing of the gypsum drywall and kept wet by the
low permeability of the vinyl-backed wall covering. The
condition is unrelated to a single identifiable storm event.
Figure 5: A condensate pan beneath an HVAC unit. Not only was a curious mix of molds
being fostered, a dead rat was floating in the water. The condition was found in several other
rooms of this upscale hotel.
Figure 4: Formboards of a poured gypsum deck having been exposed
to cycles of wetting. Repeated wetting in this manner will culture fungal
growth. Concerns about indoor air quality can be traced to this
condition, particularly in a return air plenum.
February 2002 Interface • 31
tion devices, and HVAC chases. Accordingly, it is unrelated to a
single identifiable storm event.
Topics Worth Pursuing
The risk and cost of exposure to mold remediation for an
insurance company would appear to merit research considerations.
Such topics would include:
• Does one-time saturation of wood-framed construction
irreversibly compromise building elements? Do the fungal
colonies that develop after flooding go dormant to a safe
level so that radical demolition of a structure can be avoided?
• Which types of fungal colonies develop during episodic,
short-term wetting versus long-term, pervasive moisture
conditions? Will there ever be “bright line distinctions”
among the molds associated with these two kinds of wetting?
• Can universally accepted levels of mold/mildew be determined?
Who would be the authoritative body to develop such levels?
• Are the current methods used for eliminating
mold/mildew capable of restoring an occupancy to a
“safe” level once that threshold is determined?
In the Meantime…
While standards writing and research projects take form,
there are things that can be done.
• Protocols for building condition surveys should be modified
to include better investigation of fungal colonies and
the conditions likely to generate them.
• Building maintenance practices should include examination
of surfaces that develop condensation. This is of particular
importance when such areas are obscure, dark,
and when the air from these regions mixes with that of
occupied areas.
• Owners should become familiar with their properties to
recognize probable locations of fungal development.
Crawlspaces, attics, duct chases, and related regions
should be examined for possible impact on indoor air
quality. HEPA filters are fine, but they do not dry out a
wet basement.
• Insurance carriers should better delineate coverage terms
for mold and mildew occurrences. A major storm event
usually prompts the most thorough building inspection
ever performed. The owner’s representative will undoubtedly
investigate mold occurrences that favor his/her claim
of damages. This myopic fixation has, on occasion, inflated
insurance claims to obscene levels.
Johnny Carson once mentioned the smog in Los Angeles
during a comedy routine. He repeated a health warning to
“sensitive people,” which he defined as “anyone with a pulse.”
More and more people appear to contract health disorders from
airborne contaminants; this trend is not likely to subside
anytime soon.
Meanwhile, building construction professionals may benefit
from heightened understanding of the various molds at work
and the environments necessary to culture them. In many
instances, understanding these environments can help eliminate
the molds themselves.
1. “Beware the Mold Stachybotrys,” Health Story Page (from
CNN Interactive news bulletin) posted November 5, 1997.
2. Peter Kuchinsky II and Glenn Schwartz, from “Ten Things
You Should Know About Molds,” Moisture, Molds and Indoor
Air Quality, (published by Environmental Assessment
Association, Alexandria, MN.) page 6.
3. R.L Corbin, “Attic Ventilation: Why It’s Necessary,”
Interface, August 2000, pp. 20-22.
The National Association of Mutual Insurance
Companies (NAMIC) recently launched a website that will
disseminate information about mold. provides current news, education,
scientific links, litigation updates, state legislation, and acts
as a clearinghouse for insurance industry issues relating to
mold. The site is non-partisan and not-for-profit.
“While there have been references to mold and
mildew since ancient times, we wanted to offer a 21st
Century clearinghouse for mold-related issues that might
assist the industry,” said Larry Forrester, NAMIC president.
“NAMIC has noted the importance of education and information
on this subject.”
The mission of is to provide the
most current data for insurers as they research this matter.
NAMIC plans to develop and assemble content that will
assist the industry, general public, and news media on the
subject of mold.
Lyle Hogan is a senior engineer
with Geoscience Group Inc.,
(, working
out of the firm’s Greensboro, NC
office. He is a registered engineer, a
registered roof consultant, a licensed
home inspector, and a Fellow of the
Roof Consultants Institute. Mr.
Hogan’s articles have been published
in the numerous technical journals
and conference proceedings. He is a
recipient of RCI’s Horowitz Award
for outstanding contributions to Interface journal.
This article originally appeared in Property/Casualty Insurance
magazine, a publication of the National Association of Mutual Insurance
Companies (NAMIC), Copyright, 2001; all rights reserved.