Fungi's Job is to Eat, Decompose Your House
BY MARY BETH BRECKENRIDGE
Knight Ridder Newspapers
What you don't see can hurt you. Mold in buildings can compromise structures and make people sick. Often, that mold lurks in hidden places - behind the walls, in the air conditioning system, on the underside of Grandma's old chest of drawers.
Yet people often ignore those sources, simply because they're
not visible, said Jeffrey May, a mold-investigation specialist
and author of "The Mold Survival Guide."
"People react most strongly to what they can see," said May,
who owns May Indoor Air Investigations in Cambridge, Mass. So
the slimy gunk in the shower or the black stuff in the attic may
worry them, when those probably aren't nearly as threatening as
what's under the basement carpet or behind the paneling.
Before you panic and start tearing out drywall, however, you
should know that serious mold infestations aren't rampant. In
fact, most houses don't have a significant mold problem, said
Andrew Sill, owner of Cierra Environmental, an Ohio company that
specializes in mold inspection, testing and remediation.
In those that do, there's some sort of underlying cause, such
as improper ventilation, a leak in a water pipe or a bathtub
overflow, Sill said. "The mold follows the water," he said, "and
the water doesn't just appear in the house."
Even if your house does have mold, the problem may not be
significant if no one in the house is sensitive to it, said Thad
Godish, a professor of natural resources and environmental
management at Ball State University, who has researched mold
contamination of buildings. But for people who are sensitive to
it, mold can trigger asthma, chronic coughs and more serious
Mold is in the air all the time, Sill and May said, so it's
impossible to achieve a level of sterility that would make a
house mold-free. Nevertheless, May believes mold shouldn't be
growing unchecked in any home.
So what is mold, anyway?
Mold is fungus - actually, any of many types of fungi. Mold
plays a useful role in nature, because it secretes enzymes that
break down matter.
Mold becomes a problem, however, when it starts feeding on
things we don't want it to, such as the wood frames of our
houses or the paper that covers drywall. Mold can weaken and
ultimately destroy parts of a house. It can send spores and
other particles into the air we breathe.
"Mold is out there doing its job," Godish said. "It's trying
to eat your house down. If you give it a chance, it will."
The most common types of fungi in a home - what we typically
refer to as mold or mildew - belong to the genera "Cladosporium,
Penicillium, Aspergillus, Alternaria, Stachybotrys and
Chaetomium." Different types of mold feed on different
substances, such as wood, cellulose, dust and soap scum. All
need food and water to grow.
How big a problem these molds pose depends partly on how much
is present. A trace of mold around the edges of windows isn't
likely to release enough spores to cause health problems, Sill
said, while a moldy section of basement wall could be a breeding
ground of misery.
NOT ALL ARE WORRISOME
The type of mold is significant, too. Many molds found in a
house are superficial, May said - they grow on a surface but
don't attack what's underneath. But Godish said those molds can
set the stage for other fungi to come in and hasten the
And while May said any type of mold can cause allergic
reactions when it's breathed, some molds produce tinier spores
that float in the air longer and lodge more deeply in the lungs.
"Aspergillus," for example, is often linked to a condition
called homes-in-stocktonsensitivity pneumonitis, a chronic lung disease that
he said is relatively rare but often misdiagnosed as pneumonia.
AC CAN HARBOR SPORES
One of the most common hidden sources of mold in modern
buildings is the air-conditioning system, May said. In summer,
water pools in the unit and provides the perfect breeding ground
for mold. In winter, when the mold is dry, particles are easily
picked up and blown through the air.
Basements and crawl spaces are other places where mold tends
to grow. The relative humidity typically is higher there than in
the rest of the house, and Sill said the darkness allows mold to
Mold is also common in attics and bathrooms - particularly
bathrooms that don't have a fan or that stay steamy for a long
time, Sill said. Houses that are left unheated can experience
mold growth, too, because moisture from the air condenses on the
Paradoxically, the one type of mold that's probably gotten
the most attention and caused the most fear - the so-called
toxic black mold - isn't a common source of health problems, May
and Godish said.
TYPES OF BLACK MOLD
When people talk about toxic black mold, they're usually
referring to "Stachybotrys chartarum," May said. But "toxic
black mold" is a term he and Godish avoid.
For one thing, it's technically incorrect. It's not the mold
that's toxic, Godish noted; it's the substance it produces. For
another, the term is misleading, he and May said. It tends to
make people think all black mold is highly threatening, when
it's not. Black molds are common in bathrooms and attics, for
example, but they're usually not "Stachybotrys."
While it's true that "Stachybotrys chartarum" produces a
mycotoxin that's very poisonous - you can die from eating it -
May and Godish said there's no strong scientific evidence that
the mold causes significant health problems if it's not
disturbed. It also grows only in areas that stay very wet, so
it's not all that common.
Nevertheless, the mold can cause such fear that people
overreact, Godish said. "I've seen people basically abandon
their houses with a little bit of "Stachybotrys" around their
bathtub," he said.
Overreactions to mold in general aren't uncommon. Sill said
many people have the misconception that any kind of mold
permanently harms a home's value. "It can be fixed," he said.
How mold is remediated depends on the material it has
affected, Sill said. Treatment might involve removing the mold
using a HEPA vacuum, sanding surfaces, treating with a biocide
or applying a material that encapsulates the surface. Porous
materials such as drywall, insulation and mattresses may need to
Depending on the extent of the problem, the cost of testing
remediation can be significant, although some insurance policies
will cover it.
Better to prevent the problem in the first place, the experts
Because other than the Camembert in your refrigerator, mold
in the house just isn't a good thing.
MOLD EXPERTS SHARE SOME TIPS
Here are some answers to questions about mold, gathered from
mold authorities Thad Godish, Jeffrey May and Andrew Sill:
Q: How can I prevent mold?
A: The best prevention is careful home maintenance. Never
ignore a leak, because it takes only days for mold to grow. Fix
openings in the house's outer shell where water can seep in, and
make sure your attic is properly ventilated.
In the bathroom, open a window or use a ventilating fan when
you take showers. Make sure the fan is vented to the outside of
the house, not into the attic. If you don't have a window or
ventilating fan, set a small oscillating fan on the vanity to
help dry the room. You might even dry your towels outside the
bathroom if the moisture is significant.
In the basement, use a dehumidifier if the relative humidity
there is higher than 50 percent, and keep the temperature at 60
degrees or above. That's critical in a finished basement that's
frequently occupied, May said. "It should be illegal to have a
finished basement without a dehumidifier," he said.
Carpet in basements frequently harbors mold, since moisture
condenses on the cold floor. Consider a hard floor with an area
Even something as simple as regular cleaning helps prevent
mold growth, since mold grows on dust, dirt and soap residue.
Q: How do I know I have a mold problem?
A: Mold can be hard to detect, because it often hides where
we can't see it.
A moldy smell is a tipoff, although you can have mold without
the odor. Unexplained respiratory symptoms are another clue,
particularly if they go away when the affected person leaves for
an extended period.
Suspect mold in any house that's had a leak or flood,
particularly if the problem wasn't remedied and the area dried
An older home is more likely than a newer one to have mold,
simply because the probability of leaks and other problems
increases with age, Godish said.
Q: What should I do if I suspect I have a mold problem?
A: Have an inspection done and the air in your house tested
to find out whether a problem exists. Expect to pay $100 to $250
for an inspection, Sill said.
An inspection may not be necessary if the source of the mold
is obvious, he said.
If the inspection shows you do have a problem, multiple
samples will often be required to determine the source. Those
samples need to be analyzed by a laboratory, so they aren't
cheap - about $75 each, Sill said.
Mold inspectors and remediation specialists are not all
equally qualified, so May suggested finding someone certified by
one of the following institutions: ACGIH Professional Learning
Center in Cincinnati; the Indoor Air Quality Association in
Rockville, Md.; MidAtlantic Environmental Hygiene Resource
Center in Cherry Hill, N.J.; or Restoration Consultants in
Sill suggested getting two or three estimates from mold
remediation specialists. Avoid anyone who offers ozone-type
products or promises to get rid of all the mold in the house, he
Q: Can I remove the mold myself?
A: Maybe, if you have only a small amount of visible mold -
less than 10 square feet - and you know what you're doing, May
Nonporous surfaces can be cleaned with a solution of chlorine
bleach and water. But don't just spray the bleach solution on,
Sill said; apply it with a towel, so you don't leave excess
moisture on the surface to start the whole mold-growth process
again. Wear proper gear to protect your skin and eyes.
After you've removed the mold, you can prevent a recurrence
by applying special bathroom paint formulated to prevent mildew
Porous surfaces, such as insulation and drywall, need to be replaced.