Indoor Mold Causes & Cures, continued
Ventilation. Tight homes do
trap moisture. We don't need to build homes leaky again, but we
do need to install mechanical ventilation in homes, as we have
for decades in commercial buildings.
In the North, you want to create a neutral or slightly
negative air pressure inside, so any air leakage will be cool,
dry exterior air leaking in, not moist, heated air pushing out.
Exhaust ventilation works well in cold climates. But be sure to
use sealed-combustion appliances, or conduct a "worst-case
depressurization test" to make sure any natural-draft
appliances draw properly, even when all other equipment that
can cause negative pressures is running.
In the South, we need to pull in extra air and pressurize the
home to keep the humid outside air at bay. One solution is a
direct air intake into the plenum of the air conditioner, which
leads incoming air through the air filter and cooling coil
before introducing it to the indoor space. Even better, install
a whole-house dehumidifier, ventilator, and filtration system
in parallel with the air conditioner. This will do a better job
of maintaining year-round moisture control without over-cooling
It's very important not to oversize the air conditioner,
because oversized units do a poor job of reducing humidity.
Always have the equipment sized using the Air Conditioning
Contractors of America (ACCA) Manual J
Bathrooms. The bathroom is a
wet place by definition, which makes it a common place to find
mold (Figure 5). Contrary to popular belief,
"moisture-resistant" drywall ("green board") is not a
mold-resistant substrate for tile. Use a cementitious backer
board instead. An even better approach is to skip the tile and
use a nonporous sheet material like solid surfacing. The fewer
cracks and gaps you have to seal, the better the odds of
keeping the system dry.
Figure 5.The bathroom is a naturally humid
environment and is also prone to plumbing leaks that create
continual wet conditions. Drywall, whether moisture resistant
or not, supports thriving mold colonies in moist conditions.
Use backerboard and tile instead, or a synthetic material like
Always install a good bathroom ventilation fan, even if you
have a window. There are plenty of quiet, efficient models on
the market, with controls that can respond to humidity or
motion. Timer-linked controls are also effective. Vent the fan
to the outside, not into the attic, or things have a way of
turning ugly overhead (Figure 6).
Figure 6.A dryer vent and bath fan were improperly
vented into this attic, causing condensation to form on the
sheathing and support mold growth.
Plumbing. Let's not forget
the pipes. According to insurance industry statistics, plumbing
leaks are the biggest source of water damage claims. Don't put
pipes where they might freeze and burst. Pans under water
heaters and washing machines are good insurance. Leave easy
access to drains under sinks or in cellars, so leaks can be
quickly detected and easily fixed. And be absolutely sure that
plumbing is tested for leaks before anything is closed
Mold in Existing Buildings
What if you encounter mold during a remodeling job, or get a
mold-related complaint in a home you've built? Now you're
looking at cleanup (or to use the modern 50¢ word,
Your cleanup methods have to keep the mold from spreading by
minimizing dust and spore dispersal. You also have to provide
personal protection for people who are exposed to the mold
(including the building occupants and your crew) and protect
yourself from any greater liability.
Know the standards. In
particular, you must not leave yourself open to an accusation
that you made the situation worse by not exercising due
diligence. I'm no lawyer, and I won't go into details about
liability issues, but I can say that it's a good start to know
and apply well-accepted national standards for handling mold in
buildings. If a case goes to court, it's nice to be able to
tell the plaintiff's attorney, "We got there as quickly as
possible, did a thorough visual and moisture meter
investigation to determine the extent of the damage, identified
and stopped the water intrusion at its source, and then
proceeded according to nationally respected guidelines."
Those guidelines are out there, and it's your business to know
about them. If you ignore the guidelines or, worse, knowingly
violate them, your position is very weak.
A panel of national experts convened by the New York City
Department of Health issued mold remediation guidance in 1995.
New York's guidelines have served as a template for the
Environmental Protection Agency (EPA) and other groups in
creating their published guidance materials. All these
organizations agree on the main points, and the rules aren't
hard to follow. New York's guidelines are available from the
city's Department of Health website at
EPA's guidelines are posted at
Let's go over the key points.
Act fast. Timing is
critical. Treat every water intrusion complaint like a report
of a small house fire -- because just like a fire, the problem
will quickly get worse if you ignore it. Don't say you'll be
over when you have time, get there now!
You won't see or smell mold for the first 48 hours after the
materials get wet. If you can get to the job before mold starts
to grow, stop the water at its source, and remove or dry all
the wet material quickly, mold may never be an issue.
Try to keep the relative humidity levels in the area below
60%, because mold has a difficult time growing beneath that
threshold. In fact, to speed the drying of materials, the drier
you can keep the air, the better.
By eye and nose. If you
don't arrive on the scene until things have already been wet
for several days, you may well have a mold problem. Do a
thorough visual examination of the area and all associated
areas where the water might have gone. You need to determine
the source of the water and the extent of the damage. Don't
start repairs or remediation until you find and eliminate the
source of the water -- rebuilding or cleaning the damaged area
is useless unless you're sure it will stay dry. Remember to
look in the hvac system, the ceilings of areas below the
source, and walls associated with the general area, too.
A good moisture meter is vital for the initial investigations.
There are good pinless meters now available that don't leave
holes in the wallboard, tile, or other finish materials.
Don't ignore your sense of smell. Molds have a distinct odor,
and our noses are finely tuned for detecting it. If you notice
a "moldy" or "musty" smell, track it down. Odds are it's
Don't test the mold.
Somebody may suggest testing the mold to find out what type it
is. Don't do it. Identifying the species doesn't serve any
purpose in the cleanup process. No matter what mold species it
is, we want it out of there, and you will proceed with your
remediation the same way regardless. Air sampling for spores is
also not helpful in most cases.
Whether there's mold or not, you need to stop any leaks or
condensation problems. If you do find mold growth, consult the
remediation guidelines and decide whether the cleanup is a job
your crew can handle, or it's time for a specialist to take
How much is too much? The
New York guidelines lay out a graduated response that depends
on the amount of mold present. The goal is the same -- stop the
water, protect the occupants and workers, and get rid of the
mold -- but for larger amounts of mold, the guidelines call for
qualified supervision and more stringent measures to isolate
the work area.
The guidelines recognize four levels of contamination, which
are defined in terms of the square footage affected by mold.
These range from "small isolated areas" of 10 square feet or
less to areas of "extensive contamination," which cover 100
contiguous square feet or more. There are two intermediate
classifications -- "mid-sized isolated areas" of 10 to 30
square feet, and "large isolated areas," which cover 30 to 100
The appropriate cleanup procedure for any given case will
depend on the contamination level. Levels 1 and 2 -- areas of
mold less than 30 square feet, or about the area of a sheet of
plywood -- can be handled by a general contractor's crew or a
building owner's maintenance staff, as long as the workers get
appropriate training, have the correct equipment, and follow
the steps laid out in the standard.
Areas of mold covering between 30 and 100 square feet (Level
3) require "personnel trained in the handling of hazardous
materials and equipped with respiratory protection, gloves, and
eye protection." When contamination exceeds 100 square feet
(Level 4), the standards require full containment under
HEPA-filtered negative air pressure, complete isolation of the
work area, and airlocks. This is unquestionably a job for
Large areas of mold growth
call for crews trained in hazardous materials
The area should be depressurized with
a HEPA-filtration blower and entered through a sealed
"clean room." This crew wears protective suits with
hoods, booties, and gloves, along with full-face
positive-pressure powered respirators equipped with
activated carbon filters to remove VOCs. But the crew
leader says, "This is not HAZMAT gear. It's not good
enough for asbestos or a chemical spill. It's really
just very good dust protection. We use the charcoal
canisters because we don't like the smells, not for
safety reasons. And the blowers help keep us cool
inside our hoods."
Careful dust-control practices prevent mold or
anything else from being spread around during
demolition. These trained mold remediators carefully
cut away drywall with knives and place it in plastic
bags for disposal; they use a shop-vac to suck the air
out of the bags and close them with duct tape. The bags
of debris (bottom) are not toxic waste, however, and
can be taken to a regular landfill -- the purpose of
the containment and dust control is just to avoid
exposure to allergens and irritants.
The square-foot thresholds are somewhat arbitrary, and the
standards don't claim to be based on any proven relationship
between area of mold growth and alleged health effects. It's
really a judgment call: Can a crew get rid of the mold without
spreading it or exposing anyone to elevated levels of spores or
contaminated dust in the air? The more mold there is, the
harder it is to contain the pollution; every contractor has to
make his own decision on where to draw the line.
Let's look at the minor jobs that can be undertaken by a
building owner's regular maintenance crew. The standards
recommend that the crew should "receive training on proper
cleanup methods, personal protection, and potential health
hazards." You can do this yourself with the help of some
publications available free from the EPA
Protective gear. You need to
be very strict about personal protection -- you're open to a
comp claim or lawsuit if anyone starts to feel sick. The crew
should wear masks that meet the N95 disposable respirator
standard. These are now widely available at all of the big-box
hardware stores for a couple of dollars each. (Don't confuse
these with much cheaper "nuisance dust" masks.) The crew should
also wear latex gloves and goggles, because some people may get
allergic skin reactions to the many substances molds
Who should move out? The
work area should be unoccupied, but with certain exceptions,
the family can stay in adjacent areas. The exceptions include
children under one year old; people with chronic lung diseases
like asthma, severe allergies, or emphysema; and anyone with a
compromised immune system (such as chemotherapy patients,
people with AIDS, and transplant patients). People who fall
into one or more or these groups should move out of the
building until the work is complete.
moldy materials can greatly increase the levels of spores and
contaminated dust in the air. Contaminated materials must not
be allowed to spread beyond the work area. The key to
preventing this is something called containment -- essentially
a matter of isolating the work area with overlapping sheets of
plastic that are sealed at their edges. Containment is not
required for small moldy areas under 10 square feet but is
recommended for areas between 10 and 30 square feet.
I recommend that containment with plastic be employed on all
cleanup or demolition jobs. It's cheap and effective. At this
level, there's no need to create a negative pressure field by
exhausting the air from the work area through a HEPA filtration
unit. That's not a bad idea, but the guidelines don't direct
you to do it.
To depressurize the workspace on small jobs, I sometimes buy
an inexpensive box fan and a 1-inch pleated-media filter (such
as a 3M Filtrete filter) the same size as the fan. I tape the
filter to the fan and seal the fan in the window, creating a
simple exhaust system with a filter that will easily capture
mold spores. The air is drawn from the house, pulled through
the contaminated work area, then filtered and exhausted to the
In any case, do what you can to suppress dust during your
work. One effective way is to mist the areas before cutting
into them. You don't want to soak them, just dampen them enough
that you don't stir up a cloud when you work.
Reuse or discard? Some
building materials can be easily cleaned and reused, while
others can't. Porous materials that can't be easily cleaned,
including insulation, drywall, carpet pads, carpet, and ceiling
tiles, should be discarded. Any materials you remove must be
placed in plastic bags and sealed before being removed from the
work area. Moldy possessions -- furniture and the like -- also
have to be cleaned or discarded; but if antique or valuable
fabric or carpet has mold growth on it, a professional cleaning
and restoration contractor may be able to save it.
Nonporous materials such as metal, glass, and hard plastic,
and the semi-porous materials like wood and concrete, can be
cleaned instead of removed. But in the case of wood, decide
whether it is still structurally sound. Processed wood products
like particleboard and OSB are more sensitive to water damage
than solid lumber. No materials of any kind should be left in
place unless they are sound, dry, and visibly free of
Cleaning. People often think
they should use bleach on mold, but the industry standards
recommend against it. Bleach does not kill mold spores, and the
bleach itself is an irritant and can be harmful to workers and
In any case, sanitizing or killing the mold is beside the
point. Mold is an allergen whether it's dead or alive. If the
area is clean and dry, mold will not grow; if it's wet, mold
will grow back even if you wash with bleach.
The answer is to use a good strong soap and water solution.
Mold spores have a waxy surface that repels water; the soap is
a surfactant that breaks the water's surface tension and lets
it pick up the spores and dirt for effective cleaning.
When you're finished, the surfaces should be clean and free of
mold growth. All surfaces must pass a white-glove inspection.
Any wood should then be allowed to dry completely. Test wood
with a moisture meter to make sure it's below 15% moisture
content before enclosing it again. When you're sure everything
is white-glove clean and dry, and will not become wet again,
you can rebuild the area.
Communication. Before you
take on mold, it's vital to make sure you have the owners' full
understanding and full agreement. The owners need to be
comfortable. Communication is critical to this: You must talk
to the clients frankly about what you've found, and what you
are about to do in their home. Show them the guidelines,
explain what you intend to do and how long it will take, and
answer their questions regarding safety and other issues
affecting their family. Important communications should be
supported by a written follow-up. The NAHB has some good
guidance on this issue.
To be frank, the customer may not fully trust you. I am often
hired by builders to work as an independent third party to
ensure compliance with the standards, and property owners often
speak to me about their concerns. I've found that even people
who like their builder often suspect -- rightly or wrongly --
that his real goal is to cover his own butt. You need to do
whatever you can to dispel this idea, and full disclosure is
the best available remedy. Remember, suspicion can lead to a
The best method is to assign one person to be the customer's
point of contact on this job. This should be an individual who
has good people skills, and who knows the remediation process
front to back. Ideally, this contact person should be on the
job regularly, overseeing the process and checking on details.
This way, the residents can see that the person they're dealing
with knows what's actually going on. This extra care will pay
off in successful conclusions for you.Doug Garrettis the president of Building Performance
& Comfort in Leander, Texas, a building performance
contractor serving both the residential and commercial markets.
He is currently under contract with the Texas Association of
Builders to train members in energy code compliance and
moisture management in home construction.