Increasing attention is being focused on the
importance of good indoor air quality and its affect on health. The EPA has named
indoor air pollution as one of the most urgent national problems (see Industry
Snap-Shots). While many factors can contribute to poor indoor air quality, much
attention has recently been given to the detrimental affects of mold. A recent Mayo
Clinic study published in 1999, cited mold as a leading cause of many respiratory
problems, and a contributor to nearly 100% of chronic sinus infections. In a recent study by the Canada Housing and Mortgage Corporation,
Don Fulger, a building science researcher, evaluated 400 houses chosen at random in
Ottawa. "We found that 50% of the basements had evidence of moisture damage at
some time," said Fulger. "Wherever you had chronic wetting, you had mold.
Wherever you had mold, you had at least one toxigenic mold." |
As a professional home & commercial
building inspector (and previously as a building contractor) I have noticed, with what I
believe to be increasing regularity, evidence of mold and mildew inside of homes.
For example, I am often called upon to assist in the design, layout, and implementation of
renovations in homes. It is not an uncommon occurrence to find mold inside a wall
cavity as a new window is installed - many times in homes as new as one or two
years. I have also closely followed older homes, as they have been upgraded
step-by-step, in a homeowners effort to make them more energy efficient. As new
siding, windows, doors, and insulation are installed, what were once "loose"
houses that breathed, have become "tight" houses virtually overnight with very
little fresh air flow. The following article
is a condensation of a series of seminars and workshops on "Mold In Your
Home", that was presented by DSP in 1998 and 1999, to a wide variety of
construction and real-estate related professionals. |
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2. A Brief History Of Home Construction -
Methods & Materials |
Previous to World War II,
there was not much change in the way houses were built. Of course, indoor plumbing,
central heating, and electricity were added during this period and became the norm, but
the basic building materials and overall design philosophy remained basically the
same. For the most part, dwellings were constructed out of the native materials
available in and around a very localized area. Considerable
changes occurred in building practices after World War II. The invention of
modern adhesives and synthetic plastics offered new and exciting materials such as
plywood, particle board, affordable (synthetic) carpeting, micro-laminated beams capable
of spanning great distances, caulk, etc. Also, better plumbing and upgraded
electrical service greatly added to the comfort and safety of a home. Still, while
great changes and upgrades in building materials were made during this period, much of the
overall design philosophy of homes remained the same.
With the energy crisis of the 1970's,
an entirely different building design philosophy began to take hold. In order to
save energy, building "energy efficient homes" was the craze, and several
government-subsidized weatherization programs were instituted virtually
overnight. In the zeal to button up every crack, we sealed our homes without thought
of the importance of fresh air and proper ventilation.
Many of the newly invented building materials in use, have
ingredients that "out-gas" (give off fumes). The new, tight, energy
efficient homes we started to build did not allow for the escape or dilution of these
indoor pollutants, thereby creating a whole host of problems. Also, hidden
moisture problems due to overly tight construction (inside wall cavities, attics, etc.)
began to surface, which were leading to an increasing incidence of mold growth, related
health problems, and deterioration of the affected building materials.
Tight, energy efficient construction is an
excellent idea, and saving energy is also a good idea. But fresh
air and no interior moisture problems are even
better ideas! All three of these concepts can be employed together, if good building
practices and proper planning is done. For example, submarines and space-capsules
are among the tightest and best insulated structures ever built, yet they have very good
air quality. NASA and the US Navy have both used healthy materials combined with
good air-purification techniques. Obviously, when building a home you cannot
afford, nor do you want to build a space-capsule, but some of the same basic design
philosophies can be adopted. |
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3. What Is Mold? |
Mold is one of a wide variety of
biological contaminants that can be found in a home, and which can potentially cause
health problems. Some of these include - algae, viruses, pollen, dust mites, dander,
bacteria, and fungi (includes yeast, mold, mildew, mushrooms, etc.). Shown below are
three of the more common molds that can be found in homes: |
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Aspergillus
- Can infect the entire body of an individual, especially if the person has lung damage or
another serious underlying illness. |
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Cladosprium - Typically
forms on surfaces where water condenses (windows, doors, etc.). Can cause mild
allergic responses in some individuals. |
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Stachybotrys - Presents the
most serious potential health threat. Can cause internal bleeding of the lungs, and
pulmonary hemorrhage. Has been implicated as one of the causes of "sick
building syndrome". |
While many forms of mold can
present health risks, Stachybotrys chartarum rises to the top as presenting the
most serious risk to humans and animals. In 1993-1994, it was linked to an unusual
outbreak of pulmonary hemorrhage in infants in Cleveland, Ohio, where stachybotrys was
found growing in the homes of the sick infants. Due in part to this incident, the
medical community has an increased awareness of the potential dangers of molds in homes.
For example, in 1997, the Journal of the American Medical Association carried a
news article entitled, "Floods carry potential toxic mold disease". For
some good information on stachybotrys mold, check out www.scisoc.org/feature/stachybotrys.
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Mold needs five basic
ingredients in order to grow:
- Food Source
- Air
- Surface to grow on
- Suitable temperature
- Moisture
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If any one of the above is
removed, all growth will subsequently stop. However, mold can lay dormant for many
years, and if the above are re-introduced it can continue to grow again. This is why
it is so important when remediating a mold problem to: 1). identify
the source and cause, 2). repair the problem,
and 3). remove or kill as much of the mold as possible. |
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4. Ventilation & Air-Flow Basics -
Its Effect On Mold In The Home |
Over-Pressurization | De-Pressurization
| Upgrading An Existing Home |
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Most newer homes today are constructed using
materials and methods that make them very air-tight. Many older homes that have been
upgraded by installing new energy efficient windows and doors, siding, insulation, etc.,
can become "tight" virtually overnight. The effect can be like a giant
plastic bag placed over a house, where no air can enter or escape. Both over-pressurization and de-pressurization of the interior of a
house can |
lead to inner wall and ceiling
damage. Many appliances such as wood burning fire-places, may not operate properly
due to drafting problems, etc. One characteristic of air-flow and
pressure-related moisture damage to a house and its components is that the damage
being caused is often hidden from view, and not always readily visible.
Since many of the problems occur inside a wall or ceiling cavity, they can continue
un-diagnosed for a long period of time. |
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Over-Pressurization |
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Over-Pressurization can take
place when more air is introduced into certain areas of a "tight house", than
can escape through normal leakage or through duct-work, etc. The inside of the house
will be at a positive pressure, relative to the outside. Over-pressurization can be
localized on a room-by-room basis, or it can be house-wide. Some ways in which a house can be over-pressurized are:
- Insufficient return-air venting.
- Leaky heating & air-conditioning
ducts.
- Closed doors.
- Upgrading the exterior
"shell" (siding, windows, doors, soffits, etc.), in an older home.
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A potential problem with an over-pressurized house is that moisture
laden air can be forced from the living space, into the wall or ceiling cavity. If
the "dew point" (the temperature at which air is saturated with
moisture - 100% relative humidity - and below which, condensation will occur) is reached
inside the wall cavity, condensation will be released into the wall (see diagram
below). A perfect breeding ground for mold! For a more detailed description of
over-pressurization go to "The Basic Dynamics of
Over-Pressurization and De-Pressurization".
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Click on the thumbnail image above
to see an expanded view of how excess moisture collecting inside a wall cavity can cause
wood decay & mold growth. |
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The house shown in the
photograph on the left, was only several years old when the owner called me for advice. He
was noticing some staining on the drywall along the inside walls, and the paint was
starting to peel and blister on the outside siding. When I tested the moisture
levels of the interior of the wall cavity using a digital wall probe, the levels ranged
from 15% - 31%. After having the drywall removed, I found mold already in advanced
stages of growth along the OSB sheathing (shown in picture). The fiber-glass
insulation was wet with mold growing in it, as well. All the damaged insulation
had be replaced but fortunately, no lasting damage had been done to the structural
components. All visible mold growth was removed, and the affected areas completely
sanitized.
The likely culprit here? The homeowner
had finished off his own basement, but had forgotten to install return-air vents and a
proper vapor barrier along the outside walls. Over-pressurization due to a lack of
return-air vents forced moisture-laden warm air into the wall cavities where it condensed,
causing significant damage in a short time. |
De-pressurization
can take place when more air is exhausted from a house than is returned back into
it. The inside of the house will be at a negative pressure, relative to the outside.
De-pressurization can be localized on a room-by-room basis, or it can be
house-wide. Some ways in which a house can be
de-pressurized are:
- Wind blowing over & around
house.
- Mechanical exhaust venting (clothes
dryer, range hood fan, bathroom exhaust fan, etc.).
- No combustion air venting present
for furnace, water heater, fireplace, etc.
- Leaky heating & air-conditioning
ducts.
- Closed doors.
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Some potential problems with a de-pressurized house are:
provides the potential for "back-drafting" down chimneys of fuel-burning
appliances creating a carbon monoxide risk; can increase the radon levels in a home;
moisture laden air can be drawn from the outside, into the wall or ceiling cavity;
etc.
If the "dew point" (the
temperature at which air is saturated with moisture - 100% relative humidity - and below
which, condensation will occur) is reached inside the wall cavity, condensation will be
released into the wall (see dew point diagram above). A perfect breeding ground for
mold! For a more detailed description of over-pressurization go to "The Basic Dynamics of Over-Pressurization and
De-Pressurization". |
|
Click on the thumbnail image above
to see an expanded view of how a clothes dryer exhaust can de-pressurize a house. In
this case, causing back-drafting of the water heater chimney vent.
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De-pressurization can affect a
structure and its inhabitants due to the hidden moisture potential it can create
inside wall and ceiling cavities.
De-pressurization has also been shown to be a significant
factor in increasing the radon levels found in many homes. Radon gas will be have
more of a tendency to be drawn into the house, due to the differences between inside
and outside air pressure. See Other Services for more
information on radon. |
Many homeowners living in older houses want
to protect their investment by upgrading it, when and where they can. Some of the
most frequently upgraded areas are: permanent siding along with new soffits & fascia;
new shingles; new energy-efficient windows and doors; upgrade attic insulation; etc. This
is all very commendable, but watch out! Many problems I see on a daily basis when
inspecting homes, are directly due to one area of a home being upgraded, but a homeowner
or contractor neglecting to see how the upgrade would impact another area. |
Something you need to be aware
of before making upgrades to your house is that your house is made up of many different
systems (heating, cooling, electrical, ventilation, etc) all working together to perform
their intended functions. A critical mistake many specialty contractors and
homeowners make is not to view a house as a whole. Very seldom can you
upgrade or make changes in one area of your home, without it impacting another area. |
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For instance, a homeowner recently spent a
bundle making upgrades to his house. He completely re-sided with new steel siding,
new aluminum soffit and fascia, new shingles, upgraded attic insulation, and all new
"top of the line" energy efficient windows and doors. . .spending in excess of
$25,000 in the process. Starting with the very first winter after the upgrades were
made he began experiencing water staining on his ceilings, rusting on his ceiling light
fixtures, and water running out of his wall receptacles. He put up with it for one
year, but mid-way through the second winter, he called me for help in diagnosing his
problem. Listed below are some of the
problems I found:
- The upgrades made to the house had the effect of tightening
up the exterior "shell" to the point that what was once a "loose
house" that breathed - was now a "tight house" that
didn't, virtually overnight.
- No extra attic or roof ventilation was installed to
compensate for the possible increase in moisture being forced up into the attic (moisture
that used to leak through windows, walls, etc.).
- When the new metal soffits were installed, the contractor
did not align the new soffit vents with the old, thereby greatly restricting air-flow.
- No fresh air intake was installed in the furnace room, to
assist in balancing indoor and outdoor air pressure.
- Mold growth was present on the roof decking & rafters,
with water damage to the insulation & drywall ceilings. (To see a photo of the
damage done in attic of this house, see the bottom picture under the section "Over-Pressurization"
- "The Basic Dynamics of Over-Pressurization and
De-Pressurization" ).
What everyone forgot about when they upgraded the exterior
"shell" was, they also should have considered: 1).
upgrading the attic & roof venting, and 2). upgrading
fresh air (combustion air) capacity. |
Achieving a "balance"
between the indoors and the outdoors, which will in turn create a "neutral air
pressure" in the home, is a key element in reducing moisture problems inside walls
and ceiling cavities, and resultant mold growth. Two basic concepts are key, in understanding the potential problems associated
with improper air-flow and pressurization inside a home: 1). Warm air
becoming cold is almost always bad (as it will allow for condensation to occur),
and 2). Cold air becoming warm almost never creates a moisture problem. |
Micro-climates, and the
higher humidity levels they typically have, can be major mold producers in a home.
Humidity levels in a house are a key element in reducing and/or controlling the growth and
spread of mold and mildew. The typical comfort range for indoor humidity in northern
climates is approximately 30% - 40%, in the winter months. While indoor
"core" humidity levels can be kept relatively stable, and easily sustained at or
about 40% RH (relative humidity), "micro-climates" can easily double this. Please refer to the diagram below, which shows some
"micro-climates" that can be found in a typical home. Click on an
item number for more in-depth information about a particular micro-climate: |
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If your house has a basement, then basement
water leakage and excess basement humidity levels are likely the
number one contributors to mold growth in your home. It has been documented that at
least "98% of all sub-surface basement areas will leak, at some point in their
life." In the over 5,000 home and commercial buildings I have inspected over
the years, I certainly have found this statement to be true. There can be many reasons for a damp or leaky basement (for more information on
basement water problems, check out "Basement Water
Problems" under Home Resource Materials), and they all add up to problems for you
as a homeowner, if not corrected. Actual water leakage should not
be confused with the high relative humidity typically found in basements.
Both can pose serious problems, but need very different approaches to affect a
cure.
Moisture trapped between the foundation wall and the
finished basement wall can allow mold to grow unnoticed. Long-standing moisture problems
can lead to decay, resulting in structural damage to the house. |
Please click on the thumbnail images below to
expand to full view. |
View of an exterior basement wall, where water had been
leaking in unnoticed, from a window well. All the insulation and damaged framing had
to be replaced, extending 10' on either side of the window. |
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View of an exterior finished basement wall, where a
long-standing exterior drainage issue was left un-corrected. The entire basement
had to be gutted, in order to fully remove all the mold growth from the home. |
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View of mold growing on an unfinished block foundation
wall. Normal condensation on perimeter walls due to temperature differences, can
lead to extensive mold/mildew growth. Some type of de-humidification in a basement
is a must. |
The perimeter drain tile system underneath a
basement floor and the sump basket it drains into, both serve a very useful purpose. This
system provides a key element in helping to protect your house from water damage, by
providing an artificial "low level" drainage and collection point under your
basement floor. If the system is working properly, water should drain from the tile
into your sump basket. You can then pump the excess water collected in the sump
basket, outside. Since by its very design it is
intended to carry and hold water, this system also provides an ideal breeding ground for
bacteria, molds, and mildew. |
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Please click on the thumbnail images below to
expand to full view. |
Water seepage into the basement
level can saturate the foundation walls, basement floor, and finishes. Also, the
drain tiles can hold moisture for a long period of time, allowing mold to grow unnoticed. |
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Water is often left standing inside
a sump basket, providing an ideal breeding ground for mold. The sump basket covers
are frequently left open and due to normal pressure differentials, air from inside the
drain tiles can be "pumped" throughout the house. |
The condensate drip-pan, located on top of
the furnace, can hold moisture for extended periods. Also, the older drum-type
furnace humidifiers can provide the necessary ingredients for mold growth. In both
of these systems their location is in very close proximity to an air-handling unit, which
can allow mold spores to be quickly distributed throughout a house. |
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Please click on the thumbnail images below to
expand to full view. |
The AC condensate tray is very
difficult to access, consequently it is very rarely cleaned. |
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Older rotating drum-type furnace
humidifiers are notorious for providing harborage for molds. |
Many times, mold growth can a direct result
of poor maintenance. For instance, if the homeowner had maintained his ceramic tile (photo
below left), he likely would not have incurred the expense of having to replace his
shower. Also, I wonder how long the mold on the drywall had been growing, and what
health effects he may have been experiencing as a direct result of it? The photo below right shows an infrequently used shower, with the
shower head encrusted with mold. Very little effort could be expended in order to keep
this fixture clean. |
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Please click on the thumbnail images below to
expand to full view. |
View of damaged ceramic tile inside
a shower stall, that has been leaking through to the drywall behind it. Extensive
mold growth and wall damage required that a completely new shower be installed. |
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View of mold growth inside an
infrequently used shower head. |
Some molds produce mycotoxins,
and other active compounds that can be injurious to human (and animal) health. In
parts of Eastern Europe in the mid-1930's there were reported outbreaks of a new
disease that affected horses and other livestock. Subsequently, it was documented
that mold in the hay fed to these animals was the likely culprit. There have also
been reported cases through the 1940's, where humans who handled hay infested with mold,
or slept in mattresses filled with moldy hay, suffered some of the same symptoms as the
livestock. One type of mold, stachybotrys,
presents a special health risk. If areas contaminated with stachybotrys are discovered in
your home, or if you find areas in your home that are contaminated with mold and are
unsure what type it is, don't attempt to remove it without first following the
recommended safety procedures for persons working with toxic molds
(i.e. use a respirator, gloves, proper covering for the skin & eyes, etc.). I
would also recommend that you get advice from a certified hygienist, or from your local
Health Department. You can contact the American Industrial Hygiene
Association for referrals, at (703)849-8888. |
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Some Tips On How To Protect
Yourself |
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- Be aware of any noxious odors.
When a mold colony is growing, it can give off distinctive odors that are the
by-product of its metabolism.
- Be familiar with the symptoms
of a mold-related illness. Different mold species can produce different
health effects. Some of the common symptoms of mold allergy include a runny nose,
itching of the eyes & nose, congestion, fatigue & general malaise. Ask
yourself, "Do my symptoms get better when I'm away from home for any length of
time?".
- Perform a visual inspection of
your home. Check out some of the more common places where mold could
be growing in your home. Look for any signs of past water leakage, check under
sinks, in and around bathrooms, check out your basement (don't forget to look at your sump
basket!). If you don't have a sealed cover over your sump basket, get one.
- Contact a heating/cooling
specialist to inspect and clean out your AC condensate tray, clean out and
service your furnace humidifier, clean out and service the drip-pan under your
refrigerator, etc.
- Allow for good air flow
throughout the interior of your house. Keep furniture away from walls. Allow for
adequate air-flow over your windows & doors, as they will be the largest condensing
surfaces in your house and air-flow is needed to help evaporate moisture buildup.
- Check your attic
(roof decking, rafters, etc.) for any signs of darkening that could indicate mold growth.
If you notice any suspicious areas, contact a ventilation specialist for advice.
- Check for any discoloration on
walls or ceilings. Often, this can be an indicator of moisture
buildup, insulation problems, or ventilation problems that could be associated with future
mold growth.
- Be on the lookout for signs of
excess moisture. Do your windows frequently have moisture on them in
the winter time? Excess moisture is the single largest contributor to mold growth.
- Is your heating/cooling duct work
clean? When was the last time you had
your heat vents professionally cleaned and sanitized?
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Four Steps To Reduce Or Eliminate The Threat Of Mold Growth |
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John Bower, an expert in the field of
designing healthy homes, has written a book entitled, "The Healthy House".
It is recommended reading for anyone concerned about indoor air quality and healthy
home design. In his book, Mr. Bower outlines four basic principles for healthy home
design, which can be modified somewhat, and adapted as strategies to reduce and/or)
eliminate mold growth in your home. The
following four steps provide a basic outline to follow, as a starting
point. It is important to note that no two homes are exactly alike, therefore no two
mold problems are exactly alike, therefore no two strategies for reducing mold in a home
are exactly alike. |
1. Elimination |
- Identify the source of the problem and its cause. Try
to a devise a repair strategy.
- Remove or substitute any damaged or otherwise affected area
(carpeting, wood products, etc.). Sanitize all areas where mold was growing. Use
caution when dealing with molds, as some may be very toxic!
- Eliminate any one (or all) of the five ingredients necessary
for mold growth (food source, air, moisture, suitable temperature, and a surface to grow
on).
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2. Separation |
- Separate the problem areas from the living space by building
a barrier between you and it. The reasoning is: "If a pollutant can't reach you
- it can't hurt you".
- Paint, seal, and disinfect mold & mildew stains on
walls, ceilings, and window & door frames.
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3. Ventilation |
- Ensure that you have adequate ventilation that provides a
proper exchange of air between rooms - and indoors & outdoors.
- Consider installing an air-exchanger or heat recovery
ventilator.
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4. Filtration |
- Filtration rarely works well, on its own. It is best
when used in conjunction with one (or all) of the other three steps outlined here
(elimination, separation, ventilation).
- Try to eliminate any problems you may be experiencing using
one of the other principles, first.
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Anachem, Inc. and Sandia National
Laboratories. Indoor Air Quality Handbook. Albuquerque, NM. Sandia
National Laboratories, September 1982. #SAND82-1773, UC-11. |
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Bower, John. Understanding
Ventilation: How to design, select, and install residential ventilation systems.
Bloomington, IN. 1995. |
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Bower, John. The Healthy House.
Bloomington, IN. 1989. |
|
Environmental Protection Agency (EPA). The
Inside Story: A Guide to Indoor Air Quality. Washington, DC:EPA, September
1993. #EPA/402-K-93-007. |
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Environmental Protection Agency (EPA). Home
Buyer's and Seller's Guide to Radon. Washington, DC, EPA, March 1993.
#402-R-93-003. |
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Jantunen, M.J. "Does
moisture condensation in air ducts promote fungal growth?" (Toronto:
Proceedings of the 5th International Conference on Indoor Air Quality & Climate,
Vol.2, 1990). |
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Lstiburek, Joseph and John Carmody. Moisture
Control Handbook: Principles and practices for residential and small commercial buildings.
New York:Van Nostrand Reinhold, 1993. |
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Mann, Arnold. Mold: A Health Alert.
USA Today. December 3-5, 1999. |
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National Association of Home Builders (NAHB),
Controlling Moisture In Homes. Washington, DC: NAHB, 1987. |
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Nelson, Berlin. Stachybotrys
chartarum: The Toxic Indoor Mold. 1999. The American Phytopathological Society. |
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The Journal of Light Construction. Moldy
Basements Blamed for Infant Deaths. Washington. DC Vol. 18, No. 3,
December 1999. |
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Traudt, Jon. Control of Indoor Air
Pressure for Protection of Health, Preservation of Buildings, and Conservation of Energy.
Atlanta, GA: Paper presented to the 16th World Energy Congress and 3rd
Environmental Exposition, October 26-28, 1993. |
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