Indoor Air Quality
One sure path to energy efficiency in houses is
eliminating air leaks. If you cut down the amount of
air that has to be heated and cooled, you cut your
utility bill substantially. But plugging up all
those air leaks means less fresh air inside and this
has brought on other problems.
One of the first to be identified was elevated
concentrations of volatile organic compounds in the
air. Commonly called VOC's, these compounds are used
in the manufacture of the many synthetic building
products used in most new houses today, including
carpeting, flooring, paint, cabinetry, countertops,
and the structural framework itself. Hundreds of
off-gassing VOC's have been identified, but the one
that has captured the most attention is
formaldehyde. It is a potent eye and nose irritant
and causes respiratory effects. It is also
classified by the US Government Environmental
Protection Agency as a probable human carcinogen.
In response to the concerns raised by health
officials and the public over the last fifteen
years, manufacturers of some building materials and
furnishings have altered their chemical
formulations, significantly reducing the amount of
VOC's off gassing from their products.
A brand new house will still have a significant
amount of VOC's in the air because the rate at which
the VOC's off-gas is highest initially. This
phenomenon accounts for the "new house smell" that
most new house buyers experience. Delaying a move-in
and airing out a house by opening all the windows
and running all the exhaust fans will benefit the
occupants, even if this is done for only two days,
advised John Girman, Director of the Center for
Analysis and Studies for the Indoor Environmental
Division of the US Government Environmental
Protection Agency.
Continuing to keep the windows open and ventilating
the house for several day to several weeks, if
weather permits, can also be beneficial, added Al
Hodgson of Lawrence Berkeley National Laboratory in
Berkeley, California, who has been studying indoor
air quality for the last 18 years.
After the first month or so, the rate at which the
VOC's off gas from building materials may fall off,
but Hodgson's research indicates that the
off-gassing phenomenon will continue at a slow and
steady pace for months or even years. Hodgson
measured the indoor air quality in eleven new, but
unoccupied houses one to two months after their
completion. Some were monitored over a period of
about nine months. Overall he found that the
concentrations of VOC's in the houses were not
"alarming," although the concentrations of some
compounds were high enough to produce an odor. The
levels of formaldehyde were too low to have a smell,
but high enough to cause discomfort in some
individuals.
Although the level of VOC's in new houses does fall
off over time, buyers can reduce it at the outset by
their selection of finishes. Hodgson's research has
shown while carpets are generally low emitters of
VOC's, a reasonable quality, medium-grade, nylon,
certified green label carpet may emit less than the
basic grade carpet that most builders offer as
standard. Installing the carpet with tack strips
instead of an adhesive eliminates a potential VOC
source altogether. Synthetic fiber carpet padding
emits less than the rebonded padding that most
production builders provide.
Hodgson's "certified green label carpet" refers to
the green and white Carpet and Rug Institute
emission test sticker found on carpeting that meets
their emission standard. Their testing program was
established after sensational stories about "killer
carpets" appeared in newspapers and TV news programs
in the early nineties. In a New England lab, mice
were exposed to carpet samples and subsequently
died. Scientists in other labs including the EPA
were never able to replicate these results and the
reason for the mice's demise remains unclear.
After the Carpet and Rug Institute started its
carpet-testing program, it raised the emission
standards, which has further reduced carpet
emissions. Even so, carpeting can still have an odor
that makes people think that they are being exposed
to something awful, Hodgson observed.
Vinyl flooring is a stronger emitter than carpet,
but it too should not be a cause for concern,
Hodgson said.
The oil-based alkyd and water-based latex paints
used in most houses are another source of VOC's. The
alkyds, which create a harder, more washable
surface, are usually used for bathrooms, kitchens,
and the trim around doors, windows and baseboards.
They produce a terrible smell and emit hundreds of
VOC compounds, but these are almost entirely
dissipated after about 48 hours, said John Chang, of
the EPA labs in Triangle Park, North Carolina. The
latex paints have a different smell and emit only
four or five VOC compounds, but these continue to
off gas for days and weeks after the paint is dry.
"Low VOC" latex paints are now available, but some
of these emit formaldehyde and buyers should check
the paint emission data, he advised.
Hodgson is currently studying the man-made wood
products used in residential construction because
most of them contain formaldehyde, and formaldehyde
concentrations in the indoor air of new houses have
been found to be higher than in other building
types. Large quantities of these wood products
including cabinet materials, doors, door and window
trim and baseboards are found in the finished space
of new houses. Man-made wood products are also used
extensively in their structural framework. Hodgson
is looking at the emissions of formaldehyde and
VOC's from each product as well as the amount of
exposed surface of each product. He is finding that
bare surfaces of wood products can have relatively
high emissions, but that surfaces with laminate and
vinyl finishes generally have low emissions.
In some cases, products that are considered to be
low emitters are turning out to be a significant
source of VOC's when viewed in the context of the
whole house, Hodgson said. For example, formaldehyde
and other VOC's given off by the oriented strand
board or plywood used for the subfloor in most new
houses today are low when calculated on a square
foot or a per piece basis. But Hodgson's research is
showing that when the total area of the subflooring
in a typical house is taken into account, it can be
a significant VOC source and that the overlying
carpet and carpet padding are not effective
barriers.
Other research in indoor air quality in new houses
has focused on the problem of underventilation.
Until the last 20 years or so, mechanical engineers
could reasonably assume that between air leaks and
occupants opening the windows, everyone was getting
plenty of fresh air. But as houses have become
tighter, less outside air is penetrating through air
leaks and with air conditioning; no one opens the
windows in the summer anymore.
To rectify this situation, the American Society for
Heating, Refrigeration, and Air Conditioning
Engineers, commonly known as ASHRAE, proposes that
mechanical ventilation be required in all new
houses, as it is in most commercial and office
buildings. The engineers have not dictated how this
should be accomplished, and the desired ventilation
rate varies with the size of the house and the
number of bedrooms. For a 2,400 square-foot house
with four bedrooms, for example, the proposed rate
would be .35 changes per hour. At this rate, all the
air in the house would be replenished every
threehours.
Some homebuilders have suggested that ASHRAE's
ventilation proposal could add $1,500 to $6,000 to
the cost of a new house, but ASHRAE's proposal could
be easily and inexpensively done. One continuously
running 100 cfm bathroom exhaust fan that is
exhausted to the outside would do the job for a
2,400 square foot house and this modification would
cost only $75 to $100 more than the exhaust fan and
venting that the builder would already be installing
in the bathroom, said Max Sherman, also of the
Lawrence Berkeley National Laboratory, who has
studied indoor air for 20 years. Putting a smaller
continuously running fan in each bathroom is a more
expensive solution, but it would distribute the
fresh air more evenly.
The ASHRAE proposal includes a sound recommendation
for the continuously running fan because occupants
turn fans off when they're too noisy. The dedicated
exhaust fan should have a sound level of one sone or
less so that it won't disturb a household at night
when the ambient noise level is low.
Relocating the air-handling unit from the garage to
some other place in the house would also improve
indoor air quality, Sherman said. In some parts of
the country such as Florida and California, houses
do not have basements and the air handling equipment
is often put in the garage. Unfortunately the ducts
for the system often leak so that if a car engine is
left running for any length of time, homeowners can
unwittingly introduce carbon monoxide into their
living areas.
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