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 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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