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 re-bonded 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 sub-floor 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 sub-flooring 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 under-ventilation. 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 three hours.
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.
