Indoor Air Quality
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
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
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
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
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
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
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
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.