BUILDING A HEALTHY HOUSE
BUILDING A HEALTHY HOUSE
During the energy crunch of the 1970s, homeowners added insulation, caulking, storm windows, and weather-stripping to their homes in order to make them more energy efficient. This resulted in structures that not only saved energy, but were also more airtight. Soon, there were dozens of stories in the media equating energy efficiency with poor indoor air quality. While it has since been shown that the two concepts are compatible, and not at odds with each other, the connection is still often made by the public.
Chemically sensitive people were described as early as 1962. Individuals so affected often have difficulty tolerating common building materials due to their outgassing characteristics, therefore housing for them must be as pollution-free as possible. This paper will describe a very energy efficient house that was designed and built to maintain the high degree of indoor air quality required by chemically sensitive people. The two-story, two-bedroom, two-bath house contains 1,232 sq. ft. of living space on the first floor, plus an additional 448 sq. ft. on the lower level for a home office. It is located in rural southern Indiana. The design and construction features of this house are described in-depth in a recently released series of videos.
GOALS
Several goals were enumerated early in the design phase of this project. They were:
AIR QUALITY
·Inert materials should be used wherever possible.
·The use of toxic pest control chemicals should be avoided.
·The house should be built in an airtight manner to minimize the infiltration of polluted air.
·When inert materials aren't readily available, polluting materials should only be used if they can be isolated from the living space.
·A method of ventilating the whole house should be employed to provide fresh air to all rooms, and additional ventilation should be available in rooms where pollutants or moisture are generated.
·The house should have a mechanical air filtration system to remove any pollutants brought indoors by the ventilation system.
·The ventilation system should be sized to allow for an adequate average ventilation rate when it is operated intermittently.
ENERGY EFFICIENCY
·The house should have superb insulation levels.
·Windows and doors should be energy efficient.
·The house should be built in an airtight manner for controlling the infiltration of unconditioned air.
·The mechanical ventilation equipment should be energy efficient.
GENERAL REQUIREMENTS
·The construction materials should be readily available.
·Difficult construction techniques should be avoided.
·The house should not look unusual.
·The house should be affordable.
HEALTHY DESIGN PRINCIPLES
Reducing the source strength of pollutants has come to be regarded as the most effective method of reducing indoor pollution. In this house, this was accomplished by utilizing three basic healthy-house design principles: eliminate, separate, and ventilate. Eliminating potentially polluting materials means utilizing construction products that are as low-polluting or inert as possible. As major pollutant sources, wall-to-wall carpeting, resilient floor coverings, and synthetic wall-covering materials were avoided because of their potential to release volatile organic compounds (VOCs), as were manufactured wood products capable of releasing high levels of formaldehyde. Low-odor paints, caulking, sealants, etc. were chosen from products often recommended for chemically sensitive people. Because a less-toxic insulation was not readily available locally, the second principal of separate was used to completely isolate the insulation from the living space. The principle of separate was also used to isolate the plywood subfloor from the living space. The principle of ventilate was used to provide fresh air and, at the same time, to remove stale air from throughout the house.
FOUNDATION
A concrete pier foundation was selected because it effectively separates the structure of the house from both radon in the soil and ground moisture, by lifting the house up off the ground. It was also an appropriate foundation type for the building site-a hillside with a 25% slope. The foundation itself consists of 12 concrete piers, each 12" in diameter, and each resting on a 36" x 36" x 12" concrete footing. The footings and piers are reinforced and tied to each other with steel. There is an 11/4"-diameter x 36"-long anchor bolt in the center of each pier for attaching the floor system to the foundation.
BUILDING ENVELOPE
A wall system, constructed of 2x8s on 24" centers, was used to achieve R-33 insulation levels, using high-density fiberglass batts. Energy-saving framing features-such as single studs adjacent to doors and windows, fewer studs at corners, and single top plates-were used to minimize heat loss. Window and door headers were insulated to R-19.
The floor system was constructed by bolting built-up 2x12 girders across the piers, then using joist hangers to attach the 2x12 joists to the girders, on 24" centers. The 3/4" tongue-and-groove plywood subfloor was nailed to the joists using a water-based construction adhesive. The adhesive was used between the plywood and the joists, and between all seams of the individual plywood sheets, to insure a rigid, and air-tight, floor system. Twelve-inch-thick, R-38 fiberglass batts were used between the joists.
The roof structure consists of 2x12 rafters on 48" centers. The rafters have a 2x4 nailed to the top of their length to create a deeper cavity for the insulation. There are 2x4 purlins nailed across the top of the rafters, on 24" centers, for the steel roof panels. Hat channel was nailed to the bottom of the rafters, on 16" centers, for attaching the drywall ceiling. The roof system is insulated with 12"-thick, R-38 fiberglass batts, and is vented via a 2" air-space above the insulation.
There have been literally hundreds of papers published on the potential cancer-causing ability of fiberglass, but negative health effects have shown up with other insulating materials as well. A cementitious foam insulation, made from magnesium silicate, is being marketed as a non-toxic alternative for chemically sensitive people, natural cork insulation has been in use for centuries, cotton insulation is now being produced, and there is a synthetic foam being marketed as another low-tox solution, but all can be quite expensive, and availability is limited. Fiberglass batts are available without a formaldehyde-based resin binder, but only in a limited number of sizes. The decision to use conventional fiberglass-batt insulation was made after it was decided to use airtight construction techniques to form an effective barrier between the insulation and the living space. Insulation installers, who are theoretically at greater risk than homeowners, are encouraged to wear respiratory and skin protection.
The house was sheathed with a combination of plywood (at corners for wind bracing) and asphalt-impregnated fiberboard. Aluminum siding was used for the exterior of the house, and sheet metal was used for the roofing, because their baked-on finishes are generally well tolerated by chemically sensitive people. It should be pointed out that exterior cladding materials only minimally affect interior air quality, but it was decided to use materials that were as inert as possible in this house, wherever they were actually visible and exposed (as opposed to hidden inside building cavities). Entry doors are insulated steel units with magnetic weather-stripping.
The windows have thermally broken aluminum frames, double or triple glazing, argon fill, and Low-E coatings. The house will be partially heated by the sun through passive-solar design features. The 197 sq. ft. of glazing in the house is equivalent to 11.7% of the floor area, and 41% of the glazing is south-facing, while 40% is east-facing to capture the morning sun. The roof overhang is constructed to shade the south-facing windows in the summer.
Once the house was framed and enclosed, but before the insulation was installed, all the wood members were sprayed with a low-tox boron-based termiticide. This powdered product is mixed with water, and is formulated to penetrate deeply into the wood, imparting permanent termite resistance. It will also protect the wood against fungal attack and other wood-destroying insects such as carpenter ants. However, being water-based, it cannot be used where it will be exposed to the weather, thus the reason for applying it after the house is closed up.
The house has wooden decks, on two sides, that are exposed to the weather, so the boron-based product isn't suitable for them. For the posts that are embedded in the ground, conventional salt-treated lumber was used, but for deck boards, as well as joists and railings, construction-grade redwood was utilized, and left to weather naturally.
AIRTIGHT CONSTRUCTION
The drywall in the house is foil-backed to provide a diffusion retarder to minimize the transfer of both water vapor and gaseous air pollutants. An airtight building envelope has better energy efficiency, fewer hidden moisture problems, and it allows the occupants to have more control of the indoor air through the use of mechanical ventilation equipment. With airtight construction, the living space is effectively isolated from the insulation and the outdoors. A technique known as the Airtight Drywall Approach (ADA) was used in conjunction with caulking, gaskets, and airtight electrical boxes to achieve a virtually airtight structure. The house was blower-door tested and the infiltration rate was measured at 0.04 (natural) air changes per hour (ACH). The effective leakage area (ELA) is approximately 14 sq. in. ADA involves relatively simple techniques that builders can use to construct an airtight envelope.
The lower level is used as a home office, and it contains a copy machine and laser printer, both of which emit ozone. There are also typically various papers and books lying about, all of which can affect the air quality and, thus, the chemically sensitive occupant. However, having her own workspace upstairs, she does not spend a great deal of time in the lower-level office. In order to effectively separate the lower-level odors from the upper level, the two levels were each individually built in an airtight manner to isolate them from each other. There is a weather-stripped door at the top of the stairs, which is usually closed, to further minimize the transfer of air from the lower level to the upper level. The mechanical ventilation system serves both levels, but is ducted so the air doesn't mix between levels.
It is possible to use airtight construction techniques to isolate an attached garage from the living space, thus minimizing the transfer of automobile and gasoline odors into the house. However, odors can enter the living space through the service door whenever it is opened so, to insure extra separation, this house has a detached garage.
FILTRATION AND VENTILATION
A packaged filtration unit was installed to remove pollutants brought indoors by the ventilation system. The filtration cabinet contains a 1" polyester prefilter, a 2" medium-efficiency pleated filter, five 1" polyester filters impregnated with activated carbon, and a 1" single-stage electrostatic precipitator (produces no ozone, also called a dynamic air cleaner). The filter unit does not have a blower, and relies on the fan in the heat-recovery ventilator to pull air through it.
For general, background ventilation, a heat recovery ventilator (HRV), having two removable aluminum cross-flow cores, was used to provide a capacity of approximately 0.8 air change per hour (200 cfm), at high speed, in an energy-efficient manner. The manufacturer estimates that, when coupled with the above filter unit, the added resistance will reduce the HRV's capacity by approximately one-third. This unit exhausts stale air and brings in fresh air simultaneously. When operating, it will keep indoor humidity levels down, in order to control the growth of mold and other microorganisms. The outdoor air passing into the house through the filter, then through the HRV, is ducted into the living room, near the ceiling. At the same time, the HRV exhausts stale air to the outdoors from the kitchen and from all the closets in the house, thus circulating air through all the rooms, and keeping the air pressure between the indoors and the outdoors balanced. The HRV was tested at 77% sensible recovery efficiency at -13° F in accordance with Canadian Standards Association Standard C439M.
The HRV is activated by a programmable controller (similar to a programmable thermostat). It is set to turn the HRV on in the morning, at high speed, for an hour, to air out the house quickly, then operate at a lower speed throughout the day. In the early evening, at supper time, it again bumps up to high speed for an hour, then shuts off for the night.
In many situations, outdoor pollution is episodic, and it can be dealt with by using intermittent ventilation. In other words, you only bring in fresh air when it is actually fresh. In such a case, the system should be sized to overventilate for part of the day, and the average 24-hour rate should be approximately 15 cfm per person. In the winter, in the locale in which this house is situated, wood smoke (from neighbors' fireplaces and stoves) can be difficult to filter out of the incoming air but, in most cases, it is only a problem at night, when it hangs close to the ground. Operating the ventilation system only during daylight hours, in an airtight house, prevents the smoke from entering the living space, and it negates the need for an elaborate filter system. Having the ventilation system turned off at night, also has the benefit of resulting in a very quiet house during sleeping hours.
There is a 200-cfm kitchen range hood (with a quiet, outdoor-mounted fan) to remove air pollutants, and high levels of moisture, quickly from the kitchen. The lower level bathroom (in the home office) had a quiet, 200-cfm exhaust fan that can be used to air out either the bathroom, or the entire lower level. It is activated by a manual, delayed-off timer. The laundry is located in a closet in the upper-level bathroom, thus when the bathroom is aired out, the laundry area is also.
For boosting the ventilation rate in the main, upper-level bathroom, there a motorized grille and an electronic timer-instead of a separate exhaust fan. During normal operation, a small amount of air is removed from the bathroom (through a motorized grille that is usually only partially open) whenever the HRV is operating. When extra ventilation is needed (after using the shower or toilet), the electronic timer is activated by touching its face. This simultaneously opens the motorized grille all the way, and kicks the HRV up to high speed. After the timer counts down, the grille closes, and the HRV returns to its normal speed. The duration of this timer can be adjusted internally, but the standard setting is for up to four 7-minute increments, or a maximum of 28 minutes of on-time.
Because of the airtightness of the structure, when the clothes dryer is running-and blowing air outdoors-it tends to depressurize the entire house, so there is a manually operated grille, connected to the outdoors, that can be opened whenever the dryer is used. In the kitchen, the switch activating the range hood also activates a motorized damper that opens to allow make-up air to enter whenever that fan is blowing kitchen air outdoors. When the lower-level bathroom fan is used to air out the entire lower level, a window is opened, and the fan's entire 200-cfm capacity is utilized. When the lower-level bathroom fan is only used to air out the bathroom, no window is opened, the fan depressurizes the house, and make-up air enters through the HRV, which temporarily has unbalanced airflows due to the depressurization. Because the bathroom exhaust fan must work harder with the windows closed, its capacity is diminished. If this house had chimneys, the depressurization would likely cause them to backdraft. If the house were coupled to the ground, and weren't airtight, the depressurization could also cause radon to be drawn indoors. But this house has no chimneys, and the pier foundation and tight construction, prevent the infiltration of radon.
HEATING AND AIR CONDITIONING
With the low heat losses in winter (0.72 BTU per sq. ft of shell area per degree day) and gains in summer (2.91 BTU per sq. ft of shell area per degree day), the high installation, equipment, and maintenance costs associated with very-efficient forced-air systems could not be justified. Instead, low-polluting low-temperature, hydronic, electric baseboard heaters, and a small ductless split-system air conditioner were selected. Using a more-efficient method of heating could, perhaps, cut the heating/cooling bills in half, but those bills are so low that the savings wouldn't be sufficient to justify the higher cost of the energy-efficient equipment.
The house has been evaluated by Energy Rated Homes of Indiana, and has received an Energy Rating of 5 stars. This means it can qualify for an energy-efficient mortgage, something that allows the buyer to increase their debt-to-income ratio. In the evaluation of the house, it was estimated that the total average electric bill would be $97 per month. However, the occupants typically keep the thermostat set higher in the winter (72°F) than the 68°F setting used to arrive at the estimate. Plus, this figure was based on typical electrical usage in a residence and this house, having a home office, with two computers, monitors, and various other electronic devices turned on every day, has a higher energy usage. In the first full three years of occupancy, the actual electric bills have averaged $125 per month. Because this is an all-electric house, this represents the total energy bill, and accounts for heating, cooling, lighting, water heating, appliances, ventilating fans, etc.
INTERIOR FINISHES
Those construction materials that are directly exposed to the interior space have the greatest potential to pollute that space, therefore they must be chosen with care. In this house a latex paint, water-based polyurethane clear finish, and drywall finishing compound were selected that chemically sensitive individuals often tolerate.
To avoid materials high in formaldehyde, the kitchen cabinets were custom-made from a combination of solid hardwood (tulip poplar) and galvanized steel. The galvanized steel was used in places where veneered plywood or particle board are typically utilized. The frame-and-panel cabinet ends, face frames, door frames, drawer fronts, and drawer sides are all solid wood, as are the shelves and end panels of the upper cabinets. The wider (24") shelves in the lower cabinets were fabricated at a sheet-metal shop using galvanized sheet metal. The drawer bottoms are flat pieces of galvanized sheet metal. The center panels in the upper doors were custom-made of hand-tooled brass foil. The lower doors have solid-wood panels. The bathroom cabinets were made in a similar manner.
The kitchen countertops were custom-fabricated of stainless steel with welded-and-polished seams, thus there are no crevices for bacteria to accumulate. The upper-level lavatory top is solid marble, with a porcelain drop-in sink. The lower-level lavatory top is a one-piece, synthetic marble unit. The shower/tub surrounds are one-piece, fiberglass models to minimize crevices where moisture could accumulate and result in mold growth. The tub surround's sliding doors have polished glass edges (thus no crevices), and the lower channel is free draining.
Interior doors and woodwork are solid hardwood (tulip poplar). Softwoods were not used in order to avoid the smell of terpenes indoors, which can bother sensitive people. Closet shelves and organizers are made of wire mesh with a baked-epoxy finish.
The house contains a built-in dishwasher (with stainless-steel interior), a radiant glass-top electric range, and a central vacuum system (with outdoor exhaust). Water supply lines are copper, soldered with lead-free solder. The house is connected to a municipal water supply, and a water filter, with an activated-carbon cartridge, removes chlorine from all of the water entering the house.
The finish floors are a combination of solid beech wood (in the living room, bedrooms, and lower-level office) and ceramic tile (in the kitchen, bathrooms, foyer, and central hallway). Because the subfloor is made of construction-grade plywood, it contains a certain amount of phenol-formaldehyde glue, so the finish floor system was designed to minimize the subfloor's outgassing upward into the living space. In the case of the wood floor, a layer of builders foil (instead of asphalt-impregnated felt paper) was laid down, overlapping it by a couple of inches, beneath the finish floor, to act as a diffusion retarder. In the case of the ceramic tile, a layer of 1/2" cementitious board was adhered to the plywood with thin-set mortar, then covered with glazed ceramic tile (again using thin-set mortar). The spaces between the tiles were filled with home-made, additive-free grout. In this type of installation, the glazed surface of the tile acts as a diffusion retarder, and the outgassing through the grout joints is negligible.
In order for the occupants to separate potentially bothersome possessions from the living space, there are several built-in cabinets and bookcases that are fitted with glass-and-wood doors.
CONSTRUCTION COSTS
Several features may, at first, seem make this house more expensive than conventional housing. For example, the cost of extra insulation, air sealing, and the mechanical ventilation system are added directly to the house's construction cost. However, at the same time, without a forced-air central heating system, there is a cost savings. In addition, there is a monthly savings due to low heating/cooling bills-over the entire life of the house. It's been estimated that, once a builder's crew has learned to incorporate the energy-saving and air-sealing features, the extra costs, and the cost savings, negate each other. In other words, the extra costs are offset by the savings, and the net cost to the home buyer is the same as a less-energy-efficient house. However, there is a learning curve involved and, if a builder is only going to incorporate these features in a single house, he will need to charge more, because his crew is going to be doing something they don't normally do every day. On the other hand, if a builder is going to incorporate these energy saving features into a number of houses, the cost of training his crew can be spread out over all the houses, and there should be no cost increase to pass on to the home buyer.
Depending on the particular brand of healthier paints and finishes chosen, the cost can be similar to their unhealthy counterparts. If a more expensive brand is chosen, the cost increase is typically minimal.
Finish flooring of hardwood and ceramic tile generally costs more than low-to-medium-priced, wall-to-wall carpeting. However, when all of the costs of carpeting are calculated, its life-cycle cost is high compared to these healthier alternatives. When estimating construction costs only, using healthy materials, the increase due to healthy flooring can be significant in lower-cost houses, but almost nothing in higher-cost houses. This is because, in lower-cost houses, you are substituting a higher-cost, longer-lasting material (ceramic tile or hardwood) for a lower-lost, short-lived material (carpeting). This increase can range from $3-7 per sq. ft. On the other hand, a higher-cost house may already be assumed to have wood and tile floors, or much more expensive wool carpeting. So, in a higher-priced house, there should be little-or-no cost increase when specifying healthy versions of ceramic tile and wood flooring.
The cost of healthy cabinetry varies but, in most cases, it will be higher than conventional cabinetry. There are a handful of cabinet manufacturers who use low-formaldehyde materials and finishes, or solid wood, or steel with a baked-on finish, but these cabinets are not readily available in all parts of the country, so shipping costs can be high. Custom-made cabinets tend to be the healthiest options, and there are custom cabinet makers in many locals. However, most custom cabinetmakers utilize formaldehyde-laden materials and formaldehyde-based clear finishes-just like pre-fab cabinet manufacturers. For them to switch to other materials can be disruptive to their routine, thus result in a higher cost. The custom-made cabinets in this project were designed to minimize such costs.
In, summary, the cost increase, to make a house healthy, can vary, depending on the specific materials and construction techniques utilized. However, the cost increase typically ranges from as low as 0% to as much as 25%. It is estimated that the house described herein would sell for approximately 10% more than similar, but conventionally constructed, houses in its locale.
It has been estimated that indoor air pollution results in lost productivity and health care costs in the United States of up to 100 billion dollars per year. If living in less-polluted air results in healthier occupants, then medical expenses and health insurance premiums may be decreased, thus negating any cost increase of the house itself.
RESULTS
This house was built to standards that most chemically sensitive people would be able to tolerate, and several chemically sensitive individuals have visited the house, and found the interior space to be very comfortable and tolerable. Because these people typically react to very low levels of a wide variety of air pollutants, this test, though anecdotal, would seem to indicate that the quality of the indoor air is quite good. The occupants, one of whom is chemically sensitive, tolerate the house quite well.
Written by: John Bower - Healthy Indoor Environments Conference
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