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The healthy house concept is an idea that has been requested by people with various environmental illnesses for many years. The aim is for the house to be built so that a very minimum of construction chemicals, especially formaldehyde based adhesives and pesticide treatments, migrate into the house to affect the people living there.
This subject is now becoming more and more of a concern for everyone in our society with buildings being built more tightly for energy efficiency and also with increasingly sophisticated medical research that is demonstrating physiological harms, such as asthma, various sensitivities, from extremely small long-term concentrations of formaldehyde based materials, or studies that are showing multigenerational genetic damage from pesticide exposure injuries.
This article briefly describes a house that was built with both healthy house considerations and total environmental efficiency in mind. And upon evaluation, it merited an Energy Star rating of 95 or Five Stars Plus.
The location is in the mountains west of Denver, Colorado in an aspen and conifer forest. The elevation is 9,000 feet (2745 m). The degree-day climate rating for the area is 9,300 degree-days (5150 Celsius degree-days). (Compared with a value of some 6000 (3300) for Denver.) There are occasional windstorms with winds as much as 100 miles per hour (160 kph) in the area so the design must accommodate that fact.
Fire safety is a serious concern for this building area. Many of the local hillsides are very steep (30 ... 60 degree slopes) and covered with dense second-growth conifer growth that would spread a fire very rapidly. To address this concern, trees were drastically thinned to some 200 feet (60 m) around, and especially upwind, of the house site for a defensible fire space. The house siding is a pressed cement which resists combustion. The roof is a fire-safe rated material. Additional fire protection is provided with a 36-inch (92 cm) weed barrier cloth installed around the outside of the house and weighted down with rocks. And of course, kept free of weeds and grass with hot soapy vinegar.
Another fire safety consideration that is needed for this area is an 1,800 gallon (6800 liter) water storage tank that was installed near the house. This tank must be kept filled with water, which is not available for domestic use, but must be available so in case of a fire, so a fire truck can use that water to foam down the house and hopefully prevent serious damage.
The building site is some 1,000 feet (300 m) from the public power lines, so local photovoltaic power was cheaper. This in turn made power efficiency - in both the house and appliances - very important. Which in turn led to a house design that maximized passive solar gain. This mandated a sizeable southern exposure in addition to a very well insulated house with very low infiltration.
A passive solar design requires a long house east to west and narrow north to south. The result was a house with a floor footprint of 48 feet (14.6 m) east to west and 24 feet (7.3 m) north to south. To accomplish reasonable solar gain, the south windows are 5.9% of the floor area with a solar gain coefficient of 0.70, the east windows are 1.5% of the floor area, the west windows are 1.8% of the floor area, and the north windows are 3.4% of the floor area.
The typical maximum summer temperature at the building site is around 65 degrees (18 degrees C). As such, maximum solar gain is desirable, even in the summer. To meet this need, the south roof overhang was adjusted back to six inches (15 cm) instead of the usual 24 inches (61 cm).
The roof and ceiling were made with pre-engineered solid lumber scissor trusses (carefully sealed off from the living area) that give an outside roof slope of 6 in 12 and an inside ceiling slope of 4 in 12 for a semi-cathedral inside ceiling. The roofing is SBS Rubber/Fiberglass shingles that have a Class A fire rating and are approved by some insurance companies as having adequate hail resistance to qualify for a reduction in house insurance cost.
For reasonable passive solar performance, a massive floor that can store heat during the day and release it at night is needed. This resulted in the following floor from bottom to top -
One square foot (0.093 square meter) dark ceramic floor tiles were installed on top of the concrete for a living space floor.
A further benefit of the slab on grade design and not needing any heating ductwork is that there is no need for a crawl space under the floor to accumulate mold and cause the other problems that cause so much grief. (Plumbing lines were pre-installed before the floor concrete was poured.)
To maximize passive solar heat gain, the concept of "tuned windows" was used, where windows with different heat gains and insulation values were used on different orientations. The windows on the south side were selected for high solar transmission, with a transmission coefficient of 0.70. The other windows were selected for high insulation, with a thermal resistance of 9.10 Ft**2-F-Hr/BTU. This results in an anticipated solar gain of over 25 percent of the needed building heat coming from the sun.
A very important healthy house consideration is to minimize the presence of pesticides and formaldehyde based building chemicals leaking in the living space. (Hopefully for the duration that the house is habitable!) The following wall construction was used - from outside to inside, the wall consists of -
The wall was then finished off inside with a low volatile organic compound interior paint. After a several day bakeout with the house temperature near 100 degrees, this has resulted in a very well insulated and low infiltration wall rated for 110 miles per hour (176 kph) that causes no obvious problems.
Given this design, a heating system that would supply some 25,000 BTU into the living space is adequate to keep the house comfortable down to some -30 degrees Fahrenheit (-34 degrees C) outside temperature. To obtain this heat, a sealed combustion 40,000 BTU per hour input fireplace was installed in the living room to heat the house. Which, after derating for the the elevation, resulted in some 23,000 BTU available tor heating the house. In practice, a low-flame setting of 3/8 normal flame setting provides enough heat for comfortable year-round living. There is no ductwork, either below the floor or over the ceiling, to distribute heat to the rest of the house; a simple ceiling fan and floor conduction in the concrete slab are adequate for comfortable living.
A house with a low infiltration rating must have means of allowing fresh air into the house and means of exhausting stale or contaminated air. To this end, manually operated 5-inch (12.7 cm) inlet vents were installed in the east and west walls. A 70 cubic feet per minute, outside exhausted, bathroom exhaust fan was installed in the bathroom. A standard range hood exhaust fan, again outside exhausted, was installed in the kitchen.
An insulated attached garage, 24 by 24 feet (7.3 by 7.3 m), was very well sealed off from the house with 5/8 inch (1.6 cm) fire-rated drywall and both infiltration and fire barriers. The door to the garage from the house is a tight fitting 1 3/8 (3.5 cm) insulated steel door. The outside garage door is an insulated and tight fitting 1 3/4 inches (4.5 cm) thick unit.
An interesting feature of off-grid photovoltaic systems, in the context of environmental illness is worth mentioning. Normal operation of the system is for sunlight to generate power in the photovoltaic panels which is stored in several large 1200 ampere-hour batteries at 24 volts. An inverter takes the 24 volts DC and transforms it into 120 volt AC power for powering a standard AC powered house.
A mode is available in the photovoltaic system so that when the amount of 120 volt AC house power being used drops below a certain point, such as a couple watts, the inverter is turned off (to conserve power). A test pulse is sent to the house every couple seconds or so to see if someone has turned on an appliance, in which case the inverter comes back on line for normal 120 volt AC power. By carefully managing the house electrical loads, and using DC powered appliances, such as refrigerator and freezer, it is possible for the 120 volt AC power into the house to be automatically off much of the time except when really needed. People with EHS who have visited said they felt much better when the AC power turned itself off.
The result is a house with the following characteristics -
Year Heat Index, BTU/degree-day/square foot of floor
2005 4.17
2006 2.59
2007 2.46
2008 1.96
2009 1.88
2010 1.65
2011 1.71
2012 1.80
2013 2.75
Year Power, Kilowatt-hours.
2005 1,076.
2006 1,253.
2007 1,293.
2008 1,526.
2009 1,584.
2010 1,430.
2011 1,646.
2012 1,606.
2013 1,559.
(The typical American home uses some 10,800 Kilowatt-hours of electricity a year.)
High points for the Sawmill House
The Sawmill House was included in the local 2005 Parade of Solar Homes with main points of interest being -
The big question is "does it work?" The owner has hypersensitivities to pesticides, tobacco smoke, fragrances, and several building chemicals. He has lived in the house for several years with no problems caused by the house.
Additional information about the Sawmill House -
Copyright ©2005, 2011 E. Stiltner.