Presented at the Energy Efficient Building Association Buildings Solutions Conference in Boston, MA, March 1993
Once you understand the basic concepts, healthy house construction is no more difficult than unhealthy house construction. However, it does involve more than just selecting non-toxic materials. It also requires an understanding of how a house functions - for example how a house "breathes" naturally (and why that may not be desirable), and how heating and ventilating systems interact. This paper will list fourteen dos and don'ts to use in designing and constructing a house that will not make the occupants sick.
1. Do build in a clean locale
Site selection is the first consideration in healthy house construction because if the outdoor air quality is poor, then the indoor air quality will be poor also. It is possible to install filtration equipment to clean all of the air indoors, but this can be expensive. While filtration may be necessary in some instances, it is often easier to build in an unpolluted area in the first place.
2. Do build an airtight structure
An airtight structure will minimize the amount of uncontrolled infiltration. This not only improves energy efficiency, but when coupled with a mechanical ventilation system, it gives the occupants maximum control over the indoor air. When outdoor pollution is occasionally high (e.g. neighbors applying lawn chemicals), the ventilation system can be temporarily shut off, and the indoor air will not be affected by the outdoor contaminants. An airtight structure also minimizes occupant exposure to insulating materials.
3. Do install a radon removal system
It is difficult to predict if radon will be a problem in a particular house. The house must be tested for radon after it is built. It is easy to take some basic precautions in new construction, that may or may not need to be employed later. It is much more difficult to mitigate radon in a completed house if those precautions weren't taken initially. For example, a sub-slab piping system can be installed when the foundation is being built. If measured radon levels in the finished house are high, it will be a simple matter to hook up a suction fan to the piping. If radon levels are low, the system won't be necessary, and the sub-slab piping will remain unused. The expense should be considered low cost insurance.
4. Do install a ventilation system
People need fresh air. Mechanical ventilation can supply that air at the correct rate whenever it is required. Relying on infiltration for the occupants' air supply is unreliable at best and, more often than not, insufficient. There are many approaches: supply ventilation through a fresh air duct to the return air side of a furnace, central exhaust, heat recovery ventilation, etc. The different systems have various advantages and disadvantages, but all can provide the occupants with fresh air.
5. Do use metal or solid wood cabinetry
Kitchen and bathroom cabinets are not only made of manufactured wood products that contain glues high in formaldehyde (medium density fiber board, particle board, hardwood plywood), but they are also coated with a very potent "acid catalyzed" formaldehyde finish. The finish has very high emissions for 6-12 months, after which levels decrease significantly. The emissions from the formaldehyde base glues have half lives of several years. Custom made solid wood cabinetry with a low-tox finish, or metal cabinetry with a baked-on finish, are better choices.
6. Do use water based adhesives, caulks, paints, etc.
In general, water based products are more benign than solvent based products because they have lower levels of volatile organic chemicals (VOCs). However, they are not perfect because there are ingredients besides VOCs that can be responsible for negative health effects. For those interested in even healthier products, several specialty manufacturers are now offering alternative materials that are more benign than off-the-shelf products. If solvent based products must be used for some reason, plenty of ventilation is mandatory to minimize exposures. Extra ventilation is recommended with water based products.
7. Do test materials with sensitive occupants
When dealing with sensitive occupants, it is imperative that some materials be tested for personal tolerance. This is necessary because different people can have varying reactions to the same material. The most important building materials to test are those that are exposed to the interior occupied space: paints, wall coverings, flooring, cabinetry, etc. Testing should generally be done under the supervision of a physician, but the following often works well: Allow a sample to air out until it seems odor free, then place it next to one's bed and see if sleep patterns are normal. A good night's sleep generally indicates tolerance.
8. Don't panic
If you are apprehensive about healthy construction, don't be. However, it is important to be cautions and make intelligent selections appropriate to your needs. There are a number of books and periodicals dealing with the subject on a variety of levels. Some of the better ones are listed in the Selected Bibliography at the end of this paper.
9. Don't believe everything you hear
There is an increasing amount of information available on healthy construction. As would be expected, some advice is better than others. When dealing with sensitive individuals, don't believe anyone who tells you that a product is universally tolerable. People can have very unusual sensitivities to a wide variety of products. For example, most sensitive people are bothered by synthetic materials like vinyls and acrylics. However, some occasionally report problems with natural materials like cotton, while others can tolerate synthetic paints after a period of time. This is why, when sensitivities are severe, testing is imperative.
10. Don't use carpeting
When it comes to poor indoor air quality, carpeting is one of the worst offenders. New synthetic carpeting outgasses over one hundred different volatile organic compounds (VOCs). Old carpeting is a haven for microbes, some of which are highly allergenic. Vacuuming carpet with a conventional portable cleaner blows a great deal of "house dust" into the air through an inefficient filter. House dust consists of skin flakes, hair, food particles, pet dander, insect parts, insect feces, and whatever was tracked indoors on shoes - animal waste, mold and pollen, lead dust, pesticides, etc. Shampooing is not totally effective at cleaning carpeting, and it may actually contribute to an increase in microbes. Shampooing carpeting has also been linked to Kawasaki disease in children under age five.
11. Don't use products high in formaldehyde
All manufactured wood products emit formaldehyde. Kitchen and bathroom cabinets have already been mentioned. There are two primary types of resins used in the wood products industry - urea-formaldehyde (U-F), and phenol-formaldehyde (P-F). The U-F resins are perhaps ten times more potent than the P-F resins. P-F resins are waterproof and are used in all construction grade products (construction plywood, both interior and exterior; oriented strand board; laminated beams; fiberglass batt insulation; etc.). U-F resins are used in hardwood plywood for wall paneling and cabinetry, medium density fiberboard for cabinetry and closet shelving, and particle board. Houses should have no U-F resin containing products within the occupied space. P-F resins, since they are lower in emissions, can be used in the structure, but with sensitive occupants, they should be well separated from the living space, or eliminated entirely.
12. Don't asphyxiate the occupants
If a conventionally aspirated combustion appliance is used, make sure that backdrafting and spillage will not occur. Since they can take place in the majority of houses when under "worst case" conditions, sealed combustion, solar heating, electric or heat pump furnaces and water heaters are highly recommended. Gas ranges, in addition, are probably not a good idea. Even if backdrafting and spillage are not serious enough to kill the occupants, they can result in enough low level carbon monoxide to result in flu-like symptoms.
13. Don't create a depressurized house
Depressurization can not only result in backdrafting and spillage, but also infiltration of a variety of pollutants. A depressurized basement can pull in radon, pesticides, and other soil gases. A depressurized house can pull mold spores and particles of insulation into the occupied space. Depressurization occurs because of the HVAC system's blower (MAD-AIR), powerful natural drafts in chimneys, exhaust ventilation equipment, clothes dryers, central vacuums, etc. In an airtight house having no chimneys or flues, depressurization causes no particular problems, but since exhaust devices will not work efficiently the occupants should be advised to open a window slightly when using such equipment.
14. Don't ignore physics
Construction methods are much more refined than they used to be. As a result, when houses are built without regard for the laws of physics, failures and health problems may occur. Moisture migration, wind and stack effect induced pressures, mechanically induced depressurization, and outgassing, all follow well defined physical laws. If those laws are properly understood, healthy, durable houses can be built.
© Copyright 1993 by John Bower
We would like to thank John Bower of the Healthy House Institute for his permission in reprinting this article. For more information, please visit his website at www.hhinst.com