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Indoor Air Quality: Information for the Builder and the Home Owner

By Dave Gerard & Paula Martin

Poor indoor air quality can harm your health, where the air you breathe can make you sick or, at its worst, cause deadly harm. We tend to spend much more time indoors during the colder seasons or during wet weather and, as a result, expose ourselves longer to a potentially harmful environment. Small children, with their higher breathing rate and their small lungs, have greater risk than adults. Even family pets can suffer from indoor air pollution. Luckily we know much more about indoor air pollution than we used to, about where it comes from and how to minimize its threat.

A large part of the problem of indoor air quality arises from the solution of another problem: expensive heating and cooling. Rising fuel and energy costs have forced the building industry to make homes more energy efficient, especially in the northern regions. Many of today’s homes benefit by default from improved building products and construction techniques that work toward eliminating the “leaky house” syndrome. Older homes are made more efficient by installing proper vapor barriers, replacing leaky doors and windows and by sealing cracks to the outside. When air infiltration is cut down, the building’s ability to breath (ventilate, or exchange air inside and out) is reduced, creating a risk for the “sick building syndrome”. A sick structure buildups stale air and odors, fumes, smoke, microbial by-products – pollutants remain in the air rather than get blown out with ventilation. The indoor air becomes intolerable or unhealthy.

Sources of indoor air pollution are both biological and chemical. Biological sources start from stale humid air. Moist conditions, created by plants, showers, fish tanks, cooking, poorly vented plumbing and even breathing may allow mold and mildew to grow. These microorganisms then release airborne spores and further microbial growth, causing problems ranging from dirty walls to allergic reactions, asthma attacks and respiratory infections. The dangers of black mold are known all too well to the building industry.

Chemical sources of indoor pollutants are many. Consumer products are often a culprit, including fragrant air fresheners, personal products and some household cleaning products (such as bleach). These irritants may responsible for persistent allergies and respiratory or sinus problems. Chronic conditions such as watery, burning eyes or skin irritations may also indicate unhealthy air in the home.

Combustion produces another indoor air pollutant. Homes that use gas appliances or have defective combustion heating devices can achieve high levels of dangerous exhaust gas in the home that pose immediate health dangers. Nausea, dizziness, headaches and even unconsciousness may result. All may be considered obvious signs of carbon monoxide poisoning, which is why many suggest having a carbon monoxide monitor in homes with gas appliances.

More dangerous chemical sources can arrive with home construction. The first of these is actually a category of chemicals, called volatile organic compounds or VOCs. These are often synthetic chemicals. They all share the characteristic that they evaporate (going from solid or liquid state to become a gas). VOCs are found in many of the products and construction materials used in the home. Particle board used in cabinets, counter substrate and furniture including upholstery, are all known to off-gas formaldehyde. Solvent-based finishes, oil-based paints, adhesives, paint strippers, carpets and some other flooring materials often emit high levels of VOCs. VOCs are health threats because they cause respiratory irritation, immune system problems, or, at their worst, cancer. Therefore many building material suppliers are creating products with “low VOC” ratings, to minimize risk.

Radon is another cancer-causing indoor pollutant. This pollutant has a natural origin. It is a tasteless, odorless, colorless and radioactive gas formed naturally from the decay of uranium and is most commonly found in soil, rock and water surrounding the home. Some areas in the U.S. are considered hot spots for radon gas while others have low risk, based on the region’s composition of underlying rock. Radon can seep into the home through cracks in concrete floors or other non protected penetrations and surfaces below grade or from off-gassing in the water supply during showers or other water usage. Radon has recently been discovered to be delivered to the home via some building products. Recently, unhealthy levels of radon have been detected in some natural stone products used in flooring, fireplace features and granite counter tops. Radon is a special risk because, as it undergoes radioactive decay, its breakdown products (called radon daughters) are also radioactive, but in solid form. Therefore, the radioactive gas may transform inside a home to a radioactive dust, making mitigation more difficult. The best way to deal with the threat of radon is to keep it outside your home.

People exposed to VOCs, radon gas (and its radioactive breakdown products) and other solvent-based fumes can damage the DNA in sensitive lung tissue, causing lung cancer and other serious health problems. The EPA estimates that indoor exposure to radon causes 8% of the cases of lung cancer in the US (cigarette smoking is responsible for 80%). If you or any of the occupants in your home experience symptoms associated with questionable air quality, consult an air quality specialist and have the air in and around the home tested, include testing the water if you use a private well. While many of the sources described may be obvious, VOCs and radon gas are hard to detect and require special testing equipment. If you determine you have an air quality issue, remediate the condition by first restricting or removing the pollutants at the source and increase or introduce ventilation.

According to ASHRAE (American Society of Heating, Refrigeration and Air-conditioning Engineers), the rate of air exchange is based upon square footage and number of occupants or bedrooms in the building. Based on a mechanical ventilation design, an average house of 1500-3000 sq ft with 4-5 bedrooms requires a continuous ventilation rate of 75 cubic ft per minute (cpm). If venting intermittently, the ventilation rate increases substantially. ASHRE standards have been amended for northern regions, requiring increased ventilation rates due to longer home occupation during the winter months. Protection from indoor air pollution requires appropriate air flow.

Natural ventilation methods, also know as “farm house or stacked venting,” simply employ opening doors and windows to create a “chimney effect”. While this may clear the air, it does not distribute fresh air uniformly throughout the building, plus, it wastes energy. That “fresh spring” smell of natural venting also invites unwanted spores, pollen, dust, insects and humidity to enter and be dispersed, possibly adding to the air quality problem.

Spot ventilation is achieved installing and operating fan units at know sources, directing the affected air to the outdoors via ducts. Range hoods, bath fans, and clothes dryers are all considered spot ventilators. This type of ventilation will depressurize the house and could result in air infiltration through cracks and leaks and cause combustion devices to back draft if make up air is not supplied. Clothes dryers should always be ducted to the outdoors, they product excessive amounts of moisture, lint and exhaust fumes if gas operated. Radon mitigation often involves creating a pressure differential between the exterior foundation, pulling the underground gas and venting it to the exterior air (rather than allowing it to be pulled into the interior of the structure), which helps only if the radon source is the rock upon which the house sits.

The most energy efficient and balanced systems used today are Heat Recovery Ventilators (HRV) and the whole house method. HRVs work as air-to-air heat exchangers designed to expel stale, warm air to the outdoors through an insulated duct while pulling in fresh air in a parallel duct at the unit. Because the inflow and outflows ducts are parallel, heat is partially transferred from the exiting air to the entering air, saving energy. With equal amounts of air entering and leaving, balance is achieved therefore eliminating depressurization and associated problems. Exhaust ducts are located at all pollutant sources and each living space fitted with fresh air diffusers. Whole house ventilation is an important consideration for the new home builder as it is the method by which energy can be conserved yet minimizes risk of indoor air pollution. With new construction, the builder has the opportunity to hide HRV duct work before covering up walls and ceilings. HRV control systems can be set up to run automatically. Their ventilation rate can be increased if excessive humidity, solvent based vapors and other fumes are present, and each exhaust intake location can be manually activated and run on a timer.

Builders and home owners have a greater range of choices today. With proper ventilation, the home owner can flip a switch to increase air flow and decrease health risk, especially while new furniture and carpets off-gas. Home owners can choose materials in their home (from cleaners to flooring) that release fewer fumes. Smart home buyers will consider not just the energy-star rating of their home but also its ventilation structure, to make sure they don’t buy either a leaky house or a sick one.

About the authors.

David Gerard is an expert in the building of super insulated homes and cold weather construction techniques, building in Alaska for the last 26 years. David also fabricates cabinets and countertops for his projects and is familiar with out gassing of materials.

Paula Martin is a (credintials will be added later)