Cost-Effective Ways for Building Tight and Ventilating Right
April 23, 2007
Homeowners today are more concerned than ever before about the quality of the air inside their homes. Buyers demand that their homes be free of mold growth and pollutants that may have been generated by building materials.
An increasing number of people who believe they are not getting an environmentally fit home are seeking legal counsel - regardless of whether they are right or wrong. Proactive builders and contractors will want to address this growing trend before expensive legal actions are taken against them.
Adding to the concerns of providing fresh, healthy indoor air is the fact that homeowners and many building codes are demanding tight, energy-efficient homes. Thus, a further challenge arises: how to design and build a tight, energy-efficient home with a healthy indoor environment.
The quality of the air inside many American homes has become more toxic, more allergenic, more hazardous to infants, asthmatics, seniors, and other at-risk population segments even though aggregate total outdoor emissions for carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), particulate matter (PM), volatile organic compounds (VOCs) and lead, have decreased by 51 percent over the past 35 years.
WHY THE INCREASE?According to the American Lung Association, in 2004 asthma was afflicting more than 6 million children and 14 million adults. Also, research from the Environmental Protection Agency (EPA) indicates that indoor levels of common airborne pollutants are two to five times higher than outdoor levels, regardless of whether the homes tested are in rural or urban areas.
There seems to be an automatic assumption that building practices alone account for the deterioration in residential IAQ, but it’s also important to consider that changes in lifestyles have just as much - and maybe even more - to do with the growing problem. Citing increased home entertainment options and the fact that more people work from home, the EPA estimates that on average, Americans now spend 65 percent of their time at home. That means more than 60 percent of the air most people breathe comes from inside their houses.
We cannot ignore the vastly increased use of synthetic building materials, finishes, and furnishings; the proliferation of VOC-heavy personal beauty, cosmetic, and hygiene products; the use of pesticides; as well as some questionable design and construction practices that encourage formation of concealed moisture reservoirs.
Add to all of these the fact that in the past we used natural ventilation through windows and doors to provide fresh air in our homes. Now, even in moderate climates, many residents tightly close and lock windows and doors, even when leaving for short outings.
Furthermore, most people rarely leave windows open for extended periods even when they are at home, as they prefer the temperature-controlled environment that their heating and air-conditioning systems bring.
Most people prefer to get their desired temperature inside without suffering the traffic noise, dust, loss of privacy, and potential security vulnerabilities of an “open house.” The result is that in most climates we have eliminated the natural ventilation that we used to depend upon for outside air supply.
Heightened awareness of these issues has led to an in-crease in claims of Sick Building Syndrome (SBS) and Building-Related Illnesses (BRI) among homeowners and their families. Tight construction is not the only cause of increased indoor air pollution, but it can exacerbate the situation by limiting natural air changes.
Mold and other indoor air pollutants are found more frequently in newly constructed buildings and residences; however, there is a critical need for proper ventilation, air mixing, and pollutant dilution in all types of dwellings.
CALLBACKS AND COURTROOMSContractor callbacks to investigate IAQ issues are still on the rise. Unfortunately, callbacks are one of the less harmful and least costly problems a builder can face when a homeowner is dissatisfied with home air quality or a ventilation system. Potential lawsuits are a growing concern among builders and HVAC contractors, and should be taken seriously.
Since 2000, the number of lawsuits alleging residential construction defects - the majority of them involving mold, moisture, and related health issues - has increased exponentially. The number of verdicts against contractors has also risen substantially.
The problem is, homeowners want good IAQ, but not at the expense of energy efficiency.
In July 2006, a new EPA Energy Star® qualification guideline went into effect in 44 states, mandating that certified homes “perform sig- nificantly better than code” in key energy-conservation areas, such as home envelope air leakage. The qualification also recommends mechanical whole-house ventilation systems to “ensure consistent exchange of indoor air.” Build tight, ventilate right!
Virtually every IAQ article written from 1974 through 2000 attributed the increased incidence of IAQ complaints at least partly to the tighter buildings constructed in response to the energy crisis of the 1970s.
However, looking closely at the testing done on those buildings, it has been discovered that many aren’t as tight as they were originally thought to be. Numerous other factors, including inadequate ventilation, contribute to poor air quality and moisture problems.
Modern home ventilation technology, now readily available, can provide high-quality, clean indoor air that will not compromise heating, cooling, or energy-efficiency solutions in the home. For instance, something as simple as indoor bathroom ventilation fans can help reduce moisture that causes mold to grow on material surfaces.
(For those of your customers who are demanding an energy-saving ventilation solution, models like Panasonic’s WhisperGreen ventilation fans are Energy Star-rated and designed to address the new green building movement in the United States.)
A GUIDE TO GOOD AIRThere are certainly economical ways to “build tight and ventilate right” to reduce the risk of liability involving IAQ and mold claims. The best way for builders and contractors to do this is to follow the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 62.2. Published in 2004, ASHRAE Standard 62.2 will be accepted as a standard of care and a significant factor in defining what constitutes acceptable construction practices in lawsuits relating to IAQ issues and construction defects.
In drafting Standard 62.2, ASHRAE noted that the “Environmental Protection Agency lists poor indoor air quality as the fourth-largest environmental threat to our country,” and that “asthma is the leading serious chronic illness of children in the U.S.” The standard also mentions that “moisture-related construction defects and damage are on the increase in new houses.”
Standard 62.2 defines acceptable IAQ as “air toward which a substantial majority of occupants expresses no dissatisfaction with respect to odor and sensory irritation … in which there (is) not likely to be contaminants at concentrations that are known to pose a health risk.” The standard’s authors conclude that “minimum residential ventilation can improve many of these indoor air quality problems.”
However, it is important to note that other factors affect minimum residential ventilation, such as the climate, family size, a home’s floor plan, number of bathrooms, construction type and materials, and more. For example, according to the standard, a two- or three-bedroom, 1,500-square-foot home requires fresh air intake of 45 cubic feet per minute (cfm).
In a home with a reasonably open floor plan, where there are no specific pollutant sources (e.g., a basement hobby shop), general whole-house ventilation using a high-efficiency bathroom exhaust fan is usually adequate. To further ensure good air quality, using a whole-house ventilation system is key, but it can be expensive. (Panasonic will soon release its WhisperComfort spot ERV. Like its bathroom ventilation fans, the WhisperComfort uses two ducts; one exhausts indoor air while the other supplies fresh outdoor air.)
BALANCED FLOW'S IMPORTANCEWhen ventilating an entire home, it is key to remember that air must be balanced, and the volume of air exhausted from the house is replaced with fresh outside air. If more air is drawn out of the home than is drawn in, the home could be put under negative pressure and back draft carbon monoxide and other toxins from combustion appliances.
Back drafting isn’t the only potential hazard. If the dwelling is located in a humid climate, negative pressure invites hot, humid air to infiltrate through the exterior wall of the house. A building envelope typically contains nutrient sources in the wall cavity; moisture can condense between the interior and exterior wall and mold can begin to grow. Unfortunately, a lot of organic building materials serve as very tasty nutrient sources for mold.
The opposite can occur if the home is under positive pressure. In regions that are very cold and dry in winter, such as Massachusetts or Illinois, many residents use humidifiers to compensate for the natural lack of moisture in the air. Forced-air heating systems can have a very drying effect on a home.
The temperature and moisture differential between the inside air and the outside air may create positive vapor pressure, which can force the warm, moist interior air to exfiltrate through the perimeter walls and create the same mold-friendly conditions in the building envelope as negative pressurization did in the more humid climate.
EFFICIENCY AND EQUILIBRIUMCreating a ventilation system that provides good IAQ and sufficient air dilution and mixing in an energy-efficient and temperature-regulated structure requires some preplanning and design compromises. However, this is fairly simple to do, and does not have to be very costly.
In a new home, the goal is to create a tight exterior and use indoor ventilation; as opposed to the old practice of building a loose house and counting on outdoor air leaking into the home to keep the concentration of contaminants down. That dated formula creates huge energy bills in both the summer and winter and results in homes with unacceptably large variances in temperature from room to room. It also stimulates mold propagation under high moisture and humidity conditions.
A far better solution is to implement a weatherization system that includes a breathable home wrap to provide an air and bulk water barrier, window and door flashing, caulked inlets, and tightly sealed attics with properly designed ventilation to help maintain neutral interior air pressure with minimal impact on energy efficiency.
Limiting air pollution at the source is also important. One way to do this is to use certified low-VOC and formaldehyde-emitting interior materials. Careful selection of interior finishes is one factor in minimizing the likelihood of contaminated air in the home. Green homes, which emphasize the use of natural materials and nontoxic finishes in interior construction, are inherently less likely to be contaminated by VOCs and formaldehyde than conventional homes using synthetic floor coverings, wall paint, or wallpaper adhesive that offgas chemical for months or longer after installation.
Also, take notice of combustion-fueled appliances such as hot-water heaters, clothes dryers, furnaces, stoves, and fireplaces, to ensure that these systems are venting directly outside of the home, or if absolutely necessary, that they are power vented. Install these appliances in areas that allow enough air to prevent toxic gas buildup.
USER-ACCEPTABLE HARDWAREOnce all the design and construction pieces of the balanced ventilation puzzle have been set in place, the most crucial issue becomes hardware selection. High-quality fans are key and should be employed as the system’s prime air movers.
The three most important selection factors are the fan’s operating characteristics, its energy efficiency, and whether or not people will actually use it. Of these three, the latter is by far the most important. Simply put, if the residents use the system, it will work; if they don’t, it won’t.
Why wouldn’t a homeowner use a fan? Noise. When considering whether or not residents will actually use any mechanical ventilation system often enough and long enough to generate sufficient air exchanges to adequately reduce the buildup of biological and chemical pollutants, it is useful to think in terms of a threshold of obtrusiveness. The actual threshold beyond which a user will stop or decrease their use of the system varies from person to person, but the twin components of the threshold are almost universal: noise level and inconvenience. Most studies indicate that excessive noise turns off more people (and their ventilation fans) than operating controls.
It’s reasonable to assume, however, that most people in our industrial society are pretty comfortable with the sound of a refrigerator gently purring in the background of their lives - a sound that is typically rated at about 1 sone. Since the sone measurement scale is linear rather than incremental, a 2-sone noise is twice as loud as a 1-sone noise and a 3-sone noise is three times as loud.
Most people find ventilation fans that are two or three times as loud as a refrigerator obtrusive. Fans designed with advanced noise-reduction features such as fully enclosed condenser motors, oversized double-suction blower wheels, and two-sided intake inductions are more likely to be used properly than louder fans in both intermittent room and continuous whole-house ventilation applications.
In an intermittent mode, particularly when equipped with a sensor that turns the fan on when a person enters the bathroom and turns it off 20 minutes after they leave, a fan quieter than 0.5 sone is unlikely to annoy anyone to the point of causing them to manually turn it off. In a continuous-operation system, such an extremely quiet fan quickly becomes part of the everyday background noise of the home and will likely go unnoticed.
Although noise is the main reason many homeowners do not use their ventilation fans, the convenience of operating them is also an issue. The easier things are to do, the more likely it will get done. Thus, operating a ventilation fan needs to be simple.
Requiring users to manually switch on a ventilation fan when entering the bathroom, and then returning 20 minutes later (the time recommended by the Home Ventilating Institute) to turn it off, is impractical for most users. Installing ventilation fans with motion sensors guarantee the fan will operate, without having to rely on manual operation from the user.
INHERENT CONTRADICTIONThere is a premium to be paid for energy-efficient homes with good IAQ. However, construction defects and IAQ claims can be many times more costly.
Builders and contractors who carefully design and correctly install mechanical ventilation systems will be at less risk than those who do not. Today’s highly-evolved, high-cfm, low-sone ventilation fans provide a cost-effective and builder-friendly way to reconcile demands for better IAQ without sacrificing a tightly sealed, energy-efficient home.
Publication date: 04/23/2007