INDOOR AIR QUALITY & HOUSE TIGHTNESS - CONTENTS: How tight is your energy-efficient house? How to decide if a house is too air-tight. Do air-tight homes mean poor indoor air quality? Causes of variation of indoor air quality among similarly-constructed homes. Precautions recommended for tight houses to assure good indoor air quality. Green buildings, energy savings, & indoor air quality. Critique of IAQ provisions in the current LEED designation for buildings. Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices.
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Tight houses & indoor air quality concerns:
This article discusses the question: is this house constructed too tight with insufficient fresh air intake for good indoor air quality? Tight houses are not a problem if the builder takes reasonable precautions outlined here. Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. The sketch above shows a split-level cantilevered raised ranch with chimney and bay windows - a tough house to build tight.
"The Almost Too-Tight-House - not a problem if builders take reasonable precautions" - this article appears in original form (the PDF links below) and an updated/expanded web article just below. The text below paraphrases, quotes-from, updates, and comments an original article original article (see links at article end) "The Almost-Too-Tight-House" by Steven Bliss.
How Well Ventilated are Modern Houses?
Most energy-efficient builders don't make their houses as tight as plastic bags. More often, new energy efficient houses have natural air infiltration rates of 0.2 to 0.5 air changes per hour (ACH). These houses already have almost enough average ventilation to meet current indoor air quality guidelines. But because natural air leakage in and out of buildings varies with outdoor temperature and wind speed, these homes do not ventilate reliably, and also, some parts of the home may be left unvented.
Still in some communities these almost-too-tight-houses are mandated by law or promoted with financial incentives. They often arise as a compromise between hard-core superinsulation dogma and what builders think they can build and sell.
How Air-Tight is Your House?
The two most important factors determining the tightness of a house shell are:
The quality of construction, including choice of materials and attention to best building practice details as the components of the home are assembled (for some examples see FRAMING DETAILS for BETTER INSULATION)
The type of housing - its design. All other things being equal, two-story and split-level houses leak more air than one-story homes. (For examples of leak areas on cape-cod style homes see INSULATION LOCATION for CAPES, CRAWLSPACES.)
Other factors affecting house tightness, increasing house air leakage, include:
Construction details such as failure to wrap the band joists (see VAPOR BARRIERS & AIR SEALING at BAND JOISTS) and failure to run continuous, protected polyethylene vapor barrier materials around the shell interior.
With these more-air-leak-prone building design and construction details, chances are that the building is no tighter than 0.25 air changes per hour, and on a blower door test for air leakiness, the home is probably in the range of 4-7 ACH at 50 Pascals of pressure. If you don't actually test a home, estimating its leakiness is simply anybody's guess. (See BLOWER DOORS & AIR INFILTRATION).
House Tightness and Indoor Air Quality
Simply knowing that a home is relatively air tight does not by itself permit a clear statement of the home's indoor air quality.
First, the health effects of exposure to low levels of indoor pollutants are not only unknown in many instances, and more, the sensitivity of individuals to airborne irritants or contaminants varies quite widely. Using instrumentation and careful lab analysis we (DJF) have observed clients who respond with severe respiratory distress to airborne levels of certain mold spores at airborne spore counts in the hundreds of spores per liter of air - lower than normally-accepted standards of problem indication indoors.
Second, the indoor air contaminants and their levels vary widely even between houses of the same design and constructed by the same builder. The particular indoor pollutants that may be present in a specific building vary widely depending on the materials of construction, the furnishings, and for homes that have suffered leaks or water entry, the risk of hidden mold, insects, or allergens. Housekeeping and the presence or absence of pets make an enormous difference in the level of allergens in buildings, and the combination of high indoor humidity with pets increases the level of dust mites in the home.
For at least these reasons and probably others as well, there is no direct relationship between the air-tightness of a home and the level of indoor air pollution in that home.
In general, houses that are reported to have indoor air quality problems have a specific (sometimes obvious) pollution source that can be singled out and corrected, removed, or at least controlled.
High levels of particulates in indoor air are often tied to smoking.
High levels of indoor airborne mold may be present in a home that has experienced leaks or unusual indoor humidity levels, and the mold that may actually be bothering the building occupants may not at all be the "black mold" that someone has observed on framing or drywall.
See MOLD in BUILDINGS.
Elevated levels of radon gas come from high levels of radon gas in soils below a home combined with specific cracks or leaks into a specific home - conditions that vary so widely that two identically-constructed homes side by side can have completely different radon levels.
See RADON HAZARD TESTS & MITIGATION
Effects on Indoor Air Quality When a Home is Weatherized to Be More Air-tight
In several studies of homes whose air tightness was tested before and after weather sealing, researchers found that cutting air infiltration by 20 to 40 percent in a home - typical of what professional weatherization retrofitting contractors achieve - did not degrade indoor air quality significantly.
Many pollution levels in these homes remained about the same, some actually fell. The only contaminant level that increased in these homes was radon gas. Unlike other indoor air contaminants, the radon level in homes does indeed seem to increase more or less proportionally to the air tightness of the home.
List of Reasonable Air Quality Precautions for Builders of Renovated or New Air-Tight Homes
Building retrofits to improve the energy-efficiency of an existing older home are no cause for an air-quality alarm. Unless the house was very tight to start with or you are gutting the building and adding a continuous air/vapor barrier, it is unlikely that a weatherization retrofit can be too tight. At best, a weatherized home will approach the air-tightness of new housing. If there were no air quality problems before the retrofit, there are probably none afterwards.
Reasonable indoor air quality precautions for weatherization retrofit projects on older homes include adding kitchen and bath vent fans if they were not present before. If radon levels in the area are known to be high, test for radon levels before and after the retrofit; seal basement cracks and gaps, and cover (and possibly vent) basement sump pits.
If indoor moisture levels are high in the home, identify the moisture source and correct it before other construction improvements. Following these steps are likely to improve rather than harm the indoor air quality of an older home.
Reasonable precautions for new construction of air-tight homes: in new construction the builder has more control over potential sources of indoor air pollutants. Two key strategies for indoor air quality are pollutant source control and spot ventilation (or building ventilation in general).
See INDOOR AIR QUALITY IMPROVEMENT, KEY STEPS.
Indoor air pollution source control: seal out radon if radon gas is a problem in the area; be careful in choosing building materials. Avoid large amounts of products made using urea-formaldehyde glues. Steer clear of unvented combustion appliances. If you are installing a gas stove, use a pilotless model.
For spot ventilation, install high quality (high air flow low noise [low sone]) kitchen and bath vent fans, duct the range hood to outdoors. In the bathroom, hard-wire the vent fan to the light switch. Many occupants hate this feature, but if the bath fan is a high quality quiet unit people are more willing to live with it. Add exhaust fans in high-moisture areas such as laundries.
All vented combustion appliances should have their own combustion air supplies.
See COMBUSTION PRODUCTS & IAQ.
Atmospherically vented gas appliances such as heaters and water heaters pose special problems because if they backdraft there is little warning and the possible production of carbon monoxide can put lives at risk.
See COMBUSTION GASES & PARTICLE HAZARDS.
Your main options with furnaces are sealed-combustion appliances, induced-draft heating equipment, or an isolated and fully vented utility room following the Uniform Mechanical Code (and local building code regulations).
See COMBUSTION AIR for TIGHT BUILDINGS
Provide mechanical ventilation for the whole house? If you have taken the steps described above and the house is not airtight, you probably do not need a general ventilation system to dilute indoor air pollutants - in the sense that the indoor air will be no worse than in the average home and will be better than many.
At some level of tightness, bringing in fresh outdoor air has obvious value for indoor air quality. New homes include products that release trace levels of chemicals that were not common in homes 50 years ago, and we simply don't know the effect of living in modern indoor air with these low but detectable pollutant levels.
Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.
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(June 16, 2014) Anonymous said:
And not a word about negative pressurization?
Anon the article above describes a number of hazards that are *all* associated with "negative pressures" that may be created in a tight house by natural convection or by the operation of exhaust fans or blowers used on heating equipment.
If you can add specific comments, critique, suggestions on the topic we and other readers would be most appreciative.
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Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years.
ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: firstname.lastname@example.org
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com
"How to Put the IH in LEED, Green buildings Need Industrial Hygienists' IAQ Expertise", Dale Walsh, The Synergist, April 2010 p. 25-26. Walsh directs attention to a forthcoming (2010) White Paper for Green Building, produced by the Occupant Air Quality Project team of the AIHA Green Building Working Group. Dale Walsh, Walsh Certified Consultants, Inc., Las Vegas NV, 702-468-4782 email@example.com
U.S. Green Building Council (USGBC), U.S. Green Building Council, 2101 L Street, NW Suite 500. Washington, DC 20037 - http://www.usgbc.org/ Customer Service: 1-800-795-1747 (outside the United States, call 202-742-3792) Quoting from the USGBC website:
The U.S. Green Building Council (USGBC) is a Washington, D.C.-based 501(c)(3) nonprofit organization committed to a prosperous and sustainable future for our nation through cost-efficient and energy-saving green buildings. USGBC works toward its mission of market transformation through its LEED green building certification program, robust educational offerings, a nationwide network of chapters and affiliates, the annual Greenbuild International Conference & Expo, and advocacy in support of public policy that encourages and enables green buildings and communities.
The LEED® green building certification program is a voluntary, consensus-based national rating system for buildings designed, constructed and operated for improved environmental and human health performance. LEED addresses all building types and emphasizes state-of-the-art strategies in five areas: sustainable site development, water savings, energy efficiency, materials and resources selection, and indoor environmental quality.
LEED Professional Credentials (LEED AP and Green Associate) recognize professionals who have demonstrated a thorough understanding of green building techniques, the LEED green building rating systems, and the certification process. The LEED Professional Credentials program is administered by the Green Building Certification Institute (GBCI), which was established with the support of USGBC to allow for objective, balanced management of the credential program.
The Leadership in Energy and Environmental Design (LEED) Green Building Rating System™ is a third-party certification program and the nationally accepted benchmark for the design, construction and operation of high performance green buildings. LEED provides building owners and operators with the tools they need to have an immediate and measurable impact on their buildings’ performance.
Green Building Certification Institute - (GBCI) GBCI.org Green Building Certification Institute, Washington DC 20037, 1-800-795-1746,
International Calls: +1-202-828-1145. Quoting from GBCI:
The Green Building Certification Institute (GBCI), established in January 2008, provides third-party project certification and professional credentials recognizing excellence in green building performance and practice. GBCI administers project certification for commercial and institutional buildings and tenant spaces under the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED®) Green Building Rating Systems™ addressing new construction and ongoing operations. GBCI also manages the professional credentialing programs based upon the LEED Rating Systems including the LEED Green Associate and LEED AP credentials.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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