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Controlling the flow of air in and out of a building is a key principle of eco-friendly construction. To ensure optimal air quality, a combination of strategies is the best approach.
Mechanical ventilation is the most reliable way to control air quality in a tight modern home. An air-to-air heat exchanger—either a heat recovery ventilator (HRV) or energy recovery ventilator (ERV)—removes stale air from the home, preheating or cooling fresh air as it enters the space.


One of the confusing aspects of green building certification programs is the way they lump together two different aspects of building science: saving energy and keeping indoor air safe and clean. Is a green home one that saves energy or one that has healthier indoor air than a conventional home? The answer is both. How did the two concepts get mashed together this way? Blame tight houses. As windows, walls, and basements have become less leaky, the stuff that pollutes air inside the home—glues, carpets, paints, pressed board cabinets— suddenly became a lot more dangerous. So here’s the deal. If you want to build or retrofit your home to be greener, you’ll have to control the air quality at the same time. There are three ways to do this. First, by eliminating pollutants at the point source; second, by keeping moisture levels healthy indoors; and third, by mechanically “cleaning” the air.



Here are some key products whose attributes help provide healthier indoor air:


HOUSEWRAP PASSIVE RESISTANCE
Some modern building products operate passively. House wraps fall under this description. These weather-resistant barriers allow water vapor to escape living spaces and wall cavities (where it might condense and encourage mold or mildew) at the same time preventing unwanted outdoor air from creeping into the home. Housewrap is only as good as its installation, however. The Department of Energy says that housewrap must be taped at every seam. Otherwise, it may be 20% less efficient. It’s also important that housewrap not be left exposed to sun and wind for too long, factors that can degrade its effectiveness over time.


HOUSEWRAP
Housewrap is only as effective as its installation. For example, metal flashing above doors or windows should be installed before the housewrap, not on top of it.


VIRTUES
> Reduces air infiltration
> Repels wind borne rain
> Long service life


CAVEATS
> Can’t be left exposed indefinitely
> Requires careful installation


 


TYPAR HOUSEWRAP
Typar asserts that its weather barrier housewrap has a higher level of “water holdout” than competing brands, yet with an optimal level of vapor permeability to keep water from getting trapped where it can cause problems. www.typar.com


PANASONIC WHISPERCOMFORT ERV
This compact energy recovery ventilator can be inserted between joists in a ceiling to offer quiet, continuous air exchanges for a single room. It consumes just 23 watts at the highest setting of 40 cubic feet per minute (cfm) of airflow. www2.panasonic.com

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