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Indoor Air Quality: Manage Air Flow and Materials

Posted by Green Builder Staff

Jan 14, 2015 2:29:00 PM

 ONE OF THE CONFUSING CHARACTERISTICS 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—has suddenly become 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
Some modern building products operate passively. Housewraps 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 percent 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.

Carpet
Carpets have only in the last decade or so come under close scrutiny for their environmental impacts—both in and out of the home. Most commercial carpets are made from some variation of synthetic, petroleum-based material. This material is often treated with other chemicals to improve stain resistance, wear or color retention. To make matters worse, many carpets are installed over highly toxic rubberized pads. They may also be glued to the floor with pungent adhesives. That new carpet smell you recognize is not something you want in your home. It’s a sign that your floor is releasing unknown chemicals into your living space. A few of the larger carpet makers—notably Mohawk, Interface and Shaw Industries have begun to approach carpets from a more eco-friendly perspective, not only recycling old carpets—but offering less toxic installation systems and products that have lower levels of offgassing.

Central Vacuum Systems
The carpet industry suggests that the average American family uses a vacuum cleaner at least once weekly, while about 10 percent of us vacuum our homes once or more per day. But the typical upright household vacuum cleaner may not be the solution to clearing the air in a home. These upright units are not created equal. Most lack an effective HEPA filtering system—the only reliable way to capture the fine particles that have been shown to be harmful to human health. On the contrary, a vacuum with a non-HEPA filter may simply toss tiny particles back into the air.

A whole-house vacuum solves this problem by actually taking unwanted particles outside the living space—into a garage or unfinished basement.

Energy and Heat Recovery Ventilators
You may have heard of energy recovery ventilator (ERVs) and their northern cousins, heat recovery ventilators (HRVs). This heat transfer technology is a key component of any modern “tight” house. Without them, modern houses would probably not be worth the foam, tape and caulking with which they’re sealed. These mechanical wonders take hot, unconditioned fresh air from outside, pass it over a heat collecting medium, where it gets a partial cool-down before entering the home. A study by John Bower (visit www.healthyhouseinstitute.com) found that using a heat recovery ventilator with continuous ventilation cost a Minnesota homeowner just $86 a year. It cost $188 to do the same ventilation without an HRV.





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2016 Homeowners Handbook Green Builder
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