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.
VirtuesONE 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—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:
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% 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.
The EPA offers a few guidelines:
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 (below), 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.
Carpeting is not the only source of VOCs and other harmful chemicals. After your new home or remodel project is complete, make sure you don’t compromise indoor air quality with the products and furnishings you bring into the space. This goes from everything from furniture, which can contain flame retardants and formaldehyde, to cleaning products.
It may take a little research to ensure items are completely nontoxic. Some manufactures have made it easier by revealing their products’ “ingredients” with either in-house labels or by seeking third-party certifications. Several organizations have developed standards that make it easier to specify and use low-emission products. These include UL Environment, which developed the GREENGUARD standard and which maintains a database of thousands of certified products in 28 categories.
The carpet industry suggests that the average American family uses a vacuum cleaner at least once weekly, while about 10% 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.
Chronic moisture can lead to mold growth. Exhaust fans excel at removing excess moisture that tends to build up in specific locations, such as bathrooms and kitchens. Kitchen range hoods also remove cooking contaminants. These fans have become quite sophisticated and quiet; some manufacturers such as Panasonic offer “smart” models that adjust to changing moisture conditions, or that can sense when a room is occupied. Whole-house exhaust-only ventilation systems exist, but be aware that these rely on cracks and penetrations in the building envelope to supply the makeup air that replaces the exhausted air. In tighter homes, this can create “negative pressure.” In general, we recommend using exhaust fans to supplement balanced whole-house ventilation systems.
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 they’re sealed with. These mechanical wonders take hot, unconditioned fresh air from outside, pass it over a heat collecting medium, where it gets a partial cooldown 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.
Indoor air tends to concentrate pollutants quickly. As a result, building codes typically have certain requirements for the amount of fresh air that must be exchanged with stale indoor air over a given period. Typically, this is expressed as cubic feet per minute, or CFM. An organization called ASHRAE provides guidelines for how much ventilation is needed, although the best means for achieving that ventilation are often debated. When in doubt, more ventilation is better than less, but you have to balance the resulting energy loss with improved indoor air quality. -Editor
SOURCE: Ashrae 62-2-2003
