What Type of Eco-Home Is Best For You?
(Page 3 of 5)
July/August 2008
By Carol Venolia
“With SIPs, you’re putting your money into the materials, more than into the labor,” Lerner says. “If you’re trying to support your local economy, using it probably doesn’t make the most sense. But it can be to your benefit if you’re working with a mainstream contractor because it is more systemized.” Rapid assembly makes SIPs cost-competitive with stick-frame construction if the structure isn’t too complex.
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INSULATING CONCRETE FORMS (ICFs) are interlocking, hollow, modular units—blocks or panels—that are stacked without mortar. Cavities within the rigid foam structures are reinforced with steel, then filled with concrete.
While foam, concrete and steel are all high in embodied energy and are made from nonrenewable resources, King says ICFs provide an efficient thermal system and a good structural system. The addition of recycled fly ash, a byproduct of coal-fired power plants, improves concrete’s environmental attributes by reducing the amount of energy-intensive Portland cement needed. Some types of ICFs, such as Durisol (www.DurisolBuild.com) and Faswall (www.Faswall.com), avoid the use of petrochemical-based rigid foam insulation, instead using reclaimed wood fiber in a cement matrix. Rastra (www.Rastra.com) incorporates recycled, post-consumer polystyrene, or Styrofoam.
WHAT ABOUT WOOD?
Can stick-frame construction—with walls of two-by-four or two-by-six studs—be green? “We love to work with wood,” engineer Bruce King says. “It’s more adaptable over time than many other materials. But technically, it’s a terrible building material. It splits, it shrinks, bugs eat it, it burns, and it grows mold and fungus.”
Conventional stick-frame construction can be made more eco-friendly by using responsibly harvested wood and reducing waste.
“I’d start with sustainably forested wood,” architect Kelly Lerner says. “Then I’d use advanced framing, a set of details that avoids redundant wood use. Finally, I’d improve on standard insulation by using spray foam to minimize air leakage, by adding rigid insulation on the outside, or by using a staggered-stud wall to minimize heat loss, then filling the cavities with blown-in cellulose or fiberglass insulation.”
CAN'T DECIDE? HYBRIDIZE
Combining some of these materials, using each to its greatest effect, may be the best way to respond to a variety of needs and conditions. It could be just the ticket to have an ICF foundation, a straw bale wall on the north side for insulation, a rammed-earth wall in the middle to soak up the sun’s heat and a SIP or wood-frame wall on the south side to allow for large windows.
WHO ARE YOU?
You and your family are central to your domestic ecosystem. Ask yourselves:
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