By Seth Masia December 20, 2008
A key step in making any home energy efficient is to maximize the insulation value of the exterior walls and ceilings. Half a dozen different materials are widely available for attic and in-wall insulation. Most modern construction uses cheap, efficient fiberglass batting or rigid foam panels. But these have drawbacks. Fiberglass is irritating to work with because its microfibers cling itchily to clothing and skin, and can be inhaled. Rigid foam produces chlorofluorocarbon (CFC) in the manufacturing process (it damages the ozone layer) and can continue to outgas chemicals into the living space long after construction is complete.
Several more sustainable materials have been available for years, and are now more widely distributed.
Cellulose insulation is made from recycled paper, mostly old newspaper, treated with fire-retardant borate chemicals that also help prevent mold and mildew. Cellulose is a good solution for upgrading older houses, because it can be poured directly into attic spaces and into hollow walls. A spray-on variant can be injected into walls, where it seals up gaps in the siding. I once lived in a geodesic dome insulated with sprayed-on cellulose. It was like living inside a tennis ball, but was amazingly warm and comfy.
Rock wool, or mineral wool, was introduced to the market in 1934. It’s made very much the way fiberglass is manufactured: a solid raw material is melted, then spun into fiber batting.
The raw material is iron slag, a waste product of pig iron manufacturing. Some rockwool manufacturers claim that 90 percent of their raw materials come from recycled sources, and that using it can earn a building up to 20 LEED credits.
Because it’s essentially a metallic material, it doesn’t support mold and mildew, and unlike other mineral insulations (asbestos, for instance) it’s noncarcinogenic. It’s also fireproof. As long as the wall holding it up stays in place, rock wool will halt the advance of flame.
Cotton batting is just what it sounds like: cotton fiber recycled from denim scraps supplied by the clothing industry. It’s thermally bonded, using no glue materials to outgas into living spaces. Batts come in a variety of thicknesses, with insulating values up to R-30. The stuff is comfortable to work with.
A side benefit of using cellulose and cotton is that growing the stuff locks up some atmospheric carbon dioxide.
- For more information on cellulose, see greenfiber.com
- For more information on rock wool, see thermafiber.com
- For more information on cotton batting, see bondedlogic.com
— Seth Masia