Rockwool Foundation Insulation
Some builders have always preferred rigid fiberglass over foam for insulating foundations. Fiberglass conforms to surface irregularities in concrete walls better than foam, and is made without the chlorofluorocarbons used in extruded polystyrene. Unfortunately, there are only two fiberglass boards left on the market. Neither is easy to find in the U.S., and one of them forces you to buy manufacturer's waterproofing membrane along with it. The Canadian-based Roxul, Inc. hopes to solve the supply shortage with a new product called Drainboard that's made not from fiberglass, but from high-density rockwool. The material contains 50 percent recycled slag and pure basalt stone.
Drainboard does the same job as fiberglass, but in a different way. While fiberglass serves as a drainage layer, Roxul's Drainboard is more of a water barrier, like foam. It has passed a number of water intrusion tests that showed it to be at least as good as fiberglass at keeping water away from the foundation. The manufacturer claims that it performs better over freeze-thaw cycles than foam, is more dimensionally stable and stands up better over time. It also costs less.
"We like to call it the next choice above sand," says company spokesman Tyler Nelson. It's available in Canada and the Northeast U.S.
Roxul Drainboard comes in 4x6 sheets that weigh 7 pounds each and have the same insulating value as fiberglass at around R-4 per inch.
Find Roxul, Inc. in the Oikos Product Directory
This article appeared in Energy Source Builder #43 February 1996,