Yesterday we told you about a great construction material, cellulose insulation. Another great material you may have noticed popping up in a lot of our house tours is Rockwool Insulation, also known as mineral wool or slag wool. That's right - just like fiberglass insulation is essentially spun glass, Rockwool is literally rock that has been melted and spun into fibers...
Rockwool material is one of the oldest types of insulation composed of noncombustible fibers and can withstand heat in excess of 1,800 degrees F. Unlike fiberglass or cellulose insulation, mineral wool does not melt when exposed to such high heat, thus the reason it is often used as a fire barrier. Additionally, unlike other treated insulations, Rockwool’s natural properties make it inherently flame, mold and rodent retardant.
The material is made by melting basalt and iron-ore slag that is melted, spun into fibers and held together with a phenolic resin (the process is similar to the production of cotton candy). The U.S. Government’s (EPA) Comprehensive Procurement Guidelines require 75% recycled content for mineral wool, so most Rockwool products are made with anywhere from 75-90% pre-consumer recycled slag from iron manufacturing.
One negative aspect of Rockwool is as with most fiberglass insulation, Rockwool insulation uses a urea-extended phenol formaldehyde binder. However, according to the industry, almost all of the formaldehyde in mineral wool insulation is eliminated in the production process through a chemical reaction and high heat.
Rockwool has an R-value of 4/inch and can be installed using a number of methods: wet sprayed, net & blow, loose fill and it also comes in batts and rigid boards. It also works as an excellent sound barrier.
Rockwool has been used as an insulator for years in Europe and in recent years has been gaining momentum in the states. Rockwool will typically cost around 1 ½ - 2 times the price of fiberglass, but as it increases in usage the price will continue to drop. Look for it in your local hardware store such as Home Depot; other distributors include Certainteed (under the name Thermafiber) and Roxul.