Architects currently have an increasing number of choices when it comes to specifying insulation in buildings. Among the criteria for selecting the most appropriate choice for a particular project are thermal performance over time, water and moisture resistance, and the impact on the rest of the building design. Included in this latter criterion are things like fire resistance properties, depth of insulation required, dimensional stability and overall cost. In light of all of these desired attributes and design criteria, one insulation type is emerging as a preferred material selection for many building types for both new and retrofit applications – stone wool insulation.

Properties of Stone Wool Insulation

Stone wool was discovered at the beginning of the 20th century on the islands of Hawaii where it occurs naturally as a byproduct of volcanic activity. The primary rock involved is basalt which is an igneous rock and very common in volcanic areas and the ocean floor. In addition, slag, recycled from a variety of industrial sources, is used to add to the overall properties of the finished product.

Manufacturing Process
Zero Waste to Landfill
In its manufactured state, stone wool combines the traits of rock with the characteristics of typical wool insulation. It is in fact manufactured from natural, inorganic stone to create natural fibers with no blowing agent used. The typical production process for stone wool begins with the fusion of volcanic rock at a temperature of 1500° C (2732°F). Volcanic rock, slag and coke are automatically fed from the top of a cupola furnace. The melt runs out of the bottom of the furnace and onto a machine, where wool is literally spun. Minor amounts of organic binder and oil are then added, and the wool is collected on a belt conveyor in a collection chamber. The structure and density of the wool are adjusted on a forming table which helps determine its final use as either a batt or board product. In either case, the wool fibers are typically non-directional which is important for achieving the multiple performance characteristics of the final product. It then moves to a curing oven where these final properties are maintained after the organic binder has been cured.

Stone wool is manufactured from natural inorganic materials, and no blowing agents. Image courtesy of Roxul Inc.

Once cured, the wool emerges with non-directional fibers that contribute to its specific properties and capabilities. This finished product will proceed to cutting saws and packing equipment or is led to off-line equipment for special treatment. The off-gases from the production process coming from the furnace, spinning chamber, and curing oven are typically cleaned in filters and after-burners before entering the chimney. The waste inevitably created during the production is fully recyclable.

Dimensional stability
Stone wool retains its manufactured characteristics unaltered over time. The term dimensional stability is generally defined as the materials ability to retain its original shape when subjected to external forces such as varying degrees of temperatures, atmospheric pressures, moisture content and/or other external stresses. Dimensional stability in relation to thermal insulation is a physical characteristic that is sometimes overlooked when a designer or specifier is determining which type of insulation to use for a project, particularly on roofing applications. Neglecting the dimensional stability characteristics can potentially result in the reduction of the effective R values, increased energy costs, increased environmental impacts (CO2) and the unexpected replacement of building materials due to stress and fatigue.