Stone wool rigid insulation boards for roofing typically carry UL and FM, and local fire ratings. Image courtesy of Roxul Inc.

Roofing Applications
Insulating a commercial, institutional, or industrial roof has often relied on foam plastic insulation which carries some concerns and limitations, some of which have been previously noted. Stone wool board insulation products have emerged as a real alternative to foam plastics with very attractive performance, cost, and green building characteristics. This is generally true whether flat or tapered insulation boards are used and whether addressing new construction or re-roofing of an existing building. Attention should be paid to variations in manufactured products for these different types of installations, and these conditions can be addressed. For example, some products are available with an impregnated bitumen layer which is compatible with torch or mop applied membrane. Other stone wool board products are intended for use with mechanically fastened or ballasted traditional and single ply membranes. In certain cases, the designer may opt for a hybrid system which combines both stone wool and plastic insulation.

Among the considerations for specifying and detailing stone wool roof insulation, the following should be considered:

• LEED® EBOM Gold certification re-roof project on the Empire State Building 2011/2012 using stone wool insulation. Image courtesy of Roxul Inc.

  Stable R-value – as demonstrated by NRCA testing, the R-value of many plastic foam insulations degrades over time, while the R-value of stone wool insulation remains stable. This is important for the long term performance and durability of the roof system and the building.
• Dimensionally stability – avoiding movement of the insulation board, even at the industry standard level of 2% for foam plastics, means avoiding gaps in the insulation. That translates into ongoing full coverage of the roof deck with insulation and no undue strain on the roofing membrane that needs to bridge gaps. Similarly, the shape stability of stone wool boards means that they are not prone to warping or cupping.
• Low moisture absorption – even in the best roofing assembly, the concern arises on how to deal with any moisture that may enter through condensation or penetration. In many systems, such penetration renders the insulation ineffective and requires replacement. Stone wool roof insulation boards repel water and dissipate moisture vapor away from the surface, alleviating stress on the membrane.
• Impact resistance – stone wool has tested stronger and more forgiving than foam plastics making it more resistant to hail and other impacts on the roof, including those caused by people during construction and maintenance.
• Fire resistance – UL classifications for roofing assemblies are critically important for safety and meeting code requirements. Using non-combustible insulation such as stone wool can be shown to exceed those minimum requirements and standards.

Conclusion

The unique combination of properties in stone wool insulation makes it a very versatile and attractive solution for insulating buildings. The natural stone material that it is made out of makes it more durable, sustainable, fire resistant, denser, and water resistant than other insulation materials. The variety of products available makes it an appropriate, long-term energy efficient solution for many exterior and interior applications.

Peter J. Arsenault, FAIA, NCARB, LEED-AP is a practicing architect, sustainability consultant, and free-lance writer based in New York State focused on work related to design, sustainability, and technology solutions nationwide. He can be reached at www.linkedin.com/in/pjaarch

Roxul Inc. is part of Rockwool International, the largest producer of stone wool insulation in the world. Roxul has achieved ICC-ES SAVE third-party certification for recycled content, with a minimum 75%, and certified up to 93%, on all products produced in the Milton facility. www.roxul.com