Encapsulation Methods: The distinct advantages of stone wool
To achieve an encapsulation rating of not less than 50 minutes, there are several encapsulation options that can be employed including:
- Two layers of not less than a 12.7-mm-thick Type X gypsum
- Not less than 38-mm-thick gypsum-concrete or concrete topping
- Other noncombustible material or assembly of materials that provide an encapsulation rating of 50 minutes
The use of stone wool insulation as an encapsulation material falls into the latter option. The material is well suited to the protection of structural elements. In fact, stone wool insulation is commonly used to protect elements in curtain wall assemblies and as fire-safing insulation in perimeter fire containment systems, as well as other applications where exceptional fire protection is required.
Third-party testing confirms that stone wool insulation products do not ignite, burn, support combustion or release flammable vapours when subjected to fire or heat as per CAN/ULC S114. Additionally, certain stone wool insulation products have been shown to achieve a 0/0 flame spread and smoke development rating, further demonstrating desirable characteristics when exposed to fire.
Stone wool insulation supports the need for fire protection redundancies to be built into wood buildings. The passive fire protection offered by stone wool—especially if it incorporated throughout the building—can help protect escape routes and support effective compartmentalization by potentially slowing the progression of fire. It facilitates safe egress and contributes to improved occupant safety.
Testing has shown that stone wool stays in place for a long time (well beyond 2 hours). This is significant, as the stone wool material remains in place to protect the wood from radiation long after the encapsulation time has been exceeded. Some other encapsulation materials have been shown to fall off after approximately 50 minutes, leaving the wood bare and unprotected. In fact, in the research report, Fire performance of mass-timber encapsulation methods and the effect of encapsulation on char rate of cross-laminated timber (Hasburgh et al., 2016), it was noted that “rock fibre insulation was able to improve encapsulation time by nearly 20 min, over a standard gypsum board application, and stay in place over 2 h.” This research also look at acoustic performance of the EMTC assemblies tested. It noted that rock fibre “can also provide the opportunity to improve acoustic performance and when used with a dropped ceiling will conceal building services without the need for sprinklering the concealed spaces.”
Of note to building industry professionals, as a general rule, it cannot be assumed that all mineral wool products offer the same fire performance. Architects and specifiers are encouraged to refer to manufacturers regarding product composition and fire testing data. For example, it is noteworthy that although stone wool (specifically ROCKWOOL stone wool insulation products) falls in to the category of rock fibre or mineral wool, its higher quality composition (optimized fibre chemistry, low shot content) offers a low linear shrinkage rate of no more than five per cent in the length dimension when tested in accordance with ASTM C356 at 1,000˚C. This (dimensional stability) is important when considering an encapsulation material, as it reduces potential exposure to the wood structure beneath due to shrinkage or gaps forming when exposed to fire. Conversely, slag wool, while also classified as a mineral wool, may not achieve the same performance, exhibiting greater linear shrinkage when exposed to fire. This is a result of uncontrolled fiber chemistry as a consequence of greater quantities of slag.
Stone wool’s excellent drying potential provides an important benefit during the construction phase, as well, protecting wood from the elements. Should stone wool get wet, either during construction or in service, the moisture-resistant product will dry out, retaining its full R-value and fire-resilient properties. Because it’s comprised of inorganic materials, stone wool is resistant to mold and mildew. This is a distinct advantage over hydrophilic products, which once exposed to moisture need to be replaced to prevent mold from forming. Using stone wool as an encapsulation material or as insulation for various applications in wood buildings allows construction to move forward with less concern around rain and weather.
Time on the job site is an important consideration, as well. Stone wool is light weight and easy to handle. Stone wool products, like ROCKWOOL COMFORTBOARD™, for example, come in a variety of thicknesses and can be applied as an encapsulation material in a single layer to achieve a high level of fire protection. Two layers of gypsum, meanwhile, are required to achieve a 50-minute encapsulation rating. There’s no drying time for stone wool or requirements for specific temperatures or conditions to exist prior, during or after install such as with other encapsulation products like spray-applied fire-resistive materials (SFRM), which is also not suitable for surfaces exposed to moisture or high humidity levels. In addition, the moisture may cause mold growth due to the porous nature of SFRM.