How stone wool and Passive House are shaping a low-carbon future

Fire resistance

While Passive House requirements call for higher insulating values and the use of exterior ci, designing with fire resistance and life safety in mind is essential. Stone wool insulation resists fire to temperatures of 1,177 C (2,150 F), and it works to contain fire and prevent its spread. At the same time, it does not contribute to the emission of significant quantities of toxic smoke even when directly exposed to fire. This provides a critical line of defence, helping keep occupants safe and potentially reducing property damage in the event of a fire.

Stone wool dual-density roof boards, either standard, bitumen-coated, or with a mineral-coated fibreglass facer, can be installed in low-sloped roof applications, above deck. Dual-density stone wool roof boards provide strong point load resistance and effective load distribution to minimize puncture damage to the membrane—particularly during installation.

Optimal thermal performance

Stone wool insulation is a choice that fits with the long-term thermal performance and stable indoor temperatures that are characteristic of Passive House buildings. The R-value of stone wool insulation will not change over time because it is not produced with blowing agents, which can off-gas and result in lower long-term thermal performance. Not only is the thermal performance of stone wool insulation maintained over its lifetime, but it also works as a buffer against fluctuations in temperature. The result is a stable building enclosure which, when achieved, can help dramatically reduce heating, cooling, and ventilation costs, and reduce a building’s carbon footprint.

Vapour permeability

Insulation products, membranes, and other building materials all have varying levels of vapour permeability and can potentially function as a vapour retarder. When designing enclosures with thick insulation levels, consideration with regards to the appropriate use of vapour retarders is critical. Depending on the geographic location of the building, the vapour retarder profile should be either on the interior or exterior side of the enclosure. For Passive House buildings, in combination with a vapour permeable water-resistive barrier (WRB) membrane, the use of vapour permeable exterior insulation, such as stone wool, allows for increased potential for drying without trapping moisture in the assembly. In addition, the use of vapour retarders on the interior side, also known as “smart vapour retarders,” enables drying potential to the interior, and further enhances the durability of the enclosure.

Acoustic control and comfort

The acoustical performance of a building envelope is critical when designing for a high-performance system. Noise will travel through the weakest sections of the building envelope, and the effectiveness of a high-performing wall or roof system may be reduced when the rest of the building is not equally designed for sound attenuation. As a component of wall and roof assemblies, stone wool insulation can reduce external noise, creating a comfortable and healthy living space. The density and non-directional fibre structure of stone wool makes it efficient at absorbing sound and reducing its transmission through enclosure assemblies.

Stone wool insulation in wall assemblies has similar or slightly higher Sound Transmission Class (STC) values compared to fibreglass insulation. Stone wool shows better performance at very low frequencies (below 80 Hz) with transmission loss values up to 1 dB higher. At frequencies above 800 Hz, the differences can be up to 3 dB higher, resulting in overall better performance in a wider range of sound frequencies. Stone wool’s higher mass and airflow resistivity contribute to its better performance at high frequencies compared to fibreglass insulation.

Proper installation of fibrous batt insulation is crucial for achieving a tested assembly’s evaluated performance. Stone wool, with its higher density and increased compression and pull-out forces, allows for a much tighter fit in the cavity, reducing compression of the batts, which can result in a higher performing wall.

Efficient cladding attachment systems

There are numerous generic and proprietary cladding support systems designed for use with exterior insulation available today. Many different materials are used to make these systems including galvanized steel, stainless steel, aluminium, fibreglass, and plastic. While each system is different, the approaches can be classified as: continuous framing, clip and rail, long screws through strapping and insulation, and masonry ties or other engineered systems. Systems are available to accommodate a wide range of claddings for buildings of all heights and exposures. Thermally efficient cladding attachment systems are critical for Passive House buildings to mitigate thermal bridging. Stone wool is compatible with a broad array of claddings and cladding support systems.