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

An enclosure-first strategy is key to performance goals

Passive House design necessitates an enclosure-first strategy focusing on “passive” principles to achieve low-energy intensity targets. Not only does the Passive House standard encompass all aspects of energy performance, but it also bolsters sustainability and resilience. The key benefits include:

• Energy efficiency—High R-value requirements reduce the energy demand of buildings up to 90 per cent in comparison to existing buildings, and 70 per cent in comparison to typical new constructions. This low-energy demand of Passive House results in smaller mechanical systems. As such, the energy consumption to power electricity and the total embodied energy of the construction materials used in Passive House buildings becomes more significant.
• Occupant comfort—The high-performance enclosure in combination with stringent demands for mitigating thermal bridging and air leakage results in more even interior surface temperatures, reducing cold draughts and the potential for condensation which can lead to poor indoor air quality (IAQ). Further, a highly insulated building enclosure helps improve indoor acoustics, creating a productive work environment, a healthy home, a peaceful place to recover, and greater comfort overall. Finally, the ventilation system combined with airtightness provides good air quality and offers different filtration options to reduce effects of smoke (wildfire) and pollen to occupants.³
• Sustainability and resiliency—In severe weather occurrences, should mechanical systems fail, a high-performance building enclosure increases the thermal autonomy of a building where the building can passively maintain comfortable conditions without the use of active systems. Further, the airtight and well-insulated envelope in Passive House construction makes buildings safer and typically more durable, as airtightness can help with risk mitigation, including moisture management.

When the building enclosure includes stone wool insulation, a wide variety of performance goals and benefits can also be realized, while providing occupants with improved indoor environmental quality that contributes to overall comfort and well-being. The thermal resistance of stone wool insulation is generally comparable to other common insulation materials, such as glass fibre, cellulose, expanded polystyrene (EPS), extruded polystyrene (XPS), and open-cell spray foam. The R-value of some stone wool insulation products is approximately 4.0 to 4.3 hr•ft2•F/Btu per inch. The embodied carbon of stone wool insulation ranges depending on the product and application. Therefore product-specific Environmental Product Declarations (EPDs) will provide the highest level of transparency and performance specifications for a project.

Principles of Passive House

With the right materials and assemblies, the performance requirements of Passive House, while strict, are achievable. The principles of Passive House design are fairly straightforward. The greatest opportunity for superior performance exists in thoughtful material selection, as well as careful, holistic design and construction of the building envelope, by addressing the following:

• Highly insulated walls—With high R-value walls, considerations for moisture transport and drying potential, as well as fire codes and life safety, are critical. The thickness and location of the thermal insulation depends on the type of structure, with optimal performance achieved when using all (or mostly) exterior continuous insulation (ci).
• Thermal bridge-free: free—A thermal bridge is a localized area or component of the building enclosure with a higher thermal conductivity than the surrounding materials, creating a path for heat transfer. Three types of thermal bridges must be addressed: