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

by arslan_ahmed | January 12, 2024 10:00 am

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By Mahnaz P. Nikbakht

Passive House construction is gaining momentum in cities worldwide, as advancements in building materials and construction techniques continue to unfold. With the accumulation of expertise and experience, along with the growing affordability and accessibility of components, Passive House construction is becoming increasingly feasible. This movement is further supported by various programs, grants, and incentives available for builders. Advancing government policies and stricter building codes, combined with the realities of climate change, have further underscored the benefits and practicalities of future-proofed and resilient buildings, prompting an evolution in how buildings are designed and constructed.

The pursuit of a higher performance-built environment is becoming increasingly urgent. To even come close to meeting the global warming limit of 1.5 C (2.7 F) set by the Paris Climate Agreement, it is estimated that a 40 to 50 per cent reduction in global greenhouse gas (GHG) emissions is needed by 2030.

The built environment represents significant potential for climate action and emissions reductions. In 2020, the Government of Canada reported the country’s building sector comprised 14.1 million households and 482,000 commercial or institutional buildings, while buildings overall accounted for 17 per cent of Canada’s GHG emissions, when the emissions associated with electricity use in buildings was included. The burning of fossil fuels for space heating accounted for the largest share of these emissions. With the building sector identified as the third-highest producer of carbon emissions in Canada,¹ the need to reduce its carbon footprint is clear. The path, however, can be challenging. The Passive House standard offers a proven and scalable solution.

Passive House is an internationally recognized, science-based approach to energy-based design and construction that emphasizes greater attention to the building envelope to achieve superior energy efficiency, occupant comfort, and well-being. It is a voluntary and rigorous standard that aims to minimize heating and cooling loads through passive measures including higher insulation levels, reduction in thermal bridges, the use of high-performance windows, airtightness, heat-recovery ventilation, as well as passive solar energy and shading. Active elements require energy in order to work. A high performance envelope reduces the amount of energy needed to maintain a comfortable environment (smaller or no heating and cooling equipment).

Successful Passive House design can reduce the energy required to heat or cool a building by 70 to 90 per cent compared to conventionally designed and constructed buildings, reducing the operational carbon footprint. Passive House Canada states, “Passive House is recognized by the United Nations as the optimal way to build healthy, climate-resilient, affordable, energy-efficient residential, institutional, and commercial buildings through all stages of design, construction, and livability.”

In North America, Passive House requirements are set out by two organizations: the International Passive House Institute (PHI) in affiliation with The Passive House Network (PHN), and the Passive House Institute US Inc. (PHIUS) in affiliation with Passive House Alliance US (PHAUS).

Any type of building can be certified as a Passive House project. The approach is scalable and can apply to both new and existing buildings. Passive House buildings are designed using Passive House Planning Package (PHPP) software, which now also includes the Passive House Network (PHN) PHribbon² to calculate associated embodied and operational carbon emissions, allowing an architect or builder to specify the right combination of insulation and components necessary to bring any building to the required performance standard in any given climate zone. Passive House buildings have been completed in many severe climates, from central Russia and Finland to northern Sweden, and in Canadian cities such as Winnipeg and Vancouver.

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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:

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○ Repeated (often found within the structural component of the enclosure and considered in the overall U-value calculation [e.g. steel and/or wood studs].)

○ Linear (expressed as a Psi value [Ψ] and calculated using a 2D thermal modelling software, found along the length of the enclosure occurring mainly at component joints, edges, and transitions within the building enclosure [e.g. a window-to-wall connection or slab edge].)

○Point thermal bridge (calculated using a 3D thermal modelling software and expressed as a Chi Value [X], these occur at isolated points within the enclosure [e.g. insulation attachments and/or fasteners].)

• High-performance windows—The use of triple-pane, high-performance windows that are Passive House certified are recommended for compliance, because this shortens the building certification process. Window-to-wall ratios are calculated and determined based on the orientation, glazing type, and shading mechanism to take maximum advantage of passive solar gains without risking overheating.
• Airtight enclosure—A leaky building enclosure leads to excess heat transfer, cold spots, and the potential for condensation. To achieve a continuous, airtight enclosure, close attention to detail is required at all joints and penetrations. The airtightness of a Passive House is measured by means of a blower door test.
• Heat recovery ventilation—Appropriate mechanical ventilation systems are critical to ensure clean and fresh air intake and occupant comfort. High performance energy recovery systems (energy recovery ventilator [ERV] or mechanical ventilation with heat recovery [MVHR]), required for Passive House, help reduce energy losses by taking advantage of heat energy from extract air.
• Building orientation—The orientation of a building is a crucial element in Passive House design to help with managing solar gains and losses. It is equally important to consider the influence of seasonal prevailing winds, as well as the effects of tree and building shading, on the overall performance of the building. These factors greatly impact the energy efficiency and comfort of the space and must be carefully considered during the design process.

Building enclosure requirements

• U-value recommendations:

○Opaque wall and roof U-value ≤ 0.15 W/m²K (0.03 Btu/F•hr•sf)

○Fenestration (triple-pane windows) Ug-value ≤ 0.80 W/m²K (0.14 Btu/F•hr•sf) and G-value:
0.5 to 0.62

• Thermal bridge free:

○Linear thermal bridge = Ψe ≤ 0.01 W/mK

○Point thermal bridge = X ≤ 0.005 W/m²K³

• Airtightness:

○≤ 0.6 ACH @ 50Pa

The benefits of Passive House and stone wool

Passive House buildings incorporating stone wool insulation contribute to performance objectives and allow for considerable design freedom in the building envelope design.

Depending on the construction type, above-grade wall assemblies can be designed using either only exterior ci or in combination with interior insulation to create a split-insulated assembly. For wall studs, stone wool stud cavity insulation (thermal batts) can be friction fit between studs.

Semi-rigid and rigid stone wool boards are a beneficial option as ci for above-grade rainscreen wall assemblies. Water repellent yet vapour permeable, they can be installed on the exterior side of a wall assembly.

In high-performance roof systems, high density stone wool roof insulation boards contribute to excellent thermal performance, superior acoustic performance, and fire resilience. Stone wool boards also have a much lower co-efficient of expansion and contraction, which results in increased dimensional stability over temperature changes and, therefore, minimal gapping between boards. This is an important characteristic contributing to the performance and durability of the roof assembly. By contrast, products with less dimensional stability (e.g. foam plastics) can experience greater expansion over time, larger gaps between boards and, therefore, decreased effective thermal resistance.

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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.

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Material selection and detailing are integral for achieving Passive House performance goals. Stone wool insulation solutions are available for a wide variety of wall systems that address necessary high insulation levels along with constructability in Passive House projects. Passive House solutions and guidance for a full range of stone wool assemblies/applications as well as project-specific options are available from the manufacturer.

Since Passive House buildings are aiming for a sustainable performance and a reduction in operational carbon, opting for sustainable materials with low lifecycle impacts makes sense. Product data and transparency is increasingly important in the pursuit of low carbon buildings. This includes certification and listings, EPD, life cycle assessment (LCA), Health Product Declarations (HPDs), and voluntary participation in the Declare labelling program that promotes healthy building materials through product transparency and ingredient disclosure, including the Declare Label for Red List Approved, for example.

Low carbon insulation solutions, such as stone wool, with product-specific EPDs linked to Embodied Carbon in Construction Calculator (EC3) databases, including the PHN PHribbon, allow architects and designers to review carbon data prior to making decisions and to optimize building designs to consider total cradle-to-grave carbon emission outcomes. This can also help balance project goals—including the anticipated environmental, societal, occupant, and operational benefits—with costs.

Case study: University of Victoria student housing and dining

Architects Perkins+Will have demonstrated the significant potential of a Passive House approach extends well beyond traditional residential construction and can be scaled up to include all types and sizes of buildings. In fact, the firm states they are “committed to help bring the country’s first generation of large-scale, complex civic, institutional, and commercial Passive House buildings to life.”

This goal was achieved with the University of Victoria (UVic) student housing and dining complex. The mixed-use development spans an impressive 31,000 m² (333,681 sf) and comprises two buildings. It seamlessly integrates 782 student residence rooms, a spacious 600-seat dining hall, as well as conference, academic, and common spaces. The buildings (officially named Čeq^wәŋín ʔéʔlәŋ or Cheko’nien House and Sŋéqәʔéʔlәŋ or Sngequ House) were designed to Passive House standard and, if certified, will be among the largest Passive House buildings in Canada and the first Passive House buildings at the University of Victoria.

With super-insulated and airtight envelopes, both exceed Step 5 of the BC Energy Step Code—the highest level for efficiency in the province. The project also includes the largest commercial kitchen ever integrated into a Passive House building.

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Cheko’nien House includes an electrified commercial kitchen which is six times more efficient than a conventional gas-powered commercial kitchen. This will help contribute to a reduction in GHG emissions by 80 per cent for the whole building.

The design and construction of the UVic student housing and dining project is reflective of the university’s commitment to a low carbon future as outlined in the “UVic Climate and Sustainability Action Plan 2023,”⁴ which aims to bolster climate action and sustainability while advancing the United Nations Sustainable Development Goals (UN SDGs).⁵ The new complex (Cheko’nien House and Sngequ House) represents a dramatic 90 per cent reduction in its net carbon footprint compared to the buildings they replaced.

In addition to targeting Passive House certification, the complex is also targeting LEED v4 gold. Both Cheko’nien House and Sngequ House represent best practices in energy-efficient, sustainable design, while emphasizing occupant comfort and well-being, social connection, and engagement. The project’s exterior wall system incorporates 203 mm (8 in.) of stone wool ci for a ventilated rainscreen strategy that serves a number of important functions. Key goals included:

• Radical energy efficiency.
• Extremely low operational carbon.
• Reduced GHGs.
• Superior thermal comfort and indoor environmental quality.

The institute also sought to address climate change by building for resiliency to 2050 climate projections, futureproofing in terms of performance, while endeavoring to meet the university’s climate commitments to the Clean BC Plan and those outlined in its Sustainability Action Plan. The project teams had to balance additional goals such as fire protection, moisture management, climate resilience, durability, air quality, circularity, transparency, acoustics, and more. Stone wool insulation contributed to each of the outline performance objectives.

Notes

¹ See the Government of Canada – Natural Resources Canada at natural-resources.canada.ca/energy-efficiency/green-buildings/24572.

² Refer to https://passivehousenetwork.org/phribbon.

³ For more details, see the blog by Passive House International at blog.passivehouse-international.org/summer-comfort-passive-house.

⁴ Visit www.uvic.ca/about-uvic/climate-sustainability-plan/index.php.

⁵ Consult https://sdgs.un.org/goals.

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Mahnaz P. Nikbakht is the architectural specifications manager at ROCKWOOL North America and president and chairperson of the Quebec Passive House Association (Bâtiment Passif Québec). With more than 20 years in the building materials industry, Nikbakht has served as a civil engineer, technical application engineer, product manager, and sales and business development manager in Europe and North America, as well as a representative in European Committee for Standardization (CEN), International Organization for Standardization (ISO), and ASTM standardisation committees. Her expertise span from concrete and geosynthetics to drainage, waterproofing, and insulation materials. Nikbakht can be reached at mahnaz.nikbakht@rockwool.com.

Source URL: https://www.constructioncanada.net/how-stone-wool-and-passive-house-are-shaping-a-low-carbon-future/

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