Airtightness is a critical element of Passive House construction, alongside an integrated and controlled ventilation strategy to ensure good indoor air quality for occupants. This case study highlights a recently completed offsite-constructed, modular timber frame home in Ontario, Canada.
Designed and built to achieve the Passive House standard, this self-build project was initiated by a couple in Ontario who wanted to downsize and build a future-proof, energy-efficient home. With this in mind, their goal was to create a comfortable, high-performance residence with predictable running costs in a climate with both extreme heat and cold typical of Southern Ontario. Passive House certification offered a structured path to resilience against these extremes.
To accomplish this, they collaborated with EkoBuilt, a Canadian company specialising in Passive House construction and also well versed in traditional timber frame construction (used for the screened porch they envisioned).
Although Passive House originated in Europe with a strong focus on minimising heat loss, the Canadian climate required the team to adapt the design for greater extremes. In particular, Ontario’s hot summers and harsh winters meant the building had to perform in both heating and cooling seasons. To meet this challenge, the project followed the Passive House Institute (PHI) certification, with modelling and detailing aligned to these strict standards — in fact, stricter than some regional energy codes in both the EU and Canada Airtightness and insulation detailing were adapted to suit Ontario’s humidity shifts and freeze-thaw cycles, ensuring durability and comfort year-round. Abundant natural light was included without risking overheating, thanks to careful solar orientation and shading design. A local carpentry team, new to Passive House, successfully executed the build using EkoBuilt’s builder handbook and documentation, demonstrating the accessibility of Passive House principles for conventional trades.
We needed a home that was manageable in terms of cost and maintenance. Building to Passive House standards allowed us to reduce our energy needs dramatically. We knew that air tightness would be a core factor in achieving that.” – Gillian Szollos, homeowner.
Main Challenges
Designing an airtight timber frame home to meet Passive House certification standards in the Canadian climate came with a range of technical and logistical challenges. The design team needed to deliver an exceptionally airtight building envelope, essential for minimising heat loss and achieving energy efficiency. However, the build was carried out by a local construction team with no prior Passive House experience, so the airtightness strategy had to be easy to implement with clear detailing. Additionally, the architectural design needed to balance solar gain, shading, and natural daylighting to prevent overheating during Ontario’s hot summers. A connected accessory dwelling unit (ADU) required flexibility to suit varied occupancy levels without compromising on performance. Finally, adapting European Passive House principles to the temperature extremes and moisture variations of the North American climate required high-performance, vapour-variable materials and smart detailing.
Solutions: Airtight Detailing with VARA SEAL Tape
To meet airtightness and energy performance goals, the project used Partel VARA SEAL tape, a smart, high-performance airtightness tape certified to phA class by the Passive House Institute. VARA SEAL was applied at all key junctions—wall-to-foundation interfaces, window openings, and roof junctions—to form a continuous airtight barrier critical to Passive House performance. The tape’s robust, solvent-free acrylic adhesive ensured a long-lasting seal on wood, OSB, masonry, and other substrates, while its split release liner enabled fast, accurate installation by the local construction crew. This ease of application helped bridge the skills gap and ensured the airtight detailing was completed to a high standard. Using VARA SEAL directly improved the thermal efficiency, moisture management, and long-term durability of the building envelope, contributing significantly to achieving full Passive House certification.
Smart Vapour Control with VARA PLUS Membrane
Within the accessory dwelling unit (ADU), managing indoor humidity levels posed a challenge due to changing occupancy. Partel’s VARA PLUS smart membrane was installed as the primary vapour control layer, offering dynamic moisture regulation. Its humidity-responsive vapour resistance helps maintain structural integrity and indoor air quality by adapting to seasonal and usage-based changes in moisture load, particularly important in timber frame buildings where long-term durability is linked to controlled vapour movement.
Structural Sealing with CONEXO Tape
Partel’s Alma Vert range minimises thermal bridging by introducing a high-insulation interface at critical junctions. These PET-based panels offer:
- Lightweight and compact design, ideal for offsite timber manufacturing.
- Lower thermal conductivity, reducing heat loss and condensation risks.
- Sustainable material composition, meeting high technical and ecological standardsTo ensure the long-term performance of airtight junctions, CONEXO high-bond tape was applied throughout the building envelope. This tape was selected for its ability to provide durable sealing of structural connections, particularly in high-movement areas such as corners and joint transitions. Its adhesive bonding strength contributed to continuous airtightness and helped support the Passive House goal by reducing potential leakage points in the structure..
External Weather Protection with EXOPERM MONO 150
On the exterior, the home was wrapped with EXOPERM MONO 150, a breathable weather membrane designed to protect the structure from wind-driven rain and moisture ingress. Its vapour-permeable design supports the drying capacity of the wall system, which is essential in cold climates with freeze-thaw cycles like Ontario. This layer forms part of the overall building envelope strategy, allowing outward drying while maintaining internal airtightness—balancing protection and breathability for high-performance timber construction.
Results
- Airtightness achieved to Passive House standards contributes to high thermal efficiency and indoor comfort.
- The local builder successfully executed the airtight layer with clear guidance and simple installation methods.
- Energy performance optimised, even with the inclusion of a flexible-use ADU.
- Predictable energy bills and future-proofing realised for the homeowners.
- Demonstrates feasibility of Passive House in harsh Canadian climate, with material resilience and vapour control essential to success.
Certified Passive House Verification
The project achieved Passive House Classic status according to PHPP verification (2024), with a treated floor area of 124.9 m². Space heating demand met the required threshold at 14 kWh/m²a, space cooling at 3 kWh/m²a, and airtightness verified at 0.6 ACH at 50 Pa. Non-renewable primary energy demand was calculated at 67 kWh/m²a.
Gillian reflected on the result: “It’s honestly the most comfortable house I’ve ever lived in. The heat stays in during winter, and we don’t even have to run air conditioning in summer. We just open the windows at night. That’s Passive House in action.”
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Conclusion
This Ontario Passive House case study proves that airtight, net-zero-ready homes are achievable in even the harshest climates with smart planning and the right materials. Products like VARA SEAL, Conexo, and EXOPERM MONO 150 CONNECT were instrumental in this build’s success, demonstrating the real-world value of quality air and vapour control systems.
