Built in 1967, the Ken Soble Tower is the oldest high-rise multifamily building in the portfolio of City Housing Hamilton, the housing corporation serving Hamilton, Ontario. This 18-story tower, containing 146 units of affordable senior housing, is now on track to become the first residential high-rise EnerPHit project in North America. With more than 730,000 units spread across thousands of similarly constructed concrete towers across Canada, this retrofit establishes a replicable model for rehabilitating an aging housing stock that remains critically needed. The project demonstrates that deep energy retrofits of post-war concrete towers are not only feasible but economically compelling when compared to demolition and new construction. For those exploring similar approaches, the Victorian Home Passivhaus Retrofit How A 140 Year Old Uk Cottage Met Enerphit Standards offers another perspective on applying EnerPHit principles to very different building types.
Why EnerPHit Made More Sense Than Demolition
Before committing to the retrofit path, CityHousing Hamilton evaluated several alternatives including sale, full demolition with rebuild, and capital repair. The feasibility study concluded that making significant energy performance improvements would cost substantially less than tearing down and rebuilding. Preserving the existing concrete structure also retains its embodied energy, dramatically reducing the overall carbon footprint compared to a new building. This decision aligns with findings from other projects, such as the Diy Passive House Retrofit Transforming A Drafty Marin County Home With Enerphit Standards, which similarly demonstrates that existing structures can achieve high performance without starting from scratch.
Several factors made the retrofit financially viable:
- The building was already scheduled for a major overhaul, meaning the EnerPHit upgrade added a cost premium rather than requiring a fully separate budget
- Extending the service life of the concrete structure avoids the enormous cost and disruption of demolition in a dense urban area
- Federal and provincial funding programs for affordable housing retrofits helped bridge the gap between standard renovation and passive house performance
- The 146 units of senior housing would remain occupied by existing residents after completion, preserving community ties
ERA Architects Incorporated, the lead architect, has been involved in Tower Renewal research since 2009. The firm completed the initial feasibility study in 2017, supported the funding search, and began design work in July 2018, with the tender process running through spring 2019. Graeme Stewart, principal at ERA Architects, noted that innovative projects of this type face inherent challenges, describing a gap in the market for Passive House retrofits of this scale in Ontario.
Tackling Thermal Bridges in a Concrete Tower
Existing concrete buildings present thermal bridging challenges that simply do not arise in new construction. These bridges range from the obvious structural elements to hidden pathways that quietly leak heat throughout the building envelope. The project team, which included Transsolar, JMV Consulting, and Reinbold Engineering alongside ERA Architects, methodically identified and addressed each thermal bridge. For a broader overview of this methodology, Enerphit The Passive House Approach To Deep Retrofit explains the standard approach to thermal bridge remediation in existing buildings.
The most significant thermal bridge was the existing balconies, which Stewart described as the biggest Achilles heel from an energy standpoint. In Europe, prefabricated balcony enclosures that reduce thermal losses are commercially available, but these products do not exist in the North American market, and creating custom solutions proved cost-prohibitive. Since Ken Soble serves senior residents, the existing balconies also failed to meet barrier-free accessibility standards. The solution was to remove the balconies entirely and replace them with Juliet balconies paired with full door-sized casement windows that open inward, enabling cross-ventilation during shoulder seasons.
Other thermal bridges addressed included:
- The concrete foundation slab, which was treated by surrounding it with a continuous layer of concrete-board-faced XPS insulation
- Roof drainage pipes penetrating the thermal envelope
- Sanitary stacks, which required an innovative solution in the form of air admittance valves (AAVs) that close automatically when plumbing is not in use
- Garbage chutes, another less-obvious penetration through the building envelope
The AAV solution required approval as an alternative to the standard building code, and Stewart credited the Hamilton building department for investing in Passive House training that enabled them to evaluate and approve these non-standard approaches. The project also secured approval to use fiberglass-framed windows in a high-rise application, which are typically prohibited in noncombustible construction. This submission referenced upcoming changes to the National Building Code of Canada and represented one of the first uses of fiberglass-framed windows in a residential high-rise in Ontario.
The Wall Assembly and Insulation Strategy
The wall assembly underwent significant revision during the design process. The initial plan called for an exterior insulation and finish system (EIFS) with mineral wool insulation applied to the exterior face. However, when interior drywall was removed, the team discovered mold embedded within the existing wall assemblies, forcing a redesign of the approach. The solution involved a dual-sided insulation strategy. The Diy Deep Energy Retrofit How One Homeowner Achieved Enerphit In The Scottish Highlands demonstrates a similar commitment to thorough envelope treatment, albeit at a very different scale.
The final approach combines two insulation layers:
| Location | Insulation Material | Thickness | Purpose |
|---|---|---|---|
| Exterior wall face | Rigid mineral wool (EIFS system) | 6 inches | Continuous external thermal break, noncombustible cladding |
| Interior of exterior walls | Mineral wool batt | 4 inches | Additional thermal resistance after drywall removal |
| Foundation perimeter | Concrete-board-faced XPS | Continuous layer | Thermal break at slab-on-grade |
The EIFS cladding system was chosen partly for its lower embodied energy compared to petroleum-based insulation products. This mineral wool system is widely used in European housing developments but remains uncommon in North America. The exterior insulation is noncombustible, an important consideration for high-rise residential buildings where fire safety regulations are stringent. By addressing both the interior and exterior of the wall assembly, the team achieved the thermal performance required for EnerPHit certification while also resolving the moisture issues discovered during demolition.
Mechanical Systems and Overheating Prevention
Once the thermal envelope is upgraded, a building as dense as Ken Soble Tower presents an unusual challenge: the heating load becomes very small even in Hamilton’s heating-dominated climate, while cooling and dehumidification become more significant concerns. Overheating is a known issue in large multifamily Passive House buildings, particularly during summer and shoulder seasons. The team conducted extensive dynamic thermal simulations to identify which units might be most susceptible to overheating and to evaluate specific mitigation measures. The Deep Energy Retrofit Of A Historic Carriage House In Brooklyn To Enerphit Standards faced similar balancing challenges between heating and cooling demands after envelope upgrades.
The mechanical design incorporates several complementary strategies:
- A centralized heat pump that handles both heating and a modest amount of cooling, rather than separate systems for each
- Ceiling fans installed in each suite to increase air movement and improve perceived comfort without mechanical cooling
- The option for occupants to boost conditioned air supply within their unit on a short-term basis during heat events
- Glazing with a solar heat gain coefficient (SHGC) of 0.378 on the south, west, and east facades to manage solar heat gain
- Low-emissivity interior shades on all windows, since exterior operable shading systems remain difficult to source in North America
- Dehumidified tempered air delivered directly to each suite for humidity control
The ventilation strategy also underwent a significant upgrade. The original system supplied conditioned air only to the corridors, relying on pressure differentials to push fresh air into the apartments. The existing ductwork was refurbished, and new ducts were added to deliver fresh air directly into each suite. Energy recovery ventilators (ERVs) were installed in the basement and in a mechanical penthouse on the roof, providing efficient heat and moisture exchange. A centralized ventilation system was chosen over unitized systems for cost-effectiveness and maintainability in a 146-unit building.
Lessons for the Future of Multifamily Retrofits
Ya’el Santopinto, ERA Architects’ project lead, emphasized that a complex retrofit with demanding performance targets requires a holistic approach. Every stakeholder from the design team to the trades on site must understand the constraints and targets. This includes training for air tightness specialists, often called an air boss, who maintains the integrity of the airtightness layer throughout construction. The Enerphit In Practice Retrofitting A Manhattan Townhouse To Passive House Standards similarly highlights the importance of rigorous quality control and specialized craftsmanship in achieving EnerPHit certification.
Key takeaways from the Ken Soble Tower project include:
- Early engagement with building authorities is essential. The Hamilton building department’s investment in Passive House training enabled approval of alternative solutions such as fiberglass windows and air admittance valves
- Existing conditions cannot be assumed. The discovery of mold behind interior walls forced a redesign of the insulation strategy, adding interior insulation to the original exterior-only plan
- Market gaps exist for specialized passive house components in North America. Prefabricated balcony enclosures and exterior shading systems common in Europe are not yet readily available, requiring creative alternatives
- Owner and operations teams need education on how a Passive House building functions differently from conventional buildings in their portfolio
- Dynamic thermal modeling should account for future climate scenarios, not just current conditions, to ensure occupant comfort over the building’s extended service life
The projected reduction in greenhouse gas emissions for the retrofitted Ken Soble Tower is 94 percent compared to the pre-retrofit baseline. This level of performance, achieved in a 1960s concrete tower, demonstrates that deep decarbonization of the existing building stock is technically achievable even in the most challenging building types.
Conclusion
The Ken Soble Tower EnerPHit retrofit proves that post-war concrete high-rises, often dismissed as obsolete, can be transformed into high-performance assets that serve their communities for decades to come. With over 730,000 similar units across Canada and countless more worldwide, the replicability of this model has enormous implications for affordable housing, climate policy, and urban sustainability. The project demonstrates that holistic thinking, regulatory collaboration, and a willingness to adapt standard approaches to non-standard problems are the ingredients for success. For a broader perspective on applying these lessons to other multifamily buildings, see Passive House Retrofits For Multifamily Housing Lessons From The Ken Soble Tower, which explores how the strategies developed here can inform similar projects across the housing sector.