Toronto's Gemini House: Remaking an 1870s Masonry Home 

Unfortunately, thousands of old homes are torn down every year as homeowners consider new construction to be a sounder investment and better use of their money. From an ecological standpoint, however, studies have shown that the greenest building is almost always the one that is currently standing due to the embodied energy associated with the modern-day home built with a variety of building materials sourced from around the world.

The restoration of the Gemini House aimed “to provide an alternative way of retrofitting historic buildings using “Nested Thermal Envelope Design (NTED) approach.” In essence, this approach sought to build a “box within a box” through including two thermal envelopes divided between core and periphery areas of the home. Both thermal envelopes can control the movement of air, moisture, and heat, while the core area of the house is where most of the active heating and cooling happens.

For the Gemini House, the core area includes the kitchen and dining room and the master bedroom and bathroom. The periphery areas include the basement, a ballroom, and upstairs guest bedrooms. The retrofit strategy centered on pulling in the interior walls to increase the amount of high-performance insulation drastically. Both the core and periphery areas of the home are insulated separately from one another and are controlled by their thermostats. Thus, you could have one area of the house a toasty 70 degrees in the middle of the winter while the unused periphery area is significantly colder.

While the University of Toronto expects to use the home to host visiting professors (in the core area), its spacious ballroom or meeting room could also be used for larger events. Because of the “box within a box” design, the occupants can choose to only heat the parts of the house being used. The less square footage needs to be heated or cooled, the less energy required. The perimeter area of the home also acts as a solar recovery zone allowing for passive solar heating that even further reduces the energy demands of the house during the winter.

Energy Efficiency Measures 

Besides dividing the spacious 19th century home into two core and periphery that are heated separately, the Gemini House also includes several other energy efficiency measures and technologies. The home relies on a radiant floor system for heating while also including a heat pump as an alternative heat source.

Two energy recovery ventilators, or ERVs, were placed in the insulated basement crawlspace to condition incoming air for both the core and periphery areas of the home. The old windows were replaced with high-performance, triple-glazed windows everywhere except on the façade of the house where the university wanted to maintain the heritage look. The old windows that were replaced were used as storm windows in other areas of the home as a way to upcycle old but serviceable building materials.

For insulation, the floors were also super-insulated to protect the radiant floor system, which meant that the staircase was also raised. Since the ballroom is separated from the core of the home, a pair of heavy double doors helps to protect against any potential heat loss.