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.

In Toronto, Canada, the renovation of the Gemini Home offers a unique opportunity to see how areas with older homes can radically transform the energy performance of these structures while maintaining them intact. This low-energy retrofit of a masonry home built almost 140 years ago is a living example of how older structures can be rescued from demolition, allowing homeowners to enjoy the structure's sturdiness while benefitting from 21st-century energy-efficient standards and a livable contemporary interior.

The retrofit of the Gemini Home, situated on the campus of the University of Toronto, has been the result of a long-term collaboration in low-energy retrofit research between the University of Toronto and Ryerson University.

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.

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.

Final Words 

The Gemini House retrofit project has proven that older, historic homes do not need to be torn down to have an energy-efficient home. Through the retrofits described above, the Gemini House has achieved an R2000+ envelope while also allowing the home to take advantage of solar gain and storage. The unique NTED design approach gives occupants maximum flexibility for heating and cooling the home according to their needs.