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ERA Architects


Gemini House exceeds expectations

by ERA Architects


Recent data shows that Gemini House, a green retrofit of an 1880s Second-Empire home, is a real success, with energy savings up to 72% reduced from current Ontario standards. For this project, ERA collaborated with University of Toronto and Ryerson University to transform a poorly performing heritage home into a model for sustainable design. The project challenges a common misconception that heritage architecture and sustainable design do not mix.­

Looking from dining to living room, periphery to core. Note restored plasterwork and exterior-grade doors between interior spaces.

In the Gemini NTED Model, energy savings are achieved via two simple concepts:

  • minimizing the amount of space heated on a daily basis, and
  • re-capturing heat that would otherwise be lost to the outdoors.

The building is separated into two thermally isolated zones: “core” and “periphery.” Energy savings are two-fold:

  1. Less space is heated.  The core zone (kitchen, living room, bathroom, bedroom, totaling 921 ft²) is used daily and kept at room temperature. The periphery zone (guest room, formal dining room) is used and heated minimally, and brought to room temperature on demand. This reduces the portion of the house being heated daily by 1327 ft².
  2. Heat is reused that would otherwise be lost. The periphery zone surrounds the core, allowing it to capture and reintroduce heat to the core via heat pump technology.
Diagram showing core and periphery zones
Diagram showing core and periphery zones

In effect, the team built a house within a house. New and heritage design had to work harmoniously together while remaining distinct. The new design also had to not only function in service of the Gemini concept, but effectively communicate it as well. This was achieved through the use of views from one space to another, as well as expressive material and formal transitions at thresholds such as doors and windows.

south grill crop
Deep window frame  illustrates high-performance perimeter; CNC-cut grilles illustrate air exchange systems

Recent data shows that not only is the retrofit five or six times more energy efficient than prior to renovation, but that in fact it can achieve up to 72% energy reduction over the current Ontario Building Code standard for energy consumption.

The purple bar represents Ontario Building Code standards; the grey represents projected Gemini performance; the blue represents actual Gemini performance.
Light tubes bring natural light deep within the interiors, reducing the need for electric light during the day.

These numbers make Gemini House a very useful model for sustainability projects in cold climates, and a strong demonstration of how creative planning, design, and conservation methods can open new possibilities for how we conceive of and use heritage resources moving forward.

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