The Heirloom Supplementary Dwelling Unit: A Study in High-Performance Compact Living
At A Glance
Service: Full Service Integrated Design
Construction Spec: 4-Season | New Building | 650SF | $500/SF.
Engineering Focus: High performance for resilience and low operating cost. Vapour-open assembly for maximum drying potential and durability. High-efficiency heat pump with ERV/HRV mechanical ventilation for superior air quality.
Design Focus: Simple, timeless form. Durable, heirloom quality finishes. Flexible space plan.
The Brief
Design an heirloom quality building that can withstand the rigours of full time use while maintaining a timeless presence on the site for generations. The finished building is to be a fully self-contained supplementary dwelling (optimized for low operating cost and long term durability) that provides the comfort and performance of a primary residence within a compact footprint to conform with local zoning by-laws.
Our Approach
Engineering: We designed the building around a unique framing method that permits the installation of a continuous, uninterrupted air barrier, resulting in a performance-tested airtightness of less than 0.6 ACH @ 50Pa. The envelope was engineered with a vapour-open assembly to ensure long term durability. A high-efficiency air-source heat pump and dedicated energy recovery ventilation provide year-round comfort with minimal operational costs. Conventional framing combined with thick exterior insulation provides for easy maintenance with minimal heat loss.
Design: The architectural language draws on traditional cottage ideas and early 20th century institutional buildings. It is intended to look and feel like a building that has existed on the site for years. Cedar bevel siding and divided-lite windows evoke a classic cottage and cabin style, while the interior features custom-milled trim and site-finished, locally sourced pine flooring. Every proportion was calculated to maximize the sense of volume in a small space, utilizing lofted areas and a natural material palette to connect the interior to its surroundings.
The Result: Heirloom Quality Worth Investing In
This highly capable, energy-efficient building serves as an example for what we think a modern compact house should be. It balances performance with the tactile craftsmanship and subtle detailing of the heritage buildings we admire. The result is an heirloom quality building that is worth investing in.

