AIA Homes Tour veteran architect David Baker opened his Shotwell Residence again this year as part of the annual Architecture and the City festivities in San Francisco. This time the featured home is Baker's back-of-house ‘Zero Cottage’ which, contrary to the name, actually generates net positive 30% more energy than it and the workshop below it actually uses. Read on for a look inside!
Photo by Piper Kujac
At just 712 square feet of living space over a 430 square foot workshop, every square inch of the tall thin structure has been optimized for flexibility and efficiency. A whopping 3 kW photovoltaic solar array, custom fabricated by Henry DeFauw, cantilevers off the narrow roof structure and serves as a rain screen for the exterior metal side stair below.
David Baker‘s Zero Cottage is LEED for Homes Platinum certified and is the first Passive House certified residence in San Francisco. The project is also on track to achieve Net-Zero Energy certification through the Living Building Challenge, after the first year of energy performance can be monitored.
Photo by Piper Kujac
Because the residence is part of the architect’s own home, Baker was able to experiment in ways he may not be able to with other clients. The custom exterior cladding is made from scrap metal pieces and prototype clips fabricated in the on-site workshop. Intermittent planter box panels provide a playful functionality and can be relocated to other panel locations as the seasons and sunlight angles change.
Contrary to the name, the home’s Passive House construction combines a robust (even aggressive) combination of exterior wall membrane layering, including continuous exterior foam insulation and triple-glazed windows. The goal is to capture heat generated from day-to-day use (by people, appliances, and computers) and use this heat to warm fresh air ventilated into the home. Likewise, the tight building envelope minimizes exterior heat gain on warmer days. With a 92% efficient heat-recovery ventilating (HRV) system, and an air-change-per-hour rating of 0.5, the house does not need conventional heating.
Photo by Matthew Millman
Needless to say, the interior has a lot going on for such a small footprint. The only door is on the exterior, and the open two-level plan includes what appear to be larger-than-average rooms that share the overall space. Salvaged wood floors feel great under foot and are sealed with VOC-free flaxseed oil, and similarly sourced ‘urban wood’ cabinetry is custom-built in the workshop below the cottage. Natural plaster walls provide a low-maintenance surface and high building mass, which also contributes to passive heating and cooling.
All the lighting is either daylight or dimmable LEDs, and a central light monitor operable window provides roof access and controlled ventilation through a chimney effect. Drought tolerant plants have been carefully sourced and arranged on the roof by Fletcher Studio to form what Baker calls ‘a cactus railing’.. or lack thereof. As you may have guessed, the AIA would not permit attendees onto the rooftop garden, but we can image the occupants enjoying it, at their own risk.