Last Updated: Nov 8, 2023
When you think of a location for green homes, you probably think of a spacious five-acre yard. One that allows for optimum placement, an efficient solar panel system, and advantages that come from larger lots. The Madrona Passive House in Seattle took on the challenge of achieving the world’s most demanding energy standards while being located on a city slope that was designated as an Environmental Critical Area (ECA).
Why does that matter? ECA regulations stipulated that the house had to be built on or above the site where the former building had been constructed—severely limiting the design options. Despite this constraint, the house was still able to achieve the Zero Energy Certification as well as the U.S. Department of Energy’s Net Zero Ready Certification.
The home was designed and built as a collaboration between the owners Jabe Blumenthal and Julie Edsforth, Shed Architects, and Hammer & Hand.
Due to the steep slope of the property, the home was essentially built as a structure on stilts. A structural slab that is supported by 26 piles drilled deep into the hillside essentially allows the home to float above the poor soils of the hillside, offering stability despite the difficult conditions.
The home was designed for a family of four with two older teenagers. Since the children were close to moving out, the initial design placed their rooms in the basement. This area could eventually be turned into an accessory dwelling unit and help the home generate income. The home site includes gorgeous views of Lake Washington and the Cascade Mountains; a large deck was built facing the views.
The main goal of the owners was to reduce the operational energy use of the home radically. Despite being 3,397 square feet, the Madrona Passive House was able to achieve Passive House standards, which is widely considered to be the most rigorous building standard.
How? Heating and cooling a home is typically the largest energy user, so limiting heat transfer between the inside and outside of the home naturally reduces the heating and cooling loads. As with most passive homes, it’s primarily about the building envelope and the home’s orientation towards the sun to capture and retain heat.
Due to the restrictions of living in an environmentally critical area, the home had to be built in an L-Shape, which is not optimal for a passive house seeking to maximize solar gain. However, the strategic placement of windows and opaque walls helped the home achieve the highest energy efficiency standards. Exterior mechanical blinds and triple-pane Thermoplus windows that have a U-Value of 0.123 help to control the solar gain.
The Madrona home’s airtight building envelope is surrounded by thick structural foam insulation along the retaining walls and along with the structural slab below the house. Since the home is essentially floating, this helps to eliminate thermal bridging issues from the foundation. High-density cellulose cavity insulation, a mineral wool insulation board on the exterior, and ZIP system™ sheathing for air-tightness help to optimize the thermal performance of the home.
The home has a 9.8 kilowatt (kW) solar array that allows it to produce more energy than it consumes routinely. During the 12-month performance period monitored by the International Living Future Institute, the home used 9,866 kilowatt-hours (kWh) while producing 10,768 kWh. This is over 900 kWh more than what was used by the homeowners.
They also put upwards of 8,000 miles per year on a small electric car they own. They charge it with their solar panels system and still manage to live in a “net energy negative” home.
The home incorporates a heat recovery ventilator that maintains optimum indoor air quality while simultaneously allowing the home to recuperate up to 90 percent of exhaust air for further heating inside the home.
In terms of water use and recycling, the Madrona Passive House has a green roof on the garage, an effective rainwater harvesting system from the main roof of the home, and permeable pavement for the driveway and other hardscapes on the property. The combination of these three elements helps to reduce the amount of damaging stormwater run-off while also mitigating erosion issues that can occur due to the steep slope. The landscape of the home is planted with drought-tolerant plants that are periodically irrigated from water captured by two large cisterns that are fed by the roof of the house.
For hot showers and laundry, the home operates a Sanden CO2 Heat Pump Water Heater that offers direct hot water and radiant heat into the home. Because passive houses tend to be particularly sensitive to temperature changes within the walls of the home, it took a bit of tinkering to find the optimum temperature settings with this heat pump. Part of the challenge in maintaining a comfortable temperature in the home was also related to manually controlling the blinds to either block the sun or let sunlight in.
To correctly manage and operate the energy-efficient design of the home, the owners benefit from a circuit-by-circuit energy monitoring system with an easy-to-use dashboard interface. This allows them to monitor their current energy use and identify patterns in how the home utilizes energy throughout the day and the seasons in order to further increase the energy performance of the building.
Over years of occupancy, the owners discovered the best way to keep their passive house running efficiently. Like all sustainable and energy-efficient homes, the process of living in the home reveals the best strategies and techniques for optimum performance. The owners are encouraged to continue to find ways to minimize their energy consumption.
The Madrona Passive house was recognized by Green Builder Media as the 2016 Green Home of the Year Award in the category of maximum energy efficiency. The owners hoped that their home would help to influence the adoption of Passive House homes in the Seattle area. Doing so could increase demand and lower the overall cost of the home from a life-cycle point of view. Over the years of occupancy, the Madrona Passive House appears to be achieving its lofty goals.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.