Project Green Home is a low impact home being designed and built by the Sven Thesen family in Palo Alto, California, in partnership with Arkin Tilt Architects, and graduate students both at Stanford and Berkeley. The aim is for the house to be “Zero Net Energy” – to produce as much energy as it consumes. The energy produced would not only balance electricity and gas consumption directly for the home, but also the hidden energy costs of water usage.
Thesen, who works with utility operations and sustainability strategy for transportation at a company called Better Place, has long practiced energy conservation in his personal life, so it was natural for him to want to put that same goal into practice when building a home. He explains, “When we started thinking about building a home, we saw in it a chance to examine the environmental impact of building a home, and what we could do to minimize the ‘total lifetime carbon cost’ of said home. Within this context, we decided to put theories and green rating systems we had a heard about into practice.”
He adds, “What started as seemingly straightforward soon turned into a major project with hundreds of options to consider, and with each new decision we thought: ‘since we’ve come this far, why not make it even more efficient!’ The result is an extremely energy-efficient house that pushes the limits of what is possible.”
Project Green Home, located in Palo Alto, Calif., less than three blocks from Stanford University campus, is a single family dwelling of approximately 2,500 square feet currently under construction. With a goal of beyond platinum LEED, net-zero energy, passive house, it has been designed to:
• Meet the Passive House standard, surpassing LEED platinum and California’s Title-24
• Integrate both available and cutting edge building energy efficiency technologies
• Incorporate the “best, cheapest, longest-lasting, safest” product and materials available
• Serve as a model and showcase for green/ energy efficient building technologies
• Meet California’s Assembly Bill 32, requirement for 80% greenhouse gas emission reduction by 2050, right now.
As a working model of the possible, Project Green Home hopes to serve as a real-life replicable example, creating a virtuous circle of similar sustainable housing. As such we welcome the involvement of the community and, in particular, students in evaluating the home against the above design parameters and likewise media coverage to publicize the possibilities.
Start with a family in Palo Alto desiring to change the world for the better with a focus on climate change and energy/ water use. Add Arkin Tilt Architects and Quantum Builders and a common vision is born. Combine this vision with a 7,500ft2 lot in Palo Alto, with a very small termite ridden house constructed in approximately 1918. Deconstruct the house (simultaneously recovering all the useable materials) and build a house that meets the above design parameters with the resulting following features:
There are three components to the Passive House standard. The first is that the house should be airtight, so that heat is not transferred through the building membrane. Our walls were tested using an infrared camera, to show where air was seeping in.
Passive solar design
The second component of the Passive House standard is that it uses sunlight as its primary heater in the winter. Most of the windows face south and the main living spaces are on the south side of the house. Bathrooms, storage, and staircase are generally located on the north side. Solar heat provides 60 percent of the annual space heating needs, and heat from occupants and appliances inside the house provides another 15 percent, according to a simulation in the Passive House Planning Package software.
2×8 studs at 24-inch spacing
Advanced Framing or Optimum Value Engineered framing is a system that uses wood only where it is necessary structurally. Since wood conducts heat much faster than insulation, reducing wood in the walls not only saves forests, but also saves heating and cooling energy.
Filtered fresh air ventilation
During cold weather, when having the windows open is too uncomfortable, the house gets fresh air on-demand from a MERV-filtered ventilation system located in the attic.
Unvented roof (full cavity insulation):
The entire shell of this house has full-cavity insulation. The attic is usable, conditioned space, and there is no outside air vented between the rafters.
Air Admittance Valves (AAVs)
An AAV is a durable, one-way air valve, the size of a vitamin bottle. It takes the place of a traditional plumbing vent through the roof.
A “White Roof” is not necessarily white, but is a light color so that it reflects more sunlight, keeping the house cool, and reflecting more light into space. A dark colored roof absorbs more light, and converts it to heat energy. The Palo Alto Planning Department was concerned about the aesthetic effect of glare on our neighborhood, so we are using a light grey, metallic color that is almost as reflective.
Skylight Passive Ventilation
Three electrically operated skylights near the ridge of the roof are located to passively ventilate the house.
Daikin Altherma heat pump water heater
This electric water heater transfers heat from the outside air into a water storage tank using refrigerant in a vapor-compression cycle, like a chilled water-fountain or air-conditioner in reverse.
Radiant floor heating
A variable-speed pump circulates warm water through tubing in the ground floor slab for winter comfort.
Passive House Insulation
Insulation is one of the three keys to the Passive House standard. Even though the house gets most of its winter heating from sunlight, there is still some energy spent to generate heat, and good insulation is required to use that heat as efficiently as possible. There are three different types of insulation used in this house:
• Wall and Ceiling Insulation
A Pro-Pink Complete Blown-In Wall System by Owens Corning was used to “super insulate” this home.
• Insulated headers
Headers are typically solid wood and occupy the entire thickness of the wall, creating a significant thermal bridge. Headers in this house are 3-1/2 inch-thick engineered lumber, set to the inside of the 7-1/4-inch wall, with 3-3/4 inches of expanded polystyrene insulating the header from outside temperatures. EPS (white and crumbly) is the eco-friendliest of the rigid, plastic foam insulations.
• Floor Insulation
Energy Monitoring System: The TED 5002G and will monitor solar 0 generation plus home energy use and this information will be posted live via Google PowerMeter.
Illumination: Within the constraints of the Palo Alto City Planning regulations, the lot size, and surrounding trees and structures, we have attempted to bring daylight into the house to maximize livability and to reduce the need for electric lighting. The large dormer over the loft illuminates the central space. Operable skylights light the open stairwell and a skylight lights the master bathroom. Most rooms have light from at least two sides to balance the color and quantity of daylight.
Concrete slab: The concrete mix design uses 50 percent slag and fly ash in place of Portland cement, which reduces the energy needed to make the concrete.
FSC lumber: Most of the lumber used in this house is either salvaged or certified by the Forest Stewardship Council (FSC) as originating in a sustainably-managed forest.
Metal Roof: A metal roof was selected over a conventional tile or asphalt shingle tile roof based on a number of factors including reflectivity, embodied energy, lifetime and recyclability.
Recirculating hot water line: In a “structured plumbing” design, domestic hot water is plumbed in an insulated loop through the house, like a racetrack, with the water heater as the start/finish line.
Rain Water Collection: Rainwater from all the roofs will be collected and channeled to the northeastern side of the house.