Project Participants:Arkin Tilt Architects
Eastern Sierra Residence
Site characteristics or focus during construction or remodel:
Situated on the eastern slope of the Sierra Nevada Mountains over-looking the Carson River Valley, this home is carefully designed to take advantage of the rugged beauty of the site. Working with the slope, orientation, and dramatic views, the house is structured around a shaded courtyard oasis, providing outdoor space protected from both summer sun and winter winds. While the garage and guest wing to the west blend in to the landscape via sod roofs that lift from grade, the main form juts out like a boulder, mimicking the mountains beyond. The main south-facing roof peels up at the corner for passive solar gain and for a dramatic view of snow-capped Job’s Peak to the southwest.
Guests enter between upturned sod-roofed wings into the sheltering courtyard flanked by a pond that physiologically and literally contributes to cooling in the dry summer climate, and collects water from the metal roofs. Photovoltaic panels sit atop a trellis shading the courtyard, and unheated entry separates the space from the driveway to the north.
It was the owner’s intent that this house be virtually energy independent, utilizing no fossil fuels for operation. This required careful shading, high insulation levels, and thermal mass to keep the structures from overheating in the summer, aided by flushing of cool night air. Photovoltaic panels were also placed on the main roof and trellis to generate electricity (grid-tied with battery backup), and installed solar thermal panels provide hot water and heating via sand beds under concrete slabs (described in detail under “Solar Heating”).
Natural, efficient, and durable materials were also used; primarily straw-bales with an earthen finish (using soil from the site), metal roofing and slatted cement-board siding. Salvaged materials were used throughout the project; among the most visible examples are airplane flaps employed as sunshades on the greenhouse, and ore cart wheels that support railroad track trellis beams. Salvaged and reclaimed wood is used throughout the home as well.
Solar Heating Systems:
The solar water heating and solar space heating systems are incorporated in the same system. There are solar collectors (seven 4 x 10 Heliodyne Gobi panels) mounted below the terrace for minimized visual impact. They are tilted to optimize the winter sun (±60° from horizontal), to maximize the space heating function of the system when it is needed most. During the non-space heating part of the year, the solar water heating works well because there is extra collector area at that time, with a shunt that delivers heat to the ground out doors and the lap pool in the greenhouse. One set of pipes runs from the collectors to the floor and water storage tank.
When the sun shines, the collectors get hot, and a 12V circulating pump powered by PV panels turns on and circulates the hot solar fluid from the collectors into the home. A non-toxic antifreeze solution is in the collectors and piping. All the time some of the solar fluid passes through a liquid-to-liquid heat exchanger that heats domestic hot water. A storage tank stores this hot water, which is a pre-heat to a regular water heater. During the heating season some of the hot solar fluid will circulate through Pex tubing, which is buried in sand beneath the floor slabs. The hot solar fluid transfers heat to the sand; this heat will rise evenly, warming the floors for a long time. During the cooling season the unheated thermal mass serves to help keep the spaces cool and comfortable.
More information about this heating system (and solar water heating in general) can be found in a new book called Solar Water Heating, by Bob Ramlow, the designer of this system. This practical guide is available from New Society Publishers.
During its first winter, while the house was still under construction, the weather was near or above the recorded average temperature (upon which the design was based) and the indoor temperatures remained within 10° of the comfort zone without any additional heating. Generally the sand bed was able to quickly reheat following 1-3 days of cloud cover. The following winter was one of the coldest and cloudiest on record in the Carson River Valley, and the performance of the house suffered accordingly. The electric forced air heating system was used regularly to make up for the loss of heat input from the solar panels. Still, the heating bills at this residence were 1/10th those of neighboring homes. This most recent winter the home performed admirably, especially under normal weather patterns.
In summer, the residence remains cool through most of the season, but during the hottest periods the night flush alone is not sufficient to cool all areas of the home following a hot (100°+) summer day. With the exception of these extreme weather periods, the home remains comfortable in a hot desert climate without relying on air conditioning.
The importance of a tight envelope cannot be understated. Due to design constraints, the bay at the kitchen has minimal amounts of insulation above and below, and in winter this area is a source of heat loss. The fresh air exchange, while featuring heat recovery, also contributes to lowering air temperatures.
Another lesson learned pertains to air circulation. The 12 V PV panels dedicated to powering the floor can remain covered with snow even when the solar thermal collectors are not, causing them to overheat. Conversely, early and late in the day the sun hits the PV panels but not the collectors, resulting in cool liquid being circulated into the floors. Since the house has a renewable energy system with battery backup, the 12V pump has been replaced by a 110V AC pump controlled with temperature sensors.
Perhaps the most important lesson learned is that of providing at least 24 inches (609.6 mm) depth to the sand bed. Due to the footings there were areas of this residence where the sand bed was less than 12 inches (304.8 mm) deep, and only 21 inches (533.4 mm) in others. This smaller mass heats quickly once the sun returns, but cools within two days of cloud cover.
Finally, an important lesson learned is that solar gain from morning sun—especially when on an east-facing slope—can be considerable and it needs to be controlled. Generally, we limited the size and number of these windows, and provided operable awnings at the kitchen bay, but are making plans to add shutters to a few more east-facing windows.
Passive Survivability puts forth the concept that buildings should allow people to continue to occupy a structure safely and with reasonable comfort when any or all utilities serving that building may fail. During winter, the power grid serving this area went down, as it often does in mountain regions, and neighbors called wondering why Suzanne had power when they did not. They learned that not only was her PV system powering the home, but also that she was warm despite having no gas service to the house.
Overall, the project strives to demonstrate that ecological design and good architecture are not mutually exclusive, nor necessarily mutually beneficial, but are in fact one and the same.
PROFILE PROJECT: Eastern Sierra Residence
OWNER: Suzanne Johnson
DESIGNER: Arkin Tilt Architects David Arkin AIA
DATE OF CONSTRUCTION: 2004
BUILDER: Rick Walters Sage Design/Build
AWARDS AND PUBLICATIONS:
- AIA/COTE Top Ten Green Projects Award, 2005
- AIASF Award for Energy and Sustainability, 2006
- Environmental Design + Construction Excellence in Design Award, 2005
- AIA Nevada Excellence in Design Award, 2005
- Sunset Magazine Western Home Special Award, 2005-2006
- RENO Magazine/AIA Northern Nevada Design Award, 2006
- “Redux” by Jennifer Roberts, Gibbs Smith Publishers
- “Cameo in Good Green Kitchens” by Jennifer Roberts, Gibbs Smith Publishers (Magazines listed above associated with the awards) Reno Magazine/AIA Northern Nevada Design Award, Johnson Residence, 2006