Truckee Sustainable Mountain Home

Designed by Kristi Thompson, MWA, Inc. Architecture-Engineering

Classic mountain design meets cutting-edge strategies in energy efficiency, sustainability and building techniques in this Lake Tahoe-area home.

ENERGY EFFICIENCY, COOL DETAILS, GREAT IDEAS, AND MORE

The Lake Tahoe area is a beautiful place to live and play, but it also presents severe challenges for local architects and builders – especially if the homeowner is striving for the best in energy efficiency and durability while still looking for a classic mountain design. This home is the result of an integrated team of designers, engineers and builders that more than met those challenges. The design pulls in traditional cabin and lodge style cues, including massive FSC timbers and abundant reclaimed wood finishes, while incorporating extensive customized energy and material efficient building techniques.

The key to the success of this project was forming the team early, led by the triumvirate of architect Kristi Thompson, builder Bob Heller and LEED AP Ann V. Edminster. This group was tasked with balancing the client's aesthetic and sustainability goals against the practical aspects of Truckee's severe winters and dry summers (e.g. high snow levels, very cold temperatures, high fire risk and strict seismic codes). Add to that our desire for a "scalable" house to comfortably host 2-12 people, and universal design methods to accommodate those of all abilities.

Oriented on an east-west axis to maximize both solar gain and day-lighting and to work with the natural site contours, the most distinguishing architectural feature of the house is the bridge that separates the main living areas from the garage and bunkroom. The bridge design was inspired by the local railroad heritage of Truckee, but its sustainable purpose was to allow the natural spring run-off, which in heavy snow years can swell to a roaring creek, to pass under the house and continue on its natural path. Both the entry and great room feature scissor trusses site built from FSC timbers. The house also features two living green roofs, an indoor living wall (integrated into a floating stair), and an integrated greenhouse to help bring the outside in (not easy at 6,000 ft. elevation), while mitigating some of the impacts of the very dry mountain climate.

The house is all-electric (fossil fuel free, save for the backup generator) which drove the decision to go with a mix of a solar thermal array and ground source heat pumps to provide heat to the hydronic floor system and domestic hot water. Because hydronic systems can be somewhat finicky in super-tight and super-insulated homes (double wall, R-44/R-60 ceiling) a new PC-based HVAC control system is used to manage and anticipate the heating loads. No A/C system was included due to Truckee's mild, dry summers, but a Zehnder HRV was included to provide fresh air throughout the year. The project also includes a barn, which was designed to house a solar PV system that can produce up to 9.5KW, which covers most of our home's energy needs.

Fixture and finish material selection also played an important part in the construction of the home. When possible, material and product specification focused on regionally produced and/or sourced products. The design team focused on California-made products, but expanded the search area to the West Coast and the entire U.S. when needed. Within those regions, they also sought to utilize products made with eco-friendly content (either recycled or reclaimed) and that had minimal environmental impacts. Ultimately, all of these products needed to work with the home's various systems as mentioned above. Regional materials and products include: masonry, tile, concrete countertops, cabinetry, plumbing fixtures, and lighting. Eco-friendly materials include: Corten metal siding, reclaimed wood throughout including, wall finishes made from pine boards/slabs cut from trees harvested on site, 100% wool carpets, no or low-VOC paint, plaster and stains, recycled content tile, salvaged sinks, and corrugated metal siding (on the interior, using material reclaimed from local buildings). Products compatible with the house's systems include: triple pane windows, LED lighting, water-saving plumbing fixtures, and Energy Star appliances.    

From the clients, "When we started this project we suspected our expectations might be unrealistic, but our amazing team exceeded all our design goals. We ended up with a home that received not only the highest Build It Green GreenPoint rating (199) of any home in the Sierra Nevada, but one of the highest in the entire state of California!"

Key Design features:

• Careful house-site orientation using 3-D modeling to maximize passive solar gain and day-lighting.
• Open floor plan to maximize air circulation for cooling, ventilation and heating with central fire-place.
• “Scalable” house with multi-zone floor plan and mechanical design allow house to be energy efficient for 2-9+ occupants.
• Integration of natural environment throughout with living green-roof, living wall, indoor pond, integrated greenhouse, three-season screen porch, and bridge over creek.
• Extensive water (and snow melt) runoff management re-infiltrated through trenches, bio-swales and drywells.
• House dimensions based on a 2 ft grid to efficiently use framing materials.
• All electric, fossil-fuel free house (except for back-up generator).
• Through careful use of shading and cross ventilation design, no A/C system was necessary.

Key Construction features:

• Advanced framing techniques (e.g. 24” OC double-stud, insulated headers and engineered wood).
• Airtight building using gaskets, embedded polyethylene air-barrier, high quality tape, spray foam, caulking and minimal, sealed penetrations. Multiple blower door tests conducted through the construction process found and enabled us to fix holes, resulting in a very tight, final 1.1 ach50.
• Super Insulation: Roof has closed-cell spray foam and sprayed Spyder Fiberglass (R-70); double-walls of Spyder fiberglass (R-44); Basement walls Spyder Fiberglass and EPS foam boards (R-30); sub-slab insulation spray foam (R-20).
• High Efficiency Windows: Triple-pane, low-e coated glazing with thermal spacers made from FSC wood with aluminum exterior cladding.
• A PC-based control system is used to manage and anticipate heating loads to coordinate the hydronic heating system in the super-tight, super-insulated envelope. For monitoring, a whole-house electrical and water use tracking system is used.
• A three tier hot-water heating system for both space heating and domestic hot water. A primary solar thermal system, a six-ton ground source heat pump as main winter heat source and finally electric resistance for backup. Additionally, the domestic hot water tank has an air-to water heat pump to boost DHW capacity under heavier load.
• The major living spaces can also be heated by a central, high-efficiency, sealed wood stove.
• The property has a grid-tied, micro-inverter based 9.5kW photovoltaic system.
• Entire house uses high efficiency lighting (90% LED and 10% fluorescent).
• All appliances are Energy Star rated, including induction stove-top.
• Whole house ventilation is provided by a Zehnder central HRV with Panasonic energy-star booster fans in a few rooms.
• Structured plumbing and regulated hot water recirculation pump that saves energy by only turning on when called upon.
• Integrated radon capture and venting system.
• Low-flow toilets and showers: All watersense certified.

Material selection and use:

• Reuse of site material: Felled trees used for interior finish, fencing, mulch, and firewood. Stone used for walls and paths. Topsoil re-used for landscaping.
• Reclaimed materials: Almost all finish wood is reclaimed: exterior siding (both house and barn), flooring, interior walls and ceilings.
• Recycled material: Metal siding, roof and I-beams are made from recycled US steel. Greenroof material from recycled sources.
• FSC wood: Used for all structural wood. (95+% of wood is FSC or reclaimed).
• Minimal use of “red-list” materials: such as PVC, urea-formaldehyde, polystyrene, drywall and copper.
• All interior coatings are low or no-VOC paints, stains, caulking and adhesives. Clay paints and natural plaster on interior walls.
• Recycling waste: over 95% of all off-site waste (70% excluding organic matter) Even the recycling bins are recycled!
• Local sourcing of wood, stone, rock, concrete, soil, insulation, and interior finishes.

Photos: Vance Fox