#Multiple renewable-energy sources help a Vermont home built with more or less conventional methods reach net-zero-energy use
To build a house with no carbon emissions and zero-net-energy use, the owners of this rural home in Vermont employed a strategy embracing alternative energy sources, unusually high insulation values, and conscientious fabrication.
Start with a good team and a purpose
David Pill is an architect, so he and his wife Hillary went into this project with a head start. They retained builder Jim Huntington, who had experience building energy-efficient homes and is himself a designer. Schooled in self-sustaining and socially responsible lifestyle choices, they wanted to purchase materials locally, recycle, and reuse as often as possible. Something creative would also have to be done with a derelict 14,000-square-foot covered riding arena on the 44-acre plot.
That they were successful in meeting their goals might be measured by a net gain in electricity — 192 kWh in 2008, several notable awards, and designation as the first LEED Platinum home in the state. It might also be measured by how great the place feels to live in.
Matching their plan to their needs
David points out that before they did anything else, they hired Andy Shapiro, an energy consultant, to model a best-case scenario, including orientation, passive solar design, massing, surface area, structural square footage, thermal mass, envelope design, glazing, air tightness, mechanical systems, lighting, and appliances. They then weighed possible building strategies from technical perspectives, as well as an important programmatic one — the family of four, including two children, would be spending most of their time living and working here. They settled on the premise of an ultra-efficient all-electric house (including appliances) to keep the design simple and the fuel source unified. To implement this, they commissioned a wood-frame house and installed a 10-kW net-metered wind turbine.
Local vernacular makes sustainable sense
On a sunny day the temperature of the 2,700-square-foot interior doesn’t drop below 70°F, even when it’s –10°F outside and the heat is turned off. Air conditioning is completely unnecessary in summer; the home’s ample thermal mass keeps it cool, and a few open windows upstairs send breezes through the house. Simple, but not austere, one wing is highlighted by fir columns reclaimed from a local mill, and the warmth of the locally made maple cabinetry throughout is enhanced by bright rugs and natural finishes.
The two-story house is laid out as two intersecting rectangles — one sided in painted cedar and the other in corrugated Galvalume. The look recasts the forms and textures of an agricultural heritage with clean, modern ease. The steep pitch of the standing seam metal roof sheds the heavy Vermont snows, and the large wrap-around screened porch is well used during long summer days. The wind turbine, 400 feet from the house, is barely audible.
There’s a chicken coop out back, also built to sustainable specs; a new apple orchard; and a vegetable garden. And the riding arena? It was bought by neighbors, disassembled, and reconstructed elsewhere.
Four important things
While the turbine and the ground-source heat pump (GSHP) get a lot of attention as new and exciting technologies, David has a list of things he finds just as important. Number one: solar orientation, a “no-brainer,” says David. The house is long and narrow along the true east-west axis, with simple massing.
Number two is to spend as much of the budget as possible on the shell. This one is superinsulated (EPS, denim batting, polyisocyanurate foam, and dense-packed cellulose), achieving R-values up to 58 and mitigating thermal bridging. The house has been fastidiously caulked to seal the envelope. Ultra-efficient fiberglass windows employ orientation-specific glazing: South-facing glazing allows more solar gain; the north-facing windows are more insulating.
Number three is short and sweet: “Find a builder before designing the house,” says David. “You want to work simultaneously with your contractor to create an integrated plan. Otherwise, you’ll be trying to retrofit a design after the fact” and, thus, coping with cost overruns.
Finally, number four is to “get the projected energy loads down as low as possible in the design process, so you’re not trying to overcome them later on.” Combine efforts. The GSHP, powered by a variable-speed drive, pumps water from a well that also provides drinking water. A GFX waste hot water heat recovery unit and highest-efficiency lighting and appliances further reduce energy usage. Several devices track energy use and efficiency: a wind data logger from NRG systems; a kWh meter on the turbine; a BTU meter and kWh meter on the heat pump controls; and a meter for hot water usage.
David wanted to push the economy of building the structure, so they used two-stud corners (with nailers), minimal framing for window headers, and a two-foot module for all dimensions. He thought of using a single plate and skipping the exterior sheathing, using lateral bracing instead, But Jim advised strongly against these last two, even though they are increasingly recognized as advanced framing techniques. David’s glad he listened, as winds can plow down the valley with vigor.
Because the owners went for all the bells and whistles in the GSHP assembly, installation took a lot of time, as did programming the drive that manages it. They’ll probably never use the extra lines in the radiant heat manifold that stub to the second floor — the house stays comfy from what’s in the first floor slab alone. They'll also never use the blocking in the walls for brises-soleil — it stays cool without it.
Heating system choices offer challenges and opportunites
They also want prospective alternative energy users to carefully assess the apparent cost of new technologies in context: For instance, “If you already have a well you can use [for the GSHP] and are already doing a radiant floor, the cost of it might be not much more than a standard boiler," David advises. "The benefit of a boiler is that you can put in relatively inexpensive baseboard, which itself is less costly than radiant.”
These trade-offs can get complex because the sizing of the heating system also depends on how tightly the house is sealed, among many other things. Can a non-architect manage all this? “Yes,” says David, ”but they’ll need the help of experts.” He adds, “It can be a fun learning experience.”
General Specs and Team
Cost does not include septic and well
Architect: David Pill, Pill–Maharam Architects
Builder/contractor: Jim Huntington, New England House Wrights
Energy consultant: Andy Shapiro, Energy Balance, Inc.
Foundation: 4-in. concrete slab over 4-in. EPS foam on gravel (R-16); poured 8-in. concrete walls lined with 2-in. EPS; 2x4 studs at 24-in. o.c. filled with dense-packed cellulose contained by reinforced netting (R-21 total)
Floors: I-joists at 24-in. o.c.; OSB subfloor, then 4-in. poured concrete floor, ground and polished, enclosing radiant heating system (denim batting under first floor radiant slab, R-21)
Walls: 2x6 studs at 24-in. o.c. insulated to full depth with closed-cell polyurethane spray foam; 1-in. polyisocyanurate foam board over exterior sheathing; house wrap; cedar breather mesh; painted cedar clapboard/corrugated metal exterior cladding (R-40)
Windows: triple-glazed fiberglass (U-value, .17; R-15 to R-17, Thermotech)
Roof: 2x10 rafters at 24-in o.c. filled to 9 in. with closed-cell polyurethane spray foam (R-58); 3/4-in. OSB sheathing; waterproof membrane; standing seam metal roof (Engler)
- Building envelope sealed to NACH .08 for heating 600 cfm @ 50 Pascals
- Fluorescent lighting throughout
- Open plan oriented for daylighting and maximum solar gain in winter
- Highest-rated Energy Star appliances
- GFX waste hot water heat recovery
Heating/cooling: GSHP (Econoair) with variable-speed drive (Hitachi) connected to well
Water heating: same as above plus 100-gallon storage tank (Marathon)
HERS index: 0
Annual energy use: 0 MMBtu/year
Energy production and use from January 9, 2008, to January 9, 2009:
- Total electricity usage: 6,094 kWh
- Total produced by wind turbine: 6,286 kWh
- Net electrical gain: 192 kWh
- Low-flow plumbing fixtures
Indoor Air Quality
- Low-/no-VOC paints, finishes, and most adhesives
- Natural materials
Green Materials and Resource Efficiency
LEED for Homes: platinum (90 points)
Energy Star score: 5+ stars