Super Energy-Efficient Home in Vermont
Super Energy-Efficient Home in Vermont
Waitsfield, VT
The home was built into a hillside to provide easy access to both floors. Earth sheltering also tempers heat loss in the cold climate.
General Specs and Team
Location: Waitsfield, VT
Bedrooms: 3
Bathrooms: 2
Living Space : 2000 sqf
Cost (USD/sq. ft.): $90/sqf
Builder: Al Rossetto, A. Rosetto Construction
Architect/designer: Al Rossetto
Construction
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p>Foundation: shallow frost-protected footing, gravel in perforated PVC forms/drains, 2 in. XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. (R-10) buried and extending horizontally distance of frost depth; 6-in. ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure. walls (Amvic, R-22)
Walls: 6.5-in. SIPs (Insulspan, R-22)
Roof:12.25-in. SIPs (Insulspan, R-50)
Windows: triple-pane, low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor., argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows.
-filled; SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as
a number between 0 and 1., .24, U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value.
, .2 (Kohltech, R-5)
Garage:none
Energy
Heating/cooling: radiant heating system fed by solar and gas hot-water heater, 4 flat-plate solar collectors with 120-gallon storage tank and solar heat exchangerDevice that transfers heat from one material or medium to another. An air-to-air heat exchanger, or heat-recovery ventilator, transfers heat from one airstream to another. A copper-pipe heat exchanger in a solar water-heater tank transfers heat from the heat-transfer fluid circulating through a solar collector to the potable water in the storage tank.
Water heating: shared with radiant heating system
HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0.
The older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5. score: 95.3 (old system)
Annual energy use: 51.4 MMBtu
- Concrete slab over 16-in. sand bed for significant thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night.
- Extremely tight building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.
- Solar hot water and radiant heat
- Daylighting facilitated by open floor plan and window layout
- All lighting is CFLCompact fluorescent lamp. Fluorescent lightbulb in which the tube is folded or twisted into a spiral to concentrate the light output. CFLs are typically three to four times as efficient as incandescent lightbulbs, and last eight to ten times as long. CFLs combine the efficiency of fluorescent light with the convenience of an Edison or screw-in base, and new types have been developed that better mimic the light quality of incandescents. Not all CFLs can be dimmed, and frequent on-off cycling can shorten their life. Concerns have been raised over the mercury content of CFLs, and though they have been deemed safe, proper recycling and disposal is encouraged. or LEDLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed.
Indoor Air Quality
- Interior portion of Form-A-Drain footing system (under slab) is part of a natural-draft radonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles.-venting system
- ERV(ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV.
- Solid wood cabinets and flooring
- Central vacuum system
Green Materials and Resource Efficiency
- Fiber-cement siding
- Trees cut down on site milled into stair parts and loft flooring
- Almost all construction waste recycled
Certification
EnergyStar score: 5+ stars
Modest House Built to Scandinavian Green Standards
This modest home may not seem out of the ordinary, but energy efficiency specialist Efficiency Vermont calls it extraordinary — "Best of the Best" and "the most energy efficient home in the state," to be specific. With a HERSIndex or scoring system for energy efficiency established by the Residential Energy Services Network (RESNET) that compares a given home to a Home Energy Rating System (HERS) Reference Home based on the 2006 International Energy Conservation Code. A home matching the reference home has a HERS Index of 100. The lower a home’s HERS Index, the more energy efficient it is. A typical existing home has a HERS Index of 130; a net zero energy home has a HERS Index of 0. The older versions of the HERS index were based on a scale that was largely just the opposite in structure--a HERS rating of 100 represented a net zero energy home, while the reference home had a score of 80. There are issues that complicate converting old to new or new to old scores, but the basic formula is: New HERS index = (100 - Old HERS score) * 5. score of 95.3 out of 100, and four years of energy bills to document its performance, the building deserves the accolades. Builder Al Rossetto leaves nothing to chance: he has used the same construction details to lock in five-star Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. ratings for every home he has built since.
Is Vermont the new Scandinavia?
The shallow, frost-protected footing is possibly this home's most unusual detail. Northern Vermont's deep frost line and rocky soil make building conventional foundations a challenge. A shallow bed of gravel surrounded by a horizontal apron of rigid foam insulation — a system used in Scandinavia for decades — worked well here.
When paired with an insulated concrete form (ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure.) foundation, this system ended up saving energy and materials. The walls and roof are all structural insulated panels (SIPs), which go up quickly and provide a tight shell. Energy efficient windows with triple glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill. and multiple low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. layers (also standard equipment in Scandinavia) complete the package.
A healthy indoor space was the top priority
Even though Al put a lot of effort into energy-efficient construction, his first priority was to build healthy home. He started by reviewing material-safety data sheets and scratching unhealthy products off of his list. The tile and solid wood used on the floors of the kitchen, bathrooms, and remainder of the house are easy to clean and don't off-gas harmful chemicals. A heat recovery ventilator circulates fresh air from outside without letting precious heat escape.
Flat-plate solar collectors provide 75 percent of the domestic hot water and boost the radiant heat system by preheating a 16-in. bed of sand under the ground floor. Mounting the solar panels on the ground instead of on the roof allowed Al to locate the house for accessibility and beautiful views rather than solar orientation. Only three trees had to be cut down to accommodate construction, and most of the wood was used as finished railings, flooring, and stairs. In the end, only six yards of construction waste was hauled away. Everything else was recycled.
It was four years before another home grabbed the title of most energy efficient home in Vermont. Al has no hard feelings. "I'd like to shake their hand" he says about anyone who works as hard as he does to build better, more-efficient homes.
Lessons Learned
Don't let all the fancy acronyms scare you. Green building isn't only about using exotic materials and high-tech HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. components. Building an energy efficient home is often just a matter of doing a good job. The SIPs came with an installation manual. "We read it, followed the directions and were conscientious during our work," Al explained. Paying attention to details by filling voids and cracks with spray foam and caulk isn't hard work, but it can make all the difference when it's time to turn on the heat.
Rob Wotzak is assistant editor at GreenBuildingAdvisor.com
Image Credits:
- Chris Green/Fine Homebuilding 161
- Rob Wotzak