New California Home Meets the Passivhaus Standard

Climate Zone 4, San Jose, CA

Apr 27 2015 By | 0 comments

General Specs and Team

Location: Climate Zone 4, San Jose, CA
Bedrooms: 5
Bathrooms: 3.5
Living Space : 3198 sqf
Cost (USD/sq. ft.): $350/sqf

Design-BuildCompany that handles house design and construction. Since both services are provided by the same firm, integrated design can often be more easily achieved. Team: Allen Gilliland and Bronwyn Barry, One Sky Homes

Construction

Foundation: 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. crawl space walls, total of 4 in. of EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest. plus 8 in. concrete (R-22 for perimeter wall).

Crawl space floor: 4 in. of crushed stone, polyethylene vapor barrier, 3 in. horizontal EPS (R-14), concrete slab.

Above-grade walls: 2x6 24 in. o.c., advanced framed, R-23 dense-packed cellulose cavity insulation plus 1-in. EPS over plywood sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. ; ¼-in. plastic mesh to create ventilated rain screen; housewrap, wire lath; traditional 3-coat stucco claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. .

Windows: Serious & Sorpethaler wood-framed windows with 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 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.; SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.=0.49 on south and SHGC=0.29 on north, east, and west windows; U=0.2.

Roof/ceiling construction: R-51 blown cellulose on attic floor; raised-heel trusses; foil-faced radiant barrier sheathing; asphalt shingles; continuous eave and ridge vents.

HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building.: Split-system air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps.; SEER(SEER) The efficiency of central air conditioners is rated by the Seasonal Energy Efficiency Ratio. The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is Btu of cooling output during a typical hot season divided by the total electric energy in watt-hours to run the unit. For residential air conditioners, the federal minimum is 13 SEER. For an Energy Star unit, 14 SEER. Manufacturers sell 18-20 SEER units, but they are expensive. 21, HSPF 10.

Energy

Blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas. results: 0.57 ach50

Estimated energy use: 10,000 kWh/year, of which 2,000 kWh is for heating and cooling

Estimated annual utility costs: Without PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow., $1,972; with PV $0.

Estimated annual energy cost savings: (When compared to a home built to the 2008 California Title 24 Energy Code) Without PV $1,095; with PV: $2,900.

Actual annual energy use (2013): Not counting the electric vehicle, the house used 9,325 kWh. PV production exceeded use by 1,492 kWh. Including electric vehicle charging, the PV array produced 84% of the total site electricity consumption.

PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. system: 6.4 kW of PV (28 panels, each 230 watts)

Solar thermal system: 3 solar thermal collectors are connected to a solar storage tank; backup provided by a gas-fired, 96% efficient condensing tank-type water heater.

Appliances: 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. clothes washer, dishwasher, refrigerator/freezer

Lighting: 40% 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. , 40% 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. and 20% halogen; vacancy sensors in all rooms. Closets, bath heaters, and utility lighting on count-down timers. All exterior lighting is Energy Star rated and on timers with photocell shut-offs.

Other: Energy management system. Electric vehicle charging station with prewiring for a second charger

Water Efficiency

• Low-flow plumbing fixtures

GraywaterWastewater from a building that does not include flush-water from toilets and (as most commonly defined) water from kitchen sinks or dishwashers. In some places, graywater can be collected and used for subsurface irrigation. irrigation system

• On-demand hot waterSystem to quickly deliver hot water to a bathroom or kitchen when needed, without wasting the water that has been sitting in the hot-water pipes, which circulates back to the water heater. recirculation with occupancy sensors

Indoor Air Quality

HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. with MERV 13 filters, 84% sensible heat recovery efficiency.

Night Ventilation (economizer) with MERV 13 filters.

Meets or exceeds EPA indoor airPLUS verification checklist.

Certification

  1. PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates.
  2. LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. Platinum
  3. DOEUnited States Department of Energy. WaterSenseProgram developed and administered by the U.S. Environmental Protection Agency to promote and label water-efficient plumbing fixtures.
  4. EPA Indoor Air Plus
  5. DOE Zero Energy Ready

ICFs and advanced framing techniques used throughout

This energy-efficient house in San Jose, California, not only produces enough solar electricity to meet its annual energy needs, it also complies with the stringent PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. standard.

The design-buildCompany that handles house design and construction. Since both services are provided by the same firm, integrated design can often be more easily achieved. team of Allen Gilliland and Bronwyn Barry of One Sky Homes were behind the spec home and succeeded in meeting the Passivhaus standard and the performance requirements of the U.S. Department of Energy’s Zero Energy Ready Home program.

To meet the DOEUnited States Department of Energy. Zero Energy Ready Home criteria, the home had to meet the requirements of the 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. Version 3.0 program and comply with the minimum insulation requirements in the 2012 International Energy Conservation Code. The DOE program also requires that homes be certified to the air quality requirements of the U.S. Environmental Protection Agency’s Indoor airPLUS program. In addition, the builder chose to pursue LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. and achieved platinum certification on the home.

Home took four years to design and build

The $1.1 million house could be thought of as a building science test project. The 3,198-square-foot, two-story spec home took four years to design and build, more than twice the builder’s typical construction cycle for a custom home, because Gilliland wanted to test several new construction techniques.

“It was our intention to take a real building science approach. We wanted to measure this building in every way possible, to learn from it and share what we learned. To everyone’s credit, we were very successful. The data verified that we were 'plus site energy.' (The home’s 6.4-kW photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. system produces enough electricity to power both the home for a year and an electric car for thousands of miles of charge.) And we’re providing the homeowner with a vastly better living experience,” said Gilliland.

One Sky Homes collaborated with Davis Energy Group, a research partner in DOE’s Building America program. Davis Energy Group helped the builder meet the DOE Zero Energy Ready Home criteria while testing several advanced building technologies, including a night ventilation cooling system that cut cooling costs by 98%.

High efficiency starts at the ground level where Gilliland used R-22 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.) blocks to create a 3-foot-high foundation wall that formed the insulated sides of the unvented crawl space. Gilliland covered the crawl space floor with 4 inches of ¾-inch aggregate, a heavy-gauge polyethylene vapor barrier, 3-inch-thick 2-pound rigid expanded polystyrene foam (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.) foam (R-14), then a 3-inch concrete crawl space slab. Above the crawl space are 9.5-inch-deep engineered I-joists.

Advanced framing methods saved on materials

The above-grade walls consisted of 2x6 studs spaced 24 inches on-center. Advanced framing techniques were used: for example, two-stud rather than three-stud corners, open headers over doors and windows, windows sized to the stud bay openings, and ladder blocking at interior-exterior wall intersections to reduce lumber usage and provide more room in the walls for the R-23 of dense-packed cellulose.

“Everything is sized on a 24-inch grid, which makes for faster assembly with less materials waste,” said Gilliland. Over the exterior plywood sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , a 1-inch layer of EPS foam board was installed. This was covered with housewrap. Then the stucco installers attached a ¼ inch plastic mesh rain screen that served as a drainage planePath that water would take over the building envelope. Concealed drainage-plane materials, such as building paper or housewrap, are designed to shed water that penetrates the building’s cladding. Drainage planes are installed to overlap in shingle fashion (weatherlap) so that water flows downward and away from the building envelope.. Over this they installed wire lathe that was then covered with a traditional three-coat stucco claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. .

Raised-heel trusses provided plenty of room in the attic for the R-51 worth of blown-in cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. installed above the ceiling. The OSB roof sheathing has a foil radiant barrier coating on the underside facing the open attic space. Like most ventilated attics, this attic has continuous eave and ridge vents. The attic temperatures are relatively low; Davis Energy Group monitoring confirmed that interior attic temperatures never climbed more than 20 degrees above exterior ambient temperatures.

Triple-pane glazing was a requirement

All of the home’s windows and patio doors have triple glazing with low-emissivityAmount of heat radiation emitted from a particular body or material. Emissivity is expressed in a fraction or ratio, with the lowest values indicating low emissivity and the highest indicating the high emissivity of flat black surfaces. coatings and argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows. gas fill, with the exception of one double-pane window installed for testing purposes. All of the windows are wood-framed. Solar heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss. coefficients (SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.) varied depending on the orientation of the window. Higher SHGC (0.49) windows were installed on the south side to allow beneficial passive heat gain in the winter. Lower SHGC (0.29) windows were directed toward the west to reduce unwanted late afternoon heat gain. The calculated average “installed” R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. for all of the windows was R-5 (equivalent to U-0.20).

Thanks to rigorous air sealing measures, the home was able to meet the very low air leakage target required to meet the Passivhaus standard (0.60 air changes per hour at 50 Pascals pressure difference). The blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas. showed that the home has an air leakage rate of 0.57 ach50.

Energy usage met the Passivhaus standard

The average U.S. home uses 26,252 kWh of energy (electricity, natural gas, or other fuels) annually. A typical 3,000-square-foot home might use as much as 40,000 kWh annually, with half of that consumed by heating and cooling. The One Sky zero energy home uses only 10,000 kWh of energy a year and only 2,000 kWh of that is used for heating and cooling. A split-system central air source heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump. with a cooling efficiency of 21 SEER(SEER) The efficiency of central air conditioners is rated by the Seasonal Energy Efficiency Ratio. The higher the SEER rating of a unit, the more energy efficient it is. The SEER rating is Btu of cooling output during a typical hot season divided by the total electric energy in watt-hours to run the unit. For residential air conditioners, the federal minimum is 13 SEER. For an Energy Star unit, 14 SEER. Manufacturers sell 18-20 SEER units, but they are expensive. and a heating efficiency of 10 HSPF is located in an upstairs closet. The system’s ducts are located in conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. , in the open-web trusses between the first and second floors.

To keep the air healthy in the nearly airtight home, a heat-recovery ventilator (HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. ) was installed to draw in fresh air and exhaust stale air. The air passes through a MERV 13 filter then is supplied to the bedrooms and common areas. Exhaust air is pulled from the bathrooms and laundry. The HRV uses 3-inch ducts that are completely separate from the heat pump’s 8-inch ducts. “With the heat pump, we’re moving 100 cfm of air per register. That is an order of magnitude of difference from the 10 cfm of air moving through each HRV duct. It’s hard to get 10 cfm of air to move where you want it to in an 8-inch duct,” said Gilliland.

The home uses Night Ventilation Cooling, a ventilation system tied to the central air handler that uses temperature sensors, dampers, and electronic controls to draw cool nighttime air from outside through a duct to the return side of the air handler fan when temperature sensors indicate that the outside air is cooler than the inside air and the system is calling for cooling. The technology was initially developed in the late 1990s, in part by Davis Energy Group, and is similar in principal to the economizers used on commercial cooling systems. The system is ideal for climates with dry summers and large day-night summer temperature differences. The Night Ventilation Cooling system’s performance was extensively measured and showed dramatic results. It completely eliminated overheating and met 98% of the home’s total cooling demand, with a measured coefficient of performance (COPEnergy-efficiency measurement of heating, cooling, and refrigeration appliances. COP is the ratio of useful energy output (heating or cooling) to the amount of energy put in, e.g., a heat pump with a COP of 10 puts out 10 times more energy than it uses. A higher COP indicates a more efficient device . COP is equal to the energy efficiency ratio (EER) divided by 3.415. ) of 14.

Solar thermal collectors heat water

The home has three roof-mounted solar thermal collectors that send heated water to a storage tank, which the auxiliary gas-fired 96% efficient storage water heater draws from to supply domestic hot water. To reduce water use, plumbing fixtures are water-conserving and hot water fixtures are equipped with a recirculation pump that is button- or motion sensor-activated to speed hot water to the fixture.

Another unique feature of the home is the graywaterWastewater from a building that does not include flush-water from toilets and (as most commonly defined) water from kitchen sinks or dishwashers. In some places, graywater can be collected and used for subsurface irrigation. recycling system. During the irrigation season, graywater from the home’s sinks and showers goes to an underground 50-gallon tank, from which it is pumped to several irrigation zones around the yard. During the rainy season, the graywater goes directly to the sewer. The graywater system meets 80% of the home’s landscape irrigation needs; the water is distributed via a below-grade drip irrigation system.

The 6.4-kW PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. system (28 panels, each rated at 230 watts) produced 11,000 kWh in 2013, meeting 113% of domestic demand; the extra power was used for charging the homeowners’ electric car. One electric car charging station is installed in the garage and wiring is in place to install a second one. The PV system is grid-tied, but could be upgraded with an inverterDevice for converting direct-current (DC) electricity into the alternating-current (AC) form required for most home uses; necessary if home-generated electricity is to be fed into the electric grid through net-metering arrangements. that will support independent operation in case of grid failure. Without the PV system, the energy efficiency upgrades would save a homeowner a calculated $1,095 compared to a home built to the 2009 IECC International Energy Conservation Code.. With the PV system, homeowners are expected to save about $2,900 a year compared to owners of a code-built home.

All of the home’s appliances, including the clothes washer, dishwasher, and refrigerator, are Energy Star rated. The home’s lighting includes 40% 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. , 40% LED, and 20% halogen kitchen task and accent lights. Vacancy sensor controls were installed in all rooms. Closet lights, heat lamps, and other utility lighting were installed with count-down timer controls. All exterior lighting is Energy Star rated and is controlled by timers with photocell shut-offs.

Lessons Learned

Gilliland is looking forward to the day when smart heat pumps will integrate all of the HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. functions — heating, cooling, HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. balanced ventilationMechanical ventilation system in which separate, balanced fans exhaust stale indoor air and bring in fresh outdoor air in equal amounts; often includes heat recovery or heat and moisture recovery (see heat-recovery ventilator and energy-recovery ventilator). , and night cooling — into one system with one controller for the homeowner. He noted that the 2013 California Energy Code, which went into effect July 1, 2014, makes mechanical night ventilation prescriptive in some climate zones in California and gives credit for it in other locations in the state.

Bronwyn Barry shed some more light on the cooling system: “It turns out that we didn’t need such a large mechanical cooling system which we installed in this project. We’ve found that we can eliminate additional cooling systems because in our climate we can use a minisplit in conjunction with the HRV in bypass mode to supply all the cooling we need.”

Barry said that the design of the project evolved once they decided to go for the Passivhaus standard. “The house wasn’t originally designed for the Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. standard but we discovered and used the Passive House Planning Package (PHPP) after the design was set. That allowed us to dial in everything on this house to meet our NZE performance targets." And this change now informs their latest projects. "We’ve moved away from designs that include too many bump-outs. Our newer projects are much simpler shapes as they are more cost-effective for high efficiency.”

The firm's approach to air sealing also evolved, said Barry: “One thing we now do differently: Instead of using the drywall ceiling as an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both., which proved difficult because of all our lighting penetrations, we now establish the air barrier on the exterior roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. . We typically apply an elastomeric liquid sealant to the plywood layer around our whole 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.. This is then covered with rigid exterior insulation, a WRB and a rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. finish layer.”

Gilliland said One Sky has enjoyed the experience of learning from this project and is committed to zero energy construction. His only concern is motivating buyers to seek it out. “Once people experience it, they want it. Our customers will tell you, you just can’t believe it. It’s so much better living in these homes. People just haven’t heard enough about it yet.”

That may change soon, in California anyway. The California Public Utilities Commission and the California Energy Commission have adopted as a goal that all new residential construction will be zero net energy by 2020.


Courtesy of the U.S. Department of Energy

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Image Credits:

  1. One Sky Homes

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