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Green Building News

Net-Zero For a Competitive Price

A California model home comes in at $150 a square foot — demonstrating that net-zero doesn't have to cost much more than conventional construction

Image 1 of 3
Designed for net zero. The garage and 5-kw PV array are located in the back of the house. The two-car garage includes charging stations for electric vehicles.
Image Credit: ABC Home
Designed for net zero. The garage and 5-kw PV array are located in the back of the house. The two-car garage includes charging stations for electric vehicles.
Image Credit: ABC Home
The energy-efficient ABC Green Home is a traditional bungalow optimized for low energy use.
Image Credit: ABC Home
The home has 2 inches of exterior rigid EPS foam over the framing and closed-cell spray foam in the 2x6 stud cavities. (This illustration incorrectly identifies Henry BlueSkin VP as a "vapor barrier." In fact, the product is a vapor-permeable WRB.)
Image Credit: ABC Home

The designers of a 1,700 square-foot net-zero-energy demonstration home in Irvine, California, claim that a similar home can be built by virtually anyone for less than $150 per sq. ft., a figure that’s price-competitive with conventional homes in this market.

The developers of the home — Southern California Edison and Green Homebuilder magazine — call the three-bedroom, two-bath model home “the ABC (Affordable, Buildable, and Certified) Green Home.” The home’s energy features should reduce its estimated monthly utility bills by $150 to $200 compared to a similarly sized conventionally built home.

John Morton, project manager for Southern California Edison, says that the ABC home’s energy-saving strategies are mainstream and so they shouldn’t scare off buyers who might be leery of unfamiliar technology. The mild climate means the house can achieve net-zero status with 3 1/2 inches of Demilec closed-cell spray foam in the walls (in addition to 2 inches of EPS on the exterior side of the wall sheathing) and 5 1/2 inches of closed-cell spray foam in the ceiling. The roof deck is insulated to keep the ductwork within the conditioned space.

The water-resistive barrier (WRB) installed on the walls is a vapor-permeable membrane (Henry BlueSkin VP).

The wall panels were built by high school students

The house was built in conjunction with North Orange County Regional Occupational Program. Students in seven high-school construction classes designed and built the wall panels as part of their training. The panel sections were then brought to the site (in Irvine’s Great Park), where they were assembled by a contractor. The partners spent $204,000 to build the house — about $120 per sq. ft., a figure they say could be lower with a large builder’s efficiency of scale factored in.

For a virtual tour of the ABC Green Home, click here.

The house will be on display Mondays, Wednesdays, Fridays, and weekends from 9 a.m. to 4 p.m. until October 2013. At that time, the house will be separated from its slab foundation and donated to Habitat for Humanity, which will move it to a new site. The next ABC home will be a similarly sized two-story model. California is trying to make all new homes net-zero by the year 2020.

Notable features of the ABC Green Home

  • One story, three bedrooms, two baths, a den, no fireplace or chimney
  • 1,695 sq. ft. with a 440-sq.-ft. attached garage
  • 2×6 wall studs on 2-ft. centers
  • AMX home automation system controls lighting and window shading
  • 5-kw PV array
  • “Smart” electric appliances for use with “smart” electric meter
  • Hot-water recirculation
  • Gray-water recycling
  • Rainwater collection
  • Air-to-water Daiken Altherma heat pump
  • Permeable paving stones
  • Drought-tolerant plants
  • Universal design
  • Plug-in stations for electric cars
  • Meets the NAHB Green Building Standard and requirements for the California Advanced Homes Program, USGBC’s LEED program, and Energy Star

12 Comments

  1. User avater
    Dana Dorsett | | #1

    Everybody is a critic but...
    Net Zero notwithstanding, assuming the closed cell foam was blown with HFCs (like the vast majority of closed cell foam installed in the US), how many decades (centuries?) will it take in reduced energy use to offset the greenhouse potential of the blowing agents used? That's a lot of closed cell foam!

    In an Irvine CA climate going with open cell would be a more benign choice, even if it takes a full 5.5" fill on the 2x6 studs rather than 3.5" of foam. (The 5.5" open-cell cavity fill would actually beat the partial-fill of closed cell for whole-wall R-value, with less than 1% of the greenhouse gas hit.)

    Not mentioned here (but readily found with a bit of web-surfing) the ABC house also has 2" of EPS insulating sheathing, which is comparatively benign relative to closed cell spray foam. http://atlaseps.com/about-us/press-releases

    SFAIK there's only one water-blown closed cell foam with wide distribution, and that green stuff in the picture on page 7 ain't it: http://www.gothotwater.com/sites/default/files/20121008102424701.pdf (The pale stuff in the pic for reader service #176 on page 12 is though.)

  2. Skyler Marques | | #2

    Net Zero?
    I like the concept of energy efficient homes but calling them net-zero is misleading, you can't have a traditional family living on a zero energy foot print. A complete 5kW solar system (installation not included) cost less than $10k (source: http://webosolar.com/store/en/92-grid-tie-solar-kits); for the 1,700sqf home in the article that means $5.8/sqf. which is a good number. In my own experience you cannot charge two electric cars and power a house with a 5kW solar system so I am hoping car charging is not included in the equation. I like that the house looks very traditional showing that a very complex design is not necessary to achieve energy efficiency.

  3. Gordon Taylor | | #3

    Wall construction
    There are no vertical battens for a rain screen over the EPS, which I guess makes sense since they're building in a desert. But for some reason there's a vapor barrier. Is that a WRB? If so, why doesn't the facing on the EPS serve as a WRB? Is the siding attached directly through 2" of foam? That seems like a lot of nails penetrating the thermal insulation. And if they're going to hold properly, doesn't that mean driving them hard, and potentially squashing the foam? Hey, I'm an amateur in this. I'd appreciate hearing from some of the professionals. (I think the project is laudable, by the way, even if there are things that might legitimately be criticized.)

  4. User avater GBA Editor
    Martin Holladay | | #4

    Response to Dana Dorsett
    Dana,
    The caption to one of the photos mentioned the 2-inch-thick rigid foam layer installed on the exterior side of the wall sheathing, but the text of our report article failed to mention it -- as we should have. Thanks for pointing out our omission; I have edited the text to include information on the EPS layer.

  5. User avater GBA Editor
    Martin Holladay | | #5

    Response to Gordon Taylor
    Gordon,
    Although the illustration of the wall system provided to journalists by the developers of this house identifies Henry BlueSkin VP as a "vapor barrier," that label is erroneous. Henry BlueSkin VP is actually a vapor-permeable WRB. I have edited our report to clarify this point.

    You ask, "Why doesn't the facing on the EPS serve as a WRB?" While it is possible to use rigid foam as a WRB, not all brands of rigid foam have gone through the necessary code-approval process for their products to be used as a WRB. Moreover, many builders are skeptical of the flashing details required by this method, which depend on the adhesives in flashing tapes to maintain a waterproof seal. For more information on this question, see Using Rigid Foam As a Water-Resistive Barrier.

  6. Joe Schmo | | #6

    Is the cost all inclusive?
    Are all of the notable features, e.g., PV array, pavers, garage, etc, included in that $120-150/sf figure? If so, that is extremely impressive.

  7. User avater GBA Editor
    Patrick McCombe | | #7

    Is the cost all inclusive?
    That's my understanding, Brian M.

  8. Aaron Gatzke | | #8

    Link to virtual tour player
    I checked greenhomebuilder.com but I cannot find a link to the virtual tour player.
    Would you know what it is?

    Thanks

  9. Gordon Taylor | | #9

    I have to ask...
    It says, "The house was built in conjunction with North Orange County Regional Occupational Program. Students in seven high-school construction classes designed and built the wall panels as part of their training. The panel sections were then brought to the site (in Irvine’s Great Park), where they were assembled by a contractor." Were the students paid market-rate wages for this work? If the work was donated, how did that affect the per sq. ft. price?

  10. User avater GBA Editor
    Martin Holladay | | #10

    Response to Aaron Gatzke
    Aaron,
    Here is a link to a virtual tour of the ABC Green Home:
    Virtual tour.

  11. User avater GBA Editor
    Patrick McCombe | | #11

    Student framers affecting price per square foot.

    The panel framing was done by students, but the cost estimate given above was based on the contractor who assembled the panels doing all the framing.

  12. Dan Johnson | | #12

    Any more details on the HVAC configuration?
    I was surprised to see the Altherma in the feature list. This is a super product, but quite pricey in the Bay Area of CA at the moment. I see a pair of fan coils in the attic, in one of the 3D views. Curious why the Altherma was chosen over other options like a pair of DX mini-split, inverter-driven fan coils paired with a standalone, tank-type heat pump like the AOSmith Voltex. Also, how is whole-house ventilation per ASHRAE 62.2 being achieved? Bath fans?

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