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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

Posted on Nov 26 2012 by Patrick McCombe

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 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. ) 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 spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. .

The water-resistive barrierSometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material. (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
  • 2x6 wall studs on 2-ft. centers
  • AMX home automation system controls lighting and window shading
  • 5-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. array
  • “Smart” electric appliances for use with “smart” electric meter
  • Hot-water recirculation
  • Gray-water recycling
  • Rainwater collection
  • Air-to-water Daiken Altherma 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.
  • Permeable paving stones
  • Drought-tolerant plants
  • Universal designDesign that makes a building accessible to as many individuals as possible, including older people and those with physical handicaps.
  • Plug-in stations for electric cars
  • Meets the NAHBNational Association of Home Builders, which awards a Model Green Home Certification. Green Building Standard and requirements for the California Advanced Homes Program, USGBCUnited States Green Building Council (USGBC). Organization devoted to promoting and certifying green buildings. USGBC created the LEED rating systems.'s 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. program, and 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.

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Image Credits:

  1. ABC Home

Nov 26, 2012 5:08 PM ET

Everybody is a critic but...
by Dana Dorsett

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.

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: (The pale stuff in the pic for reader service #176 on page 12 is though.)

Nov 26, 2012 8:40 PM ET

Net Zero?
by Skyler Marques

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:; 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.

Nov 27, 2012 1:18 AM ET

Edited Nov 27, 2012 2:07 AM ET.

Wall construction
by Gordon Taylor

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.)

Nov 27, 2012 9:38 AM ET

Response to Dana Dorsett
by Martin Holladay

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.

Nov 27, 2012 9:45 AM ET

Edited Nov 27, 2012 9:52 AM ET.

Response to Gordon Taylor
by Martin Holladay

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.

Nov 27, 2012 12:22 PM ET

Is the cost all inclusive?
by Joe Schmo

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.

Nov 27, 2012 12:30 PM ET

Is the cost all inclusive?
by Patrick McCombe

That's my understanding, Brian M.

Nov 28, 2012 12:03 AM ET

Link to virtual tour player
by Aaron Gatzke

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


Nov 28, 2012 4:31 AM ET

I have to ask...
by Gordon Taylor

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?

Nov 28, 2012 8:09 AM ET

Response to Aaron Gatzke
by Martin Holladay

Here is a link to a virtual tour of the ABC Green Home:
Virtual tour.

Nov 28, 2012 10:12 AM ET

Edited Dec 3, 2012 10:08 AM ET.

Student framers affecting price per square foot.
by Patrick McCombe

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.

Dec 6, 2012 1:54 PM ET

Any more details on the HVAC configuration?
by Dan Johnson

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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