Zero Energy Home Design Goes Mainstream

As construction science improves and equipment costs go down, both production and manufactured homebuilders are entering into the zero energy home design space.

Milwaukee-area Tim O’Brien Homes started work in May on Wisconsin’s first Zero Energy neighborhood. When building is complete, all homes at Red Fox Crossing in New Berlin will be certified under the Department of Energy’s Zero Energy Ready Home program as 40 to 50 percent more efficient than a typical new home. They will also include rooftop solar panels.

Buyer response has been encouraging; with homes selling more quickly than in the company’s other neighborhoods.

All homes will be connected to the electric grid, but thanks to Net Metering laws the utility will buy any solar-generated power the homes don’t use. According to Craig North, Director of Construction for Tim O’Brien Homes, panels will generate as much electricity, averaged annually, as the home uses, so the electric bill “nets out” to zero.

The panels’ cost should add around $40 to the mortgage payment, but the energy savings should more than offset that cost.

Built by Science

While you can slap solar on any roof, net zero solar requires the type of energy-conserving homes that Tim O’Brien builds—homes with thick insulation, air sealing to eliminate drafts, efficient heating, cooling and lighting, and ventilation to ensure fresh indoor air. Crafting them requires a builder steeped in the science of building.

Such builders are multiplying. The Department of Energy’s Zero Energy Ready program website lists more than 300 of them, and training groups are doing a brisk business. Nancy Bakement, Executive Director of the Energy and Environmental Building Association (EEBA), which hosts building science seminars around the U.S., says that it trained 1,500 construction professionals last year, the most ever.

These professionals are taking zero energy construction from a small niche to housing’s mainstream.

Shrinking Arrays

One such pro is Dave Packer, a semi-custom builder in Bakersfield, Calif. In 2005 he completed a 3,000 square-foot home with a 10-kilowatt (kW) solar array that left the homeowners with “just a small annual electric bill.” Then in 2016 he built an equally sized home for the same clients with system half that size. At end of the first year they received a $100 refund from the utility.

Packer credits this improvement to building science education, to panels that cost half what they did 10 years ago, and to improved system efficiencies.

Packer is also one of the first builders in his market to offer a Tesla home battery system. Bakersfield has time-of-day pricing, so when rates are low in midday, the panels place excess power in the battery. The home can draws from this stored power in late afternoon and early evening when rates triple. The battery also provides backup power if the grid goes down.

These technologies let him make a bold claim. “The energy savings can recoup the cost of the panels in as little as 5 to 7 years,” he says. “After that, power is free.” With most solar manufacturers estimating a 25-year service life, that’s 18 to 20 years of free power, according to Packer.

What if the homeowners don’t play to stay put for more than a few years? A Lawrence Berkeley National Lab (LBL) study found that a home with solar sells for an average $15,000 more than comparable home without it and sells 20 percent faster.

Scaling Up

Favorable economics are fueling another trend: zero energy developments. Tim O’Brien Homes is testing the waters at the 34-lot Red Fox Crossing, but other builders have gone in at a larger scale.

One of these is Thrive Homebuilders in Denver, which will certify all of the 240 homes it completes this year under the Zero Energy Ready program. CEO Gene Myers says that the company’s homes include rooftop solar panels and a Tesla battery, though as Tesla struggles to fulfill orders, Myers is also evaluating batteries from Sonnon and Panasonic.

He also understands that the typical buyer will only pay for solar if the cost zeroes out. This isn’t an issue with most of Thrive’s homes, with are priced from the $500,000s (mid-market for the Denver area), but it has proven a challenge in lower-priced townhomes.

To address the challenge, Thrive has partnered with Sun Street Solar, which installs and owns the panels on the townhomes Thrive builds and agrees to charge homeowners no more than 80 percent of the prevailing electric rate. (Solar City and Sunrun offer similar pricing models.) While the homeowners never enjoy free power, they get a reduced rate at no additional cost to them.

Like North and Packer, Myers emphasizes that solar will only deliver its full value in a very efficient home. “The house should conserve so much energy that a small solar system can satisfy its needs,” he says.

Factory-Made

Myers is also a believer in offsite construction, where large, factory-built wall and floor panels are assembled on the job site. He suspects that the quality and cost control possible in a factory could be the key to a mass market for zero energy.

That’s why he has been in discussions with Unity Homes. In 2017, Unity opened an automated plant in Keene, NH that can manufacture the panels for 100 zero-energy homes per year with a single shift of just 20 workers. Now it wants to open a plant in Colorado, with Thrive as its main builder customer.

Like manufacturers of everything from shoes to SUVs, Unity has embraced Lean production, a systematic program for eliminating waste in all its forms.

Results of the Lean approach show up in all of Unity’s processes. For instance rather than drawing each floor plan, architects select from a database with thousands of pre-configured floor plan areas, or “patterns.” These range from individual rooms to combinations like bedroom/closet/bath or bedroom/entryway that they can quickly assemble in an endless array of combinations.

Optimization continues at the factory, where the company makes pre-insulated panels (a rarity in the U.S.) and is looking at ways to pre-install wiring and drywall. At the jobsite, crews install rubber gaskets wherever two panels meet.

One tough spot to air seal is where the second story floor framing sits on the first-story walls. Unity solves the problem by placing the second floor frame on the inside of the walls panels. It sits on 2.5 inch thick service layer, the stud wall through which electricians run wiring. The service layer is fastened in a way that transfers the floor’s weight to the main wall panels. “It’s a highly engineered system,” says Andrew Dey, Unity’s Operations director.

With automation and optimization, Unity can build super-efficient, zero energy homes priced for mainstream buyers. Its 1,100-1,500 square foot “Xyla” homes sell for $134 to $195 per square foot. “You will find places where these costs are high relative to conventional building, and places where they’re competitive,” says Unity founder Tedd Benson. However he says that costs approximate those of other high-performance builders.

By prioritizing efficiency at the factory, Unity can also focus its skilled workers on the home’s visible craftsmanship. That was evident In June, when it hosted an open house at a three-bedroom, zero energy Xyla in Guilford, Vt. The home had a 10-kW solar system and a Tesla Powerwall 2.0 battery but those weren’t what made the biggest impression. That credit went to the interior, a bright and inviting space with vaulted ceilings, visible posts and beams, and custom milled hickory flooring.

It’s those qualities that have sustained Myers’ interest in Unity’s product. Like every builder we spoke with for this article, he understands that people want a beautiful home that enhances their lifestyle, and will only consider solar once those needs have been met. “We want our typical buyer to fall in love with one of our home designs,” he says. “Then we tell them oh by the way, this home makes its own energy.”