$188,000 homes in Colo.
Inspired by what he saw, Walker decided to replicate the building. With the help of students from a University of Denver work-study program, his company was able to complete two experimental net-zero homes -- the second of which recently sold for under $190,000.
Having perfected its net-zero design, Oakwood plans to start marketing more of the homes in Colorado later this year. Each four-bedroom house will feature rooftop solar panels, a high-efficiency tankless water heater, super-insulated windows and airtight construction.
With a $188,000 price tag -- only $9,000 more than Oakwood's Energy Star version of the same house -- it could soon be the most affordable net-zero home in the country. With about $750 in energy savings predicted annually, homeowners are expected to see a full return on their investment in less than 12 years.
"We've hit a price point that no one else has been able to hit in our marketplace," says Walker, and "we've gotten a lot of great response."
At least a dozen other U.S. commercial homebuilders have begun to offer net-zero residences. The Los Angeles-based company KB Home recently introduced a net-zero option for its houses in parts of Florida, Texas, Colorado and California. Another company, Nexus EnergyHomes, is building 59 duplex units in Frederick, Md., and 14 additional houses near the Chesapeake Bay. The duplexes are about 1,700 square feet -- the same size as Oakwood's homes -- and sell for $275,000 and up.
Each commercial and residential building employs a unique blend of renewable energy and architectural design to reach net zero, but there are some characteristics that nearly every structure shares. Most use solar panels to achieve the bulk of their power and have numerous windows to minimize the need for artificial light. Tight insulation and low-energy appliances are also key elements. Paradoxically, most buildings actually receive electricity bills -- though not very many.
This happens because a net-zero building may need to draw electricity from the grid to power its lights at night, for example, then returns that energy the next day, when its solar panels are most efficient. Likewise, residents may have to pay for heating costs in the winter, but in the summer they would receive a check for their overflow of energy.
Transitioning into a net-zero world without electric bills may sound like a no-brainer, but the technology still faces significant obstacles.
Cost and space remain drawbacks
The success of a building depends largely on the people who use it. If occupants aren't committed to reducing their personal energy use by shutting windows and turning off appliances, a net-zero structure can easily lose its status, becoming just another "efficient" building.
Some areas are also poorly suited for net zero. A building needs enough sunshine to power its solar panels, and that's not always possible in a densely populated city, where tall buildings can cast shadows onto shorter ones. It's also tough to keep structures cool in very hot and humid climates, like in the Southeast, says Hobart. But most experts agree the main barrier is still the price.
"Most building owners aren't going to add 1 percent to their costs. They are just going to build to code," Hobart says. And retrofitting existing buildings to be net zero becomes even costlier.
"When you put all the pieces together, the payback becomes so great that it doesn't make sense," Walker says of the retrofits. Aside from solar panels, thicker windows, and a new heating and cooling system, buildings often need far more insulation than the walls can hold. That requires shrinking rooms or expanding the exterior, which isn't cheap. Walker believes net-zero upgrades are for people who "are less worried about payback and more concerned to do something good for the environment."