When zero adds value.

The lights are on at the three-bedroom rancher in Liberty Lake, but nobody's home.

Sound wasteful? It's for an earth-friendly cause. Along with the home's other appliances, the lights use energy produced by the 19 solar panels on the roof, with power consumption carefully recorded and studied. The model home doubles as a prototype "net-zero" home built by Greenstone Corp. — it generates as much renewable energy as it uses.

Sound expensive? A net-zero home's cost depends on how you look at it.

Net-zero homes cost 4% to 12% more than their standard counterparts, depending on the house and whom you ask. But there's a good chance you'll save more on energy than the difference in your monthly mortgage, the U.S. Department of Energy says. It's something for future-minded homebuyers to consider now, as net-zero construction becomes the norm elsewhere and as rising global temperatures are expected to boost energy demand. (While the Environmental Protection Agency expects Americans to use less energy for heating, it expects we'll use that much and then some for cooling.)

Gavin Tenold has already noticed more homebuyers seeking net-zero options, compared with a decade ago. Tenold, construction manager at Copeland Architecture & Construction of Spokane, also co-owns Northwest Renewables, a solar company.

"It's a pretty clear choice, and all our clients see this," Sam Rodell says.

Buyers around 35 to 42 seem particularly interested, he says: "We recognize that climate change will affect the marketplace," including energy prices.

In Liberty Lake, the three-bedroom rancher would use more energy if people lived in it. But, as a prototype, it works so well — in fact, producing more energy than it uses — that Greenstone plans to build five more as it keeps trying to figure out how to build comfortable, cost-effective net-zero homes en masse; the developer puts up about 250 Inland Northwest homes a year.

"Really what it's telling us is, ‘Hey, this works,'" says James Morgan, Greenstone's purchasing manager.

Architects and builders already working on custom net-zero homes agree that while upfront costs are higher, the energy savings make them a savvy choice.

The extra money goes toward features and systems that collect energy (such as solar panels or wind turbines) and conserve it (such as airtight construction, smarter insulation, and triple-pane windows).

Architect Sam Rodell's firm provides cost comparisons to each client: One set of monthly numbers for their house built "to code." Another set for the same house built with super-efficient construction and systems. Every time, the second set — based on energy rates and the family's expected consumption— shows net savings starting in Month 1, Rodell says.

Meanwhile, net-zero homes' insulation, windows, sealing, and heating and cooling systems provide even temperatures and quiet. Filtration systems minimize pollutants (imagine: no wildfire smoke). As quality-built structures, the DOE says, these homes provide lasting value.

"It's a pretty clear choice, and all our clients see this," Rodell says. "No one says, ‘Build the worse building that costs more.'"