Solar panels installed on the roof as part of the renovation of a 90-year-old rowhouse in Petworth are expected to generate all the energy the house needs, making it a “net-zero” property. (Photo by Tanya Topolewski)

Ever since Washington-based builder Tanya Topolewski quit her job with a large developer and struck out on her own, she’s specialized in environmentally friendly building projects. But her latest overhaul of a 90-year-old rowhouse in D.C.’s Petworth neighborhood takes things to a new level.

The house was completely rebuilt to use only a fraction of the energy it once required. With the addition of solar panels on the roof, it is expected to produce all of the energy it will take to run the four-bedroom, 31 / 2-bath home, possibly allowing the new owner to say goodbye to electric bills.

It’s Topolewski’s third residential rehab in Petworth and the one that finally achieved a goal she’d been aiming at since she founded her company, True Turtle, in the mid-2000s.

“To say that you’ve built a net-zero building puts you at a different echelon of green builder,” Topolewski says. Or, as her general contractor, Chris Toussaint of C.A.T. Consulting Service, puts it: “We just did this to say that we could — for the bragging rights.”

Not only is it a milestone for the Takoma-based developer, it maybe the first “net-zero” overhaul of a rowhouse in Washington, according to several people in the local green building community.

“There are very few net-zero gut rehab projects,” says Courtney Baker, residential operations manager at the U.S. Green Building Council, which runs LEED, the country’s most popular energy- and the environment-focused construction certification program.

The USGBC has just three net-zero home remodeling projects listed in its national database of LEED-certified homes. None are in the Washington area. And they represent a tiny fraction of the buildings the group has certified in recent years, Baker says.

“It’s a lot easier to build a new home to be more energy-efficient than to fill all the leaks in an old D.C. rowhouse,” he says.

Nonetheless, experts say we’re going to need more of these super-insulated, energy-efficient overhauls if the country is ever going to get serious about curtailing global warming. Buildings account for 30 percent of the country’s total greenhouse gas emissions, according to the U.S. Environmental Protection Agency. And, as builders in European countries such as Germany are demonstrating in greater numbers, turning a drafty architectural relic into a paragon of energy efficiency is a daunting but not impossible task.

Topolewski, who sold the house in July for $725,000, is also seeking LEED Platinum certification. But it’s net-zero status that sets it apart, says William Updike, an official with the D.C. Department of Environment.

He says one of the special things about this project is that “it shows what’s possible” in the world of commercial development.

“Obviously, she’s getting a return on her investment,” Updike says. “She’s a good role model for other developers. If one rowhouse can do it, then all rowhouses can.”

Topolewski says she made 15 design changes over the winter and spring before she locked in the right mix of energy efficiency and solar panels. She says she spent $50,000 on the green elements of the house, which included $25,000 for the solar panels; $10,000 for the energy recovery ventilator, heat pump, hot water heater, windows and insulation; and $15,000 to meet the requirements of the LEED certification.

She says such work is typically much more expensive, but her crew’s previous experience allowed them to work more efficiently and keep labor costs lower.

Rowhouses have only so much roof space, limiting the size of solar arrays. So before even contemplating the panels, she focused on making the house 50 percent more energy-efficient than a new house built to D.C. zoning code. Then Topolewski calculated exactly how much solar power it would take to heat and cool the place, keep the lights on, and run all the appliances, televisions and other electronics used in a typical home of its size.

In a final energy audit to see if it really would perform up to the “net-zero” standard, the house scored a zero on the U.S. Department of Energy’s Home Energy Rating Score (HERS) index. Most existing homes have a HERS score of about 130. An Energy Star home has a HERS of between 70 and 85.

But getting there was a struggle for a number of reasons, Topolewski says.

Complicating matters was the east-west position of the house. A southern exposure gets the most sunshine, but when it comes to rehabbing existing homes, builders must make the best with what’s there. Topolewski packed the roof of the house with nearly as many panels as it could hold. The solar company installed them at the maximum 25-degree tilt (any greater angle would have been a wind hazard, she says) in order to soak up enough rays to power the entire house.

The house’s brick walls posed another challenge.

“You could literally put your hands on the walls and feel the air passing through” the walls, Topolewski says.

Then there were the party walls, or walls shared with the neighboring homes. One would think the attached houses would provide stellar insulation. But on their last job, a LEED Platinum overhaul of a rowhouse on Varnum Street in Petworth, Topolewski and Toussaint belatedly discovered how much heating and air conditioning escaped through those walls. In the end, the pair abandoned hope of going net-zero on that project.

“We just didn’t make it with the Varnum house,” she says. “We got close but it was just too onerous and expensive” to reduce the energy load so dramatically.

This time around, they took special care to insulate the party walls, as well as the area around the house’s original chimney and any place where walls and floors came together.

“We spent $1,500 just on cans of spray foam” insulation alone, she says.

And still, there were lots of surprises. Results from an early spate of energy efficiency tests were dismal.

“It was pretty shocking, especially since we had already done a ton of work” to seal up the worst drafts and tighten the overall building envelop, Topolewski says.

She was so concerned about failing to reach the efficiency goal that she came up with a backup plan: At that point, the roof had room for just two more solar panels. She was ready to install the additional solar and awnings to shade the back of the house. But in the end, the house hit its numbers without additional changes.

Whether the solar panels will actually produce enough energy to cover all the home’s electricity usage, however, will depend largely on the lifestyle of the new owner, cautions Andrew Corral, a green-building rater with Elysian Energy, who conducted the HERS testing.

“For a renovation, they did a great job,” says Corral, noting he comes across few such extremely green residential rehabs because they are so hard to do well. He says most of the energy-efficient projects he rates in the Washington area are new construction.

That’s also the trend nationwide, according to Michelle Desiderio, a vice president at Home Innovations Research Labs, an Upper Marlboro-based subsidiary of the National Association of Home Builders, which runs a national green building certification program that competes with LEED. Desiderio says the group has certified far fewer green remodeling jobs than new buildings, “which is too bad, because the biggest bang for the buck is going into these older homes and multi-family buildings and making those improvements,” she says.

Desiderio says she thinks home remodelers may be reluctant to push costly green renovations in today’s economy. But the degrees of difficulty and risk are also factors.

“You just never know what you’re going to find [when you remodel an existing home] — what the previous homeowner did or what’s behind the walls,” she says.

The new owner, Florence Petizon, says she wasn’t looking for a net-zero home.

“I was just a regular person looking for a regular house in D.C.,” says Petizon, who came to Washington to work for an international organization six years ago and decided it was time to buy her own place. She says the environmentally friendly attributes weren’t on her priority list, but they are a big plus and she’s extremely happy that the house is going for LEED Platinum certification as well.

“At the beginning, I just loved the house and the way it was built,” she says. “But I am extremely happy . . . to able to live in a more sustainable environment.”

Christine MacDonald is a freelance writer.