The Seibert brothers are green builders entering new territory, literally, by renovating a former Mount Airy warehouse down the block from the famed Weavers Way market.

Scott and G.C. Seibert grew up in Jeffersonville, near Norristown, helping their parents renovate and maintain investment homes. The brothers got their start in the building business with projects such as Weccacoe Flats, a green-conscious development in Queen Village done through their company, Bancroft Green.

Then Scott Seibert moved his family into a 100-year-old house in Mount Airy. The neighborhood "is a real gem of diversity," he said, "and my wife and I wanted to expose our kids to that."

Now, the Seiberts are razing a warehouse on Carpenter Lane to construct a 25-unit condo and mixed-use building.

The project, 520 Carpenter Lane, will be Leadership in Energy and Environmental Design-certified (LEED). Construction is scheduled to start in early 2015 and, with some modular designs, should be completed in six to nine months, G.C. Seibert said.

Re:Vision Architecture is designing the three-story building, which also will include a public courtyard and garden, cafe tables, and shared work space available for rent.

Elfant Wissahickon is the real estate broker for the units, which range in price from $250,000 to $450,000.

The Seiberts also hope to incorporate "passive-house" design, to reduce the need for insulation and multiple water heaters.

Instead of a 50-gallon water tank in each unit, for example, they may install a 2,000-gallon tank that can service them all and be heated by solar power.

"It's like using a one-liter bottle vs. a six-pack," said G.C. Seibert. "There's less waste and less overhead."

Scott, 38, and G.C., 43, bought their first fixer-upper homes when they were in college.

"Our parents fixed up properties, and we spent weekends helping them do that," said G.C., who studied mechanical engineering at Lehigh University, then earned an MBA there.

Scott attended Carnegie Mellon for business and then worked at the Wharton School at the University of Pennsylvania.

Once they decided to go into business together, the brothers wanted to do things differently. Under the Bancroft Green name, they built Bancroft Green I and II and 715 S. Bancroft, employing features such as geothermal heating, green roofs to collect storm water runoff, reclaimed brick, bamboo flooring, dual-flush toilets, recycled-rubber patio materials, and herb gardens.

At Weccacoe Flats in Queen Village, the distinctive double-wide, single-floor design also featured heating/ventilation/air-conditioning contracted with MaGrann Associates. That firm recommended and installed such energy-efficient systems as mini split-air-source heat pumps for heating and cooling, and energy-recovery ventilators for energy savings and fresh-air flow.

Weccacoe Flats also employed modular building. It was set in place by crane after being built largely in a factory.

At 520 Carpenter Lane, the Seiberts are especially proud of the "coworking" space designated for the entire bottom floor.

The area will be divided into a multiuse party/conference/computer area with a common kitchen. It can be converted into guest rooms available to residents to rent for overnight stays.

The rear of the area will be landscaped with hammocks, a fire pit, and planters.

Currently, the brothers and their lone employee are working out of an Airstream trailer on the site of one of their next projects, a 30-unit student housing development for La Salle University. But Mount Airy will be their business' new home.

"Our corporate headquarters will be there, as well," Scott Seibert said of 520 Carpenter Lane.

He also hopes to operate the space as a type of incubator for start-ups.