Anthony Maschmedt, founder and principal of Seattle-based Dwell Development, prefers to use a different term than “duplex” to describe his new project in Kirkland, Wash.

“This is luxury housing—they’re two large single-family homes that just happen to be attached,” Maschmedt says. The sizable homes (3,800 and 4,200 square feet) are larger than their two detached neighbors in the four-house development, which serves as an example of how to build to the highest standards of environmental sustainability within a contemporary aesthetic that resonates with buyers. The two attached homes sold for an average price of $476 per square foot, well above the market rate.

Since 2005, Dwell Development has built about 200 houses—all infill projects—in the Seattle area. Maschmedt learned that a parcel in Kirkland, a Seattle suburb, was coming on the market and negotiated the sale of the neighboring property as well. At 85 feet wide, one of the lots was appropriate for two detached homes, while the other 65-foot-wide parcel was better suited for two attached homes since the required setbacks would have meant a 5-foot loss of interior space for each home. The attached homes are divided by two separate party walls, each heavily insulated (R-14) for soundproofing.

Designed by Medici Architects of Bellevue, Wash., the two attached homes have very different floor plans. The larger (shown here) has three levels and features a more traditional layout: The main level comprises the living, dining, and kitchen area, while the upper level holds three bedrooms, and the lower level has a guest room and rec room. The smaller, two-­level home has a master suite on the main level; the lower level offers an additional master suite and two bedrooms. Both have expansive decks with sweeping views of Lake Washington and downtown Seattle. Interiors feature zero-VOC painted surfaces and flooring that is a mix of polished concrete slab and solid black walnut. The exteriors are landscaped with native plants and the driveways are paved with pervious concrete. The houses are clad in a contemporary mix of white standing-seam metal panels, fiber cement siding, and reclaimed barn wood.

From the beginning, the firm has only produced homes that are Built Green 5-Star certified, the highest rating for the area’s own sustainable building program. According to Maschmedt, who is the chair of Built Green’s executive committee, the rating is roughly equivalent to LEED Platinum. Since 2009, all of its homes also have been net-zero-ready per DOE standards; the company follows the Passive House program to get there.

While the homes’ energy-saving features are abundant, the company’s “reclaimed modern” aesthetic is often the bigger selling point, notes Maschmedt. “It’s a constant battle to educate our buyers about what makes a home healthier and better,” he says. The good news is that there is a high demand for Dwell Development’s projects, meaning the firm often gets the pleasure of selling to customers who are truly committed to the homes’ sustainability goals.

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