Small homes offer eco-advantages that larger ones do not: fewer building materials to consume, less space to heat and cool and furnish. They’re also financially efficient, which appeals to an increasing number of home buyers these days. It’s chic to build small, but when Asheville, N.C., builder Brian Knight went searching for house plans several years ago, he had trouble finding modest-size homes designed for passive heating and cooling.

That led Knight, who has degrees in business, construction management, and technology, to create his own. “Passive solar design is so site-specific, it’s hard to find in stock plans,” says Knight, owner of Springtime Homes. “Because our cottages are small, they can be positioned on a variety of lots with minor changes.”

Dubbed Springtime Cottages, the houses, which range from 1,433 to 1,544 square feet, consist of an open living area and master suite on the first floor and two bedrooms and a bath above. To keep construction costs at $139 to $150 per square foot, Knight designed a rectangular box with a 12:12 pitch roof and south-facing shed dormer. Not only is it economical to build and insulate, but the floor plan easily flips to accommodate site conditions. And with just four corners, it invites customization with wraparound porches, bump-outs, or a basement. These homes also offer the square footage of a full two-story house but with better thermal performance, since there’s less surface area where conditioned air can escape.

Not that these homes give up much energy. Designed to be oriented east-west, the building envelope is made of Eco-Panels polyurethane SIPs (R-26) and triple-pane fiberglass windows on all but the south side. Knight uses operable casement windows, which are comparatively airtight and thermally efficient. “The whole window opens for ventilation, acting as a scoop for breezes blowing by,” Knight says, “and compared to double-hung, there’s more glass per window area to let in light.” Mechanical systems include solar collectors that supply hot water, a heat pump for heating and cooling, and an Energy Recovery Ventilator that circulates fresh air.

Knight aims to fill a market void by balancing affordability, aesthetics, and performance. The two Springtime Cottages already constructed achieved HERS scores of 47 and 51. They’re also certified by the N.C. HealthyBuilt Homes program. “Our main approach to green building is to make the houses as cost-effective as possible,” Knight says, “while offering the best possible energy efficiency and the healthiest indoor air quality.”