Keyan Mizani and Alexia Zerbinis, the husband-and-wife architects behind eMZed Architecture, have grown accustomed to passers-by pausing on the sidewalk outside their home and studio in Portland, Oregon.

“I’m just thrilled by the number of exclamations I hear, how intrigued people are,” Keyan says. “We did build this as a demonstration house. We wanted to show what you can do with limited means.”

$6,000 Deconstruction & Salvaging (After City Grant)	$382,250 High-Performance Shell	$2,400 Mini-Split HVAC
$10,100 Zehnder Energy Recovery Ventilator	$32,000 Cabinets & Counters	$3,000 Sliding Sunscreen
$12,200 9.5 kW Solar PV Panels (After Rebates)	$19,200 Wood Flooring	$5,775 Wood Stairway
$19,500 Tile	$35,000 Drywall	$13,575 Steelwork
$418,000 Other Construction Costs
Grand Total: $950,000

With its pitched roof, inviting front porch, and lush landscaping, the Treehouse, as its designer-owners call it, fits well into its leafy neighborhood of early 20th-century bungalows. Looking closer, though, reveals not only an ultra-green home with a carbon footprint dramatically less than that of a conventional design, but also an architectural Swiss Army knife of indoor/outdoor configurations, spaces within spaces, and creative use of materials to save money.

The couple’s ground-floor architecture studio not only has its own glass storefront entrance, but can be converted to either an accessory dwelling unit (ADU) or a garage. A sliding exterior sunscreen on the top floor helps minimize summertime heat gain.

The cantilevered front balcony can become an extended part of the living room thanks to a sliding glass partition behind it, and its automated roll-down screen can make it feel even more like interior space. A guest room and full bath on the ground floor can be closed off with pocket doors to create a private suite in keeping with barrier-free design principles, should the couple need as they age.

Yet those neighbors pausing on the sidewalk may miss Treehouse’s most important design feature: its achieving net-zero energy.

While the couple readily admit their $950,000 budget doesn’t seem cheap, the amount represents a home and a separate design studio (as well as potential revenue if the space is leased as an ADU). But more importantly, Keyan and Alexia pay essentially nothing for electricity or heating while staying comfortable year-round. That’s because the house has as robust a building envelope as a certified Passive House.

“We focused on creating a sustainable, highly durable, high-performance building shell,” explains Keyan, “which costs money: specialized windows, an extra layer of insulation wrapped around the outside of the structure, and super energy-efficient HVAC equipment and lighting. The challenge was, ‘Can we do this for about $250 a square foot?’”

The couple, who share the five-bedroom, 3,800-square-foot home and office with two teenage sons (along with Keyan’s mother for several recent months in the guest suite), estimate they spent about $15 extra per square foot on the thermal envelope. This allows their 9.5-kiloWatt rooftop photovoltaic system to supply the home’s total electricity and heating needs throughout the year (more than they need in summer and slightly less in winter, equaling out over the course of a year), save for a $12 grid-connection fee.

To offset the investments in insulation and other high-performance systems, the couple found other ways to save. They used HardiePlank fiber-cement lap siding for much of the exterior instead of wood. What appears to be Japanese-style shou sugi ban charred siding on the balcony is actually just stained cedar.

Inside, walls are mostly simple drywall, and the kitchen makes use of IKEA cabinetry as well as simple birch plywood. They also made creative use of color, creating a green, blue, and orange painting scheme to further break down the house into parts; outside, plants like tangerine scream, witch hazel, and Washington Hawthorne trees were chosen in part for their matching tones.

While the house can be sealed as tightly as a Thermos, the design is all about fresh air and natural light. Glass patio doors at the rear dining area act in tandem with the front-balcony movable glass to make the inside feel like an extension of the outdoors. Above each doorway is a transom window.

“We always try to paint with light,” Alexia says. “Make the shapes simple and beautiful, and let the light make them sing.”

The Treehouse design may stop pedestrians in their tracks not just because it balances traditional and contemporary sustainable design principles, but also because it reflects Alexia and Keyan’s complementary architectural skills. It’s teeming with ingenious design moves, but also retains a visual clarity.

“It would be easy to say that we split by personality into big picture, pattern ideas (me) and precise, detailed ideas and project execution (Keyan),” Alexia adds, “but that would be missing the alchemy of how it gets mixed up between the two of us. Keyan is good at generating many options; I’m often useful in paring them down. We both like residential projects as an act of technical problem solving and tailoring to merge the pragmatic and the poetic.”

More Budget Breakdown:

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A DIY Couple Turn a Bus Into a Dreamy, Off-Grid Home for $20K

Project Credits:

Architect: eMZed Architecture

Builder: Birdsmouth Construction

Structural Engineer: BK Engineers

Energy Modeling and Net-Zero Certification: Earth Advantage