Kaplan Thompson Architects

Kaplan Thompson Architects works out of Portland, Maine on Passive House homes, deep-energy retrofits, affordable multifamily and institutional projects, generally within about four hours' travel of the office. Health is not the firm's top-line pitch — the stated priorities are beauty, sustainability, affordability and community — but every project page carries a structured wellness block, and the firm publishes an embodied carbon figure alongside each project, which almost no residential practice does.

Spark Side, a house in Durham, New Hampshire, is the best-documented project in the portfolio, and the documentation comes from Phius rather than the architect. Phius's own results page confirms it as the single-family winner of the 2025 Phius Passive Projects Design Competition, judged on performance, difficulty, cost-effectiveness, design, craftsmanship and health — the last defined as the use of non-toxic materials. The certification tier is PHIUS+ 2018 Source Zero, the predecessor of today's Phius ZERO. The house tested at 0.25 ACH50 behind double-stud walls holding twelve inches of dense-packed cellulose at R-45, an R-95 roof and triple glazing at U-0.13, and its published embodied carbon is 146 gCO₂e/m². Phius also recorded a site-tested 83% efficiency on the Zehnder Q450 ERV — a commissioned number rather than a specified one, which is rarer in this field than it should be. The house took a 2025 AIA New Hampshire Merit Award as well.

One figure travels with the project and deserves its scope kept intact: Spark Side requires 90% less energy to heat and cool than a code-built home of the same size. That is heating and cooling only, measured against an unnamed code baseline, and it originates with the project team rather than an independent assessor — though Phius certified the building and chose to publish the number under its own masthead, which is about as strong as a project claim gets. The trade press has already dropped the words "to heat and cool" in at least one caption and overstated it. The four words matter.

The wellness specification at Spark Side is specific: an EPA Indoor airPLUS qualified home, optimised daylighting, mechanical fresh air, low- and no-VOC finishes to LEED-H criteria, formaldehyde-free construction. Other projects add Health Product Declarations and Red List compliance. What does not exist is measurement — no indoor air quality, CO₂ or particulate data has been published for any completed house, and no filter ratings are named anywhere. The firm builds and specifies the preconditions for good air, and documents its material choices better than most. It does not test the result.