Cornerspring Montessori School's Belfast, Maine campus — the first high-performance institutional building in the city — pairs a boldly contemporary form with Montessori pedagogy and the stringent Passive House standard for energy efficiency and indoor air quality. A superinsulated, air-sealed shell (R-50 walls, R-100 roof, triple-glazed windows) cut annual heating costs from $8,600 at the school's previous location to near zero, while a 16kW photovoltaic array and heat-recovery ventilation system round out the energy strategy — all without adding cost, since the shell investment was offset by simplified mechanical systems.

The single-story plan centers on a bar-like volume of four elementary classrooms bending around a flexible common space, with a smaller volume for circulation, administration, and the toddler room beneath a barn-like roof. A cantilevered gable entrance nods to the traditional rural schoolhouse. Large north-facing windows, direct outdoor access from every classroom, and a 35-acre wooded campus with bioswales and trails extend the learning environment well beyond the walls.

The design is shaped throughout by Montessori philosophy: independent learning, outdoor activity, and interaction among age groups, alongside accessibility, safety, and security. The four classrooms and central gathering space can be reconfigured in a variety of ways, supporting multi-age activities, performances, and community events, and reinforcing the building's role as both a learning environment and a civic presence for the school.

As the school's middle school program grew, OPAL returned to add a freestanding 1,000-square-foot Annex, matching the original building's form, materials, and Passive House performance while giving older students their own space. The Annex showcased a new construction method: prefabricated panels combining cross-laminated timber and wood fiber insulation, produced by OPAL's affiliated companies Timber HP and OPAL Build. Precision-cut from a 3D design model with windows and doors preinstalled, the panels assemble quickly on-site into a weathertight, all-wood envelope — increasing construction speed and precision while cutting site disturbance and carbon footprint.