For heating a space of such peculiar dimensions, Bonnifait and Giesen turned to a solar design principle called the Trombe wall—after Félix Trombe, the French engineer who popularized it in the 1960s—which they created in the corridor between the guest rooms and main house.
Oriented to catch the best afternoon and winter sun, the corridor is made of ten-inch-thick concrete blocks on the southern side, and a ten-inch insulated concrete floor. The thermal mass of these elements absorbs the heat from the sun through a double-glazed wall and distributes it throughout the house. Thus, what looks like a narrow buffer zone for privacy becomes the all-important heat sink.
“Ultimately, when there are no guests here, the door at the far end can be closed so all the heat will come through to the rest of the house,” Giesen says. “And because it’s a lower ceiling, the heat will want to rise up and come through here.”
For particularly chilly days, underfloor heating has been installed in seven independent zones, allowing for manual and automatic, sensor-driven operation. “When the heat drops below a certain level that will kick in,” Giesen explains. “Hopefully, most of the time, the sun will do that job.”
If all else fails, Giesen suggests a time-honored New Zealand approach. “There used to be a saying,” he says. “‘If you’re cold—put on a jersey.’”—K.P