David Horobin has a photo archive of about 5,000 photos he’s taken so far of the green house project he’s building for his family on a Napa hillside.

Among them are what he calls the “milestone” days, like getting the roof overhead and a floor underfoot.

Working with contractor Patrick Bentley, owner of Bentley Construction and Concrete, Inc., in Napa, Horobin, a Cambridge-trained architect and long-time proponent of buildings that are healthy both for people and the earth, launched his project last June. The Register is checking in periodically on the progress — and the decisions an architect makes when building for his own family.

The Horobin family is putting in a considerable amount of “sweat equity” on the project. A partner in the design firm Estudio Verde, Horobin is operating from a temporary office in the rooms in his new house, while his wife, Lynn and sons, Christopher and Andrew, have done everything from help laying the radiant heating system in the floor to helping assemble the innovative foam blocks that provide the super insulated and highly fire-resistant walls.

With the interior steel frames in place, the next challenge was a race to install the roof and beat the first rains of autumn.

The house’s hip roof, made from insulated panels that look like a giant’s ice cream sandwiches by Premier Building Systems, was assembled on the ground and hoisted into place by a crane.

The advantage of constructing the roof on the ground is safety for workers, Bentley said; but in addition it saves time and therefore labor, he noted. Among Horobin’s photo archives is a video showing Bentley at the controls of the crane that lifted the huge completed roof structures into place, a procedure that required considerable precision. The alignment needs to be exact before the roof is lowered, Horobin explained, which is no easy task.

“Patrick’s finesse with machines is amazing,” Horobin said. “I would not want you to print this because it might go to his head, but having the right contractor makes all the difference.”

Horobin also had high praise for the crew Bentley brought in to pour cement floors once the Horobin family had installed the yards and yards of piping for the radiant heating in the floors in the kitchen, dining and living room — a project, Horobin said, that took the family about four or five hours to complete. Once the Pex tubing was in place, the crew poured a four-inch thick cement covering over it. “You never see the pipes again,” Horobin said. “You just feel the warmth.”

Horobin plans to heat and cool the house by means of a swimming pool, a method he has promised to explain in detail in a future article. Water will be piped through the floors (and in some cases the ceiling) and controlled by thermostats so that the Horobins can select the temperature for different zones in the house. 

Whether he puts radiant heating in the floor or the ceiling “depends on the function of the room,” Horobin said. Floor heating, for example, is preferable in a living room where the family might choose to sit on the floor; in a home office, however, where there will be “a lot of things on the floor” he would choose to install the heating system in the ceiling.

“I prefer the comfort of radiant heating,” Horobin said. “One of the things I hate is the drafts from forced air heating. Whatever goes into the system goes throughout the house.”

Horobin said his source for radiant heating is a Napa company, Warm Floors, headed by Mike Lutrell.

Horobin said the other key milestone is the windows, which he’s placed throughout the house with another precise eye for the path of the sun over the house. He’s opted for Jeldwin insulated windows.

Roof, walls and floors in place, the Horobin house is definitely looking more like a home and less like an intriguing arrangement of white foam.

In fact, they’ve even had their first meal in the house: pancakes, bacon and sausages cooked by Lynn Horobin on a grill the family brought over for the occasion.

Next up we’ll be watching Patrick Bentley’s team install the concrete counters that will be a centerpiece of a green kitchen.

And then one of these days, Horobin is going to explain how his swimming pool will heat and cool his green house.