Four Boxes and a Roof The net-zero Great Diamond features double 2x4 stud walls, creating ample insulation space and a thermal break.

Four Boxes and a Roof The net-zero Great Diamond features double 2x4 stud walls, creating ample insulation space and a thermal break.

Credit: Trent Bell

Screen Shot The Great Diamonds airy screened porch,  breezeway, and garage are prefab add-ons.

Screen Shot The Great Diamond’s airy screened porch, breezeway, and garage are prefab add-ons.

Credit: Trent Bell

Low-Carbon Copy

Originally stick-built for real clients, this modular home merges middle-class affordability with net-zero status.

Net zero–energy custom homes are common enough, but rarer is the architect-designed building that achieves net zero for $139 per square foot, including a 6-kW photovoltaic (PV) system and basic site and foundation work. Kaplan Thompson Architects, partnering with Keiser Homes, makes affordability its mission. Case in point: the Great Diamond, occupying the neglected middle ground between custom homes and basic modular products.

“Custom homes typically start at $200 per square foot in our area,” explains Phil Kaplan, principal of Kaplan Thompson. “Keiser’s manufactured homes for the affordable market are about $90 per square foot. So we’re able to quote $139 per square foot to clients without causing sticker shock.” The key to hitting that price point, he says, is using energy modeling to find the equilibrium between mechanical, insulation, and PV performance. That precision has a second pay-off: When potential buyers question the negative numbers, out come the spreadsheets.

Part of the Modular Zero Collection, the 1,680-square-foot Great Diamond began life as a conventionally built home for carbon-conscious clients. The team value-engineered a concise box with double-stud framing and dense-pack cellulose insulation, resulting in R-40 walls and an R-60 roof. Not only is the near-perfect square efficient to build and insulate, its traditional New England form is a cinch to customize.

“When we decided to create the collection with Keiser, the house became a prime candidate” for net-zero modular conversion, Kaplan says. “When people want something a little different, we can change some of the details to make it more contemporary or traditional.”

While mirroring the original, the road-ready version is made of four 14-foot-by-30-foot modules—two on each floor—and a panelized third story with dormers, which can be ordered prefinished for a combined 2,200 square feet of living space. With a pitched metal roof atop classic old-fashioned proportions, its appearance belies how seriously it takes today’s environmental mandate. The house is clad in durable fiber-cement siding—4x10 sheets with battens on the lower part, horizontal boards above. Triple-glazed windows double up on envelope efficiencies, and sun-protecting overhangs wrap the south and west corners. Add-ons include a screened porch, garage, and breezeway.

Can a prefab business model honor individuality? In this case, yes. The firm will modify floor plans, within reason. “Everyone is asking us to tweak it a bit, that’s the irony of this,” Kaplan says. “Everyone who wants something at this level wants to make their mark.”