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Lakesideca News

Maine Firm Offers Net-Zero In-Law Flat

BrightBuilt Home sees a growing need for small, high-performance accessory dwellings

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BrightBuilt Home's In-Law Flat is available in one- and two-bedroom versions. It's designed to meet rising demands for small, energy-efficient dwellings.
Image Credit: BrightBuilt Home

Maine-based BrightBuilt Home is betting that changing demographic patterns will mean increased demand for small, energy-efficient dwellings that can be ready in less time than conventional site-built houses.

The is the 11th design in a series of high-performance BrightBuilt houses. Kaplan Thompson Architects spun off the company as a separate entity in 2013. Since then, BrightBuilt has built or designed 67 houses.

The line of net-zero homes has its origins in the , designed for a site in Rockport, Maine, in 2005 and built in panelized form by Bensonwood. The BrightBuilt line now includes a range of styles and sizes up to 2,700 square feet, including two that can be configured with as many as five bedrooms.

But it was a number of demographic trends that convinced the company of a growing need for smaller houses that could operate at net-zero energy and be kept relatively affordable with the efficiencies of off-site modular construction. According to a statement from the firm, those trends included an increased number of multi-generational households, an increase in the divorce rate of people over 50, and the “staggering growth” of interest in short-term rentals, especially in New England.

In-Law Flats start at $135,000, not including site work. The one-bedroom model is 14 feet wide and 42 feet long; the two-bedroom model adds 12 feet to the length. It has triple-glazed windows, double-stud exterior walls 10 inches thick and insulated with cellulose, I-joist floor framing, and a truss roof.

In a telephone call, Phil Kaplan said the base model is heated with electric resistance heating. Although the strip heaters use more electricity than a heat pump would, they are a lot less expensive to install, and the design skirts potential problems that can crop up with the outdoor compressors that air-source heat pumps need.

“The way we like to think about it is that it counts as net-zero if you can get enough solar on the roof,” Kaplan said, “and with these [heating] loads we can.”

BrightBuilt director Parlin Meyer said in an email the houses arrive solar-ready. “We’ve run modeling per typical occupancy, usages, and all appliances and arrived at a solar array of 4.2 kW for getting to net-zero,” she said. “More than ample room on the roof to support an array of this size.”

The house is delivered to the site in essentially finished condition, Kaplan said, requiring little on-site work for completion. House and roof are shipped separately, and because the air barrier is located at ceiling rather than roof level, airtightness can be tested at the factory. The goal is 1.5 air changes per hour at 50 pascals.

Flexibility is key to the design

Kaplan sees a variety of uses for the In-Law Flat. One could be installed as an accessory dwelling to a larger home for use by parents or other relatives, and moved to a different location when it’s no longer needed for that purpose. The firm is working on an off-grid version suited for remote locations where builders versed in high-performance houses are scarce, and a connection to the grid prohibitively expensive.

“Flexibility is huge,” Kaplan said. So is the potential demand. Sixty people contacted the firm in the first week after the design was announced.

For now, BrightBuilt Home uses two modular builders — Simplex Modular Homes in Pennsylvania, and New England Homes in New Hampshire — and counts the swath from Maine to Virginia as its principal market. Although most BrightBuilt models are either modular or panelized, Kaplan says that in some cases it’s more economical to stick-build the houses on site.

“Just in the last year or so we’ve loosened up on our mandate that everything must be built in the factory, must be off-site construction,” he said. “We’ve realized that particularly in Maine, where most of our houses are sold, labor is cheaper. People understand high performance, so site-built sometimes makes more sense.

“But they’re all high-performance,” he added. “We’ve never done anything that’s not. That’s kind of off the table.”


  1. User avater
    Dana Dorsett | | #1

    No air conditioning?
    "Kaplan said the base model is heated with electric resistance heating. Although the strip heaters use more electricity than a heat pump would, they are a lot less expensive to install, and the design skirts potential problems that can crop up with the outdoor compressors that air-source heat pumps need."

    A half-ton PTHP with it's own internal strip-heat / backup would have half the space heating power use (or less), and cheaper than the additional PV required to run the resistance heating. (It might even be cheaper to install than electric baseboards in each room.)

    It would also be able to cool a Net Zero house that size more efficiently (and quietly) than a window-shaker.

    Was that option even explored?

    The floor plan doesn't indicate a location or type water heater (probably the largest energy use category in this house, more than space heating.) What is the hot water source?

  2. User avater GBA Editor
    Scott Gibson | | #2

    Heat pumps are an option

    Buyers can specify a heat pump if they want one.

  3. User avater
    Phil Kaplan | | #3

    RE: no air conditioning?
    Dana, there's a 40-gal insulated electric Marathon water heather just outside the bedroom, not labeled.

    A PTHP or heat pumps, as Scott mentions, are options and improvements, energy-wise. My guess is that many people will choose them instead. The optional tradeoff we've made for the base model is based on what can ship directly out of the factory.

  4. User avater
    Dana Dorsett | | #4

    Thanks Phil
    So the water heater is the unlabeled circle inside a small closet at one end of the "SLEEPING NOOK OPTION"- got it!

  5. Peter L | | #5

    1 Ton Mitsu
    A 1 ton Mitsubishi A/C with heat pump can cool/heat that home with ease. Priced at $1,600 with install, that's a hard to beat heating/cooling system. They are very reliable so I don't understand why they believe they are "problematic" ??

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