NAPA and VALLEJO — A new phase of North Bay home manufacturing is rolling out of factories in Napa and Vallejo.

Manufactured homes are nothing new to the North Bay, including production at now shuttered GV Custom Modular in Healdsburg and Codding Steel Frame Solutions in Rohnert Park. But now, Napa-based Healthy Buildings Technology Group (www.hbtg.com) and Blu Homes (www.bluhomes.com), based in Boston and San Francisco, are producing homes with largely finished light-gauge steel–framed panels and including dozens of above-code environmentally friendly features.

Healthy Buildings Technology Group last week completed its first of two showcase OHome dwellings in Napa. Blu Homes has been rolling out the first 19 of its novel folding-panel construction homes from its 4-month-old Vallejo factory, and 50 are on order.

Last month, mostly finished wall and roof panels for a 640-square-foot, one-bedroom home left the company's south Napa factory and were trucked by flatbed to a site at the end of Darling Street in north Napa. Five days were scheduled for moving the panels into place by crane and screwing them together on the previously poured concrete pad, but assembly was done in two days, according to Chief Executive Officer Bob Massaro, LEED AP.

A second demonstration OHome unit, this one with 1,260 square feet and three bedrooms, will be built next to the first one. Both will share a garage on the property.

"The showcase models are demonstration homes designed to introduce our technology, green features, and materials and finishes to prospective buyers," Mr. Massaro said.

The company, launched early last year as an outgrowth of Mr. Massaro's nearly 13-year-old Healthy Buildings USA green-oriented construction business, is finalizing contracts with several single-family clients in areas from San Diego and Los Angeles and four in the Bay Area, according to Mr. Massaro. He said several developers also in discussion for projects that combine panels together for multifamily dwellings.

"They are interested in our speed of construction and the numerous green and net-zero energy features," Mr. Massaro said.

OHome models range in size from 150-square-foot loft-bed tiny homes to 1,600-square-foot, four-bedroom dwellings. In addition to a multifamily option, there is a 1,000-square-foot hexagonal interconnecting pod structure designed for offices or activity centers (OCenter) and classrooms (OClass) and a 100-square-foot building designed for beach or campground services called OKiosk. All the units are designed to be assembled on site by five workers and ready to inhabit in three weeks.

At Blu Home's 250,000-square-foot converted submarine periscope factory on Mare Island, the company has built and shipped four homes so far — the first went to Sonoma near the beginning of this year — five more were set to ship shortly and another 10 units are on the production floor, according to Maura McCarthy, co-founder and vice president of sales and marketing.

"Ninety-five percent of the orders are from individual owners, so we're really connected to real consumer demand," she said. "We can really feel when the market is excited or scared or afraid. We seem to be in a green spot in housing."

Blu Homes sales have tripled every year for the past three years, and this year bookings are on pace to top $30 million, Ms. McCarthy said.

In January, the company moved all its production from a Massachusetts plant to Vallejo because the Mare Island factory is more sophisticated and has a steel-and-glass look that's an effective metaphor for the company's design approach, she said.

The Solano factory also is closer to core buyer markets and is near a large concentration of skilled craftspeople and engineers, she added. Ten BluHome units previously had been delivered and unfolded in Sonoma County.

The Vallejo factory currently employs 80 and will be increasing to 100 in the next few months. The company plans to hire another 80 by mid-summer.

"We're doubling our workforce every six months," Ms. McCarthy said.

BluHome offers seven versions, ranging in size from the three- or four-bedroom Breezehouse model, one of which was delivered to Healdsburg, to the one-bedroom Element model. The proprietary design of strategically placed hinges allows portions 19 feet wide and with ceilings as high as 16 feet to occupy half the space when shipped by flatbed. A crane lifts the parts onto the foundation, and the entire home is unfolded and connected in one day. As much as possible is finished in the factory, including installation of appliances, radiant floor heating and solid-wood cabinetry, so that the on-site construction schedule can be only three weeks from foundation to final inspection, Ms. McCarthy said.

That can cut delivery costs dramatically compared with traditional modular homes, according to Ms. McCarthy. For example, instead of $35,000 to ship a modular home in sections up to nine feet wide from Northern California to Southern California, including police escort in certain places, the cost of a BluHome shipment can be as little as $3,000.