Plant Prefab: The LivingHome 10 ADU

The annual Palm Springs celebration of all things modern, Modernism Week, isn't only about vintage or mid-century modern architecture, landscapes, fashion, cars, music, tableware, furnishings, and culture of Southern California. Those are highlights, to be sure.

But the signature festival, which occurred this year from February 13-23, also addresses how the principles of mid-century modern—from the clean lines and structural openness of the architectural style to the use of  "honest" materials—continues to manifest in contemporary architecture. Even in sustainable residential design. Even in an accessory dwelling unit (ADU) designed to be net-zero.

This year, delivered to a high-profile site right next to CAMP (Community and Meeting Place), Modernism Week's bustling headquarters and central hub, was a fresh-off-the-assembly-line structure by Plant Prefab: LivingHome 10. At just 496 square feet, the net-zero accessory dwelling unit included a living area, bathroom, bedroom (big enough for a queen bed), and fully equipped, galley-style kitchen. From the minute LivingHome 10 opened in the morning until the doors closed at night, curious passersby packed the ADU eager for a look.

This prototype, assembled in two months and with a price tag of $180,000 with the trailer, elicited hundreds of questions about construction and cost. One of the most curious remarks came from a gentleman who asked: "Has anyone put this on a barge as a floating home?" He then added, "I can think of a lot of places where this ADU would work. For people who don't want to wait close to a year to have something built, this is so fast and efficient."

The 411 on ADUs

ADUs are housing units built on an existing residential property—usually in the backyard. Also known as second suites, casitas or guesthouses, in-law suites, granny flats, and in Canada, laneway homes, ADUs usually are sized at 350 to 1,200 square feet. ADUs are quickly becoming a popular addition to our housing stock. They appeal to a wide range of buyers - from city governments and housing agencies to homeowners in urban areas where increased density is addressing population growth amid housing shortages.

In cities ranging from Minneapolis-St. Paul to Vancouver, Portland to Austin, Seattle to Los Angeles, ADUs present an affordable option to young or retired couples looking to purchase a home. ADUs also give homeowners an opportunity for parents or grandparents to age in place near family. Other homeowners build ADUs to live while constructing their primary residence, then lease them as AirBnBs or other longer-term rentals. Or they build ADUs intended as rentals from the get-go. 

Plant Prefab's LivingHome 10 goes further. The ADU provides a net-zero option that's fully customizable. The sustainable LivingHome 10 was also designed and constructed according to the company's rigorous Z6 environmental health and sustainability framework.

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Plant Prefab's Sustainable Option  

Plant Prefab started as the residential design studio LivingHomes, which in 2006 completed the first home internationally to achieve LEED Platinum certification. The late Ray Kappe designed that home. It was installed in eight hours!

Since then, the company has designed an additional 27 LivingHomes that were certified LEED Platinum. Five more have been certified LEED Gold. Architects at Plant Prefab and LivingHomes designed some of the models that clients can choose from and modify if they wish. Internationally known architects such as Yves Béhar, Kieran Timberlake, Douglas W. Burdge, and Toby Long have also designed LivingHomes. 

LEED, however, had limitations for Plant Prefab, says Amy Sims, Plant Prefab's Director of Design. She has concluded that the points-based program "doesn't address head-on many key environmental measures that we believe need to be minimized." So Plant Prefab developed its own environmental program or set of standards called Z6. The system clarifies and quantifies six critical metrics, Sims says: zero energy, zero water, zero emissions, zero carbon, zero waste, and "zero ignorance."

She adds that projects with a score of 85% or more "are considered achieved." None of the LivingHome models has yet achieved zero on every metric. "The point," she continues, "is to get as close as possible. We always, when designing a home, attempt to minimize or neutralize any negative environmental impacts. We also are constantly learning and improving, so that can positively address environmental issues with elements that, for example, sequester carbon and improve indoor air quality."

The ADU: LivingHome 10 

During a tour during Modernism Week, Sims talked about how the one-bedroom, one-bathroom prototype (which also sported a deck for the occasion) had been designed and constructed to demonstrate possibilities for potential homeowners. At the same time, the ADU had everything one needed to move in immediately.

Visitors entered the ADU via a multi-slide glass entry. Tall windows brought Palm Springs's abundant sunshine into the home, as did a clerestory window that also maintains privacy in the bedroom.

Built-in closets with walnut veneer panels provide plentiful storage. The bathroom included low-flow and dual-flush fixtures. "As design director," Sims adds, "I'm always looking for the most sustainable and yet cost-effective materials and products. It's quite a balancing act."

The all-electric house included an induction stove in the kitchen and a Mitsubishi mini-split system for heating and cooling. While solar panels hadn't yet been installed on the standing-seam metal roof, Sims said, "there are provisions in the electrical panel for solar, so it's ready to go."

The super-insulated ADU, which includes rigid insulation on the exterior to help with thermal break, comes in at R30 in the floor, with an R38 roof and R23 walls. "We exceeded California Title 24 efficiency ratings for insulation," Sims says. The ADU also features cradle-to-cradle certified floor tiles, and no-VOC millwork and finishes. Walking around the exterior of the ADU, clad in western cedar and sustainable cement siding, Sims opens up a set of slatted doors to reveal an electric tankless water heater. "Isn't it cute?" she says with a laugh.

Feedback and Interest 

Founded 2016 by Steven Glenn, Plant Prefab now has its own factory, a 62,000-square-foot facility in Rialto, CA. During Modernism Week, several real estate developers from the Palm Springs area expressed interest in adding LivingHome 10 as an ADU or standalone space on potential properties. 

A couple, retirees based in Southern California, was impressed with the ADU's clean, contemporary design and cost-effectiveness. They also discussed with Plant Prefab reps ways in which they could add LivingHome 10 to their residential lot. 

Questions about the cost and delivery approach abounded. A lot of people were also curious about Plant Prefab's installation process and the fact that, in most almost cases, the ADU could go up in a mere two days. Other visitors were enamored with Plant Prefab's ability to create all of its homes—from the ADU to a variety of architect-designed custom homes—in the Rialto factory. 

As more people look for building options that minimize negative impacts on the environment—while also reducing construction noise, waste, and inconvenience in neighborhoods during construction—factory construction of prefab or modular homes is fast becoming a viable option. Fast, efficient, sustainable, and cost-effective, "our homes," Sims adds, "are built to the same code as site construction." Now, more than ever, prefab is here to stay.

Article by:

Camille LeFevre

Camille LeFevre is an architecture and design writer based in the Twin Cities.