When Norwegian-born architect Casper Mork-Ulnes, who splits his time between Oslo and San Francisco, took on a remodeling project in the Bay Area for Lars Richardson and Laila Carlsen, the endeavor led to a decade-long adventure in designing innovative yet wondrously eccentric buildings.

Richardson, an entrepreneur dealing in Scandinavian art and antiques, and Carlsen, a painter, are also from Norway and share Mork-Ulnes’s penchant for energy-efficient architecture. On the couple’s three-acre Sebastopol farm, about an hour north of San Francisco, they’ve all happily collaborated since 2005 on the design of several new structures. Spread around a 1920s Arts and Crafts-style farmhouse, the constructions are all predominantly green—none more so than a dining pavilion Mork-Ulnes completed this year.

“Nature is important to us,” says Richardson. “We find it to be a big part of our life and spend much of our time outdoors. That’s why Laila’s art is also often inspired by nature.”

In keeping with those sentiments, Mork-Ulnes and his wife’s brother, Nick Damner, cofounders of the prefab company Modern Cabana, designed and built the first of their small structures for Richardson in 2005. Since then, the collaboration between architect and client has continued to include renovated trailers, greenhouses, and a 2,000-square-foot barn that features a dramatic inverted butterfly roof and contains Carlsen’s art studio and Richardson’s home office. Mork-Ulnes even built an aviary that serves as a bird infirmary on the property.

“They like to take care of rescued animals including dogs, cats, and hens. Halfway through the barn project, we got an urgent call from them to design an aviary to protect some endangered birds from wild animals,” Mork-Ulnes says. He quickly obliged and built one.

Within this architectural smorgasbord, Mork-Ulnes’s newest opus, an amoeba-shaped addition to the barn, also wholeheartedly embraces nature and the outdoors.

“Lars wanted an outdoor kitchen and dining room that he could use year-round,” Mork-Ulnes says. “The idea was to let the landscape bleed in and out of the building. He imagined it as a jungle, with plants inside and out.”

Inspired in part by Richardson’s friend, wood craftsman Evan Shively, who has a similar indoor/outdoor setting in Sonoma County, the 713-square-foot structure built by Natal Modica has eight-inch-thick S-curved cement walls. They were formed by spraying several layers of Shotcrete cement onto vertical screens of recycled wood barn siding that were later dismantled and used to build fences.

The curving concrete walls rise in height from about seven and a half to 13 feet, and their considerable thermal mass keeps the room cool in the summer and warm on chilly days. The addition’s sloped roof, held up by scissor-truss beams, lets in light through skylights. Curb mounted above the roof trusses, the skylights are multi-paneled with an operable rectilinear section in the middle; the side sections are custom fitted to the curved walls.

The room’s undulating concrete floor slab seems to flow out to the garden, where Richardson has introduced bamboo, aloes, bird-of-paradise plants, a fig tree, edible taro, and some creeping vines. Although sliding doors can seal off the pavilion from the elements, the garden creeps back inside in the form of ovoid plant beds that are scattered like floral rugs on which even chickens can roam free.

The dining room that Mork-Ulnes refers to as the Amoeba works particularly well in Sonoma County’s clement weather and is yet another experiment in an unusual estate that exemplifies the creative spontaneity of the owners and their architect.

“Lars and Laila thrive on seeding new ideas constantly,” Mork-Ulnes says. “With this new garden pavilion, they’ve added another wonder to their world.”