NIKO Design Studio has completed Umino Marumi, a two-story chiba timber guesthouse on a hillside above the Pacific coast of Chiba, Japan. The house is built around an enormous circular opening in its dark facade. In the garden, a much smaller sauna hut has a curved roof shaped by the trees around it.
The house was completed in 2025 as a second home where the owners could gather with family and friends. The owners also wanted this chiba timber guesthouse to be a welcoming presence in the local community. The architects met both goals with an engawa, the traditional Japanese veranda.
A circular opening that faces the neighborhood
The circular opening is the house’s most recognizable feature. Behind it, the architects built a series of staggered outdoor platforms that climb through the building and connect to the upper floor. Roughly one-third of the covered structure is given over to this semi-outdoor space.
Visitors can sit, meet, or move between levels without entering any enclosed room. From outside, passersby catch glimpses of people moving through the timber. The opening effectively turns the facade into an inhabited space that faces the neighborhood.
Cedar logs and hand-cut joinery in the chiba timber guesthouse
NIKO Design Studio built the frame of this chiba timber guesthouse from cedar logs about 400 millimeters in diameter. The structure uses traditional kanuki joinery, in which horizontal timbers pass through openings cut into the round columns. The method keeps the wood’s natural shape intact.
If the cedar joinery caught your eye, Tokyo Home Reimagined with Adaptable Timber Framework shows another Japanese house built on flexible wooden structure.
The carpenters suggested cutting the joinery holes with chainsaws. The approach was inspired by forestry techniques. The team followed their advice.
The sloping site needed a retaining wall. The team assembled one from stone during a two-day workshop, using nozumi, a traditional stone-stacking technique. The stonework sits beside the large timber structure.
A sauna shaped by a neighboring palm
The owners first asked for a japanese sauna hut for three or four people. When the architects placed commercially available models into a model of the site, they looked surprisingly bulky. The team then studied the surrounding landscape more closely.
That study revealed a palm tree on a neighboring property, growing out over the boundary. The architects treated its continued growth as the starting point for the sauna’s curved roof.
The architects worked with carpenter Murakami of Murakami Carpentry Workshop. They sourced naturally bent timber from trees that had grown along a hillside. These curved members form the roof, so its profile rises and dips around the surrounding vegetation.
The timber arrived thicker and longer than the team expected. Rather than cut it down, the team kept the extra length. The beams now project past the roofline, and that detail gives the small building much of its character.
Five square meters for up to six bathers
The sauna has a foundation of just two by two meters. Including its stepped portion, the total floor area is five square meters. Timber-lined surfaces and a tall ceiling keep the interior from feeling cramped.
The sauna was designed for three or four bathers, but the finished space can hold five or six people. It combines electric and wood-fired heating. A skylight admits daylight into the compact room.
The sauna opens onto the surrounding terrace and connects to the house’s bathroom. That bathroom can serve as a cold bath between sauna sessions.
For wood at monumental scale, Michele De Lucchi’s Sustainable Timber Pavilion Celebrates Woodcraft shows craftsmanship on a 50-meter canvas.
Marumi and its small companion explore two scales of wooden architecture at this chiba timber guesthouse. The house opens itself toward the neighborhood, while the sauna adjusts its form to the trees already growing in the garden. Together they show how a single site can accommodate both a public-facing gesture and a quiet, tree-shaped retreat.
Via designboom.com
Frequently asked questions
What is the circular opening on the Umino Marumi guesthouse used for?
The circular opening leads to a series of staggered outdoor platforms that climb through the building and connect to the upper floor. Roughly one-third of the covered structure is this semi-outdoor space, where visitors can sit, meet, or move between levels without entering an enclosed room. The opening also turns the facade into an inhabited space that faces the neighborhood.
What material and joinery method built the chiba timber guesthouse frame?
The frame was built from cedar logs about 400 millimeters in diameter. It uses traditional kanuki joinery, in which horizontal timbers pass through openings cut into the round columns, keeping the wood’s natural shape intact.
Why does the sauna in the garden have a curved roof?
The curved roof was shaped by a palm tree on a neighboring property that was growing out over the boundary. The architects sourced naturally bent timber from trees that had grown along a hillside, so the roof rises and dips around the surrounding vegetation.
How many people can the sauna accommodate?
The sauna was designed for three or four bathers, but the finished space can hold five or six people. Its total floor area, including the stepped portion, is five square meters.
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