NIKO Design Studio Completes Chiba Guesthouse With Giant Circular Opening
NIKO Design Studio has completed Umino Marumi, a two-story wooden guesthouse on a hillside above Chiba's Pacific coast. A huge circular opening exposes a timber veranda, and a small curved-roof sauna sits in the garden beside it.
NIKO Design Studio completed Umino Marumi in 2025, a two-story wooden guesthouse on a hillside overlooking the Pacific coast of Chiba, Japan, where a giant circle frames NIKO’s timber veranda. A much smaller sauna hut with a curved roof stands in the garden.
The owners conceived the house as a second home for family and friends. They also wanted it to be a welcoming presence in the local community.
A veranda that faces the street
The most recognizable feature is the enormous circular opening cut into the dark facade. Through it, passers-by can see timber columns and raised walkways beneath the pitched roof.
The architects built the design around the engawa, the traditional Japanese veranda. They turned it into staggered outdoor platforms that climb through the house and connect to the upper floor. About one-third of the covered building is given over to this semi-outdoor space.
Visitors can sit, gather or move between levels without entering the enclosed rooms. The levels suit both small gatherings and larger groups.
Cedar logs and hand-built stonework
The team used cedar logs about 400 millimeters in diameter for the structural frame. They joined them with traditional kanuki joinery, in which horizontal timber members pass through openings in the round columns.
Carpenters suggested cutting those holes with chainsaws, a technique inspired by forestry work. The method keeps the natural shape of the wood.
The site slopes, so a stone retaining wall was assembled during a two-day workshop using nozumi, a traditional stone-stacking technique. The rough stonework sits alongside the large timber frame.
A sauna shaped by a palm tree
The owners first asked for a garden cabin for three or four people. Commercial models looked bulky when the architects placed them in a model of the site.
The team then noticed a neighboring palm tree reaching over the property boundary. Its continued growth became 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, and used it to form a roof that rises and dips around the vegetation.
The timber arrived thicker and longer than expected. The team chose to keep the extra length, so the beams project past the roofline.
The sauna’s foundation measures two by two meters, with a total floor area of five square meters including the stepped portion. Timber-lined surfaces and a tall ceiling make the interior feel larger, and the finished sauna can hold up to six people.
