twin leaf-shaped roofs unfold atop nursery school by NIKKEN SEKKEI in japan

Leaf-Shaped Roofs Compose Poppins Nursery School in Karuizawa

Poppins Nursery School Karuizawa Kazakoshi, designed by NIKKEN SEKKEI, is a single-story wooden nursery school in Japan. Located in a highland resort area of Karuizawa, near Lake Shiozawa and Kazakoshi Park, the structure overlooks Mount Asama. The building is positioned diagonally at the center of the site to naturally separate the south-facing playground from the north-facing parking area, making use of the site’s existing slope and minimizing the need for new barriers along the western retaining wall.

The project is defined by two leaf-shaped roofs of different heights. Childcare rooms are placed beneath the lower roof, while the higher roof covers the hall and staff facilities. The floor plan is designed so that all childcare rooms face the outdoor garden, and the hall functions as the central gathering space where children engage in group activities. Large windows introduce daylight and provide views of the surrounding landscape throughout the year.

Spatial divisions rely on wooden columns rather than enclosed walls, creating a continuous interior environment that supports movement and visual connection across age groups. The six nursery rooms, grouped into zones for ages 0-2 and 3-5, feature lower ceiling heights and a smaller spatial scale suited to young children. Each room connects to the hall through column-defined openings, allowing for gradual transitions between spaces and enabling interaction between different age groups.

all images by Norihito Yamauchi

NIKKEN SEKKEI employs Timber framework and Dual Roof Planes

The design team at NIKKEN SEKKEI opts for material and environmental strategies that emphasize wood as the primary interior finish. This approach aims to create a unified atmosphere across childcare rooms, circulation zones, and the hall. High-side windows located between the two roofs supply natural light and support gravity-based ventilation during mild seasons, reducing dependency on artificial lighting and mechanical cooling.

Structurally, the project employs two simple, untwisted roof planes cut into organic, leaf-like geometries that taper toward the eaves. These roof surfaces were constructed using standard laminated timber without special curved components. Columns are slightly angled along the curve of the plan so that their intersections with beams remain nearly vertical, allowing the use of common connection hardware and reducing the need for custom structural fittings. Double timber columns (120 × 240 mm European red pine) are arranged at regular 1,820 mm intervals, corresponding to plywood module dimensions and creating a rhythmic structural grid reminiscent of loosely defined forest-like zones.

By standardizing short-span joint details and optimizing material use, the project maintains a clear structural expression while remaining efficient to construct within a limited schedule and budget. The spatial volume beneath the high roof accommodates the hall, kitchen, and staff areas, while mechanical equipment is placed in the ceiling space under the low roof to maximize usable interior area.

a leaf-shaped roof defines the low, child-scaled volumes of the nursery

the building sits on a highland site overlooking Mount Asama

wooden columns replace walls to create an open interior flow

large windows bring natural light into the hall

column-defined openings allow gentle transitions between spaces

wood surfaces unify the childcare rooms and circulation areas

double timber columns create a rhythm across the interior grid

all childcare rooms face the outdoor garden

nursery rooms are divided into zones for ages 0-2 and 3-5

structural spacing corresponds to standard plywood module dimensions

mechanical equipment is placed beneath the low roof to maximize space efficiency

high-side windows between the two roof levels channel light in and out of the interior

project info:

name: Poppins Nursery School Karuizawa Kazakoshi
architect: Nikken Sekkei Ltd | @nikkensekkei_global
location: Karuizawa, Kitasaku-gun, Nagano Prefecture, Japan

site area: 2699.04 sqm

total floor area: 494.46 sqm

contractor: Seibu Construction Co., Ltd.

photographer: Norihito Yamauchi

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edited by: christina vergopoulou | designboom