The House NA Sou Fujimoto Designed: Living in a Tree

Few houses of the last two decades have been photographed and discussed as widely as the House NA Sou Fujimoto designed in Tokyo. Completed in 2011, it is a small residence for a young couple that abandons the idea of rooms and walls altogether. Instead, it offers a transparent cluster of floor plates at different heights, linked by short stairs and ladders, which its architect compared to living in the branches of a tree.

This article looks at the concept behind the house, its spatial organisation, the structure that makes it possible, the questions it raises about privacy and climate, and its place in contemporary Japanese architecture. For background on the architect, see the companion article on Sou Fujimoto in this series.

Context: the Tokyo house as experiment

Tokyo has long been a laboratory for residential architecture. Small plots, relatively short building lifespans and a culture open to experiment have produced a remarkable tradition of tiny, inventive houses. Our articles on Japanese housing and the Japanese tiny house describe the conditions that make this possible.

House NA sits on a small site in a residential neighbourhood of Tokyo. Published figures give a total floor area of roughly 85 square metres on a plot of a little over 50 square metres. Within that compact envelope, Fujimoto set out to rethink what a house could be.

The concept: living in a tree

Sou Fujimoto has long been interested in architecture that sits between nature and artifice, and in the idea of a “primitive future”: spaces that recall caves, forests and nests rather than conventional rooms. In House NA he explored the tree as a model for dwelling. Rather than a series of enclosed rooms, the house offers a variety of places at different heights, each with its own character, much as a climber might find a resting place on a branch.

The idea is that the occupants move from place to place within their own home according to the time of day, the activity or their mood. The design supports this by blurring the boundaries between furniture, floor and room. A floor plate at one height may be a place to sit; the next plate up becomes a table or a desk; a higher one is a place to sleep.

This approach connects with traditional Japanese ideas of flexible space, in which a single room could serve many functions throughout the day, and with the notion of ma, the meaningful interval between things. Our article on ma in Japanese design explains this concept further.

Spatial organisation: 21 floor plates

The house is organised around some 21 separate floor plates, each set at a different level, rather than conventional storeys. The plates vary in size, from small platforms to larger floors, and are connected by short flights of stairs, ladders and steps, and in places the plates themselves double as steps, desks and seats.

Because the heights change in small increments, the relationship between plates can be read at different scales. A difference in level comparable to a chair height turns one plate into a seat for the next; a difference comparable to a table height turns it into a work surface. A larger vertical gap creates a distinct place with its own enclosure. The result is a continuous, three-dimensional landscape rather than a stack of separate floors.

There are very few walls. Some functions, such as the bathroom, need enclosure, but most of the house remains open, with visual connections in every direction. The occupants can always see one another, or at least be aware of one another’s presence, while still finding places that feel distinct.

Structure: a slender steel frame

The design depends on its structure. House NA uses a thin, split-level steel frame, finished in white, that reads more like a lightweight lattice than a conventional building structure. Slender columns and beams define a grid of cubic volumes, and the floor plates are hung or seated within this framework at the required heights.

From a structural engineer’s perspective, this is a demanding brief. A frame with many floor plates at different levels has numerous connections and discontinuities, which complicate load paths. Slender members must still provide adequate stiffness against vibration from footfall, lateral stability against wind and, crucially in Japan, resistance to earthquakes. With so few walls, the frame cannot rely on shear walls for bracing. Achieving this with members thin enough to preserve the sense of lightness requires careful analysis, precise fabrication and well-designed connections. Our articles on steel buildings and earthquake-resistant design explain the principles at stake.

The lightness of the frame is, in other words, an engineering achievement as much as an architectural one. The house only appears simple because its structural complexity has been carefully resolved and concealed in thin sections.

Transparency, privacy and climate

The most striking feature of House NA from the street is its transparency. Large areas of glazing reveal the interior to passers-by, especially at night, when the house glows like a lantern. Window treatments can temper this, but the house deliberately challenges the expectation that a home should be an enclosed refuge.

This raises reasonable questions. Full transparency in a dense city requires an unusual tolerance for exposure. A lightweight steel and glass envelope also brings challenges in thermal performance, solar gain and condensation, particularly in Tokyo’s hot, humid summers and cold winters. Such a design depends on careful attention to glazing, shading and building services. In a tropical climate like Singapore’s, the same strategy would face even greater challenges of heat gain and glare, and would need significant adaptation.

These issues do not diminish the house’s value as an architectural statement. Rather, they show that it is a deliberately radical experiment, a prototype for a way of living, rather than a model for every home.

Where the House NA Sou Fujimoto designed sits today

House NA belongs to a lineage of Japanese architects exploring lightness, transparency and the dissolution of boundaries. It shares concerns with the work of Toyo Ito and with Kazuyo Sejima and SANAA, as well as Junya Ishigami, all covered elsewhere in this series. These architects have pushed thin structures and open plans to extremes, questioning conventional ideas of rooms, walls and enclosure.

For students of architecture, the House NA Sou Fujimoto designed is a powerful reminder that a house is not defined by its rooms but by how people live in it, and that structure, space and lifestyle can be designed as a single idea.

Frequently asked questions

What is House NA?

House NA is a small residence in Tokyo designed by Sou Fujimoto and completed in 2011. Instead of conventional rooms, it consists of around 21 floor plates at different heights within a slender steel frame, enclosed by large areas of glass.

Why is House NA compared to a tree?

Fujimoto conceived the house as a series of places at different heights, like the branches of a tree, where occupants can move, sit, work and sleep at different levels rather than in enclosed rooms.

How big is House NA?

Published figures give a total floor area of roughly 85 square metres on a site of a little over 50 square metres, spread across many floor plates rather than conventional storeys.

What is the structure of House NA?

It uses a thin, split-level steel frame. The slender members support floor plates at many different heights, which demands careful structural design to provide stiffness, stability and earthquake resistance with very few walls.

Could a house like House NA work in Singapore?

The concept could inspire designs here, but full glazing in a tropical climate would bring heavy solar gain, glare and privacy issues. It would need extensive shading, high-performance glazing and careful environmental design.

Considering a lightweight steel frame or an unconventional house structure? Talk to our consultancy or get in touch for accountable structural advice.