Yoshinobu Ashihara

Published in 1970, Exterior Design in Architecture is Yoshinobu Ashihara’s best-known work and one of the few Japanese theoretical texts widely cited across both East and West in architectural education. The book’s core argument is simple yet powerful: the spaces between buildings — plazas, streets, courtyards, parks — are not the “leftover” of architecture but a design subject requiring equally serious treatment. Ashihara named this space “exterior space” and defined it as “architecture without a roof.”

Ashihara proposed a series of precise analytical tools in the book. The most famous is the D/H ratio: the ratio of the width (D) of a street or plaza to the height (H) of bordering buildings determines the spatial feeling — at D/H=1, the space feels balanced; at D/H<1, it generates enclosure and intimacy (like European medieval streets); at D/H>1, it begins to feel alienating (like modernist new towns). This metric remains one of the most widely used tools in urban design teaching and practice.

Ashihara also proposed the concepts of “negative corner space” (inwardly recessed space) and “positive corner space” (outwardly projecting space). He pointed out that good urban space is always composed of “negative corners” — inward spaces enclosed by buildings, not outward spaces left over after buildings occupy a site. He criticized modernist urban planning for excessively focusing on building objects themselves (positive corners) and neglecting the design of the “negative form” between buildings — the spaces where people actually live and interact. This criticism has become almost common sense in today’s urban design discourse.

Yoshinobu Ashihara was not just a theorist — his built works deserve equally serious consideration. The Tokyo Sony Building in Ginza, completed in 1966, is his most iconic work. Located at Ginza’s most prominent intersection (Sukiyabashi Crossing), the building unfolds with a distinctive “flower-petal” plan — the façade is divided into multiple vertical blocks, each tilting slightly outward like a blooming flower. This design is at once a spatial manifesto (transforming a corner into a “flower petal” opening toward the city) and a clever response to Ginza’s extremely compact sites.

Another innovation of the Sony Building is its “vertical street” concept. Ashihara viewed the building’s internal vertical circulation — escalators and stairs — as an extension of the city sidewalk. He created a split-level atrium so that a portion of every floor is visible from the atrium, encouraging people to wander and linger within the building rather than merely reach destinations efficiently. This approach of extending “exterior space” ideas into the building interior was extremely avant-garde in global commercial architecture at the time.

Ashihara’s other significant works include the Kanazawa Bunka Hall (1977) — a public cultural building translating traditional Japanese sukiya aesthetics into modern concrete language; the Tokyo Metropolitan Theatre (1990) — a large-scale cultural complex in Ikebukuro; and the Okayama Symphony Hall (1991). These works may not be as formally radical as the Sony Building, but they consistently embody Ashihara’s theoretical concerns: relationships between spaces, human perspective, and the gentle interface between architecture and city. He died in 2003 at 85.