The Japan National Stadium Eaves Design Analysis

After seeing Zaha Hadid’s proposal that never materialized, Kengo Kuma’s design for the Japan National Stadium may look ordinary. But it was intentional in many ways. One of the principles he leveraged in order to incorporate “Japanese-ness” in the design of the Japan National Stadium (which was one of the requirements) was to achieve “circular” construction system what Japanese carpenters practiced for long time. They would standardize timber based on the most commonly available wood in different parts of the country, and used it to build new buildings and repair/replace existing ones. The cycle would continue based on the most ordinary timber. Kuma calls it “great ordinary.” Kuma embraced the beauty of “great ordinary”  to realize the National Stadium for the Olympics – an extraordinary project.

Kuma used one of the most commonly available timber to finish eaves. “I wanted to use the timber with the width of 105 mm, because it’s the most widely used product. Even small wood processing facilities in rural regions can produce it. I wanted to make sure that every single supplier all over Japan had change to bid for the project.” 105 mm cedar timber may not be the most sexy material to build a large stadium, but he pursued the “great ordinary.”  

By the way, why did Kuma use layers of eaves? It was because eaves are part of traditional Japanese architecture. The reason why Japanese put so much efforts on eaves was because of the climate.

Japan is humid with lot of rain. In order to keep wooden structure in such a climate, it is very important to minimize the damage from rain. Eaves became deep in order to project the building.

Most notable Japanese architecture with layers of roofs is multi-storied pagoda. 

The three-storied pagoda at Yakushiji temple. 
Although Kuma got inspiration from five-storied pagoda at Horyuji temple,
you can see mokoshi more clearly on this one. 
Each roof has mokoshi, which is smaller and with simpler design. 

Kuma leveraged eaves for both aesthetic and functional reason. The wooden louvers sort of disassembles huge mass of the stadium into small parts. It looks a lot less overwhelming and people can feel comfortable. Eaves also protects people from direct sun and rain and ensure the durability of the stadium.