", buildings consist of layers, and each has its own value and speed of change. He quotes six components of differing time span: stuff, the space plan, services, skin, structure and the site.
(diagram inspired by Stewart Brand, How Buildings Learn, page 13, the pie diagram shows the changes to systems in a US office building over an average lifespan of 35 years [figures from Stewart Brand, How Buildings Learn, pp12-13])
The site has eternal life whereas elements like the space plan (e.g. the organization of the interior walls) might have a life expectancy between three to thirty years. The question rises whether a building can evolve over time? Likewise, designing flexible buildings is a key to sustainable design. It makes sense to design structures that are built to last. Nowadays, it is even hardly possible to change an apartment building to an office building or vice versa.
Architecture sometimes is rather "tailor-made" for a certain program than open to different functions. Shouldn’t be our buildings be more flexible in design?