The four-and-a-half-mat tearoom was originally modeled on the yin-yang five-elements system. It means that the entire universe is encompassed within that single room. One theory holds that the tearoom arose from the study of Zen, and that it derives from Vimalakirti’s ten-foot-square hut. This, however, is incorrect. As for its origins, it derives from the I-ching, the Book of Rites, and other texts. The tearoom is built facing south, since originally the rooms are to be built so that they receive light from the southeast. It goes without saying that in the midare kazari tea procedure one must use a tray decorated with the eight trigrams, but in all tearooms, you should make the eight trigrams your model. It is for this reason that the tearoom is to be constructed in such a way that the daisu sits in the north, with the trigram for north directly across from you. You should know that this is why one sits facing north when conducting a temae.
from Gengensai Chadō Sōsho