上棟下宇，以待風雨，蓋取諸大壯。繫辭下傳第二章011

上古時候，冬天則藏身洞穴，夏天則在野外居住，後世聖人，爲了防止洪水猛獸的侵襲，遂教民建築宮室，上有棟梁，下有檐宇，以防禦風雨，是取象于大壯卦。

上古穴居而野處，後世聖人易之以宮室，上棟下宇，以待風雨，蓋取諸大壯。

In the highest antiquity they made their homes (in winter) in caves, and (in summer) dwelt in the open country. 

In subsequent ages, for these the sages substituted houses, with the ridge-beam above and the projecting roof below, as a provision against wind and rain. 

The idea of this was taken, probably, from Da Zhuang (the thirty-fourth hexagram).