Quadrangle courtyard, also known as "Siheyuan" in Chinese, is a historical type of residence that was commonly found throughout China, especially in Beijing. The name literally means a courtyard surrounded by four buildings.

The ancient Beijing quadrangles are not only precious historical architectures, but also the culture symbol of Beijing. However, the contradiction between use and protection of these ancient houses always exists: on the one hand, each brick and tile of these quadrangles has its historical value, which means that a large-scale reconstruction is extremely hard; on the other hand, poor facilities have caused many inconveniences to residents' lives.

In August 2013, several architects displayed the inner box structure design for ancient quadrangles at the Beijing Design Week. The inner box structure is a prefabricated module constructive system that can renew the function of ancient architectures. It is in essence a "house in house". The design has won many domestic and international prizes afterwards.

This year, the inner box structure has become part of the renovation plan of Beijing's Dashilan area. As the inner box structures are built in many ancient quadrangles, these ancient houses have been revived.