[2][3] Housing policy dating back to the early stages of the Cold War instigated the incorporation of basement air raid shelters into newly built residential buildings.
Encouraged by Deng Xiaoping's economic reforms, migrant workers began emigrating from rural areas to more urban ones, lured by the benefits of higher salaries and standards of living.
Shortly after, the Ministry of Housing and Urban-Rural Development formally banned residential rentals of basements and air raid shelters due to safety concerns.
[5] While still illegal, many migrant workers choose to live in these centrally located conditions to avoid a longer commute to their workplace.
[6] According to a 2013 study, the median area for an underground room in Beijing was 9.75 square metres (104.9 sq ft) and the average price was 436 yuan per month.