He began by tearing down the toilet and kitchen that had been illegally built outside to allow light and air in and then added a horizontal partition into the 3.6-meter-high studio to create two floors.

He added waterproof boards, foldable furniture and movable walls to create more privacy, and big windows to further amplify the space.

Within two months, he had transformed it into a two-bedroom home with a study, dining room, kitchen and luxury bathroom. Naturally, the family was thrilled.

"I realize now how misguided my views of lane houses were before," he says. "This project was a real eye-opener into how people live in these buildings that date back to the 1930s."

This is not Wang's first public welfare program. In 2013 he helped renovate a 17-sq-m apartment as well as a house with a bizarre layout for local residents.

Shanghai is notorious for its meager housing resources. The average living space per person in the late 1970s stood at just 4.5 sq m as the population exploded. It was billed as the local government's "No 1 headache" by the 1980s.