Yesterday a friend of mine asked me about this. At first I thought it was Chinese but then it turned out to be a construction/housing term in Japanese. There is a website that discuss this term but it didn't really explain it thoroughly: 新設住宅着工床面積
It is exactly as the bottom website translates it: floor space of newly built houses.
It is used in economics as a measure of the health of the economy. People building new houses with more and more floor space indicates an expanding economy. People building new houses with smaller floor space is indicative of a contracting economy.