Public Housing, typically 75-90sqm per family of 3 to 4 pax. It comes free - meaning the buildings are state-owned, but provided to the people.
A newly married couple is eligible to apply for a new flat. Should they state they would live with parents, they would be allocated a larger flat.
Those unhappy with their flats can go to the residents office to submit their names for a 'swap', or if they have special requests to live on lower levels, e.g. if they elderly has movement problems. They may also be upgraded to better apartments if they have made significant contribution to the state.