The Maharashtra government has issued a notification, stipulating builders developing a housing project on a 4,000 square metre plot must reserve 20 per cent of the area for affordable housing. It will not be applicable to schemes where commencement certificates were issued on or before November 8, 2013.    As an incentive for the 20 per cent reservation for public housing, the developer will receive 20 per cent extra floor space index (FSI). It will benefit low income groups (LIG) and economically weaker sections (EWS), who will be allotted the 323-538 sq ft tenements through a lottery by Mhada, the state housing authority.    The scheme will create more housing stock at a time when Mhada does not have much land with it in Mumbai.    The notification said that when the developer intimates Mhada about granting of an occupation certificate (OC) by the planning or civic body to his newly built apartments, Mhada has to decide within six months if it will purchase the 20 per cent tenements or allot them to those selected through a lottery system.