There is no limit within existing legislation covering the extent to which a local authority can purchase houses in an existing residential estate for social housing purposes. However, my Department has issued guidelines on Quality Housing for Sustainable Communities (available at the following link: http://www.environ.ie/sites/default/files/migrated-files/en/Publications/DevelopmentandHousing/Housing/FileDownLoad%2C1979%2Cen.pdf) which covers issues such as tenure mix, estate composition and specific local needs.
When identifying acquisitions for social housing purposes, local authorities should ensure that all such issues are considered. The parameters under which my Department provides capital funding to local authorities for the acquisition of houses and apartments for social housing are set out in Circular Housing 24/2015, which is available at the following link:
http://www.environ.ie/housing/social-housing/social-housing-strategy/circular-housing-242015-social-housing-capital.