Zoning changes to mandate more affordable housing in Amherst Amherst Town Hall GAZETTE FILE PHOTO By SCOTT MERZBACH AMHERST — As Amherst continues to miss its goal of developing around 50 affordable housing units annually, town planners are crafting zoning revisions requiring developers to include homes in their projects for low- and moderate-income households. In what members of the Planning Department describe as a significant amendment, all development of townhouses, apartments, mixed-use buildings and planned unit residential developments, or PURDs, with more than nine units, will be required to include affordable units as well as market-rate housing. “This is a really big change,” Senior Planner Nathaniel Malloy told the Town Council during a presentation this week.