A nonprofit group that builds affordable housing in Chelsea and Revere was recently awarded a $15,000 grant to support its work. Chelsea-based Neighborhood Developers was among 21 grass-roots community organizations that will share in $282,000 in grants awarded by Episcopal City Mission, a faith-based ministry in Boston that promotes social and economic justice as it works with congregations, organizations, and people within the Episcopal Diocese of Massachusetts. The funding was awarded through the mission’s Burgess Urban Fund program. The grant awarded to Neighborhood Developers will help support the group’s efforts in Revere, according to Melissa Walsh, the organization’s director of community engagement. “We are thrilled to have the support of the Episcopal City Mission for our work in Revere,” she said.