The town house is a Manhattan icon, and from the outside, The Heckscher Foundation for Children on East 70th Street looks like an exemplar. But it takes only a step inside to find that the building’s gut renovation by local firm Christoff:Finio Architecture diverges from the norm. “This was an effort to carve out a new type of town house,” says Taryn Christoff. “It’s a rethinking of how a town house can be organized,” concurs partner Martin Finio, AIA.