‘The numbers should work, and they just don’t’: Is Cambridge’s affordable housing rule backfiring?

Cambridge is one of many local communities that require most new housing developments to include units set aside at below-market rents — in its case, 20 percent of the building, which is among the highest rates in Greater Boston — with the intention of creating more affordable homes in a city that is starved for them…..Put another way, a policy aimed at generating affordable housing may actually be preventing it.