“It is hard to estimate exactly how many [illegal] basements can be conversed to meet the official standards because it very much depends on the design of the house, size, and structure of the basements,” said Sarah Watson, Deputy Director at Citizens Housing & Planning Council.

Watson outlined the regulatory barriers that impede the development of smaller, denser units: complicated building codes, confusing density regulations, and challenging procedural requirements to add an accessory dwelling units, including high permit costs and long-waiting time. “Local regulations in singe-family residential areas are designed to prevent the creation of any additional dwelling units,” Brown said.