Adding a Unit...or Two?

[Lindsay Wilcox]

House was originally a SF, but was remodelled into a quad with three 1-bd apts on main floor and 2-bd in basement. Basement unit was decommissioned when egress window laws passed and is now a mostly unfinished basement. Home also has large attic.

How would you decide whether refinishing the basement and adding an egress window and/or finishing the attic into an efficiency or 1-bd would be worth it? Is there anything else to consider, like zoning laws, that would prevent turning a triplex into 4 or 5 units?