The cost to make a basement legal is enormous in terms of physical and monetary requirements. As someone who ponder and look into the cost - its not worth it not to mention the ongoing liabilities of a basement units. It be cheaper if I raise the roof of my house and build another unit. If the city offered me money and allowed the exception to my zoning to build another floor and keep it rent regulated for 15 yrs. Then its worth considering and better for the renter than any legal basement unit ever be.