Q: I had rented a house that had an apartment built in its former garage in Darien, Conn. I later discovered that the apartment, an accessory dwelling unit that was included in our lease, was built without permits or inspections and never received a certificate of occupancy. I moved out before the lease was up for other reasons. I asked the landlord to return my security deposit and final month’s rent and cancel the remaining months left on my lease. The landlord refused, and now has a new tenant. Since the apartment was falsely advertised and not properly inspected or permitted, am I entitled to a return of my money and cancellation of the remainder of my lease?

A: Connecticut has strict laws about illegal apartments, but whether you are entitled to your security deposit and last month’s rent is dependent on the facts in your case.

Your landlord has already found a new tenant, and should not be collecting rent twice for the same house — once from you and once from the new tenant.

“Residential landlords technically cannot just keep a security deposit because a tenant breached a lease,” said Mark Sank, who practices landlord-tenant law in Stamford, Conn. “Especially if they re-rent the apartment immediately.”

You’re potentially responsible only for rent covering the gap between your departure and the new tenant’s arrival, and the costs associated with re-renting the unit.

The law requires a landlord to return a security deposit plus interest or account for damages within 21 days of the tenant vacating the apartment, or 15 days after a forwarding address is given, whichever is later. If the law isn’t followed, the tenant can sue the landlord for twice the deposit amount. If you leave early, the landlord must try to rent out the apartment.

Whether you can get out of any remaining lease obligations because part of the rental property was illegal depends upon whether Darien specifically requires a certificate of occupancy for this type of unit, whether any exceptions apply, the facts around your tenancy, and any relevant case law, said Joseph Colbert, who practices real estate law in Westport, Conn., and New York.

But if a residential property is required to have a certificate of occupancy and doesn’t have one, the landlord is generally prohibited from recovering rent.