Here is the link for homes built before 1979:
A rental license is required to rent a single-family dwelling with the following exceptions: the tenant is the landlord's parent, son, daughter, sibling, grandchild, grandparent or in-law; the landlord is an active member of any branch of the United States Armed Forces, Diplomatic Corps, or Foreign Service who maintains the subject property as her or his domicile and permanent residence; or the landlord has been relocated for employment or education, maintains the subject property as her or his domicile and permanent residence. A rental license application can be obtained from Housing Enforcement at (301) 883-6100.
Check with them
Rocsheen R. Holston