Does the Baco Code require double 5/8 on the ceiling in a garage when there is living space above?
In residential construction up through duplexes, 1-hour Fire rating (1 layer) is required on the garage side of the ceiling and walls when there is a living space on the other side. 

When you have 3 units or more, then you MAY need 2 layers, depending on the size of the complex and type of construction. 

For ceilings in 1 and 2 unit residential units: 1 layer installed on 2x lumber and/or I-joists correctly gives you “1-hour” construction. In order to obtain the “1-hour” designation 5/8” type-X gypsum board must be installed on joists at 24” on center (max.) fastened with Type W or S drywall screws at 12” on center along all supports, and then “rough” taped. (See ICC Table 721.1(3), item 21.)