In Chapter 3 of the 2016 California Residential Code (California Code of Regulations, Title 24, Part 2.5), section R302.6 contains provisions related to the separation required between residential garages and adjacent living space. Table R302.6 Dwelling-Garage And/Or Carport Separation lists the required separation material for habitable rooms above the garage or carport as:
“Not less than 5/8-inch Type X gypsum board or equivalent”
Thus for a living space framed with wood I-joists above a garage or carport, a single layer of 5/8” Type X gypsum board is required on the bottom of the joists. Though most time duration rated assemblies for wood I-joists require two layers of fire-rated gypsum board for one hour fire-resistance, the CRC Table R302.6 requires the prescriptive single layer 5/8” Type X gypsum board or equivalent in the separation between residential garages and adjacent living space, not a specific one-hour assembly.