Do I have to finish my basement/walls before I occupy my residence?

Because of the nature of foam plastic insulation in contact with fire, it is required by code to meet a thermal barrier requirement. This requirement is that there be a barrier that will stay in place for a minimum of 15 minutes in the USA, and 10 minutes in Canada. There are provinces in Canada that require a 15 minute barrier as well, however, the same ½” (12.7mm) gypsum board will satisfy both 10 and 15 minute time spans. Drywall of larger thicknesses, cement board, ¾” (19mm) plywood will also serve this purpose, but may not always be as cheap or efficient.