I have a question on insulating a sub floor. He is what we have done and doing. We are building a raised sub floor on top on concrete garage floor in order to extend our laundry room from main house. We built a 2 x 8 frame and used pressure treated laid flat on floor to create air flow. We will be using tounge and groove 3/4 floor boards. My question is do I have to insulate in the cavaties of framing. The garage is dry and insulated. The space between finshed floor and concrete is about 12" I will probably be putting tile on floor. Can I simple add R13 or R19 faced insulation on upper part of floor (not directly on concrete)? Or can I just put loose insulation directly on concrete?

Thanks for any input