Building room with floor joists over slab. Moisture?
I want to convert the back of my attached garage into a small laundry room. The garage slab is above grade, but still gets rather humid on a rainy day as the garage has no ceiling and is vented to the outdoors.
I want to frame joists over the slab to make the floor of the new room even with the rest of the house. I could use 2x6 joists as the room will only be 6'x14'. This would leave about 2" between the joists and the slab but would be well ventilated on 3 sides and screened to protect from rodents.
How would YOU do this? I intend to fully insulate the floor and install screened 2" vent holes at each end of the space between joists. Could I wrap rubber underneath the room structure to protect it from moisture or would this be asking for trouble from moisture buildup? What type of insulation should I use?