My house is 50 years old and is lacking in insulation in the garage ceiling. Above the garage are bedrooms. Currently there is 3 of fiberglass with an aluminum vapor barrier within a 2x10 joist. I'd like to put R-30 fiberglass in the cavities but the 25' rolls of insulation are unfaced and the faced R-30 rolls are only in 48 batts. 4' sections are easier to put up but that is not a concern of mine.
Don't use a plastic sheet, use 15# asphalt impregnated felt or a fabric like Tyvek. The vapor barrier must be able to breathe or you run the risk of trapping dampness which will lead to mold.
Yes you need the moisture barrier and it also helps with the hollow sound of the laminate. when you go to put down the barrier make sure to keep it a little long at the walls, make sure seams are tight and taped together with duct tape it will help keep out the moisture. after the floor is installed go back and trim the edges of the barrier but keep enough to sort of tuck under the edge of the wall, if you have moisture coming in you want it to go under the barrier not on top it will cause the floor to mold, expand, warp etc.
Yea you can do that .Get a good stapler to ad hear the plastic to the wood. No stapler , Use Tacks. or even nails..
