There is a 2x4 foot sheet metal air vent that runs from the back of my building, under the floor joists of my living room and small bedroom and exits into an airshaft(I live in a NYC tenanment). I took up the the oak floor and subfloor and put down 2" rigid insulation sealed the seams with foam, then a 5" cotton denin insulation (r-19) and finally on top of that a 5/16" "Reflectix" Alumin foil insulation. All this to keep the floor warm.

My question is, Is there any problem using the foil insulation on top of the styrofoam and cotton batting insulation or is this OK to do? Not sure if I'm seeing much of difference compared to the uninsulated floor I haven't done yet in the small bedroom.