I am renovating a house that was built in1896. The first floor has pine board floors nailed directly onto the floor joists with no underlayment. Over time the boards have shrunk and in places I can see directly into the basement. I just had the floors refinished and they look great but I am wondering should I insulate under the floor. I have never seen insulation in a basement under a floor. If I should what type of insulation should I use?