Craig writes from Bellbrook, Ohio: "I am getting ready to finish a basement and I want to add sound proofing in the basement ceiling (floor joists) so we don't hear the kids as much. I have heard various suggestions, but it sounds like unfaced fiberglass insulation is the best approach. 1) I was wondering if there was a dB attenuation chart as a function of R value or insulation thickness. 2) I am also leaning towards a suspended ceiling for access reasons and was wondering if there would be significant reasons against this approach (sound or fire). 3) Finally, for exterior walls I was planning on putting sheet plastic between the basement wall and the frame, but it sounds like this is not recommended any more. Should I avoid using plastic?"

Answer: 1. Your question about the sound absorbing performance of insulation cannot be answered due to the variety of factors that contribute to sound transmission or control In an assembly, insulation can contribute a loss of 3-10dB depending on thickness and the rest of the assembly's components. The first inch of insulation provides the most reduction. Typically, acoustic insulation is 3.5" because of this. Additional thickness does improve performance but the amount of improvement decreases per inch as you increase the thickness.

2. Many drop ceilings are acoustically rated and provide excellent sound attenuation. Adding insulation above the drop ceiling will increase the benefit.

3. Our recommendation is to not have a vapor barrier in the basement because there tend to be many vapor drives in different directions. We recommend controlling the humidity levels in the basement to prevent airborne moisture issues. If you are have any leak issues you will want to correct them prior to finishing your walls.