Spray Polyurethane foam can aid in reducing sound transmission in walls and ceiling cavities. In your case, however, since you cannot remove the ceiling gypsum to access the cavity, SPF may not be your answer. Any attempt is going to be pretty tricky, not tested, and the results may not be consistent without being able to see what’s going on in that cavity and control how it is filled. Filling the void completely could cause enough pressure to damage the existing ceiling. There may be other products out there, but I don’t think SPF is the way to go in this situation without being able to remove the ceiling. Best of luck. Please consult one of the SPF manufacturers for more information on sound transmission testing
Feel free to click on the "Contact the FAQ Administrator" to ask me a follow-up question.
Copyright © 2011 NCFI Polyurethanes