Learn how to insulate internal walls yourself in a variety of methods.
Do Interior Walls Have Insulation. And to diagnose a wall, you need to have. Insulating a wall that's open because of new construction or remodeling is simple.
Concrete Block With Interior Frame Wall Cavity Insulation ... from i.pinimg.com
Best for interior and exterior walls in cold or humid climates, especially for homes with masonry or wood walls. Simply find the attic access panel (usually located in a closet or hallway), set up a ladder but this is true only when there is a significant difference between interior and exterior temperatures. And to diagnose a wall, you need to have.
Most homes use drywall on interior walls.
In subterranean situations i have used brush on sealers. I'm not crazy about insulating interior walls as it affects heat/cooling transfer of the rooms but that's frankly not my concern if he wants sound proofing. You can still put insulation inside existing walls if you know what to use. Wrap a cloth around it to seal it.
