Soundproofing Basement Walls

Q: How can I soundproof the stud wall that divides the family room from the utility room in my basement? Is it enough to install fiberglass insulation within the wall, before drywall?

A: Yes, you can install fiberglass between these wall studs, but that alone won’t hold the noise back much better than a hollow wall. The main thing to understand is that effective sound isolation depends on differing density levels throughout a wall. When the cross-section of a wall includes soft, lightweight elements as well as dense ones, it dampens the natural resonance of the structure and the resulting sound transmission. If this were my project, I'd start by installing fiberglass batts in the existing wall frame. Next, assemble a second 2x4 stud wall on the floor of the utility room, tilting it upright after it’s together and installing it against a layer of 1-inch rigid foam tacked to your existing wall. Fasten the bottom of the new wall to the floor with Tapcon screws tightened directly into predrilled holes in the concrete. You’ll find 3 1/2-inch deck screws do a great job securing the top of the wall to the joists that run across the ceiling. With the new wall up, fill the inter-stud space with more fiberglass, then add a layer of exterior fiberboard sheathing on the frame before fastening drywall, taping, sanding and painting. Be sure to seal all areas around the edges of the walls with acoustic caulking, too. Even the tiniest cracks can lower sound resistance tremendously.