Q: My problem is an in-law apartment downstairs. We can hear everything in the unit — talking, cabinets closing, the shower. We re-carpeted our unit, but the noise from downstairs actually got worse. I blame it on the new carpet, which didn’t have the dense backing our 1970 carpet had.

The rooms below us have open-beam ceilings. Since the beams are 9 inches deep, my thought was to put soundboard between the beams and then staple carpet over the soundboard.

Do you think this is the way to go?

A: Kudos to you for thinking outside the box. It’s tough to eliminate all sound between adjacent spaces but relatively easy to substantially reduce it.

Your situation is common in many older homes. We have seen many an in-law unit carved out of an existing home.

One of the first projects we did together was to finish a family room addition that a seller failed to complete in a duplex Bill purchased in Alameda, Calif. The exterior had been finished, but the interior was just studs and joists. Bill decided to convert the unfinished family room into a studio apartment. So the duplex became a triplex.

Bill added insulation to the common walls but did nothing more to dampen the sound between the two units. He was fortunate to have quiet, considerate tenants for the most part.

As to your noise from below, we think you’re on the right track. But we think adding a couple of extra steps to the project, at little cost, will pay great dividends.

We wouldn’t attach the soundboard directly to the subfloor above. From what you have described, the ceiling in the in-law unit is the subfloor of the living space above. The open beams double as floor joists.

To dampen the sound, we suggest you nail ledger boards to the sides of the beams about 5 inches from the subfloor and nail or glue the soundboard it. When you do this, you are creating a cavity of 4 inches to 6 inches between the soundboard and the bottom of the subfloor above.

Before attaching the soundboard, install non-faced insulation batts in the cavity. R-13 should do for a 4-inch-deep cavity. The result should be a significant reduction in sound transmission from the in-law unit.

If you still want to attach the carpet to the soundboard, go with a fairly thick cut-pile carpet. The idea is to disrupt the sound waves, and cut pile will accomplish this better than a smoother carpet.

You can do all this yourself, and we’d encourage you to go for it. Material cost is not much and after good day of your labor, things should quiet down quite a bit.


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