Fixit: After-the-fact soundproofing can cut noise from neighbors

Q The builder of our townhouse saved himself some money by not soundproofing the common walls in our units. While most of us have adjusted our habits so as not to annoy our next-door neighbors, it would be nice not to have to worry about the problem. What are some ways to soundproof our walls?

A To quiet your townhouse (or condo or loft), you need to deal with two types of noise: airborne (voices, TV) and structure-borne (footfalls, sound-system vibration).

That's accomplished with absorbers, to absorb the sound that makes its way into your space, and barriers to reduce the amount of sound that gets in, said acoustics specialist Steven Orfield at Orfield Laboratories in Minneapolis.

Absorbers lower the "liveness" or reverberation in a room. Liveness can be measured by the length of time you hear reverberation, such as an echo when you clap your hands. Reverberation lasts one second in condos with carpet, two to three seconds in units with bare floors. Adding significant absorbers to your unit can help, Orfield said. They include area rugs or carpet; fabric-covered fiberglass panels (acoustical wall panels); furniture, especially overstuffed fabric (not leather) pieces; drapes on windows or even walls (the heavier and the more folds, the better). All will reduce reverberation time in your room, but that's only half the equation. With high liveness, your neighbor's place amplifies sound before it moves into yours; once there, it's amplified again. Work with your neighbors to lower the liveness in their condos, too, for both your sakes.

Adding barriers basically means improving the construction of your walls and, if necessary, ceilings.

Typically, it's a matter of adding layers and isolation (vibration breaks). One method is to add clips to stop vibration and create a cavity that's filled with insulation. A couple of layers of gypsum wallboard are then attached. The isolation is critical. Attaching the wallboard directly to existing walls, without isolation between layers, provides very little benefit. Adding an isolation damping layer (such as "Green Glue") and then adding wallboard can make a big difference.

In addition, seal cracks or gaps. Check electrical plates and baseboards. Less than 1/16-inch gaps can be caulked with acoustical caulk. Larger ones need a troweled application of drywall mud. For more details, search for "reducing noise" at www.cmhc.ca. Search for "noise" and "noisy apartment." The information applies to condos, lofts and townhouses.

How to proceed

An acoustics expert can measure and prescribe what is needed. Use an accredited acoustical consultant. They are listed in yellow-page directories. Avoid starting with acoustical contractors -- they're typically not acoustics experts. Or, experiment yourself, adding absorbers and barriers. Acoustic materials are available at www.kineticsnoise.com and www.pac-intl.com. Do it yourself and save money. With either approach, these measures, done correctly, can noticeably quiet your home, Orfield said.

Send your questions to Fixit in care of the Star Tribune, 425 Portland Av. S., Minneapolis, MN 55488, or call 612-673-7032, or e-mail fixit@startribune.com. Past columns are available at www.startribune.com/fixit. Alas, Fixit cannot supply individual replies. Fixit appears every day except Friday.