By Jeanne Huber
Special to The Washington Post
Thursday, September 28, 2006

Q I live in a duplex in Northwest Washington. My problem is that when my neighbor is talking in her living room, I can hear every word, so she probably hears me, too. Is there a way to add soundproofing that will quiet things for both of us?

A There are ways to dramatically improve your situation, even if it doesn't achieve the perfect results implied by the word "soundproofing."

When people share a building, problems often arise from two sources: the sounds of voices, music, radio or TV; and the impact of footsteps, dropped books and rearranged furniture.

Most of the sound that travels sideways through a structure is the first type, just as you describe. Some of this sound is absorbed by the drywall or plaster on both sides of the wall separating the two spaces. But wall coverings don't have much mass and are attached to wooden or metal studs, so much of the sound travels right through.

The best ways to avoid that are much easier to accomplish when a structure is being built. For example, builders can erect a double wall between units, with studs spaced differently on each side. Separating the top and bottom pieces of framing by even a slight gap will break the connection between the walls. Or builders can hang the drywall on special clips that allow the sheets to jiggle slightly as sound waves hit, which dissipates their energy.

Insulating between studs also helps because it traps the sound waves within the wall cavity. Builders also can include sheets of a sound-absorbing material known as mass-loaded vinyl under the drywall or add several sheets of drywall to each side of the wall.

Soundproofing can be built into existing structures, too. If your duplex is configured so that you could lose a five-inch strip of space along the shared wall, you could build an additional wall set slightly in from the existing one, using one of the techniques mentioned above. Remember that doing this may throw off the symmetry of windows or doors, and you'll lose a bit of floor space.

A simpler solution might be to cover the existing wall with half-inch-thick sheets of soundproofing drywall -- a product combining two layers of drywall and a layer of a plastic material that is amazingly efficient in absorbing sound -- sold under the brand name QuietRock; one area supplier is Marjam Supply Co. in Waldorf (301-396-4158). The manufacturer ( http://www.quietsolution.com ) can point you to other local sources. The price -- $50 to $60 a sheet -- seems exorbitant, given that standard half-inch drywall sells for about $10 a sheet. But the simplicity of this approach might make it a bargain. You can do the work yourself or hire a drywall contractor.

Huy Tran, a regional technical support person for Quiet Solution, says tests have shown that this approach can reduce noise through the wall by 65 percent and convert a standard interior wall into one that's nearly as soundproof as today's building codes require between residential units in new construction. If you think that won't be good enough and are willing to spend more money, the company makes thicker products with even higher noise-reduction scores.

You might wonder whether soundproofing drywall will stop noise coming through the ceiling from an apartment above. According to Tran, the product can muffle music or voices but might not soften footsteps or other impact noises appreciably.

Effective solutions for impact noises need to take place where the impact is occurring -- in the upstairs unit. A thick carpet or rug would make a major improvement. For those who don't want carpeting, the best result (though pricey) would be to remove existing flooring and install soundproofing material with new flooring on top. Quiet Solution has solutions for this, too, or you can investigate options for floating floors, in which pieces either interlock or are glued together, rather than being nailed to floor joists. You'll find many, many options, from true wood to laminate, including bamboo, cork and true linoleum.