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Soundproofing before selling a home?

December 21, 2011

Market Ready

Q. The neighboring apartment has a loud dog. Should we add soundproofing along the shared wall?

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A. Effective soundproofing can be expensive, but it may be worth it if potential buyers are going to be put off by noisy neighbors.

Ilsa Vasquez, a sales associate with MNS Real Estate in New York, said: “I’ve had the issue myself, and I’ve also had the issue of selling an apartment with very thin walls. If it was bath time next door, you would know about it. That’s how clearly you could hear.”

Loud noises can be deal breakers. Although many New Yorkers expect to encounter sounds in the city, “There’s a different conversation to be had if it’s a dog or a baby crying next door,” Ms. Vasquez said.

In such cases, she recommends investing in soundproofing along the shared wall.

But sellers should not expect absolute silence. Soundproofing is a game of incremental improvements: the goal is to reduce noise as much as possible.

Devin O’Brien, the owner of Brooklyn Insulation and Soundproofing, said the first step to improving the noise-muffling capabilities of a wall is to add blown-in cellulose insulation, assuming the wall isn’t insulated already. “That would give you about a five-decibel reduction for airborne sound, which is noticeable, but not major,” he said.

The next step up, he said, would be to add a second layer of drywall to the existing wall and to put Green Glue, an elastic damping compound, in between the layers to “cut down on the resonance.” That could reduce sound transmission by about 10 decibels, he said, noting that for every 10-decibel drop, “Sound is perceived as half as loud on the other side.”

A more effective, even extreme, solution, Mr. O’Brien said, is to remove the existing drywall and add insulation and sound isolation clips to the studs (the clips have “a rubber shock absorber” attached, he said). The seller would then install two layers of drywall with Green Glue in between. This assembly, Mr. O’Brien said, could reduce sound transmission about 25 decibels.

While every installation is different, the cost for this type of soundproofing generally starts at about $4,000 per wall, Mr. O’Brien said.

Mason Wyatt, owner of City Soundproofing in Manhattan, offered a similar approach, but noted, “Some buildings prefer that you don’t disturb the existing walls for code and fire rating.”

For that reason, Mr. Wyatt said, “We normally recommend adding an isolated wall next to the existing wall.” A layer of heavy vinyl soundproofing material is applied over the existing wall, followed by thin framing and insulation, and two layers of fire-rated drywall with Green Glue in the middle. This kind of installation, which costs about $35 to $40 a square foot, “takes up about three inches of space altogether,” he said, and can cut neighborly noise substantially.

But even when using such elaborate measures, Mr. Wyatt said, “I never promise that something is going to be soundproof, 100 percent. That’s almost impossible.”

Questions about repairs or redecorating in preparation for putting a home on the market may be sent to marketready@nytimes.com. Unpublished questions cannot be answered individually.