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Though the steps may expedite the selling and renting of apartments, they’re also meant to satisfy residents’ demand for quieter living spaces.

“In today’s market, this basic issue has become more important than ever,” said Colin Carpenter, a project manager for 37 Bridge Street, a condominium in

Yes, the six-inch Dagwood-sandwich-like layering of boards, steel and insulation at 80 Metropolitan costs 30 percent more than standard walls, Mr. Lindsey said, but it works. “You probably wouldn’t know the TV was on,” he said.

Whether this quietude is a selling point is unclear, since it has not been used in flogging 80 Metropolitan’s 56 units in the two years they have been on the market, said Juliet Cullen-Cheung, the manager of the project, where studios start at $399,000. But “now we’re starting to realize how unique and important it is,” she added.

Soundproofing from scratch is one thing, developers say, but ripping out walls to re-insulate them is a much trickier endeavor.

Insulating windows with transparent inserts may be feasible, according to Yolanda Queen, a property manager with Bellmarc Realty, who is overseeing that type of retrofit at Regency South, a 22-story white-brick rental at 250 East 63rd Street in Midtown.