Brian Goldfarb of Citi Habitats, who is a listing broker on the apartment, says a keeping-up-with-the-Joneses mentality may be stoking interest in washing machines. “They go out and see all these new condos that have them,” he said, “and it plants a seed in their head.”

New technology is also helping to fuel the trend. The washers sold today, especially the front-loading type, tend to be smaller than the top-load models, making them an easier fit for, say, a kitchen alcove, said Allan Schuster, a manager at Gringer & Sons, an appliance store on First Avenue in Manhattan.

The new appliances generally require less water and electricity than older models. In addition, ventless, or “condensing,” dryers don’t need an air pipe. That is a boon for city residents who can’t breach their exterior walls, said Mr. Schuster, who has been selling washers and dryers for almost four decades.

The divide between buildings that allow washers and ones that don’t is not as simple as prewar versus postwar. Both exclusive co-ops with a few units per floor and more densely packed 1950s white-brick buildings can have problems if the pipes get clogged with soapy residue, managers say. But buildings that can monitor the condition of their plumbing and take steps to cut down on suds can usually handle washers.

Some buildings — like Museum Tower at 15 West 53rd Street, a 240-unit condo built in 1985 — are reversing long-term bans. In the summer of 2009, the board changed House Rule No. 37 to allow washers and dryers, said Corinne Vitale, a broker at Brown Harris Stevens who has sold dozens of units there.

“I thought we were losing deals,” Ms. Vitale said, “and I made my thoughts known.”

And it isn’t happening just in the “for sale” market. Luxury rentals, too, have washers and dryers, among them a couple in Williamsburg, Brooklyn: the new 34 Berry and 184 Kent, a converted warehouse.

At the same time there are holdouts. At 180 East 79th Street, a prewar co-op, the board decided to ban washers as a preventive measure in the 1980s after engineers on the board voiced concerns about wear and tear from too much soap, said Pierrette Hogan, a Sotheby’s broker and resident.