True or false?

In 1940, almost half of all American houses had one or no bathrooms.

In the 1950s, the typical new house had one lavatory.

Until 1980, most new houses had just one full bathroom and a powder room.

All true.

Now guess how many bathrooms are being built in new houses.

If you said 2 1/2 or three, you win, say experts at the National Association of Home Builders in the District.

Custom-built, luxury houses often have a bath for each bedroom, plus a powder room. Think seven bedrooms, eight baths in a custom home in, say, Potomac. Or more, depending on whether the family also wants a toilet and sink off the family room, basement or kitchen.

What's going on? Have Americans just discovered cleanliness in the past 60 years? Or are we now obsessed with the loo?

Not exactly, say building, remodeling and behavioral experts, who invariably laugh when asked. There are reasons for our fascination with fastidiousness, they say.

Home buyers today want convenience: They want a toilet near wherever they spend time in a house. And with houses today twice the size they were in 1940, that means at least twice the bathrooms.

They want luxury: That means more space -- or spaces -- than in the one or two 5-by-7 water closets of yesteryear. They're also upping the number of johns to keep up with the Joneses, especially in well-to-do neighborhoods.

And they want to be alone: That means, if they've got the money, they're not interested in teaching the lessons they learned from their parents about the merits of sharing. They want privacy.

"We all shared a bathroom -- parents and five children -- when I was a kid," said Better Homes and Gardens editor and bathroom maven Joan McCloskey, "but I have no idea how we did it."

It's a different planet from the 1780s, when Ben Franklin brought the first bathtub to the United States from Europe, and from 1851, when President Millard Fillmore was criticized for indulging in "monarchical luxury" when he had a bathtub installed in the White House.

It's also a far cry from the 1940s, when almost one-third of the nation's 37.4 million houses had no running water, when 13 million houses had no flush toilets and when 16 million had no bathtub or shower. It's also far different from the experience of baby boomers who shared with siblings in the 1950s or 1960s.

"The biggest change in housing in the past 60 years has been in plumbing," according to Kermit Baker, director of the Remodeling Futures Program at Harvard University's Joint Center for Housing Studies.

"Now, increasingly, the majority of new homes have three bathrooms," Baker said. "And some people have at least one for every bedroom in the house -- as many as we have TV sets."

"It really comes down to convenience," said Gary Uhl, director of design for fixtures giant American Standard Cos. in Piscataway, N.J. "As homes get larger, people don't want to trek all the way across the house. They want a bathroom next to the deck, next to the pool house, next to the home office."

The standard for decades, said McCloskey of Better Homes and Gardens, was 1 1/2 bathrooms -- one for the family and a powder room for visitors.

"During the gluttonous '80s, we started adding them," she said. As houses got bigger and bigger, Americans wanted more and more extras of all kinds, she said.

"While lots of things from those days have disappeared [from new construction] -- like the gigantic two-story foyers that were a ton of wasted space -- the bathrooms have remained," she said.

In particular, builders added baths for the children. The reasoning is simple, McCloskey said: "We're doing this because everybody is up and out on the same time schedule these days. Moms who used to stay at home and stagger bathroom schedules are working now."

Adding bathrooms "is just a way to get peace," she said. "Your kids don't fight. They don't yell at each other. Then the moms and dads don't have to yell at the kids. So they get some peace."

Home buyers, said Gopal Ahluwalia, research director of the National Association of Home Builders, are also seeking more bathroom space for themselves -- sometimes in the form of his-and-her master bath suites, perhaps with double sinks or larger shower stalls with double shower heads.

"They want a place where they can think, where they won't be bothered. And there aren't a lot of places where that can happen," he said.

In customer surveys, American Standard's Uhl said, "women tell us that the bathroom is their number one getaway place. In theory it's the place you go to close out the world, unless you happen to have kids or pets."

(Men, said Uhl, report in surveys that their favorite place of refuge is the garage or basement.)

Even single homeowners or couples with one child "won't buy a house today with less than three bathrooms," Ahluwalia said. The perception, he said, is that such a house won't sell.

And the proof is in the research data. According to NAHB's latest survey of home buyers, 47 percent wanted 2 1/2 baths or more.

Of the rest, 36 percent preferred two bathrooms, 14 percent preferred 1 1/2 and 3 percent preferred only one.

Ahluwalia said, however, that "even if you want to buy a [new] house today with 1 1/2 baths, you cannot get it. You have to get at least two."

The national standard in new construction changed to 2 1/2 bathrooms from two bathrooms at the end of the 1990s, Ahluwalia said. But developers routinely build more than that in well-off metropolitan markets such as Washington. "It's a bicoastal phenomenon that goes along with where the homes are more expensive," he said. "It's a lifestyle thing, to keep up with the neighbors."

Some say we've gone too far. "We have too many bathrooms," said Sarah Susanka, architect and author of the 1998 book "Creating the Not So Big House."

"This proliferation, where you have to build a bathroom if you build a bedroom, may not be a good use of money," she said. "Bathrooms are one of the most expensive parts of the house."

Susanka argues it might be smarter to expand existing bathrooms by turning powder rooms into potential guest baths, with tubs or showers screened from view and a hallway to keep out children.

"If someone were to say, 'Here's $10,000, how would you like to spend it?' -- and you think about how the guest bathroom is only used once in a while when someone comes to visit -- most people would say, 'Damn, no, I'm not spending it on that,' " she said.

Susanka said, however, that homeowners are driven to add bathrooms by "cultural norms" that suggest that each person is entitled to a separate bathroom and that it's better for resale purposes to add a small bath for each bedroom than to have larger shared spaces that might better meet the family's needs.

If the master bathroom is where the family gathers, she said, then that's a good spot to add square footage and a whirlpool tub. But if the parents want privacy, then "don't consider putting a soaking tub in there. The reality, in many families, is that the tub is used most often by children under the age of 5."

Area home builders, such as luxury developer Toll Brothers Inc., say they start with 2 1/2 baths, but many local clients want more.

"As customers' children are aging, they want separate bathrooms for them," particularly if they're teenagers, said Toll Brothers Vice President Walter Music.

Other new-home buyers request an additional full bath for guests or visiting parents, Music said. "A lot of our floor plans have 3 1/2 baths," he said.

"Increasingly, in larger homes, I see a lot more floor plans where each bedroom has its own bathroom," said Kathleen Parrott, a kitchen and bath specialist in the Department of Near Environments at Virginia Tech.

This bedroom/bathroom trend, said Parrott, seems to have accompanied the growing interest in the luxury master bath.

"Master bathrooms these days can be almost as big as the sleeping space," she said. "People have a shower, a private compartment for the toilet, a soaking tub to relax in, and each person [using the master bath] has their own grooming space. Some people are putting a TV in, or an exercise area."

Because "Americans consider it a virtue to be clean," the idea of having a private refuge or two master bath suites isn't seen as selfish or isolating, Parrott said. "It's not like what I'm really doing is hiding in there, luxuriating; what I'm doing is grooming, and grooming is considered good."

Remodelers agree that homeowners want more bathrooms, either to keep the out the children or to provide themselves more pit stops.

Almost one in fiveof all existing houses had bathrooms added between 1985 and 1999, according to Harvard's remodeling research.

Real estate agents and builders say bathrooms are second only to kitchens as the top selling point for both existing and new houses.

And adding a bathroom is an improvement that almost pays for itself, according to the latest "Cost vs. Value" assessment in this month's Remodeling magazine.

The average cost of updating an existing 5-by-9-foot bathroom that is at least 25 years old was $9,455 and added $8,048 to the value of the house, or 85 percent of what was spent, according to the survey.

The return in the Washington area was even better: The cost was $9,298, but the payoff was $9,688, or 104 percent.

The same improvement in a Baltimore home cost $9,632 but only added $5,337, or 55 percent.

Remodeling experts say most homeowners don't base their decisions on resale value but on their needs and wants while they live in a house. Getting the money back later is a plus, however.

"In eight out of 10 cases, the people that contact us [to remodel a bathroom] purchased the house three to five years earlier, and now the family's grown, additional children have come along and things are just tight," said John Coburn of Bowers Construction Group in McLean.

Even in upscale McLean and Arlington neighborhoods, older houses have small master baths; owners either want to expand them or add a bath elsewhere, Coburn said. "In a lot of the homes, you can open the door to the master bath and almost hit the sink."

"Most of the houses in Northwest and throughout the District just didn't have first-floor baths" when they were built, said Chris Landis of Landis Construction Corp. in the District. So adding first-floor powder rooms and baths is the reason a lot of people call Landis, he said.

Case Design/Remodeling Inc. in Bethesda frequently adds baths in basements or attics as well as expanding master suites and hall baths, said Mark G. Richardson, the company's president.

"It's a result of lifestyle decisions," Richardson said. "When folks are moving, one of the first things they consider is: 'Can I live with someone else's bathroom?' It's one of the more private, intimate rooms in the house, and one of the desires is to start fresh."

"Twenty years ago, a bathroom was a bathroom was a bathroom," Richardson said. "A master bath didn't look very different from a hall bath. Now the master bath is very different. And the hall bath is for storage or maintenance or for the kids."

The average cost of adding a hall bath is between $13,000 and $20,000, he said. An average master bath costs somewhere in the $20,000s. "But we have done $60,000, $70,000 and $80,000 master baths."

Sandy Spring Builders, a custom builder in Bethesda, is currently building a million-dollar-plus house with seven bedrooms, seven full baths and three half-baths, said Phil Leibovitz, a partner in the company. Leibovitz said the firm's clients usually "want a minimum of 3 1/2 bathrooms."

Leibovitz, who grew up with six siblings and one bath, finds the idea of not sharing a bath understandable but not always a necessity.

"Some people still want their kids to learn how to share," he said. "That's how you learn how to live with each other."

When Leibovitz was a child, he and his siblings "took a lot of baths together, and I have a lot of good memories about it," he said. "If you're raised in a situation where you don't know any different, then you never thought about it, you never thought about being shortchanged."

Leibovitz said his two boys share a bath; his daughter has her own.

Sarah and Wilbur Pace bought a one-bath house in Cleveland Park two years ago.

"It didn't bug me, we could have lived there for a long time," said Sarah Pace, a District schoolteacher who has taken time off from work while having two children.

They hired Case Design soon after they bought the house to add a full bath in the basement. They needed the extra bath, said Sarah Pace, because her parents were planning to visit a lot and would be staying downstairs. "I didn't want my parents to trudge up two floors to go to the bathroom," Pace said. "And we just knew it would add to the value."

The Paces sold the house in May because "the market had gone crazy" and a real estate agent convinced them they could afford a bigger house in Chevy Chase.

"Now I have 3 1/2 bathrooms," marvels Sarah Pace, whose family expanded to four last year. "Life is grand with a bathroom on the first floor," she said. "It's like you've arrived."