Brace yourselves, boomers. The split-level house is now a historical form of architecture.

That's right. That icon of 1970s style, the once oh-so-hip home of the Brady Bunch, has achieved vintage status by virtue of its advancing age. It has been around for more than 50 years, which elevates its significance in the eyes of architectural preservationists.

That's not to say they're rushing to save the splits as prized examples of American architecture just yet. In fact, a Virginia preservation consultant named James Massey and his professional partner and wife, Shirley Maxwell, were floored to discover that a couple of dedicated restorers were moving on to a split level after having renovated Victorian and Arts and Crafts houses. "That was the first sign of restoring a split level, and we were all amazed," Massey said.

Split levels still are more likely to be the butt of jokes than the object of house hunters' desire, especially among those who associate them with orange countertops and Spanish-style swag lamps. But splits did help popularize the open layout that continues to dominate American home design, and many split-level owners love them for that very reason.

Carol Hurd figures she can easily fit 20 or 30 people into her three-bedroom house in Copley Township, Ohio, more than her neighbors with homes of similar size but more compartmentalized layouts. The kitchen, living room and dining room open to each other on one floor, and just seven steps down is a family room with more gathering space. Hurd's college-age sons, Aaron and Jason, particularly like the family room because it is separated from the rest of the house just enough to give them some privacy when their friends visit.

The Hurds' house has two sections with three levels plus a basement under the main living area, a relative rarity in split-level design. The steps separating all those levels might become a problem eventually, Hurd said, but until then she and her husband, Arthur, intend to stay where they are. "I love my house," she said.

So, evidently, did the hordes of Americans who flocked to split levels after World War II. It was the hottest home style among suburban developers in the mid-1950s, especially in the Northeast and Midwest, Massey said, and its popularity continued for about 25 years.

The split-level concept grew out of Frank Lloyd Wright's Prairie Style of architecture, said Elwin Robison, an architectural historian at Kent State University in Ohio, who jokingly refers to his own split level as "neo-Wrightian." Robison noted that one of Wright's home designs, published in Ladies' Home Journal in the early 1900s, contained many of the external elements that became common in splits, including hip roofs, casement windows and broad, overhanging eaves.

Most split levels, however, lack the internal features that flavored Wright's designs, such as a focal-point fireplace, Robison said. That's because split levels, like much postwar housing, tended to be mass-produced by builders who kept cost and production time down by eliminating complicated decorative elements.

Among the earliest evidence Massey and Maxwell found of split-level designs was Sears, Roebuck and Co.'s 1933 Modern Homes catalog, which included a handful of three-level homes that resembled Cape Cods but had a ground-level recreation room with bedrooms a half-story above it. "They were not big sellers," Massey said, "but they were there."

A few years later, some builders in Chicago, where Sears is based, started constructing multilevel homes, Massey said. Nevertheless, he said, the style didn't seem to venture beyond the region for about another decade.

The post-World War II building boom changed that. Returning GIs fueled a market for affordable homes that could be built quickly, and builders responded first with the boxy, cookie-cutter houses that characterized developments like Levittown, Pa. Then "people wanted just a little bit more," Robison said, and split levels seemed to be just the thing to appeal to style-conscious young buyers.

It's hard to say why split levels caught on, Massey said, although he thinks economy had a lot to do with it. Incorporating a garage into the design allowed for a compact foundation, and the low, shallow-pitched roof was easy for construction crews to walk on and economical to produce.

Tim Merkiel believes that's why his company, Ryan Homes, built so many split levels in Northeast Ohio starting in 1964. The company built its last split about 1988, when it moved its focus away from serving primarily first-time home buyers, the people for whom split levels were a popular choice, he said.

"I'm sure the reason we sold a lot of them was price," said Merkiel, Ryan's regional production manager. Buyers got a lot of living area for their money, including a basement they could finish if they wished, he said.

The design also had functional aspects that appealed to home buyers, Robison said. It included space for the car, which was assuming an ever-more-important role in the American family. Its short flights of steps meant occupants never had to climb the long stairs common in older, high-ceilinged houses. And the overhanging eaves allowed windows to be left open even in the rain, making the house more comfortable in hot weather.

Some architects say the rise of television also contributed to the popularity of the split level. The house style allowed for an informal living area that was far enough away from the rest of the house that TV noise wasn't a problem, but closer than the basement rec rooms that were popular at the time.

Mostly, though, the split level simply represented a dramatic shift in home design. "It was a whole new house type that had never been seen before. . . . These were appealing because they were something new and different," Massey said.

Split levels come in many variations, he said, but most have two wings with a half-story difference, creating three levels. The living room typically is on a separate level from the bedrooms, and it often has a picture window. Although any building material could be used, many had a brick on the lower part and wood framing on the upper story only.

Somewhere around 1980, the split level fell out of favor as reinterpretations of classical home styles became the latest fashion. Massey suspects some homeowners just got tired of all those stairs, although he thinks the main reason was the very force that made splits popular in the first place: the desire for change.

"I think people got tired of them," he said. "Design-wise, I don't think they're the most attractive house."

Still, he sees room for a resurgence. Architectural styles are a lot like women's clothing, he said: They tend to follow cycles of popularity. With bell bottoms back in style and shag carpet showing up in tony shelter magazines, it's not a stretch to think split levels could be next.

Besides, people tend to look back fondly at the house they grew up in, Massey said, and many look for something similar when they're buying their own homes.

That could mean Cindy, Bobby, Greg, Marcia, Jan and Peter are all in the market right now for split levels in which to raise their own little Brady bunches.

Arthur and Carol Hurd, with sons Aaron and Jason, in front of their split-level house, which has the kitchen, living room and dining room on one floor, and a family room just seven steps down.