Donald and Helen Olsen’s house in Berkeley, Calif., looks a lot like it did when he built it in 1954.

New York Times / MATTHEW MILLMAN

In her job as a Realtor at William Pitt Sotheby’s in Darien, Conn., Ellen Kelley sees so many homes they sometimes blur together. But several years ago, she visited one she can’t forget.

“I almost expected Donna Reed to come to the door,” Kelley said, recalling the colonial-style house. “It was a classic 1940s. The appliances were still intact, it was meticulously maintained, everything was ... frozen.”

In other words, a time capsule — a home untouched for decades and giving visitors the sensation of being in a decor-warp.

In the wake of the last decade’s renovation boom, when home equity lines were easy to obtain and house-flipping became common, such homes have become rarer. But some homeowners — despite years of residence and the seemingly ubiquitous influence of home-improvement TV shows — have managed to resist the urge to replace the yellow Formica counters or even buy a new couch.

Why a home remains stuck in the past is unclear. In some cases, the owners may have lacked the money or the desire to update; in others, they may have found a style they liked and see no reason to change.

Leon Hoffman, a psychoanalyst in Manhattan, said a house can provide a “secure base,” a bulwark against change. “Some people are more stuck in their ways,” Hoffman explained. “There’s a bit of anxiety about what the new stuff brings.”

Identifying exactly when a home became stuck is easier. “Pink-tile bathrooms, Dishmaster faucets, colors like aquamarine and sunbeam yellow — all very 1950s,” said Pam Kueber, who runs retrorenovation.com, a Web site devoted to midcentury design. Shag carpet and avocado appliances indicate the ’70s. Lava rock and ultrasuede? As ’80s as a Rubik’s Cube.

Kueber posts midcentury time capsules on her site, with photos provided by readers, often taken from real-estate listings. “I think the owners of these homes were tremendously invested in them emotionally, as well as financially,” she said. “They came from an era where a house was very hard-won.”

As a rule, she said, the homes were well cared-for, and the belief was “Why change something if it’s not worn out?”

Each of the following homes reflects a particular decade and aesthetic, some of them once on the cutting edge of design. Why didn’t their owners keep up with the trends? The reasons are as varied as the spaces.

1950: DEDICATED MODERNISTS

In March, the floating glass house that Donald E. Olsen, an architect, built in 1954 as his family residence on a sloping lot in Berkeley, Calif., became a city landmark, heralded as a fine example of modernism. The designation means Olsen and his wife, Helen, cannot significantly alter the home without permission — a directive they will have little trouble following, if their living area is any indication.

“The couch is George Nelson, and that was bought in 1955,” Helen Olsen said. “The leather chairs we purchased when we were in Switzerland. That was in 1953.”

There’ve been a few changes over the years. The George Nelson couch was recovered in the ’60s, and the Formica counters were replaced with marble a few years later. With each passing decade, the panorama of downtown Oakland and the Golden Gate Bridge was more obscured behind thickening redwoods.

Beyond that, though, the elegant steel-and-glass house looks much as it did when the couple took up residence in the mid-’50s. “Things don’t change — they get added to,” Helen Olsen said, referring to family photos or artwork on the walls.

When asked why she never replaced the furniture, she explained, “I picked it carefully, and love every bit of it. They are works of art.”

1960: WHY ALTER A MASTERPIECE?

Like much of the furniture in Alice Atkins’ home in Livingston, N.J., the two-tiered white living-room coffee table has been there for decades, which might suggest she likes it. In fact, that’s not the case. “To be honest, I’m not in love with it.”

So why didn’t she find a replacement over the years?

“I don’t know. Why didn’t I, Steve?” Atkins, 82, asked her husband, Stephen Atkins, 84.

“I was in no mood to refurnish,” he replied.

Stephen Atkins, a semiretired builder, worked with an architect to design the house, creating richly wooded surfaces and built-ins in the manner of Frank Lloyd Wright.

“We were told that for this area it was way ahead of its time,” he said.

Atkins believes he got it right the first time. “The things we did, you couldn’t do in today’s world — the cost would be astronomical,” he said, citing the walnut, cherry and ash paneling and the curved wall he had his men build in the entry, laboriously wetting and bending the pieces of wallboard into shape.

1970: IT’S CONTEMPORARY TO HIM, ANYWAY

Jason Reitzin’s home in Encino, Calif., features all the hallmarks of upscale ’70s design — walnut paneling, glass-and-chrome dining table, black lacquer console.

Reitzin and his wife, Lillian, bought the home in 1974. “We had a good decorator come up, Sally Sirkin,” he said, referring to the designer Sally Sirkin Lewis. According to Reitzin, she transformed what had been a “bland” interior into something more stylish, introducing elements like an Italian glass table in the living room and suggesting he dye the beige-gold bedroom carpets to match the color scheme in the living areas.

Retired as an executive for Allway Tools, Reitzin said he carefully maintained the house, one reason he thought alterations were unnecessary.

There is an additional motivation for making sure everything looked just as it did when Nixon was in office: Reitzin rents the house as a period setting for film and TV shoots like Charlie’s Angels. The ’70s original, in fact.

1980: CUTTING EDGE, AGAIN

Richard and Barbara Rubens own an interior design firm that prides itself on being modern. In the 1970s, they popularized the mirror trend, and worked on the interior of the Manhattan disco Regine’s. Even today, Rubens said, “We love to be right there on the edge of design.”

And the couple’s 3,000-square-foot triplex town house in Riverdale, in the Bronx, is totally cutting edge — circa 1984.

The kitchen cabinets are all-black polyester lacquer and the countertops are black granite; the toilet is from Kohler’s Pillow Talk line, introduced in the 1980s. In the living room, a black leather sectional curves around a black coffee table. Upstairs in the master bedroom, a platform bed upholstered in ultrasuede faces a mirrored wall unit. The feeling is bold, stark, masculine and sexy — like the bachelor pad of a Reagan-era stockbroker.

“When we did it, it was very up to date,” Barbara Rubens said.

So how did these two designers come to live in a time warp? “It’s a husband-and-wife business, and husband and wife can’t agree,” Barbara Rubens explained.