Under-appreciated and usually smaller than today's McMansions, modern houses from the 20th century are disappearing from the architectural ecosystem. Some champions, though, are finding ways to save them.

The American Dream does not always align perfectly with the goals of architectural preservation. “Though certain homeowners consider themselves custodians of important works of architecture, most people draw the line somewhere between the greater good and their individual property rights,” points out Sue Mossman, executive director of Pasadena Heritage, a preservation nonprofit and advocacy group. “'My home is my castle' is an idea so embedded in our culture,” she adds, “and any government intervention in that realm comes with a degree of tension.”

In recent years, wrecking balls have hovered perilously close to modern homes by Rudolph Schindler, E. Fay Jones, and Frank Lloyd Wright, as well as key works by lesser-known talents. Currently, the survival of the 1958 Richard Neutra'designed Connell House, tailored to a spectacular site in Pebble Beach, California, has been the subject of a two-year battle; and the owners of a 1966 residence in Coral Gables, Florida, by one of the region's leading midcentury Modernists, Alfred Parker Browning, are suing the city for upwards of $7 million for denying them the option to raze it. The clich' of homeowners' or greedy developers' bulldozing architecturally remarkable houses, obliterating the cultural heritage to make way for McManors or McChateaus, reflects widespread reality.

The opposite of today's bigger-is-better mindset, the Modern movement championed efficient design and modest scale—which leaves irreplaceable buildings of that era susceptible to death by teardown, particularly if they occupy large or otherwise coveted sites. Adding to that predicament, crisp midcentury designs “don't look so good with the wear or patina of age the way, say, a Colonial would,” observes Dana Robbat, president and cofounder of Friends of Modern Architecture in Lincoln, Massachusetts. “So, when they're neglected or tired, they look very tired—and that makes them even more vulnerable.”

But even condition and size are not always at issue. One well-maintained yet endangered house is the 8,500-square-foot 1970 home Romaldo Giurgola built in Wayzata, Minnesota—the upscale community where Frank Lloyd Wright's 1914 Little House was razed in 1972 (sending its great living room to the Metropolitan Museum of Art and other fragments to collections across the country). Giurgola's clients were members of the Dayton family, Minneapolis-based department store magnates with an exemplary history of architectural patronage. But for the latest owners, this pure-white, geometrically striking house is only their temporary quarters while they build a home more to their taste elsewhere on the lakefront site.

The fate of this icon, bought in 2012 reportedly for nearly $10 million, hangs in the balance as the owners' representatives evaluate moving it off-site. Though interested parties have come forward, the costs and logistical challenges may prove overwhelming. (Relocation of the small Gehry-designed Winton Guesthouse from a far more accessible site on the same lake, in 2008, required cutting it into eight pieces and trucking them out separately.)

For the Giurgola house, a teardown permit has not yet been requested, according to Irene Stemmer of the Wayzata City Council'appointed Historic Preservation Board. “And before demolition can occur, our board gets to photograph each property inside and out,” she adds. “But we can't go in to save a place. We can talk to owners, we can encourage them to renovate, but that's it. Last year, we lost 13 significant houses.” (Municipal policies vary widely. Progressive leadership in Coral Gables has reversed this common hierarchy, giving final authority on demolition permitting to its preservation officers instead of its city council.)

Clearly, moving a building is a costly act of last resort, sacrificing location specificity. But such a Herculean feat will transport Frank Lloyd Wright's 1954 Bachman-Wilson House from its original New Jersey site, plagued by rising waters, to safe ground at the Crystal Bridges Museum in Bentonville, Arkansas.

Though other cultural or academic institutions have occasionally rescued endangered houses, sometimes the very parties expected to defend a precious architectural legacy jeopardize its future. The Museum of Modern Art—entangled, this past year, in controversy over its proposed demolition of the American Folk Art building—was instrumental in the loss of an extraordinary house, the 1963 Long Island home of architect Gordon Bunshaft. His sole residential work, the design dovetailed with the art collection it displayed. After Bunshaft's widow bequeathed it to MoMA, along with the paintings and sculpture, the museum emptied out the art and sold the place in 1994 to Martha Stewart, without preservation protections. The sad story ended with the building's demolition in 2004 by the next owner.

In an equally startling maneuver, the University of Arkansas at Fayetteville's 1998 master plan showed the 1950 Hantz House, an early E. Fay Jones work, replaced by a parking lot. And this is a university with a school of architecture named for Jones, its most celebrated alumnus and longtime faculty member. Though the latest campus expansion plan reverses this travesty, the privately owned Hantz House and neighboring 1951 Durst House (designed by the architecture school's founder, John G. Williams) made the Historic Preservation Alliance of Arkansas's 2013 list of the state's Most Endangered Places. Encroaching large-scale construction (with site blasting) and erosion of the steep hillside where these two small houses are perched have compromised their condition. Even though the pair's owner is committed to preserving them, their situation remains fragile.

Among the most interesting models for reclaiming endangered homes is the work of the nonprofit Cape Cod Modern House Trust (CCMHT). Since 2006, it has salvaged midcentury dwellings owned by the Cape Cod National Sea Shore, structures acquired incidentally when the National Park Service consolidated this mostly wild land in 1961.

The significance of this remote seacoast area in the evolution of Modernism dates back to the 1930s, when self-taught architecture buffs began creating modest houses, influenced by local tradition and cutting-edge work abroad. Later, the influx of immigrants teaching at Harvard and MIT brought such architects as Walter Gropius, Marcel Breuer, and Serge Chermayeff to the town of Wellfleet. Many built summer retreats here: humble rather than showy experiments in Modernism, some are scattered within the National Sea Shore. Several were lost through neglect, while the remaining few—by such locally known talents as Charles Zehneder, Olav Hammarstrom, and Paul Weidlinger—stood dilapidated, vacant, and slated for demolition. Then CCMHT convinced the Park Service to grant it long-term leases to restore them for artist/scholar residencies and other cultural or educational uses.

Occasionally, a house is so recent and widely acclaimed that few would imagine its demise. Yet the 1988 Berkowitz-Odgis House on Martha's Vineyard that Steven Holl designed is no longer standing. About four years ago, its most recent owners hired the local firm of Hutker Architects to renovate and expand the interior space. Without changing the height or footprint, the architects designed a lower level that would solidly fill in where the original, almost shacklike beach house had hovered lightly on stilts above the sand. Other “bones” of the original exposed skeleton would also have been enclosed. Soon after construction began, engineers working with the architect deemed the existing building “structurally unsound and poised to fail, with rot and decay through and through,” says project architect Greg Ehrman. So the owners demolished the original house. They later halted reconstruction, eventually placing the property (and a set of plans) on the market. There it has languished. The original house is gone—and it's unclear that preservation protections could have altered the outcome.

In general, historic or landmark designations can be sought at national, state, and/or city levels, but they are typically reserved for buildings more than 50 years old. And the final word usually rests with local ordinances, should they exist. But none of these classifications guarantees against demolition.

The most powerful preservation tool is the conservation easement, a legal agreement on top of such a designation, providing protection, in perpetuity, against destruction or incongruous change to an historic property. Since the easement is permanently attached to the deed, however, many people are hesitant to restrict themselves, potentially making a sale more challenging. But the provision suits owners who consider the house's ongoing preservation a top priority.

Unprotected homes that have been lost include Lloyd Wright's 1959 Moore House, on California's Palos Verdes Peninsula, and Anthony Ames's 1984 Hulse Residence and 1978 Hulse Pavilion, in Atlanta. Witnessing the destruction of a house you designed can be a painful experience for an architect. As Ames wrote in an open letter in late 2013, after the Hulse compound had been razed (following the death of his client), “The house was sold, pillaged, left for dead, and then demolished by the new owners. I was surprised, saddened, and angry by this insensitive, mindless, and premature destruction.”

Some houses at risk, however, have parachuted to safety at the eleventh hour. For example, Schindler's 1940 Van Dekker House, in Woodland Hills, California, was derelict (though structurally sound) after decades of neglect by its longtime owner. As with many severely rundown houses, a valid issue was whether the restoration costs would price Schindler's house out of its local market. After beginning the extensive work required, one buyer put it back on the market. The house's future looked grim. But a chance meeting connected it with the rare buyer who could make this demanding project economically viable: a local LEED-certified construction management expert, named Frank Gamwell, who has his own building crews and a track record of restoring historic properties. “I love that house and can't wait to live there,” he said a month ago, after rhapsodizing over the “gorgeous copper, textured like embossed leather” that he is fabricating to precisely replicate the original roof surface.

Undeniably, the right match between house and owner are essential to a happy ending.