Wegetation clings to a row house in Baltimore on one of many abandoned blocks slated for demolition through Project CORE, an initiative to raze a chunk of the city's 17,000 vacant houses. (Patrick Semansky/AP)

Why do some aging, frequently sizable buildings in cities and suburbs face demolition while others are saved from the wrecking ball? What determines the life span of a building, whether a strip shopping center, a school or library, an apartment house, a private office building or a government administrative edifice?

Drive around Washington and you will see older commercial, institutional and residential buildings being torn down and replaced. Equally evident are aging structures being repurposed, remodeled, expanded or absorbed by new, larger edifices.

During a recent broadcast of “The Kojo Nnamdi Show” on WAMU (88.5 FM), we talked about why aging buildings live or die.

The radio conversation inevitably touched on Case in point: the planned demolition of the J. Edgar Hoover Building in downtown Washington. The FBI building’s fate stems from its functional and technical obsolescence, reinforced by the prospect of achieving enhanced, taxable development of its strategically located site on Pennsylvania Avenue.

Deciding to demolish a building, regardless of age, can be justified for one or more reasons.

Functional obsolescence: A building’s overall configuration and layout, floor plans and perhaps location can no longer satisfy programmatic and functional needs of current or prospective owners, investors, tenants and building users. Functional obsolescence is usually the result of technological, cultural and marketplace changes. Large shopping malls come to mind.

Technical obsolescence: A building’s mechanical, electrical and conveyance systems (elevators) perform poorly, are energy-inefficient, and may be unreliable and unsafe. The exterior skin, roofing and other construction materials are deteriorating. Annual maintenance, repair and replacement costs are accelerating and increasingly unaffordable. Along with functional obsolescence, this is one of the FBI building’s many problems.

Site underdevelopment: An aging building’s total floor area, volume, height and permitted uses are substantially below what is allowed under applicable zoning policies and regulations. For property owners, investors and local taxing jurisdictions, demolition of an undersized, financially underperforming building is reasonable. This puts in jeopardy many strip shopping centers near transit stations.

Renovation unfeasibility: The projected expense of saving and renovating a building in poor physical condition is cost-prohibitive. Reconstruction, modernization and expansion appear to be a losing investment proposition. Demolition and new construction can be more cost-effective and profitable than saving a seriously dysfunctional building.

Fortunately, many aging buildings are worth saving and deserve longer lives. Their functional and technical obsolescence can be remedied in ways that are financially feasible. They can be successfully remodeled, reconfigured or enlarged and, equally important, repurposed to efficiently meet current and future requirements.

Two additional justifications help extend the life of aging buildings: historic preservation value and intrinsic sustainability value.

Deciding to save a building for historic preservation reasons transcends justification based on functional, technical or economic utility, or even on sustainability. Saving and protecting recognized, historically landmarked buildings preserves the architectural legacies of the nation’s towns, cities, and urban and suburban neighborhoods.

Preservation value is predicated not only on the aesthetic quality and significance of a building’s design, but also on its uniqueness and importance as a historical place or cultural symbol. Happily, many such historic buildings — the White House, the U.S. Capitol, the National Building Museum, Victorian school buildings, venerable churches — in fact continue to function.

Every existing building embodies immense quantities of previously invested resources: materials, labor, energy and money. These resources were invested initially to construct the building and subsequently to operate and maintain the building over many years. Today, these resources are worth much more than they were when first mobilized.

Demolition wastes all these embedded resources. Thus, saving and continuing to use an aging building, rather than demolishing it and constructing anew, conserves these costly resources and represents a primary sustainability strategy.

Ever more retail stores and malls are closing as shopping habits shift. Office building vacancy rates are rising as workplace patterns and practices change. In future years, tens of thousands of buildings constructed during the past few decades will be candidates either for saving or for demolition.

It seems inevitable that an increasing amount of future development, throughoutacross the nation as well as in metropolitan Washington, will entail saving, renovating and repurposing older buildings. Given the diminishing availability of affordable housing, let’s hope many of these recycled buildings can become places for people to live.

Roger K. Lewis is a practicing architect, a professor emeritus of architecture at the University of Maryland and a regular guest commentator on “The Kojo Nnamdi Show” on WAMU (88.5 FM).