In recent years, a number of Washington’s stylistically modern but not-so-new commercial and institutional buildings have gotten at least a face lift and often a totally new skin. In future years, the facades of many more such buildings will be completely redesigned and reconstructed.

Not too long ago, the U.S. General Services Administration replaced the facades of the hulking U.S. Department of Transportation headquarters building at Seventh and D streets SW, designed decades ago by Edward Durell Stone, architect of the Kennedy Center. Privately owned, 1970s-era office buildings on 18th Street NW, flanking K Street, sport new skins. Other downtown buildings have gone under the “facadectomy” knife.

Exterior makeovers are justified by two skin-related problems: aesthetically deficient facades, and technically dysfunctional and deteriorating facade components. For investment real estate, these issues create an economic problem by detracting from a building’s image, limiting its upscale market appeal and diminishing potential rent revenue.

Consequently, buildings have been re-skinned to enhance their appearance, to alleviate technical deficiencies and to reduce maintenance and energy consumption, thereby lowering a building’s annual operating costs. Ideally, a facade makeover investment can be amortized and paid for by operating cost savings and, for commercial real estate, higher rents.

Modern-era facades are curtain walls, literally composite skins wrapped around and hung on a building’s concrete or steel skeleton. Connected to but structurally independent of the skeleton, a curtain wall can be removed and replaced with little effect on a building’s overall size, shape and interior. This is especially true for boxlike buildings in downtown D.C.

Thus, curtain wall composition, not a building’s form or structural skeleton, establishes the exterior image and stylistic character of most commercial and institutional buildings in Washington. Publicly visible facade materials and details, window patterns, glazing systems, solar control devices, surface textures and ornamentation are what impart architectural expression.

Facade veneers include brick; dimensioned stone — marble, granite, limestone; precast concrete panels; and metal panels. These are attached to and braced by unseen support walls consisting either of concrete block or metal framing. Behind exterior veneers are vapor barriers and insulation, indispensable for keeping out rain, reducing conduction of heat and ensuring interior comfort.

But curtain walls designed and installed decades ago using then-available materials have become physically vulnerable. Many deficiencies are attributable primarily to moisture, the persistent enemy against which a curtain wall is the first line of defense.

Over time, expanding and contracting masonry or precast concrete veneers can develop cracks, deform and become permanently stained or damaged by surface-penetrating particulate matter and water-borne chemicals. Mortar and caulk joints weaken, open up and, like cracks, let water into and behind veneers. Punctured vapor barriers allow moisture to reach more deeply into curtain wall assemblies. When insulating glass edge seals fail, moisture enters the space between glass panes, condenses and permanently fogs up windows.

It gets worse. In the persistent presence of moisture, metallic connectors holding veneers in place can eventually corrode and fail. Water vapor can penetrate insulation and condense, reducing thermal performance and wasting energy. Moisture residing in walls fosters growth of mold and mildew, a health hazard, while also staining and warping interior wall and ceiling finishes.

Today’s state-of-the-art curtain walls are more robust and greener, thanks to improvements in the technical quality, performance and durability of veneer materials, glazing, insulation, vapor barriers and sealants. Architects are now cladding buildings entirely with metal-framed, high-tech glass wall systems.

Undertaking an exterior facade makeover for aesthetic reasons depends on personal taste, qualitative value judgments about a building’s architectural merit and perceptions of marketability. Are the building’s original style and image, an owner or tenant might ask, appropriate for the here and now? In real estate lingo, this is a question of “curb appeal.”

Reflecting architectural design tastes and trends long out of fashion, many buildings 30, 40 or 50 years old can look dull, dated and downright ugly. Class A tenants may resist leasing space in such a building even if it is well located and functional and offers competitive rents. If a more aesthetically pleasing building promises to attract new tenants willing to pay higher rents for higher architectural quality, and if acceptable financing is available, owners may be motivated to opt for a face lift.

In the hands of talented architects, countless aesthetically and technically dysfunctional buildings can become much more attractive and sustainable. Even the almost universally unloved FBI building on Pennsylvania Avenue could become reasonably attractive with a skillfully executed facade makeover, saving it from the wrecking ball.

Roger K. Lewis is a practicing architect and a professor emeritus of architecture at the University of Maryland.