(Amanda Voisard/FOR THE WASHINGTON POST)

On a recent WAMU broadcast of the Kojo Nnamdi radio show, I was among four guests discussing the challenges of pop-ups in Washington residential neighborhoods.

Pop-ups — single-family row houses that have been expanded vertically well beyond the prevailing height of neighbors’ homes — is a hot-button issue here. They have elicited much citizen opposition, even though stretching a row house vertically may be allowed under existing zoning laws regulating height and density.

Citizen objections to pop-ups focus on several concerns: architectural incompatibility with streetscape character and prevailing size and scale of existing houses along the street; blockage of sunlight and views enjoyed by adjacent houses; sometimes poor design quality of pop-ups and their facades; and increased density when popped-up, single-family row houses become multi-story apartment buildings, presumably changing neighborhood character and increasing competition for on-street parking spaces.

In response to citizen concerns, the D.C. Zoning Commission is considering an amendment in selected R-4 zones (single-family-attached dwellings) to reduce allowable building height and permit no more than two units per row house lot. This is essentially a neighborhood preservation initiative.

Some homeowners in R-4 zones oppose this. They want to retain the right to expand their homes to gain more living space, perhaps to create an accessory apartment for an aging parent or to produce rental income to defray their housing costs. Real estate developers and planners likewise are opposed, arguing that enabling row house expansion helps meet the need to increase the District’s housing supply.

As we briefly discussed during the broadcast, just being either for or against pop-ups and either for or against the proposed zoning masks the real issues and variables that pop-ups represent. The proposed citizen-driven zoning amendment to protect neighborhood character is a simplistic, overly broad-brush way to address the complexities of fine-grain physical growth and real estate development.

Indeed, reducing height and density limits in R-4 zones to suppress pop-ups is not only questionable policy, it is a symptom of the systemic weakness of conventional zoning for managing change. Zoning is in fact a crude, ineffective urban design and architectural tool.

Every neighborhood, street and individual building site is somewhat unique. A taller building that may be aesthetically undesirable on a mid-block lot could be desirable at the corner of a block, flanking and framing an intersection.

Topography may be a key factor in deploying taller buildings along a street and assessing how such buildings are viewed, or how they affect views.

Taller, denser buildings may make sense if they face or back up to a public park or a wider street. On the south side of an east-west street, somewhat taller row houses facing the street may be acceptable, as they cast shadows northward onto the street and not on the yards of adjacent houses or houses to the south.

Row houses near the ends of streets may abut existing, taller apartment buildings at corners of blocks. Expanding and stepping up vertically those particular row houses might be aesthetically desirable and justifiable.

Variables relevant to density include availability of on-site parking versus on-street parking, and access to transit. For row houses near Metro stations, less parking may be necessary, thereby enabling an appropriate local increase in numbers of dwelling units.

Neighborhood or local street transition already underway is yet another variable. Places exist in D.C. neighborhoods where changes in occupancy and density have started and acquired momentum. In such places, somewhat different real estate design and development criteria should be applied.

Finally comes the independent variable of a pop-up’s architectural design, the compositional quality of massing, facade patterns, materials and detailing. Zoning is mute about architecture. Shouldn’t D.C. and other jurisdictions articulate design aspirations and establish a design review process to eliminate or at least minimize the risk of ugliness?

Zoning’s one-size-fits-all approach and focus only on setting limits, while easier to administer, is not the way to design cities, neighborhoods and the shared public realm of streets and public spaces. The pop-up debate clearly illustrates this.

Roger K. Lewis is a practicing architect, a professor emeritus of architecture at the University of Maryland and a regular guest commentator on WAMU’s Kojo Nnamdi Show.