As one of its study projects, my architectural school class designed the Pan American Health Organization building on the triangular site bounded by Virginia Avenue and 23rd and E streets NW, just north of the State Department. Built in 1964, it had been the subject of an inter-American design competition.

Each of us in the studio struggled primarily with one major issue for several weeks: how to "mass" the building, given the site's three-sided geometry, constraints of zoning and the client's list of programmatic requirements.

None of the solutions we proposed looked at all like the building that stands there today -- a curving slab with vertical fins, convexly facing Virginia Avenue, while its concave side faces southwest to form a backdrop for the circular auditorium building at the corner of E and 23rd.

Most of our schemes filled the site and conformed to the District's prevalent street and block pattern. Our facades lined the sidewalks and streets on all three sides, and the interior of the mass was removed to create a trapezoidal courtyard. A few designs were L-shaped, the legs of the L being along 23rd and E, leaving an open triangular-shaped court facing Virginia Avenue.

Each scheme within the class exhibited differences in dimensions, height, facade treatment and small-scale volumetric moves. Some of us further subdivided our large building masses in ways that made the project appear to be an assemblage of smaller volumes. In each case, however, there was a conscious attempt to "control" every square foot of the site.

Building siting and massing are among the first design questions that an architect must consider when undertaking a project, whether for a new building or an addition to an existing building, sometimes an even more difficult problem.

At the outset of a siting and massing design study, perhaps during the feasibility determination stage, owner and architect first will have established a general program for the project reflecting its purpose, size, relationships between activities, budget and other requirements that might affect the design.

Simultaneously, the characteristics of the site will have been analyzed, because they, too, will influence the building's shape and location. These include the site's natural features -- configuration and orientation, topography, hydrology, soils and microclimate (patterns of prevailing wind and sun).

Important as natural factors are, however, they alone rarely determine a design solution. Existing buildings on or adjoining the site must be accounted for. These man-made contextual elements have their own massing and architectural characteristics -- relationships to streets, to each other and to abutting open spaces. Relative to the project site, they may be neutral, confining, high, low, continuous or discontinuous, axial, orderly or disorderly, simple or complex. Judgments must be made about how these contextual pressures apply.

Then there is zoning, invisibly fingering and sculpting the still inchoate mass. Zoning works in two ways. It constrains on the one hand by setting maximum limits for building use, height, size and lot coverage, while setting minimum limits for yard dimensions and parking. On the other hand, it can relax certain limits as an incentive for special design amenities.

In the face of all this, the architect somehow must take that unformed, metaphoric lump of clay -- whose volume is roughly analagous to the building volume representing the client's program -- and ascertain if, where and how it can fit on the site.

This architectural act of assimilation and invention usually combines accident and intent. The designer and the client may have a preconceived notion about the siting and massing of their building; on in-fill or otherwise constricted lots, it may be effectively prescribed by zoning. But often such notions evolve unpredictably as the architect continually imposes his or her compositional will, along with the constraints provided by nature, technology, the marketplace, the client and the law.

Initial massing studies, undertaken with sketches and models, are a process of trial and error. The architect must understand the scale and size of the project, even while conjuring up abstract patterns or searching for appropriate imagery. The clay stays lumpy as it's modeled and tested.

Questions are asked and ideas postulated -- and often rejected -- relating to overall building geometry, plan and space patterns, height, programmatic organization and cost. Should the building have an atrium? Should the building stretch horizontally or vertically? Should the center or corners be volumetrically accentuated? Should the roof height vary, step down or step up? Should it be perceived as one mass or three masses? Should the main facade wall be in one plane or several?

These early design decisions obviously are critical ones, particularly from an urban-design point of view. They vitally affect the streetscape and the quality of public spaces next to the project. Yet, fundamental siting and massing decisions do not begin to complete the architectural picture. In fact, the architectural design task is just beginning.

The site/massing concept, however original or elegant it may be, is still only a three-dimensional diagram for a building. It must be transformed into architecture through hundreds or thousands of hours of additional study and refinement leading to a precise, constructable artifact. Detailed floor plans, elevations, cross-sections, landscape plans and interiors must be developed; the artfulness with which they are designed will determine the project's ultimate architectural character and quality, even more so than the massing concept.

Compare, for example, two well-known Washington buildings whose siting and general massing are similar but whose architectural characters contrast sharply: the Treasury Building and the Old Executive Office Building flanking the White House. Or consider the old-plus-new Willard Hotel on Pennsylvania Avenue. The complex massing of the set-back, stepped-down, midblock addition contrasts strongly with the simple, corner-turning massing of the original hotel. Their relationship to one another is cemented by replicative roofs, decorative details and the entry courtyard.

Across the street at National Place, much subtler massing occurs through changes of plane and carving away parts of dominant volumes that nevertheless fill most of the block's envelope. These tactics, plus changes in materials and window types, impart an entirely different character to this block of the avenue by comparison with the adjacent Willard.

Clearly, the perceived style of both projects would be altered radically by changing only surface treatments and fenestration, with no changes in basic massing. The same applies to hundreds of downtown office buildings whose massing is generally undistinguished.

Much more distinguishing is the massing of the National Gallery's East Building and the Guggenheim Museum in New York City. Likewise, many suburban buildings and custom-designed homes flex massing muscles to achieve their expressive imagery.

In New York, Chicago and other high-rise cities, architects again are exploring more complex massing for office buildings, especially at their bottoms and tops. Although this may lead to increased perimeter skin area, greater energy demands, fewer standardized floors and higher costs, developers are becoming convinced that such imageable buildings, if well designed, eventually result in classier tenants and higher rents.

The next time you drive down the street, look at the massing and siting of buildings, not their skin and stylistic elements. You may see things you never noticed before.

NEXT: Facades