Conceptual Design: From Program to First Plans

Conceptual design is the program's first translation into space: preliminary site plans, floor plans, diagrams, and elevations that define the facility's form and function. Formally it sits either as a fleshing-out of programming sketches, at the front of Schematic Design (first of the customary three phases: SD, Design Development, Construction Documents), or as its own phase on complex projects. Its method is alternatives: massing and siting, footprint within property and zoning limits, architectural theme, entry and exit locations with equipment provisions, pedestrian access and core placement, ramping and circulation with its floor-level consequences for the architecture, layout and level count, mixed-use incorporation, expansion provisions, above- versus below-grade extent, and structural-system accommodation, developed for comparison and narrowed by a comparison matrix: key criteria against each alternative, weighted and scored on complex projects, so the selection is evaluated rather than merely intuited.

Sizing from efficiency. The first quantitative move is estimating the area the programmed count requires, via parking efficiency: total floor area divided by spaces, in square feet per space. The manuscript's first-estimate table: long-span structures at 300 (8.5-foot stalls) or 330 square feet per car (9-foot stalls); short-span at 370 or 400; surface lots at 340 or 370. The worked example carries the method: 500 cars in long-span construction with required 9-foot stalls, at 330 square feet per car, needs about 165,000 square feet, the number that then drives footprint and level count. The efficiency figures are first-pass planning values, moved in practice by local geometry requirements, landscaping, and structural configuration; the functional-design modules refine them.

Siting in building blocks. Positioning the facility on its site respects existing buildings, topography, streets, setbacks, easements, height limits, destination proximity, utility service and conflicts, mixed-use frontage, the master plan, subsurface and groundwater conditions, and expansion plans. The manuscript's estimating device is the building block tied to the parking module: with stalls commonly required at 18 to 19 feet and aisles from 13 feet (steep-angle one-way) to 24 feet (two-way, 90-degree), and two-way 90-degree parking generally the more efficient, the starting block is 61 feet wide: 18-foot stalls both sides of a 24-foot aisle, plus one foot of structure. Vertical circulation requires a minimum of two bays unless topography lets every level meet the street, so the minimum initial width is two blocks, 122 feet, with additional bays added in 61-foot increments; double-loaded bays beat single-loaded for efficiency wherever they fit. Block length is governed by site dimensions, floor-to-floor height, maximum ramp slope (building codes effectively cap parked-on ramps at 6.67 percent, 1:15), whether one bay carries all the ramping, and whether the end bays carry exterior parking.

The access rules. The entry/exit location checklist is the module's most quotable content: offset access points 100 feet or more from intersections (many jurisdictions refuse closer curb cuts); do not split entries and exits to different locations (driver confusion); avoid configurations that run circulation against street traffic ("English" traffic); align access with the end bays, not mid-bay, so inbound and outbound traffic never crosses the predominant internal flows; align with the ramping for direct upper- and lower-floor access; eliminate hard turns into and out of the access lanes, with space provided where turns are unavoidable; and separate from pedestrians to the extent practical.

Cores, support, and levels. Pedestrian cores go where they orient walkers to their destinations, ideally within the footprint at the corners where parking is omitted anyway, with vehicle traffic kept off the pedestrian routes and collection points. Building support (manager's office, electrical, data, security, generator, elevator rooms) largely fits the dead space under the ramps, where shrinking headroom precludes parking, so support need not cost spaces; amenity space (restrooms, bike storage, lockers, transit shelters, kiosks) and true mixed use (retail most commonly, occupying part or all of a ground-level bay) do consume parking area and enter the efficiency math. The level count then falls out of the arithmetic: the example's 165,000 square feet on a 122-by-300-foot footprint (36,600 square feet per level) yields 4.5, rounding to five levels. A final sketch pass (structural system and member layout, facade elements, massing against the surroundings, landscape and hardscape) readies the concept for the matrix.

Source crosswalk -- Module 16