Parking Structures Are Highly Dimensional Problems - the Geometry Must Work Before Anything Else Can
Parking structure design is dominated by dimensional constraints more than any other building type. The size of a standard parking stall, the drive aisle width required for two-way circulation, the turning radius for ramp transitions, and the structural column spacing that accommodates parking without columns in awkward locations - all of these dimensions are relatively fixed, and the parking structure plan must accommodate them simultaneously. A parking structure whose geometry doesn't work - stalls too narrow, aisles too tight, ramps too steep - will be rejected by users regardless of how well it is detailed or designed architecturally. The ARE PA exam tests parking structure planning dimensions as a building type planning competency, asking candidates to evaluate whether a described plan configuration meets standard dimensional requirements or to identify the correct dimension for a described parking configuration.
Stall Dimensions
Standard parking stall: 8.5 feet wide × 18 feet deep for 90-degree parking (perpendicular stalls). Some jurisdictions accept 8.0-foot-wide compact stalls up to a defined percentage of total stalls (typically 20-30%). ADA-accessible stalls: 8.0 feet wide + 5.0 foot access aisle = 13.0 feet total; van-accessible stalls: 8.0 feet + 8.0 foot access aisle = 16.0 feet total (or a 11.0-foot-wide stall with 5.0-foot aisle). Angled parking (45° and 60°) reduces stall depth requirement but requires one-way drive aisles and typically reduces lot efficiency compared to 90-degree parking.
Drive Aisle Widths
Drive aisle width depends on the parking angle: 90-degree (two-way): 24 feet minimum; 60-degree (one-way): 18 feet minimum; 45-degree (one-way): 13 feet minimum. The standard module (stall depth + aisle + stall depth) for 90-degree perpendicular parking on both sides of a double-loaded aisle: 18 ft + 24 ft + 18 ft = 60 feet. This 60-foot module is the fundamental planning unit for structured parking levels. Structural bays that are a multiple of 60 feet (or 30 feet for single-loaded aisles) allow columns to align with stall ends without interrupting the drive aisle or the stall geometry.
Ramp Configurations
Parking ramp slope: maximum 20% (1:5) for straight ramps; 12-15% maximum at ramp curves. Ramp width: same as drive aisle (24 feet for two-way); single-lane entrance/exit ramps: 12-14 feet minimum. Ramp configurations: straight double-helix (efficient; level changes occur entirely on the ramp); opposed ramps (ramps at either end of the structure; efficient column grid); split-level (half-level differences between adjacent bays; continuous floor plate with no full-height floor transitions but requires ramps within the floor). Floor-to-floor height for parking: minimum 7 feet clear inside (8-foot-2-inch structural depth at minimum for van-accessible compliance); typical: 9 feet 6 inches to 10 feet floor-to-floor to accommodate structural depth and provide adequate clear height.
Key Exam Points
- Standard stall: 8.5 ft wide × 18 ft deep (90-degree).
- Two-way 90-degree aisle: 24 ft minimum.
- Double-loaded module: 18 + 24 + 18 = 60 ft (standard planning unit).
- Van-accessible stall: 8 ft + 8 ft access aisle = 16 ft total, or 11 ft stall + 5 ft aisle.
- Ramp slope: 20% max for straight; 12-15% at curves.
- Clear height: 7 ft minimum inside (8 ft 2 in structural minimum for van compliance).
AREprep's PA building planning content covers parking structure planning as one of several specialized building type planning topics - giving ARE PA candidates the dimensional planning knowledge the exam tests in site design and building planning scenarios where parking geometry and structural bay coordination are the key design constraints.
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