Functional Design

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What are some typical standards for parking garage functional design?

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The best design of a parking facility depends first and foremost on a number of factors including user, location, federal/state/local codes, building size, functional layout, etc… However, there are typical design standards common in many parking garage designs. The following are some useful standards that may help answer some of your most common questions:

Parking Space Size

The size of parking spaces allowed is mandated by the local zoning or land development ordinances. For example, in Philadelphia commercial districts, the minimum size parking space allowed is 8’6” x 18’0”.

The size for parking stalls should be based on typical use. A general rule for this is: the lower the turnover, or the more urban a location is, the smaller the parking spaces can be tolerated by users. On the other hand, areas with high turnover, and which are less urban, will generally have larger spaces. However, variances or design wavers are often sought for parking space dimensions when conditions justify the design.

Vehicle width vs. Parking Stall Width

A car door opening clearance is approximately 20 to 24 inches. Adjacent parking spaces share this clearance while vehicles are parked.  When parking adjacent to a built wall or structure, a common practice is to add an additional foot of stall width to the typical space.

Vertical circulation for ramps

Ramp slopes with parking generally range from 5% to 6.67% maximum (per Building Code). When additional overhead height is required at a tier, a speed ramp can be incorporated into the design for vehicle circulation.  Speed ramp slopes can range from 6.67% to 16 % with appropriate transition slopes included at top and bottom.

Considering vertical circulation of floor to floor heights, these typically range from 10’0” to 12’0”. Applicable Building Codes, Accessible Codes and local codes dictate minimum required overhead clearance heights.Typical minimum required overhead clearances are 8’-2” for van accessible parking spaces, and 7’-0” for typical spaces and other accessible spaces. In multi-level parking structures, van accessible parking spaces are permitted to be grouped on a single level.

Garage footprint dimensions

The minimum dimensions for a garage footprint consist of two structural bays. Two 60 foot clear parking modules (2-way, 90 degree parking) would result in a width of 123 feet when including applicable structural members. On the other hand, two one-way bays with angled parking would be slightly less wide. Additional overall parking garage width would increase in increments of the established parking module.

For general planning purposes, the minimum garage length consists of the ramp, plus the turning bays located at each end of the garage. For a garage with two-way traffic there is typically 180 feet of ramp, two end bays of 28 feet, and two spandrel widths of 1 foot. For improved efficiency, the garage with two way traffic with end bay parking must have 180 ft. of ramp, two end bays of48 feet, and two spandrel widths of one foot.

Variations of a typical garage layout are sometimes required based on project requirements or site constraints. An example is when the site will not accommodate a typical length ramp and both structural bays are required to be ramped at half levels to meet overhead height requirements.

A single helix with a two-way circulation design should be limited to five or six tiers because of the number of turns required to pass all parking spaces. However, for a double threaded helix with one-way circulation, the design allow for a vehicle to circulate up and then back down without making a Y-turn at the top. Additionally, a crossover is provided at ramp mid-points to allow vehicles to switch from upward to downward travel to shorten the distance needed to exit the facility.

Accessible Spaces

Typically, accessible spaces are a minimum of 8’-0” wide with a minimum 5’-0” wide access aisle. Two adjacent spaces may share the 5’-0”access aisle. Van accessible spaces are minimum 8’-0” wide with a minimum of 8’-0” wide access aisle.

Accessible parking spaces should always be located in the most convenient location for the user traveling to their final point of destination. Further, when possible, accessible spaces should always be located in covered areas.

Federal, state and local codes should always be examined, as they may require additional design requirements for accessible parking.

*Federal, State, and Local codes govern most of these requirements and should be thoroughly investigated. Data presented herein should be considered guidelines only.  For more specific information and assistance with implementation of these guidelines, please contact THA Consulting, Inc. via email at


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