Thoughtful design may include planning for a second life for parking structures.
If we are to buy into the notion so persuasively presented in the online seminar "Thinking Beyond Technology: How autonomous vehicles will change everything we know about cities", we may come to agree with the seminar leader's conclusion that at some time in the not-so-distant future the need for daily warehousing of automobiles will be drastically reduced. In a YouTube presentation (link below) they predict that adoption of autonomous vehicles will follow an exponential growth path similar to that of the iPhone and Android mobile devices and that our current parking paradigm will no longer be valid. Their conclusion? The need for parking lots and parking structures will be drastically reduced.
The notion that a fleet of cost-effective and convenient autonomous vehicles can replace the private automobile is a developing reality. And, whether this sea change occurs in 10 years or 20 years, the basic premise appears to be gaining general acceptance as both a planning constraint and an opportunity that must be accounted for when planning new parking structures. Adding to the recognition that these buildings must be designed to adapt to an uncertain future is a very real desire and demand that parking structures be designed to be good neighbors in both the city and on the campus. While marginally better than vast seas of surface parking, the typical parking structure presents a blank street-side dead zone façade to the world, severely degrading the pedestrian urban experience.
As an architect who has been tasked with developing parking structures for urban college campuses with significant, justifiable, and, at least in the near term, growing demand for parking, the challenge becomes "How do we responsibly meet current very real parking needs while planning for future obsolescence?"
One solution appears to be to conceive of the parking structure as an opportunity to accommodate future space needs with a mixed-use design that is flexible and easily adapted to other uses. In recent years, parking structures have been increasingly developed as adaptable mixed-use facilities with retail operations on the first floor and level floor slabs on the parking deck levels with sufficient floor-to-floor spacing to allow for future re-purposing as retail, office, or classroom spaces. This trend is most frequently found at new urban or higher education parking projects.
This notion of a more pedestrian-friendly structure with the potential to be economically re-purposed at a later date represents a significant shift in design thinking away from the typical stand-alone garage. However, this is a shift that seriously affects the cost, function, and appearance of the parking structure. When planning for a forward-thinking, mixed-use and adaptable parking structure we must address several issues:
First Floor Retail and Floor-to-Floor Height: Most parking structures are typically designed to have a floor-to-floor height in the range of 10'-6" to 12'-0". Depending on the type of structural system and the needs of the mechanical systems, first floor mixed-use retail space bumps the floor-to-floor height to something more like 16'-0" to 20'-0". Similarly, all floor spacing above the second level will need to be adjusted up to 12'-0" to 16'-0".
Ramping and Level Floor Plates: The most efficient, lowest cost parking structures employ "parked-on" ramps, with a slope of 5% to 6%. When the floor-to-floor height is increased to incorporate first floor retail, these efficient parked-on ramps are most likely not going to work simply because there is not enough building site to accommodate the required ramp length. More importantly, the sloping parked-on ramp does not lend itself to future re-purposing. Planning for future adaptability will require level floor decks in addition to a more generous floor-to-floor spacing. As a result, a stand-alone express or speed ramp will need to be introduced which will affect the parking efficiency (square footage per stall), complicate the structural framing system, and result in higher costs.
Upper Levels Structural Framing: Most stand-alone parking structures are framed with long span beams that allow for unobstructed parking bays. This type of framing will typically trade off a relatively high amount of deflection and vibration in return for increased parking efficiency. While this is acceptable for parking, it may not be appropriate for retail, office, or classroom facilities.
One approach to counter this vibration and noise is to incorporate shorter span structural framing along with the requisite flat floor slabs. The addition of the necessary additional columns required for the shorter framing spans will, unfortunately, negatively affect parking efficiency: There will be fewer parking slots available on each floor.
Mechanical, Electrical, and Plumbing Services: Mechanical, electrical, and plumbing design and construction costs necessarily increase for a mixed-use and adaptable parking structure in two ways: Engineering infrastructure will need to be provided for any first floor retail operations and provision for future mechanical, electrical, and plumbing work must be factored in to the floor-to-floor height.
Building Services: There are an array of everyday building services such as deliveries and trash pick-up, that are common to retail, office, and classroom spaces but are not required for the typical parking structure. Although not difficult to accommodate, these additional program elements made erode parking capacity and drive parking efficiency down.
Clearly, there is a premium to be paid for the mixed-use, adaptable parking structure. However, this premium will deliver a building that is pedestrian friendly, is a responsible urban neighbor, and will remain viable as a long term development. A structure able to be transformed into something other than a warehouse for automobiles if (or when) the autonomous vehicle revolution takes hold.