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area with growing demand for commercial, office, or residential space is a more suitable candidate for adaptive reuse than one in a low-density region that may not have sufficient demand to drive the conversion. Likewise, in dense, high-value areas where building costs are higher, the cost of converting an existing parking facility instead of demolishing it and building a new building type from scratch can pose potential long-term cost savings.

Structural Design Considerations

While it seems counterintuitive, the structural load on a building for parking cars is about half the load needed to support an occupied space, such as an office or housing. Therefore, the effective design load of a parking structure is relatively low compared to other uses. Identifying and incorporating are future loading needs will make adaptation much easier. The structural floor framing would also need to be considered. Parking structures typically use either a short or long span system, which have advantages and disadvantages depending on the later intended use. The most efficient system for parking cars is a long span system, where beams span the entire parking bay. While a long span system can park more cars in the same footprint and improves the user experience by avoiding the need for columns between parking stalls, it does not translate well for occupied uses. Long span floors can be a little bouncy with support beams that extend approximately 30 inches below the underside of the floor above. To accommodate a future alternative use for ducts, etc., a long span system would require a higher floor-to-floor height. On the flip side, while a short span system has additional columns, it does provide a stiffer floor and there are typically no beams to contend with during the retrofit, which allows the greatest flexibility for running ducts, plumbing, and conduit while reducing the overall height of the building. The short span system is generally cheaper for the same footprint as a long span system, but the additional columns reduce the number of cars that can be parked and users are required to park between columns. Whatever structural framing is selected for the design, understanding what challenges and opportunities it poses for future conversion is an important consideration. For converting a parking structure to office or residential, the short span 28 PARKING & MOBILITY / AUGUST 2021 / PARKING-MOBILITY.ORG

system is generally the best choice to blend parking requirements with future uses such as office or residential.

Increased Floor Heights

Since occupied uses require higher floor-to-floor heights than are necessary for storing cars, floor heights should be determined based on the future occupancy needs. Another factor that affects floor-toceiling height is accounting for sloping floors. Parking structures are typically designed with sloping floors to allow water to drain. One approach to dealing with this issue for later conversion is to provide enough clear height and structural capacity to add a future flooring surface that will fill drain areas and “flatten” the floor. To accomplish this, the building floors should be at a constant level around the perimeter and slope to area drains at the middle of the structure.

Design for Daylight

Most traditional parking garages have large, deep floor plates, which can cause the central portions of the structure to feel dark and therefore less desirable for human occupancy. However, one way to mitigate this involves careful consideration of ramping configurations. Ramps, while inherent to the design of typical parking garages, are not conducive to occupied uses and should be designed with removal in mind. By locating the ramps in the center bay of the garage and using modular components that can be disassembled and removed in the future, the center of the building can be transformed into an atrium. This provides natural light and ventilation to the inner portions of the converted building, and perhaps a courtyard amenity for building occupants.

Pedestrian Circulation

Most occupied buildings place stairs and elevators in the center of the building, to open up as much of the perimeter as possible to bring daylight into the space. However, in most garages, the stairs and elevators are located in the corners of the building, making use of space that cannot be used for parking. The number of and width of egress pathways, stairs, and elevators must also account for a future use.

Facade Design

Unlike occupied spaces, above ground parking garages typically rely on natural ventilation. Therefore, to