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Answers to eight of our most commonly received parking structure questions.

What is the most efficient configuration for a parking structure in order to maximize the number of spaces?

Ninety-degree parking stalls allow for the most efficient parking garage layout. Angled parking should only be used when the parking garage’s footprint doesn’t allow for 90-degree parking. Another tip for achieving more parking spaces is to reduce the length of the ramp as much as possible and allow for end bay parking. This layout typically leads to better efficiency than using the end bay as only a turn bay.

Can I host a party or add an amenity space on the top level of our parking structure?

Per the International Building Code, parking structures are designed for a live load of 40 pounds per square ft of live load. The top level of a parking structure is designed for that plus the snow load – typically 54-60 psf of total live load for the roof level.

The IBC requires that public assembly areas be designed for 100 psf. It’s hard to believe that a party can actually create more weight than vehicles, but it’s true. To have a public gathering on a parking level, the access would have to be monitored and restricted in order not to not exceed the design live load for the parking structure.

We have designed plenty of parking garages that incorporate amenity spaces. It’s a matter of discussing it with your structural engineer early in the design or working with him/her to design reinforcements that can accommodate the need in an existing structure.

Can I have parking stalls on each side of the drive aisle if my parking structure’s traffic pattern is currently designated as one way?

A common misconception is that the aisle width is solely based on one-way or two-way traffic. The aisle width is actually based upon the angle of parking and having enough space to back a car out of the parking space. With 90-degree parking, an aisle of at least 22 ft wide (24 ft is recommended) is required to back out of the parking space. The aisle width can be reduced with angled parking because it is easier to back out. The more angled the parking space, the less the aisle width can become. Hopefully your original parking consultant maximized parking stalls for your needs; in that case, you most likely won’t have space to add stalls on both sides of the aisle.

How much space do I need for parking stall widths and drive aisles?

The parking stall widths, drive aisles and overall circulation is dependent on the type of facility the parking garage is intended to serve. Aisle widths and stall widths should be larger where users have little familiarity with the parking garage and when there is a high turnover rate (think hospitals, casinos, stadiums, etc.). In parking garages where the users are familiar with the parking layout, such as apartments, the parking space width and drive aisles could be reduced. The reasoning is for guest safety – you’d want more accessibility and visibility for users who may be distracted by being in a new environment. Stall widths typically range from 8.5-9 ft and aisle widths range from 22-26 ft depending on use.

How much space or how may levels do I need to get the appropriate amount of parking spaces?

A typical efficiency rate for parking structures is 320-350 sq ft per parking space. This rating assumes there is no retail or any other space that would detract from the parking structure’s efficiency. A typical parking bay, with either one-way or two-way traffic, is 54-62 ft wide. Assuming the footprint of the parking structure can accommodate the parking bays, dividing the square footage of the footprint by an efficiency rating of 320-350 sq ft per space will give an approximate number of parking spaces per level.

How much slope should a parking level have for drainage? Is it only required at the roof level?

In general, a slope of ¼ inch per ft is ideal. A minimum of 3/16 inch per ft should be maintained throughout the parking structure.

A common misconception is that only the upper level of a parking structure should accommodate those slopes. It is important that all levels of parking structures have adequate slopes to get water and chlorides from the vehicles to the drains. Cars bring in ice, slush, salts, etc. on the typical levels of the parking structure and the lower levels don’t get the benefit of rainwater washing the salts off the slab. It’s important to get the water and chlorides to drains as quickly as possible. On top of that, proper drainage keeps water from freezing and creating a liability issue on the typical levels.

How do I address snow removal on the top level of the parking structure?

There are different options for addressing snow removal. We discuss them with the owner and its maintenance department to determine the best option.

  • Option 1 | Designate an area of the parking structure where the snow will be stored. The area should be designed for an increased snow load, accounting for the snow load of the entire roof area concentrated in one specific area.
  • Option 2 | Provide a means for removing the snow from the top level of the parking structure. Snow can be pushed into a snow chute, a shaft designed on the interior of the building leading from the top to the ground level. The snow can then be removed from the lower level of the garage. Similarly, a snow gate can be used to push the snow off of the edge of the parking structure. A snow gate is an interruption in the perimeter guardrail system; it can open enough for snow to be pushed off of the edge of the parking structure. During the snow removal, the lower level must be secure so that no person or property can be impacted by the falling snow.

Can I drive a forklift through the parking structure during construction since the floors have been designed for parking?

All construction equipment should be reviewed by the engineer of record. Although most forklifts, or similar equipment, are comparable in weight to a standard vehicle, their wheelbases are much less. Therefore, the load from the equipment is far more concentrated. In addition, the load on the front of the equipment produces a high front axle load that is in excess of a standard vehicle. Do your part to keep site workers safe by maintaining open communication with your structural engineer.

There you have it – the parking structure questions we answer the most. We’re seeing fewer and fewer single use and standalone parking structures anymore; it’s a fun challenge to collaborate with clients who are either immediately or planning for a future multi-use. Have more parking structure design questions? Leave us a comment, but also check out our post debating precast vs. cast-in-place construction for your parking structure.

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