Open Vs. Enclosed Parking Garages

4/15/2020

For architects and engineers designing parking garages, two questions commonly arise when determining whether the garage should be an open or enclosed garage. These questions are:

When can a parking garage be considered open?
What are the differences in code requirements for an open garage vs. an enclosed garage?

In this post, we’ll provide a concise overview of the requirements related to these frequently asked questions. I use this writeup as a quick reference guide instead of opening up to the code every time. Hopefully it's helpful for you too! All code references are to the 2015 International Building Code (IBC).

A naturally ventilated, open parking garage (image courtesy of Steve Morgan).

When Can a Parking Garage Be Considered Open?

Parking garages must meet all of the requirements of 406.5 to be considered open. In most cases, the limiting factor for an open vs. enclosed garage is meeting the opening requirements for natural ventilation.

To achieve natural ventilation, an open parking garage must (IBC 406.5):

Have uniformly-distributed openings on two or more sides
Have openings not less than 20% of the perimeter wall area of each tier
Have openings not less than 40% of the perimeter length of each tier
- This 40% length requirement does not apply if the openings are uniformly distributed on two opposing sides of the garage

One additional point is that these opening calculations are for the free area of the openings. If a screen or other form of cover is applied to the opening, the free area ratio of the screen must be multiplied by the area of the opening to determine the free area.

What are the differences in code requirements for an open garage vs. an enclosed garage?

Key differences in the code requirements are:

Ventilation
Where open garages are naturally ventilated, closed parking garages require mechanical ventilation complying with the International Mechanical Code (IMC). Mechanical ventilation alone can add hundreds of thousands or even millions of dollars to a project.

Sprinkler Protection
Open parking garages are not required to be sprinkler protected. Enclosed parking garages require sprinkler protection in accordance with NFPA 13. If the garage is not maintained above 40 degrees Fahrenheit, a dry-pipe sprinkler system is required by NFPA 13. Both open and enclosed garages typically require standpipe systems.

Enclosure of Vertical Openings
Stairs serving an enclosed parking garage are required to be enclosed with rated construction similar to any other vertical opening in a building. In an open parking garage, enclosure of vertical openings, including stairs, is not required. In both cases, the vehicle ramps connecting levels are not required to be enclosed.

Height and Area
For an open parking garage used exclusively for parking (with an exception for a small office and waiting area at grade), the number of tiers and area is permitted to comply with IBC 406.5.4, which is an increase over the allowable height and area limits in IBC Chapter 5. The numbers in IBC Table 406.5.4 can be further increased when the garage has open sides on at least ¾ of the building perimeter. Enclosed garages cannot take this approach and must comply with the limits set forth in Chapter 5.

Fire Resistance Ratings of Exterior Walls
Both open and enclosed parking garages are required to comply with the exterior wall rating requirements of IBC 602. However, per Footnote C to IBC Table 602, open parking garages with a fire separation distance of 10 feet or greater are not required to have a fire-resistance rating. Enclosed parking garages do not have this exception and would require a 1-hour exterior wall unless the fire separation distance is 30 feet or greater.

Conclusion

An open parking garage must meet the minimum requirements for both area of openings and perimeter of openings to allow for natural ventilation. If a parking garage does not meet these requirements, it is considered an enclosed garage and must be provided with mechanical ventilation, sprinkler protection, and it must also meet the other requirements listed above.

19 Comments

Melissa Spires

12/4/2020 01:34:59 pm

I have had a recent plan review that said the 20% open requirement had to occur on opposite sides of the garage. When I read the code, I do not interpret it that way. To me it reads that if you meet the 40% length requirement the 20% open area can be distributed however it wants. What is your interpretation.

Chris Campbell

12/18/2020 11:41:32 pm

Hi Melissa,

Sorry for the delayed response, I have been on leave for the last couple of weeks.

I agree with your interpretation - if you have openings distributed amongst 40% of the perimeter of the exterior walls, there is no requirement for the openings to be on opposite sides.

I'm happy to chat with you directly on this particular plan reviewer's comments!

1/29/2021 03:18:15 am

Great article. Can you point me to the code section that says vertical openings in enclosed garages need to be enclosed and open in open garages?

thanks

1/29/2021 11:09:46 am

Hi TK,

IBC 712.1.10 is where you get the allowance for unenclosed openings.

Chris

Shelley House

2/12/2021 04:35:14 pm

Thank you for your article. I am interested in your comment about calculating free area when screens are added. These are becoming popular to “dress up” parking garages, but make it more challenging to meet opening requirements.

How would you suggest calculating free area of, for instance, a 10’ wide x 40’ tall 40% open mesh panel that was held off the face of the building a foot?

2/13/2021 09:34:38 pm

Hi Shelley,

The typical approach there would be to multiply the area of the openings by the free area of the mesh. So for a 10'x40' opening, that would be 400 SF x 40% = 160 SF of opening.

Chris

Renee Clarke

4/28/2021 02:48:33 pm

Chris,

Have you heard of any requirement to factor in potential ice buildup on the mesh when calculating the free area? Thanks!

Renee

Justin link

6/30/2021 05:57:04 pm

Do you have any estimate to the number of open vs. closed parking structures in the US?

Cesar Villavicencio link

8/21/2021 09:54:18 pm

Hi Chris,

Great article indeed.

In order to determine if a parking-garage is considered open or closed could you please explain what does it mean having uniformly-distributed openings on two or more sides?

1. On two sides means that we could have adjacent forming an edge? In other words we would not necessarily need two opposite sides?

2. uniformly-distributed openings means equally separated all along the sides?

I would appreciate your answer.

Tks

8/23/2021 08:32:59 am

Hi Cesar,

Thanks for the reply.

1. The openings only need to be on opposing sides if you are using that to provision to NOT provide openings equal to at least 40% of the perimeter length of each tier. If your openings are more than this length, there is no requirement for the openings to be on opposing sides.

2. In my opinion, uniformly distributed means that the openings are consistent across the side of the garage in which they are provided. For example, if you are providing openings on the south wall of the garage, the openings would be consistent across that wall, not bunched together only on the southwest or southeast end.

Hope this helps!

Linda Rumbaugh

8/27/2021 10:46:12 am

Can there be windows as openings, that tilt out for open?

8/27/2021 10:52:54 am

Hi Linda,

I think most AHJs would not count operable windows towards the area requirements for an open garage.

Tom Handle

8/29/2021 05:35:23 pm

I don't get why you wouldn't have sprinkler requirement on an open
parking garaged

Go look up King’s Dock car park in Liverpool on New Year's eve 2017. Over 1,000 vehicles were destroyer. The fire could have been worse if it wasn't for the work for the firefighters.

Sprinkler should be mandatory in any parking garage.

8/30/2021 08:10:04 am

Hi Tom,

These are just the code requirements from the IBC. Many local jurisdiction amend the IBC and would require sprinklers, even in open parking garages. I would also note that the 2021 IBC will require sprinklers in new open parking garages over 55 feet in height or new open parking garages over 48,000 square feet in fire area.

Chris

Branden Piks

9/15/2021 09:38:22 am

In an enclosed garage, we have two 3-hr rated vertical stair shafts that go from level 6 to grade as part of a deck wrap apartment building. We have one instance where the second vertical shaft landing does not align with the parking deck and we need to add an interior stair in the deck, outboard of the rated shaft, to rise up 2'-2" to meet the landing for the rated shaft. I can't find anywhere in the code if this small, internal stair is required to be enclosed in a rated shaft as well or can remain open and connected to the rated shaft. The whole deck will be sprinklered. Any help or direction would be great!

9/15/2021 01:31:30 pm

Hi Branden,

I don't know the specific code or local requirements that apply, but I can speak generally regarding IBC requirements. A stair that is connected two different floor levels on the same story is typically not required to be rated. However, note that stairs connecting different levels on the same story cannot be counted towards an accessible means of egress.

Hope this help!

Chris

Erika Sicam

10/11/2021 01:58:13 pm

Hello,

Thanks for the article. For below grade parking to be considered 'open' air parking, quoting the section below, is the outside horizontal clear space requirement a minimum or it has to be exactly that ratio?
The only 'side' that can be opened in this case is the ceiling of the basement. Is it possible to have an 'open' air parking at the basement without treating its perimeter walls that are retaining walls?

406.5.2.1 Openings Below Grade
Where openings below grade provide required natural ventilation, the outside horizontal clear space shall be one and one-half times the depth of the opening. The width of the horizontal clear space shall be maintained from grade down to the bottom of the lowest required opening.

10/12/2021 03:48:53 pm

Hi Erika,

In my opinion, the 1.5:1 ratio is a minimum, not intended to be an exact ratio requirement.

Chris

Ron Cosentino link

10/15/2021 09:05:01 am

Hi Chris
The Code says "Area of openings not less than 20% of total perimeter wall area" What is considered wall area? Only exterior wall above grade, or entire interior wall area? This is not clear in the Code, appreciate your response.

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