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The Building Code Blog

Occupied Roof Decks - Code Changes in 2018 and 2021 IBC

3/26/2021

8 Comments

 
As more and more states move to adopt the 2018 IBC, it's important to know about a few code updates that impact the design of occupied roof spaces. And if you're jurisdiction is on the ball and already adopted the 2021 IBC, there are a few additional items that apply to you.
Picture
Occupied roof at the Facebook headquarters in Menlo Park, CA (image courtesy of Facebook).

Occupied Roofs Under the 2018 IBC

In the 2015 IBC and prior editions, the code remained silent in regards to occupied roof decks and requirements for allowable height and area.  Under the 2018 IBC, there are now specific provisions addressing this issue.

First, IBC 302.1 has been updated with specific requirements for classifying an occupied roof space:
Where a structure is proposed for a purpose that is not specifically listed in this section, such structure shall be classified in the occupancy it most nearly resembles based on the fire safety and relative hazard. Occupied roofs shall be classified in the group that the occupancy most nearly resembles, according to the fire safety and relative hazard, and shall comply with Section 503.1.4. (Excerpt from 2018 IBC 302.1)
This added language forces designers to classify an occupied roof with an occupancy, whereas some jurisdictions has not previously required it.

Next, IBC 503.1.4 brings in a major new requirement:
A roof level or portion thereof shall be permitted to be used as an occupied roof provided the occupancy of the roof is an occupancy that is permitted by Table 504.4 for the story immediately below the roof. The area of the occupied roofs shall not be included in the building area as regulated by Section 506.
This section limits the occupancy on an occupied roof to those allowed on the story immediately below the roof. So if your building construction type allows an assembly occupancy on the top story, you are also permitted an assembly occupancy on the roof. The code does offer two major exceptions:
  1. If your building if fully sprinkler-protected (NFPA or 13R) and you have fire alarm notification on the occupied roof, you are permitted to have any occupancy on the occupied roof.
  2. If your building is Type I or II construction, you are permitted to have assembly occupancies on the roof of parking garages.

Take the image below for an example, a 4 story building consisting of Type IIIA construction. If the building is fully sprinkler protected in accordance with NFPA 13, a Group A-3 occupancy would per permitted on Level 4. As long as occupant notification is provided on the roof, the 2018 IBC now explicitly allows a Group A-3 occupancy on the roof.
Picture
Sketch of a 4 story building with occupied roof. Assuming Type IIIA construction, fully sprinkler-protected with fire alarm notification throughout, a Group A-3 occupancy is now explicitly permitted on the roof.

​The provision of Section 503.1.4.1 do limit elements on the roof to no more than 48" above the roof surface, with exceptions for penthouses, tower, domes, spires and cupolas. If you have elements above this height, the roof would have to be classified as a story. As an example, the overhang in the image above of the Facebook building would likely trigger the roof being classified as a story.


Another common question is whether an occupied roof can trigger classification as a high-rise building.  The IBC itself does not address this issue, but this staff opinion from the ICC is very helpful in clarifying the intent.  The opinion clearly states, "Just because a roof is an occupied roof does not make it a floor with respect to the definition of a high-rise building. "

Occupied Roofs Under the 2021 IBC

The 2021 IBC updates Section 503.1.4 to explicitly clarify that an occupied roof should not be included when determining building height or number of stories per IBC 504. Language was also added to clarify that this only applies when penthouse and other rooftop structures, when present, comply with IBC 1511. This further supports the notion described above that an occupied roof should not by itself trigger a classification as a high-rise building.

Additionally, the 2021 IBC clarifies that the Exception 1 to 503.1.4 for occupant notification would only require a voice fire alarm system on the roof if the system is required elsewhere in the building. In other words, if you aren't required to have a voice fire alarm in the building, you don't have to provide it on the roof in order to use Exception 1.

Finally, the 2021 IBC updates Section 1511.2.2, Use Limitations for Penthouses, to specifically allow "ancillary spaces used to access elevators and stairways" to be considered part of a penthouse. This means that a stair or elevator tower to the roof will not force an occupied roof to be classified as a story, even though those elements are taller than 48" from the roof surface.
Picture
The 2021 IBC clarifies that spaces used to access an elevator or stairway providing access to the roof are permitted to be considered a penthouse, and therefore not a story (Image courtesy of Dana Schulz).
8 Comments
William Sullivan
4/12/2021 10:25:09 am

Are firefighters still expected to climb the stairs and address fires and other emergencies located on an occupied roof? Are they still required to perform primary searches and open bulk heads pushed up another 10 ft for occuppied roofs?

The added toll on resources dictates that an occupied roof shall be considered when determining the building as a high-rise.

Reply
Best Access Doors link
8/23/2021 09:09:47 am

I like the helpful info you supply for your articles. Thanks for sharing a smart thought.


Reply
Access Doors and Panels link
9/2/2021 07:24:20 am

Thanks, what an informative post! Everything we need to know are found in this article. We hope you keep posting quality articles.


Reply
Sylvia Nielsen link
1/21/2022 12:49:16 pm

So if your building construction type allows an assembly occupancy on the top story, you are also permitted an assembly occupancy on the roof. Thank you for the beautiful post!

Reply
Damon Robinson
1/24/2022 02:13:32 pm

Helpful commentary. Thank you.
But in the case of occupied roofs/rooftop assemblies, IBC should really be more clear with the use of "floor/level" and "story" when describing high-rise requirements.
If you look at the definition of story in IBC: "Story- That portion of a building included between the upper surface of a floor and the upper surface of the floor or roof next above...." (IBC Section 202 Definitions 2018).
Conversely, there is no official definition for the term "floor" or "level". This poses a problem because most rooftop assemblies would not be considered a story by definition due to having no ceiling. But the high-rise requirement in IBC states "occupied floors" not stories: "A building with an occupied floor located more than 75 ft (22 860 mm) above the lowest level of fire department vehicle access. " (IBC Section 202 Definitions 2018).
I would disagree with the ICC staff opinion referenced in this blog because even though the roof is considered a "roof" because it is covering the top-most "story", it is now being occupied as an assembly space thus making its use now more than just a "roof". We actually have people (likely without intimate knowledge of the building) using it for a gathering space. In reality, this roof would be designed for human occupancy in which individuals congregate which triggers the A-2 designation for life safety of the space.
We have to remember the sole reason for why a certain building height in IBC would trigger the high-rise classification: FIRE DEPARTMENT ACCESSIBILITY! Fire Department aerial ladder trucks typically are equipped with 100' span ladders. But because the aerial ladder always positions a certain distance from the building during fire fighting/rescue operations, that reach length decreases to about 60'-75' at best. In fact, the farther away the aerial ladder truck is away from the buliding, the less building height it can access.
If we are going to make it standard practice to not include a building's rooftop assembly spaces as counting towards the high-rise criteria of "occupied floors", then you are allowing a building to disregard life safety components that should be in place for occupants because the fire department can't reach them.

Reply
Gulf Shores Roof Repair link
5/8/2022 04:06:23 pm

When evaluating the impact of occupied roof decks on the overall building size limitations, another consideration is whether the project qualifies as a high-rise building. I’m so thankful for your helpful post!

Reply
larry link
6/24/2022 12:57:21 pm

Can you explain further why you think the Facebook photo example you posted would be considered a floor? (setting aside that this is actually a roof deck/balcony accessed from the enclosed floor in the left of the photo). I assume it is because of the roof covering?
The Code restrictions on roof top structures specifically addresses ENCLOSED structures and not roof coverings. Elsewhere in the code enclosed structures are described as structures with walls not just roofs.

Reply
Chris
8/11/2022 06:39:48 pm

Larry- not quite right. When calculating Building Area, the Ch 2 definition states that "Areas of the building not provided with surrounding walls shall be included in the building are is such areas are included within the horizontal projection of the roof or floor above." Similarly, Gross Floor Area definition notes "The floor area of a building, or portion thereof, not provided with surrounding exterior walls shall be the usable area under the horizontal projection of the roof or floor above." So the roof canopy above makes this occupied roof part of the floor, and building, area, and thus a Story.
Additionally, 503.1.4.1 limits enclosing elements to be less than 48" - the enclosing elements are the walls, guards, and parapets that surround and enclose the roof. In the background of the Facebook photo you're referencing, there is clearly an enclosing wall greater than 48", so that also makes this example a "story:

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The views, opinions, and information found on this site represent solely the author and do not represent the opinions of any other party, including the author's employer and the International Code Council, nor does the presented material assume responsibility for its use.  Local codes and amendments may vary from the code requirements described herein. Fire protection and life safety systems constitute a critical component of public health, safety and welfare and you should consult with a licensed professional for proper design and code compliance.
  • Home
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