Atrium Design Considerations
The use of vertical openings within buildings is a common design feature. Large spaces, typically in the center of a building, created by vertical openings through floors and ceilings are commonly referred to by architects as an atrium. Atriums are desirable to some building designs because they allow for light and ventilation within a space and allow for many parts of a building to feel connected with each other. However, atriums and other vertical openings pose some unique fire protection and life safety hazards that must be considered such as limiting the spread of fire and the products of combustion throughout the building.
The base requirement in NFPA 101, The Life Safety Code, states that every floor that separates stories of a building must be constructed as a smoke barrier. If there are openings in the floor, these openings must be enclosed with fire barrier walls that extend from floor to floor or floor to roof. These two main base requirements apply to all occupancies unless a specific occupancy chapter provides an alternative option. This base requirement of separating stories exists to minimize the number of occupants that are exposed to the effects of a fire.
There are exceptions that permit unprotected openings within floors that separate stories. The following protection packages are outlined in NFPA 101 and are permitted to be used under certain conditions:
- communicating space
- partially enclosed two-story opening
- convenience opening
When selecting an unprotected vertical opening protection package, the first thing to consider is the number of stories that are open to each other. If the opening connects three stories or fewer, then you will need to look and see if you can meet the requirements of a communicating space or convenience stair opening, if the opening connects 4 stories, then the space will need to meet the requirements for an atrium or convenience stair. If more than 4 stories are connected, then the requirements for an atrium will need to be met. For a deeper dive into types of vertical openings take a look at this blog.
Let’s assume that the vertical openings within the building need to be protected as an atrium. Section 8.6.7 of NFPA 101 provides the requirements for an atrium, which include:
- an engineering analysis for smoke layer development
- separation from other spaces
- exit access requirements
- permissible contents
- sprinkler protection
- and if provided, requirements for a smoke control system (smoke management system)
In this blog I am going to focus on the engineering analysis for smoke layer development and separation requirements.
Where atriums are used, there is a need to minimize the risk of occupants on other floors being exposed to untenable conditions, such as low visibility, heat, and dangerous concentrations of smoke and toxic gases. To ensure that occupants are afforded tenable conditions, an engineering analysis must be completed to confirm that the smoke layer will stay at least 6 ft (1830 mm) above the highest walking surface within the atrium space for a period that is equal to 1.5 times the calculated egress time, or 20 minutes, whichever is greater. It should be noted that the requirement for an engineering analysis does not mean that a smoke control or smoke management system is required in all atriums because there are cases in which tenable conditions can be maintained without a smoke management system.
The engineering analysis should include the following elements:
- Fire dynamics, including the following:
- Fire size and location
- Materials likely to be burning
- Fire plume geometry
- Fire plume or smoke layer impact on means of egress
- Tenability conditions during the period of occupant egress
- Response and performance of building systems, including passive barriers, automatic detection and extinguishing, and smoke control
- Response time required for building occupants to reach building exits, including any time required to exit through the atrium as permitted in NFPA 101.
If the engineering analysis shows that a smoke control system (smoke management system) is required in the atrium to keep the smoke layer at least 6 ft (1830 mm) above the highest walking surface then the system will need to be designed and installed in accordance with NFPA 92, Standard for Smoke Control Systems. NFPA 92 allows for different design approaches to smoke management including natural smoke filling, mechanical smoke exhaust, gravity smoke venting, and opposed flow to prevent smoke movement. For more information on smoke control systems take a look at this blog.
To protect the occupants in adjacent portions of the building, NFPA 101 requires that atriums be separated from adjacent spaces using one of the following methods:
Fire barriers with not less than a 1-hour fire resistance rating.
Any number of levels are permitted to be open directly to the atrium based on the results of the engineering analysis.
Glass walls and inoperable windows can serve as the separation provided they are protected with closely spaced sprinklers on either side of the glass. Want to learn more about atrium design?
Want to see all the referenced requirements within the codes and standards? Take a look at our atrium design situation in the DiRECT feature on NFPA LiNK. This situation goes into more detail on design requirements as well as sprinkler system and fire alarm system design considerations. For more information on how to access NFPA LiNK with a 14-day free trial on your computer or mobile device go here.