NFPA Journal

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Recently, the department responsible for providing answers to technical questions on NFPA 13, Installation of Sprinkler Systems, received some inquiries regarding the sprinkler requirements for cloud ceilings.

Although this subject was newly addressed beginning with the 2016 edition of NFPA 13, many jurisdictions have not yet adopted the most recent editions of the standard. Even so, it is important to be aware of the fact that the most recent edition of the standard reflects the technical committee’s latest intent on the subject. That means that even if your jurisdiction hasn’t adopted the latest and greatest, and the situation you are dealing with is addressed in a more recent edition, be sure to discuss options with your authority having jurisdiction (AHJ).

The first question many have is whether NFPA 13 defines “cloud ceilings.” If referencing the 2016 edition or later, the answer is yes. Cloud ceilings are now defined as any ceiling system, not including sloped ceilings, installed in the same plane with horizontal openings to the structure above on all sides. Cloud ceilings are now addressed in Subsection 9.2.7 of the 2019 edition, which provides the specific installation requirements for cloud ceiling applications.

The key takeaway from this section is that sprinklers can be omitted above cloud ceilings where four conditions are met.

First, the combined total area of the openings around the cloud are less than or equal to 20 percent of the area of the ceiling, construction feature, or plane used to determine the boundaries of the compartment. The intent of this provision is to ensure the openings along a wall or between clouds are not too large. Fire modeling has shown that when the openings are too large, heat will collect above the cloud ceiling. The sprinklers installed on the lower ceiling should activate when the opening dimension is no greater than 1 inch per foot of elevation above the floor. When the opening is too large, the space above the ceiling should not be considered a concealed space.

Second, the cloud width, the opening gap width between clouds, and the maximum sprinkler protection area are all in accordance with Table 9.2.7.1. The main concept to understand here is that for every vertical foot between the floor and the cloud ceiling panel, there is one inch of separation allowed between cloud ceilings without having to install sprinklers above the cloud (in the structural ceiling). In other words, if you have a distance of 10 feet between the floor and the bottom of the cloud ceiling, and the distance between cloud ceilings (or the cloud and the wall) is 10 inches or less, sprinklers can be omitted above the cloud. The associated annex language provides a simple equation to determine the appropriate column to use in Table 9.2.7.1.

Third, the requirements of 9.2.7.2 must be met. Those include:

» All sprinklers need to be quick-response standard spray or extended coverage pendent or upright sprinklers.

» The ceiling height cannot exceed 20 feet.

» The maximum spacing and area of protection cannot exceed the maximum spacing requirements for light hazard occupancies provided in Table 10.2.4.2(a), or ordinary hazard occupancies as provided in Table 10.2.4.2.1(b).

» Where extended coverage sprinklers are used, the maximum distance between sprinklers cannot exceed 16 feet.

» Correlating with the definition, cloud ceilings are required to be of smooth ceiling construction.

For irregularly shaped clouds (i.e., not rectangular), the minimum width dimension is required to be the smallest width dimension of the cloud, and the gap between clouds or adjacent walls is required to be the greatest dimension

Fourth, spaces above cloud ceilings must contain either noncombustible or limited-combustible construction with minimal combustible loading.

These requirements are based on the findings of a 2013 Fire Protection Research Foundation project that analyzed how cloud ceilings impact sprinkler actuation thresholds with the intent of determining sprinkler installation requirements for large contiguous clouds. Read the report on that research at nfpa.org/cloudceilings.

JACQUELINE WILMOT is an NFPA senior engineer, Building & Life Safety. Top Photograph: ARMSTRONG CEILING & WALL SYSTEMS