By Brian O’Connor

A sprinkler system is comprised of many components working together to help improve fire and life safety of the built environment. An often-overlooked component of the sprinkler system is the ceiling itself, which can have a huge impact on how the system needs to be installed. Sprinklers are specifically designed and tested to be installed beneath certain ceiling types, and the requirements of NFPA 13, Standard for the Installation of Sprinkler Systems, reflect that. 

A common question we receive is whether a ceiling can be too high to install sprinklers. The answer, like so many great engineering answers, is “it depends.” Experience and testing have shown sprinklers to be effective and necessary at heights in excess of 50 feet. For this reason, most installations should not have a limit on the height they can be installed. One exception relates to storage occupancies, where NFPA 13 specifies maximum ceiling heights for the installation of certain sprinklers. That information is shown in tables in Chapters 20–25, which cover storage occupancies. 

Since heat rises due to its buoyancy, the ceiling acts as a barrier to prevent the heat from escaping vertically. In doing so it causes heat to build up at the ceiling, which allows sprinklers to activate, discharging water on the fire. Ceilings with significant irregularities can prevent the heat from moving uniformly. This can cause sprinklers farther from the fire to activate prematurely, delaying the activation of sprinklers in the area of the fire. To prevent this, many sprinklers are only allowed to be installed below smooth, flat ceilings.

Ceiling pockets and skylights are common characteristics of ceilings, and in some instances sprinklers can be omitted from those features. Sprinklers are not required to be installed in ceiling pockets if they are small and/or shallow enough, are spaced far enough away from other pockets, and have noncombustible or limited combustible finishes, provided that quick response sprinklers are used in the room and cover the entire floor area. Skylights don’t require sprinklers as long as they do not exceed a certain size and maintain a certain distance from other skylights or ceiling pockets.

A number of other considerations also exist, including the angle of a ceiling—most sprinklers installed beneath ceilings with a slope exceeding one in six are required to increase their area of operation by 30 percent without revising the density. Cloud ceilings—a type of suspended ceiling with openings around the sides—were historically required to be sprinklered above and below, but new requirements allow sprinklers to be installed below only in certain situations. Drop-out ceilings are designed to shrink and fall away during the early stages of a fire—they aren’t considered permanent ceilings since they are only an aesthetic cover for the ceiling above. Sprinklers are required above these ceilings but not below. Drop-out ceilings are evaluated to verify that they do not contribute to fire growth and that they do not significantly delay the operation of the sprinkler system above.

While there are many factors to consider when installing a sprinkler system, the ceiling details should not be overlooked. Knowing which type of ceiling is installed and how it could alter your design is critical to installing a compliant system that lives can depend on.

SOURCE: NFPA