NFPA Journal - May/June 2020 - 49

In Compliance

NFPA 13

Water-based fire
protection systems

Sprinkler protection for
various ceiling types
By Brian O'Connor
sprinkler system is

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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,

We are often asked
if a ceiling can be too
high to install sprinklers.
The answer, like so many
engineering answers,
is "it depends."

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.
Brian O'Connor is a fire protection engineer at
NFPA. NFPA members and AHJs can use the
Technical Questions tab to post queries on NFPA 13
at nfpa.org/13.

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