Copyright 2018 National Fire Protection Association (NFPA®).
Licensed, by agreement, for individual use and download on 12/20/2018 to New Haven University Of. No other reproduction or transmission in any form permitted
without written permission of NFPA®. For inquiries or to report unauthorized use, contact licensing@nfpa.org. This NFCSS All Access subscription expires on September 30, 2019.
34 Chapter 3 • Definitions
(3) Smooth Ceiling Construction. The term smooth ceiling construction as used in this
standard includes the following:
(a) Flat slab, pan-type reinforced concrete
(b) Continuous smooth bays formed by wood, concrete, or steel beams spaced more
than 7½ ft (2.3 m) on centers — beams supported by columns, girders, or trusses
(c) Smooth roof or floor decks supported directly on girders or trusses spaced more
than 7½ ft (2.3 m) on center
(d) Smooth monolithic ceilings of at least ¾ in. (20 mm) of plaster on metal lath
or a combination of materials of equivalent fire-resistive rating attached to the
underside of wood joists, wood trusses, and bar joists
(e) Open-web-type steel beams, regardless of spacing
(f) Smooth shell-type roofs, such as folded plates, hyperbolic paraboloids, saddles,
domes, and long barrel shells
(g) Suspended ceilings of combustible or noncombustible construction
(h) Smooth monolithic ceilings with fire resistance less than that specified under
item A.3.3.41.2(3)(d) and attached to the underside of wood joists, wood trusses,
and bar joists
Combustible or noncombustible floor decks are permitted in the construction speci-
fied in A.3.3.41.2(3)(b) through A.3.3.41.2(3)(f). A.3.3.41.2(3)(b) would include stan-
dard mill construction.
In general, smooth ceiling construction, which is discussed in A.3.3.41.2(3), does not incorporate sup-
porting members that are less than 7½ ft (2.3 m) on center or have members that would interfere with
the distribution of water from sprinklers. The 7½ ft (2.3 m) length serves as a threshold value, the maxi-
mum distance at which a standard spray sprinkler can be placed from a wall for light hazard and ordinary
hazard occupancies. In small rooms, standard spray sprinklers can be placed up to 9 ft (2.7 m) from one
wall (see 10.2.5.2.3). Exhibit 3.7 illustrates smooth ceiling construction consisting of a suspended ceiling.
EXHIBIT 3.7 Smooth, Flat,
{7d1cf25d-f130-43e0-8b7f-041dc4ddd530} Horizontal Ceiling Construction
Consisting of Suspended Ceiling.
(Courtesy of American Fire
Sprinkler Association)
(4) Standard Mill Construction. The term standard mill construction as used in this stan-
dard refers to heavy timber construction as defined in NFPA 220.
(5) Truss Construction (Wood or Steel). The term truss construction refers to parallel or pitched
chord members connected by open web members supporting a roof or floor deck with top
and bottom members not exceeding 4 in. (100 mm) in depth. [See Figure A.3.3.41.2(c).]
Wood truss construction, which is discussed in A.3.3.41.2(5), is similar to bar joist construction, except that
the top and bottom chords typically are of a heavier wood construction, and the chords typically are con-
nected by wood or steel web members rather than steel bars.
Exhibit 3.8 and Exhibit 3.9 illustrate different types of heavy timber construction.
2019 Automatic Sprinkler Systems Handbook
BK-NFPA-13HB19-180218-Chp03.indd 34 11/2/18 8:05 AM
