GLT-299-7-2(3) Rev.0
Mar 23, 2018
9
8.2.2
Ceiling construction and heat detectors
When installing heat detectors on other than flat and smooth ceilings or at ceiling height greater than 3 m (10 ft.),
spacing must be adjusted. The table below shows the reduction in listed spacing to be applied when detectors are
mounted on ceilings higher than 3 m (10 ft.). This reduced spacing allows the detectors to have the equivalent
response of detectors located on a 3 m (10 ft.) ceiling.
Ceiling height
Percent of listed spacing
0 to 3 m (0 to 10 ft.)
100
3 to 3.7 m (10 to 12 ft.)
91
3.7 to 4.3 m (12 to 14 ft.)
84
4.3 to 4.9 m (14 to 16 ft.)
77
4.9 to 5.5 m (16 to 18 ft.)
71
5.5 to 6.0 m (18 to 20 ft.)
64
6.0 to 6.7 m (20 to 22 ft.)
58
6.7 to 7.3 m (22 to 24 ft.)
52
7.3 to 7.9 m (24 to 26 ft.)
46
7.9 to 8.5 m (26 to 28 ft.)
40
8.5 to 9.1 m (28 to 30 ft.)
34
Spot type detector ceiling height reduction percentages
8.2.3
Exposed solid joists
Exposed solid ceiling joists may impede the heat flow to the detectors. A joist is defined as a solid member projecting
down from the ceiling surface for a distance of more than 10 cm (4 in.) and spaced at intervals of 91 cm (36 in.) or
less, center to center. The spacing of heat detectors must be reduced by 50% in the direction perpendicular to the
joist. The detectors shall be mounted on the bottom of the joists.
Figure 7: Heat detector spacing
— solid joist construction (side view)
