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NOTE: This is an unformatted excerpt from our online fire protection training library.

Fire Alarm Plans and Code Requirements

Construction Elements

Joists

For the purposes of NFPA 72, a joist is the same as a beam, with one major exception. Whereas a beam is more than three feet apart center to center, a joist is three feet or less apart. The same four-inch depth from the ceiling applies.

Thus, a parallel chord truss, or “bar joist”, in a light weight steel building will not be considered a “joist”, as there will be no solid structural component that extends from the roof to a depth of four inches or more. It will be considered “invisible” for detector location purposes.

The presence of beams or joists in the building affects the specific location and spacing of detectors in a building.


A very typical light steel roof support assembly, using steel bar joist on steel columns.

NOTE: This is an unformatted excerpt from our online fire protection training library.

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