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

Plan Reading and Symbols

Construction Elements

Joists

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

Thus, a parallel chord truss, or “bar joist,&rdquo in a lightweight 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 has an effect on the specific location and spacing of detectors in a building. Specific location and spacing is reviewed later in this program.


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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