NFPA 72 code sections · NFPA 72 Overview
"Shall" is a requirement, "should" is advice
NFPA 72 uses two very different words. "Shall" means mandatory — you must do it to comply. "Should" means recommended, and it only appears in the annexes. Annex A text (the A.x.x.x paragraphs printed after the main chapters) explains the intent of a rule and is not enforceable by itself. When an inspector cites you, it has to be a "shall" in the body of the code or a requirement the AHJ has adopted locally.
NFPA 72 reference
Chapter 3 — Definitions; Annex A
3.2.6 (Shall), 3.2.7 (Should); A.1.1 (Annex material is explanatory, not a requirement)
References use NFPA 72 2019/2022 numbering — section numbers can shift between editions, so confirm in the edition your AHJ has adopted.
On the job
An inspector tells you the smoke detectors in a corridor "should" be spaced closer per Annex A. You can point out that the annex paragraph is guidance; the enforceable spacing comes from the body of Chapter 17 and the manufacturer's listing. Then confirm with the AHJ, who can still require more under local amendments.
Quick check
1. In NFPA 72, the word "shall" means the requirement is:
2. Where does "should" language appear in NFPA 72?
3. Annex A paragraphs are:
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