Which area of this building is likely to have more stringent regulations for cable insulation...

The correct answer is the Air Plenum area — the space above the ceiling tiles used for air circulation in HVAC systems.

According to NFPA 70: National Electrical Code (NEC) and referenced in the AVIXA CTS Exam Guide, cabling run through plenum spaces must meet stringent fire and smoke safety standards. This is because if a fire occurs, the plenum area can rapidly spread smoke and toxic fumes throughout a building.

From the CTS Exam Guide (5th Edition), under Chapter 2: Infrastructure, it states:

“Plenum-rated cable is required in spaces used for environmental air (plenum spaces), as these cables are designed with fire-retardant jackets that emit low smoke. Non-plenum cable cannot be used unless it is enclosed in a conduit rated for plenum use.”

— AVIXA CTS Exam Guide, Chapter 2, p. 42–44