Sprinkler Concealed Space if Minimal Wood?

I'm working on a mid-rise 5-story residential building.

The building structure is permitted to be combustible construction per 3.2.2.50 of the National Building Code of Canada.

For sound proofing the developer decided to build with cast in-place concrete columns and slabs, but decided to use combustible studs for the interior partitions .

So far, nothing wrong here. Now being that the ceiling is 10-ft high, a drop ceiling was built creating a concealed space for the duct and wiring and so on. The architect says that the top part of the interior combustible partition needed not to be drywalled inside the concealed space to the underside of the concrete slab.

The concealed space is made up of a concrete slab with fire separations sealed to the underside of the slab containing every unit individually without sharing any concealed space with the other units.

On the other hand the sprinkler guy says that the exposed 2x4 studs surface in the concealed scape are not considered "limited combustible material," per NFPA 13 Section 8.15.1, and the space should be sprinklered or filled with non-combustible insulation.

Being that the building was permitted to be of combustible construction and the developer went above and beyond with the concrete structure, I'm not sure whether the space needs to be sprinkler protected or not.

Anybody had this scenario happen before, and if so, how should it be addressed?

Thanks.

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