Obstructed construction by NFPA 13 2013 3.7.1  or not ?

Discussion created by gestionjft on Apr 14, 2017

The type of construction look like exhibit 3.34 (type know as Semi-Mill) handbook 13 2013. Roof planking supported by wood beam 5'' width and 20'' depth spaced 6 feets center to center. The wood beam rest on girder. The girder are W610 i-beam steel spaced about 20 feets. The space between top w610 and the roof is unfilled. The bays exceeds 300 ft2. Is that type of construction meet  A.3.7.1 (1) Beam and Girders construction or (5) Semi-Mill construction ? The goal is to installed sprinkler 22'' below the roof.

I know the area limitation of 300 ft2 for panel construction with no unfilled cross-sectionnal but that is for beam spaced more than 7.5 feets...