English to German Tech/Engineering Construction / Civil Engineering

Hallo,

in meinem Text geht es um den Aufbau von Büroräumen:

Walls between meeting rooms and reception or offices, to be solid stud partitions, 45dB
Meeting room to receive glass front.
Coordinate length with IWG provided space plan
Glass partitions to be single glazed, 38dB
Provide walls floor to slab, or *floor to underside*, scheduled ceiling with acoustic baffles above, to ensure 45 dB / 38 dB.

Ich frage mich wie underside (in Abgrenzung zu slab) hier zu verstehen ist, Hat jemand eine Idee?

Vielen Dank!