Good Blocking (STC 40) – Plenum Barrier (Preferred)

January 1, 1

Research conducted by Rockfon and NGC Testing Services1 shows that a lightweight plenum barrier made of stone wool insulation or gypsum board positioned vertically above the wall, blocking the plenum, can provide an STC/CAC 40 level of blocking when combined with a stone wool ceiling system. This design approach can decrease the cost of the ceiling, allow for greater aesthetic flexibility and prevent the need to control noise leaks through the ceiling system.


RFN-NA, optimized acoustics, good sound blocking, STC 40 alternative plenum barrier

STC 40 Alternative Plenum Barrier


  • 1-1/2” thick Rockfon® Plenum Barrier Board
  • Screw to 1-5/8” wide metal track at top and bottom
  • Tape vertical seams with metal tape (optional)
  • STC 40 with ceiling (lab test #NGC6016016)



RFN-NA, optimized acoustics, sound blocking, single layer plenum barrier, grid detail - continuous over the walls

Single Layer Plenum Barrier, Grid Detail - Continuous Over The Wall


Running the ceiling grid continuously over the tops of interior partitions is sometimes utilized so that future reconfiguration of the walls does not require replacement of the ceiling grid. In other cases, pre-manufactured demountable walls typically stop at the underside of the suspended ceiling. When the ceiling grid passes over the walls, install the single layer plenum barrier as shown in the detail above.


RFN-NA, optimized acoustics, good sound blocking, STC 40 plenum barrier

STC 40 Plenum Barrier


  • 5/8" gypsum board (type X) – 1 layer
  • Quick install3 (no tape or caulk)
  • STC 41 with the ceiling (lab test #NGC0615037)





1 Madaras, G. and Heuer, A. (2016). “Optimizing Ceiling Systems and Lightweight Plenum Barriers to Achieve Ceiling Attenuation Class (CAC) Ratings of 40, 45 and 50”. Proceedings of the New England NoiseCon-16: Revolution in Noise Control conference, Providence, RI, 13-14 June, 2016. Electronic publication by the Institute for Noise Control Engineering.
2 Kruger, K. "The Effect of Various Parameters on the Sound Isolation between Offices with Suspended Ceilings." Canadian Acoustics, 16 (2), 1988, pp. 9-23.
3 The 'quick install' method for the gypsum board plenum barriers uses rectangular cut pieces of gypsum board without cutouts for penetrating elements. Large holes in the plenum barrier around penetrating elements are stuffed with stone wool, batt and insulation. Small holes, joints, screw heads, perimeter edges, etc. are NOT taped or caulked/sealed.
4 The referenced laboratory test(s) are part of an extensive, multi-year, testing program conducted by the National Research Council Canada (NRCC) and published by the Institute for Research in Construction (IRC). For more details, including 1/3 octave band transmission loss data, refer to internal reports IRC-IR-693, October 1995 and IRC-IR-761, March 1998. The research program was partially funded by ROXUL, Inc. ROCKFON and ROCKWOOL are subsidiaries of the ROCKWOOL Group.

Explore our ceiling product range

Additional acoustics content