How do different wall and floor constructions perform?


Lined Brickwork

This example shows a 100mm brick partition with a gyproc outer layer with timber stud and acoustic clip construction and fibreglass cavity filling:ST1

  • Air gap: 100mm
  • Stud spacing: 400mm
  • Fibreglass density: 10kg/m3
  • Fibreglass thickness: 60mm
  • Predicted RW: 65dB





Does cavity filling material make a difference?


^60mm fiberglass cavity filling (RW 65) ^empty patition (RW 52)

Filling a partition with insulation (for example rockwool or fibreglass) can provide a significant improvement to RW values over empty partitions. As you can see from the above example, cavity insulation of 60% the width of the air gap provides a 13dB improvement in weighted sound reduction index.


Steel stud plasterboard partition

This example shows a wall with 12.5mm plasterboard partitions with steel stud construction and rockwool cavity filling:

  • Air gap: 100mmST3
  • Stud spacing: 400mm
  • Rockwool density: 33kg/m3
  • Rockwool thickness: 60mm
  • Predicted RW: 45dB




While an RW of 45 is acceptable, it is possible to improve performance by a further 5dB by the inclusion of an extra layer of 12.5mm thick plasterboard:

ST4 ^ double layered plasterboard (RW50)


Masonry flooring

This example shows a 150mm concrete floor with a 12.5mm plasterboard layer:


Ln,w: 79dB







Lightweight Floor Construction

This example shows a lightweight plasterboard floor mounted on timber joists on gypsum plasterboard:


  • Air gap: 100mmST7
  • Stud spacing: 400mm
  • Cavity insulation: Rockwool (33kg/m3)
  • Insulation thickness: 60mm
  • Ln,w: 79dB





Steel Ceiling Construction

This example shows a steel ceiling with a suspended light steel grid and a layer of plasterboard panelling:




  • Air gap: 100mm
  • Steel thickness: 120mm
  • Stud spacing: 400mm
  • Cavity insulation: fiberglass (22kg/m3)
  • Insulation thickness: 50mm
  • Panelling thickness: 12.5mm
  • RW: 83dB


It is possible to increase the weighted sound reduction index by approximately 5dB by adding an additional layer of plasterboard, however the same improvement can be achieved by increasing the size of the air gap to 200mm.

Including the 50mm fiberglass shown in the above example yields a 10dB increase in predicted RW, however if performance is improved by increasing the air gap as described above, proportionally increasing the insulation thickness (100mm for a 200mm air gap) does not give a proportional increase in RW.

If improved RW is required it is recommended that only one of the above solutions is implemented, as implementing both provides diminishing returns, with performance only improving by 2dB over the 5dB achieved by implementing one solution.