Sound Test Failure and Retest after treatment
We were asked to provide pre-completion sound insulation testing for a small block of two new build flats. One flat was on the ground floor with one to the first floor. Both airborne and impact tests were carried out. Unfortunately, one of the airborne tests failed. Our client was in a difficult situation the flats were complete and sold, and a speedy resolution to the situation was required.
The separating floor construction in place was as follows;
- Carpet with underlay
- 18mm chipboard
- Foam to the timber joist tops.
- Timber joists approx 200mm deep with 100mm mineral wool insulation between.
- A double layer of 15mm Soundbloc plasterboard fixed to resilient bars.
The airborne test result produced a result of 41dB Dntw +Ctr. (48dB Dntw, -7Ctr). The structure was generally weak across the frequency range, due to the scenario of a timber floor with Blockwork walls surrounding (exact details unknown). There was however a significant low frequency weakness.
The client was advised that the improvements required are likely to involve ceiling works and potentially a lining to the blockwork walls. However, before this was considered it might be possible to add mass above the separating floor to enhance the test result. This will likely provide a low frequency improvement, which at best would just meet the regulations. The client agreed it was worth a try with this being a far less destructive method.
Approximately 30Kg/m2 of mass was added to the separating floor in the form of an 18mm cement particle board and Acoustilay 15. This was supplied by the sound insulation store, with the manufacturer of the Acoustilay 15 being Sound Reduction Systems Limited.
The test result improved from 41dB Dntw + Ctr, to 46dB Dntw+Ctr. The 5dB improvement turned the airborne test into a passed result, meeting the requirements of the performance standards of Building Regulations Document E 2003 of 45dB Dntw+Ctr or greater. Please see the following graph showing the graphical improvement of the test result. It can be seen that the low frequency improvement of the separating floor was significant, while above 250Hz there was very limited change.
