Understanding how sound works
Sound is simply audible vibration conducted through a medium. In built spaces, there are two forms of conduction;
Airborne sound comprises sound generated within a room and transmitted through the air. Typically, this includes people talking, typing, walking and moving objects; phones ringing; noise from heating, ventilation and air conditioning; printers; and sound/music systems.
Structure-borne sound comprises sound generated by any physical impact on the building and transmitted through the structure itself, which typically includes footfalls in the office above, vibrations from heavy equipment such as air conditioning units, and impact sound like drilling or hammering in adjacent rooms.
We measure the quantity of sound in decibels (dB), a logarithmic scale where an increase of 10 dB is perceived as a doubling of the sound level, or a reduction of 10 dB as a halving. 30 dB is very quiet – for example, a bedroom at night. A typical office is around 50-60 dB.
The New Zealand Building Code, G6 clause aims to protect from excessive noise between building units with two performance requirements – a STC (Sound Transmission Class) of 55 and an IIC (Impact Insulation Class) of 55 is required.
The code allows 5dB for testing in a field situation; i.e., FSTC 50 and FIIC 50, where the letter “F” in the designation refers to “Field”.
Generally speaking, bare 150 mm concrete has an IIC of 25 – but this can be higher depending on insulation being placed in ceiling cavities or other sound insulation techniques being used in or around the concrete slab. Add to that a plasterboard cavity with insulation, ceiling batts and you will often get to a IIC of around 40 to 45. Flooring is used to make up the shortfall to get you to the magic 50 FIIC/ 55 IIC number to meet code.
There are many options available in the market to achieve the IIC rating of 55.
Below you will find tests for Interface and Forbo flooring options that exceed the FIIC requirement of 50.