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  3. Airborne and Impact Sound: NZ Building Code Clause G6

What is the Airborne and Impact Sound Building Code Clause G6?

The Building Code G6 Clause aims to protect households from excess noise between household units with two performance requirements - an STC (Sound Transmission Class) of 55 and an IIC (Impact Insulation Class) of 55.  STC relates to sound travelling through walls, floors and ceilings, IIC just to the impact sound of footsteps and furniture movement travelling down through floors. 

For both performance requirements there are Acceptable Solutions listed in the G6/AS1, showing diagrams of suitable wall, floor and ceiling assemblies to meet the STC or IIC 55 requirements.

The easiest option if specifying for inter-tenancy household units is carpet on underlay as this forms part of the Acceptable Solution (the other parts being the floor structure itself and the ceiling below).  There is no specification for the weight of the carpet or the underlay.


Although carpet on underlay is the only floor covering that is included in the Acceptable Solution, other flooring types can also be specified, provided they can be proved to make up an IIC of 55.    Alternative products are usually harder - tiles, wood or laminate, but may also be resilient products like vinyl and LVT.  All will likely require some sort of underlay, or be an 'acoustic' or cushion version (this is often built into the vinyl and LVT products if they are for residential use).

Foam or rubber underlays are the most common, in varying thicknesses.  Thicker doesn't always mean they're acoustically better.

Ask for a test result that gives the dB reduction value using both the product you're considering and the underlay together.  This value is an indication of the difference in impact sound that was achieved between a bare concrete floor and the same concrete floor with underlay and product laid on it.  Any test results like this are an indication only, and a field test with the subfloor and ceiling assembly still needs to be performed to ensure the IIC value of 55 is reached.