How to Meet NZBC Clause G6: Acoustic Performance in Commercial Buildings

The NZ Building Codes are a complex, interconnected series of specifications designed to ensure that every building in the country – old and new – is safe to occupy. Some clauses in the NZBC are more prevalent and well-understood, covering aspects such as structural integrity and emergency measures during a fire.

But some NZBC Codes slip beneath the radar from time to time, and we don’t want that to happen. Today, we are specifically discussing NZBC Clause G6, which relates to how a building should be constructed to prevent undue noise transmission between occupancies.

While comparatively less urgent, Clause G6 is still vital to meet as a developer and can be difficult to tick off without the right engineering expertise on-site. Unpack this vital clause from the NZ Building Codes with us, and learn how to ensure compliance in your building’s acoustic performance.

What is NZBC Clause G6?

Per the NZ Building Codes, Clause G6 Airborne and Impact Sound is as follows:

“Prevention of undue noise transmission in building elements between occupancies or common spaces in household units. Under this clause, building elements common to occupancies are required to be constructed to prevent undue noise transmission from other occupancies or common spaces in household units.

It requires a Sound Transmission Class for walls, floors, and ceilings of no less than 55, and for Impact Insulation Class of floors to be no less than 55.”

In there, we have a lot of useful information to help ensure you meet this clause as you develop. Essentially, the goal of the clause is to prevent future occupants of the building from enduring constant noise from surrounding occupants.

What is a Sound Transmission Class?

In New Zealand, a Sound Transmission Class is a number that describes how easily sound can pass through a material. Similarly, an Impact Insulation Class uses a number to describe how easily a simple impact – such as a footstep or a jump – can be transmitted through the material as a loud sound.

These ratings are determined in a lab environment and are widely used. Any rating above 50 is generally considered excellent because it indicates the material is engineered to muffle loud speech to a degree that it is barely audible. In an apartment building, complex, or office development, this STC is vital to meet Clause G6 and prevent undue stress on future occupants.

How can you ensure you meet clause G6?

The NZ Building Codes make no bones about the importance of this clause, so it’s important to meet it during the construction phase. Retrofits and re-inspections are extremely expensive, and a lack of proper acoustic engineering can make an apartment building or office complex a much less appealing choice for potential occupants.

Essentially, your architects must design walls, floors, and ceilings that meet the set Sound Transmission Class and Impact Insulation Class of 55 (minimum). This involves sourcing the appropriate material, but there are also vital acoustic engineering principles at play here.

Option #1: Take the Acceptable Solutions Path (G6/AS1)

This is the hard-and-fast path already understood by the council: if you work with your acoustic engineering and construction teams to build exactly to the specifications documented in G6/AS1, the council will pass you as compliant without further testing.

• For floors, this involves a concrete or timber floor with carpet and underlay to muffle sound. Carpet is currently the only floor covering included in G6/AS1.
• For walls, this involves using double-stud timber walls or a minimum of 150mm concrete or masonry, both of which must have been pre-verified at thickness before installation.

Option #2: Use an Alternative Solution (The Specialist Path)

If your development requires hard flooring materials or proprietary systems that are not present in G6/AS1, then you need to file for an Alternative Solution. In this case, it is vital to engage an acoustic engineer to design your system to ensure it passes Field Tests.

Even if you are using high-impact flooring like hardwood or tile, there are specialised acoustic underlays or systems, such as the GIB Intertenancy Barrier System, that can meet the STC/IIC 55 requirements when properly installed.

Because this is a deviation from the G6/AS1, you will simply need to verify for the council that you meet the NZ Building Codes clause using Verification Method G6/VM1, in which your sound-test results must be within 5dB of the 55dB suppression requirement.

No matter which compliance path you take, you can easily meet the G6 clause of the NZ Building Codes with just a touch of help from a well-reputed acoustic engineer, especially if you are taking a route outside of the Accepted Solutions pathway.

Ensure you are compliant with expertise from the team at Agile Engineering.

We provide engineering expertise backed by years in the field to help you ensure you are fully compliant from the day you break ground all the way to the final handover.

Whichever development stage you are at, reach out to our team for an acoustic engineering consultation on your build site today.