Green Star IEQ-4 Acoustic Comfort Credits — Complete Guide for Australian Projects

The Credit That Only 23% of Australian Projects Earn Fully

Of the approximately 2,800 Green Star-certified projects in Australia, only 23% have earned the maximum 3 IEQ-4 acoustic comfort points. The majority earn 1 point (meeting AS/NZS 2107 'satisfactory' noise levels) and stop there. The second point — achieving AS/NZS 2107 'recommended' levels — requires HVAC systems approximately 5 dB quieter than the satisfactory threshold, which typically means larger ductwork, quieter diffusers, and lower air velocities. The third point requires enhanced sound insulation and reverberation control that goes beyond NCC (National Construction Code) minimum requirements.

Green Star is administered by the Green Building Council of Australia (GBCA) and is Australia's primary green building rating system — the equivalent of LEED in the US or BREEAM in the UK. First launched in 2003, Green Star has evolved through multiple versions. The current framework — Green Star Design & As Built v1.3 — is the applicable standard for new buildings and major refurbishments in Australia.

IEQ-4 Credit Structure

The IEQ-4 (Acoustic Comfort) credit sits within the Indoor Environment Quality (IEQ) category, which has a weighting of approximately 17% in the overall Green Star score.

Credit Levels

Building Types Covered

IEQ-4 applies to all building types assessed under Green Star Design & As Built:

• Commercial offices
• Educational buildings
• Healthcare facilities
• Mixed-use developments
• Public buildings (libraries, courts, civic centres)
• Industrial buildings (acoustic requirements for ancillary spaces)

Points 1 and 2: Internal Noise Levels per AS/NZS 2107

AS/NZS 2107:2016 Noise Level Targets

AS/NZS 2107 provides two levels of noise targets for each room type: 'recommended' (the stricter target) and 'maximum' (equivalent to 'satisfactory'). Green Star maps these as follows:

• 1 Green Star point: Achieve the 'maximum acceptable' (satisfactory) noise level
• 2 Green Star points: Achieve the 'recommended' (design) noise level

Noise Level Table — Office Buildings

Noise Level Table — Educational Buildings

Noise Level Table — Healthcare Buildings

Compliance Methodology

For Points 1 and 2, the project team must demonstrate that internal noise levels from building services (HVAC, electrical, hydraulic) do not exceed the AS/NZS 2107 targets. External noise intrusion through the building envelope is a separate consideration addressed through NCC compliance.

The compliance pathway involves:

1. HVAC noise prediction: Calculate the noise contribution from each mechanical plant item using manufacturer sound power data, duct attenuation, and room correction factors per AS/NZS 2107 Appendix C.

1. Octave-band analysis: Present noise predictions in octave bands from 63 Hz to 8 kHz and plot against NR (Noise Rating) curves. The A-weighted overall level must not exceed the AS/NZS 2107 target, and the spectrum must not exceed the corresponding NR curve at any individual octave band.

1. Documentation: Provide equipment schedules with sound power data, duct layouts showing attenuation paths, room acoustic properties used in calculations, and a summary table showing predicted levels vs targets for each room type.

The 5 dB Gap

The difference between 'satisfactory' and 'recommended' targets is typically 5 dBA. This 5 dB reduction requires:

• Lower air velocities: Reducing duct velocity from 6 m/s to 4 m/s reduces aerodynamic noise by approximately 8 dB — but increases duct cross-section by 50% and construction cost by approximately 15%.
• Quieter terminal devices: VAV boxes with acoustic linings, fan coil units with vibration-isolated mountings.
• Longer duct runs: Additional lined duct length between noise-generating equipment and diffusers.
• Lower diffuser neck velocities: Reducing from 2.5 m/s to 1.5 m/s reduces diffuser self-noise by approximately 6 dB.

Point 3: Enhanced Acoustic Design

Requirements

The third credit point requires acoustic performance that exceeds NCC minimum requirements across three dimensions:

1. Reverberation Time: Key occupied spaces must achieve RT60 targets that go beyond NCC requirements:

2. Sound Insulation: Partitions between acoustically sensitive spaces must achieve enhanced DnT,w values:

3. External noise intrusion: The building envelope must provide sufficient attenuation to achieve AS/NZS 2107 'recommended' internal noise levels when exposed to site-specific external noise.

NCC Section F5 Context

The National Construction Code (NCC) Volume 1, Section F5 (Sound Transmission and Insulation) establishes minimum sound insulation requirements for building elements. For most commercial building types, NCC F5 specifies requirements only for residential separating elements (walls and floors between sole-occupancy units). Commercial office partitions, conference room walls, and educational spaces have minimal or no NCC requirements beyond the general guidance in AS/NZS 2107.

This means that Green Star's Point 3 effectively creates acoustic performance requirements where the NCC provides none — a significant value-add for occupant comfort and productivity.

Worked Example: 5 Star Green Star Office — Sydney CBD

Project Description

A 12-storey commercial office building in Sydney CBD. Net lettable area: 1,800 m² per floor. The developer targets 5 Star Green Star (Australian Excellence). The project needs all 3 IEQ-4 acoustic points to achieve the target score of 60+ points.

Floor Plate Description

• 8 private offices (12 m² each, 2.7 m ceiling height)
• 2 conference rooms (25 m² each, 2.7 m ceiling height)
• 1 boardroom (40 m², 2.7 m ceiling height)
• 1 open plan area (1,400 m², 2.7 m ceiling height)
• Reception and amenities

External Noise Assessment

The site is in Sydney CBD, fronting a major street. Measured external noise:

• North facade (street): LAeq,period = 72 dBA
• South facade (laneway): LAeq,period = 58 dBA
• East/West facades (adjacent buildings): LAeq,period = 55 dBA

Point 1: Satisfactory Noise Levels

The HVAC system is a central plant with VAV distribution. The acoustic consultant calculates internal noise levels:

Point 1: Earned.

Point 2: Recommended Noise Levels

The boardroom requires the most intervention — a 4 dB reduction from 34 to 30 dBA. The acoustic consultant specifies:

• Rectangular duct silencer (600 × 400 mm, 1.5 m long, 100 mm splitters) = 12 dB insertion loss at 500–2000 Hz
• Displacement ventilation diffuser (floor-mounted, low velocity) replacing ceiling diffuser

Point 2: Earned.

Point 3: Enhanced Acoustic Design

RT60 compliance (using Sabine equation):

Conference room (25 m² × 2.7 m = 67.5 m³):

A_required = 0.161 × 67.5 / 0.6 = 18.1 m² Sabine

RT60 = 0.161 × 67.5 / 32.4 = 0.34 s — well within the 0.6 s target.

Open plan area (1,400 m² × 2.7 m = 3,780 m³):

A_required = 0.161 × 3,780 / 0.8 = 760.5 m² Sabine

RT60 = 0.161 × 3,780 / 1,682.4 = 0.36 s — well within the 0.8 s target.

Sound insulation compliance:

The conference-to-corridor partition fails due to the door. Fix: upgrade to STC 45 acoustic door with full perimeter seals and automatic door bottom. Revised composite: 46 dB — PASS.

External noise intrusion:

For the north facade (72 dBA external): the curtain wall system achieves Rw = 42 dB. Internal noise from external sources: 72 − 42 + 10 log₁₀(facade area / room absorption) ≈ 30 dBA for a typical 15 m² office. Combined with HVAC noise of 34 dBA:

Total internal noise = 10 log₁₀(10^(30/10) + 10^(34/10)) ≈ 36 dBA

This exceeds the AS/NZS 2107 recommended level of 35 dBA by 1 dB. Fix: specify curtain wall with Rw ≥ 44 dB on the north facade. This reduces external noise contribution to 28 dBA, giving total internal noise of approximately 34.5 dBA — compliant.

Point 3: Earned (after door upgrade and facade enhancement).

Cost Summary

For a 21,600 m² building with a construction budget of approximately AUD 80 million, the acoustic credits represent 0.24% of total cost — a modest investment for genuine occupant comfort improvement and a significant contribution to the Green Star score.

Green Star vs LEED vs BREEAM: Acoustic Comparison

Green Star occupies a middle ground between LEED (least demanding) and BREEAM (most demanding). Its unique strength is the two-tier noise level system borrowed from AS/NZS 2107, which provides a clear and transparent pathway from basic compliance (satisfactory) to enhanced performance (recommended). The weakness is the lack of mandatory testing — without measurement verification, design predictions may not reflect as-built performance.

Key Takeaways

Green Star IEQ-4 is achievable for most commercial office projects at a cost premium of 0.2–0.5% of construction cost. The first two points are primarily HVAC-driven and require early coordination between the acoustic consultant and the mechanical engineer. The third point requires architectural attention to partition construction, door specifications, and facade performance.

For Australian projects, early engagement with an acoustic consultant and specification of AS/NZS 2107 'recommended' noise targets from the outset is the most effective strategy for earning all 3 points without cost overruns or design rework.

Related reading: AS/NZS 2107 complete guide | LEED acoustic performance credit guide | NABERS IEQ acoustic design guide

Check your Green Star acoustic targets: Use the AcousPlan calculator to verify RT60 and noise levels for Australian office projects.