NABERS IEQ Acoustic Performance — Design Guide for Australian Office Buildings

The Rating That Changed How Australia Values Office Acoustics

Before NABERS Indoor Environment ratings launched in 2012, acoustic performance in Australian offices was largely invisible to tenants and investors. HVAC noise was assessed against AS/NZS 2107 during commissioning, then forgotten. There was no ongoing performance rating, no benchmark comparison, and no market signal that differentiated acoustically excellent buildings from acoustically mediocre ones. A premium-grade office tower with NR 30 background noise and a B-grade building with NR 42 both appeared identical in lease negotiations.

NABERS IE changed this dynamic. By providing a publicly visible star rating that includes acoustic performance as one of four equally weighted pillars, it created a market incentive for acoustic quality. Today, approximately 850 office buildings hold NABERS IE ratings in Australia, representing over 12 million square metres of office space. Buildings with 5-star or 6-star IE ratings achieve rental premiums of 5–8% and vacancy rates 40% lower than comparable buildings with lower ratings.

What Is NABERS IE?

NABERS (National Australian Built Environment Rating System) is administered by the NSW Department of Planning and Environment. It provides performance ratings for Australian buildings across several categories:

• NABERS Energy: Operational energy performance (mandatory disclosure for offices > 1,000 m²)
• NABERS Water: Water consumption performance
• NABERS Waste: Waste management and recycling
• NABERS Indoor Environment (IE): Indoor comfort and environmental quality

The rating uses a 1-to-6 star scale:

The Acoustic Assessment: What Gets Measured

The NABERS IE acoustic assessment combines objective measurements and subjective occupant feedback. Both contribute to the acoustic pillar score.

Objective Measurements

1. Background Noise Level (LAeq)

• Measured in dBA using a Class 1 or Class 2 integrating sound level meter per IEC 61672-1
• Measurement conditions: room unoccupied, all HVAC operating at normal conditions, doors and windows closed
• Minimum 5-minute measurement per position
• Minimum 3 positions per floor plate, covering:

The results are compared against AS/NZS 2107 targets for the room type:

Note: These thresholds are indicative. NABERS uses a proprietary scoring algorithm that weights the octave-band spectrum, not just the overall dBA level. A noise spectrum with a prominent low-frequency tone (e.g., from a transformer or chiller) receives a lower score than a smooth, broadband spectrum at the same overall dBA level.

2. Reverberation Time (RT60)

• Measured per ISO 3382-2:2008 using interrupted noise or impulse response method
• Reported as T20 or T30 averaged over 500 Hz, 1 kHz, and 2 kHz octave bands
• Measured in the furnished but unoccupied condition
• Minimum 2 measurement positions per floor plate

Subjective Assessment: Occupant Survey

The second component of the acoustic pillar is an occupant satisfaction survey. NABERS uses a standardised survey instrument that asks building occupants to rate their acoustic environment on a scale. The survey questions cover:

• Overall satisfaction with noise levels at workstation
• Disturbance from HVAC noise
• Disturbance from speech from neighbouring workstations
• Disturbance from external noise (traffic, construction)
• Ability to have private telephone conversations
• Ability to concentrate without acoustic distraction

The Objective-Subjective Weighting

NABERS IE combines the objective measurements and the subjective survey into a single acoustic pillar score. The exact weighting is not publicly disclosed, but industry guidance suggests approximately 60% objective / 40% subjective. This means that a building with excellent measured noise levels but poor occupant satisfaction (e.g., due to speech privacy issues not captured by background noise measurements) will score lower than a building that performs well on both dimensions.

This dual assessment approach is a significant strength of NABERS IE compared to Green Star (design-stage only, no occupant feedback) and LEED (no mandatory measurement, no occupant survey).

The AS/NZS 2107 Connection

NABERS IE's acoustic assessment is fundamentally built on AS/NZS 2107:2016. The noise level benchmarks map directly to the AS/NZS 2107 'recommended' and 'maximum acceptable' values for office spaces:

This means that a building designed to AS/NZS 2107 'recommended' levels will automatically score well on the acoustic objective component. The challenge is the subjective component — occupant perception is influenced by factors beyond background noise, including speech privacy, reverberation, and noise from fit-out elements (printers, coffee machines, doors) that are outside the base building scope.

Worked Example: 2,000 m² Sydney CBD Office — NABERS IE 5 Star Target

Building Description

A mid-rise commercial office building in Sydney CBD. The tenant occupies a full floor plate of 2,000 m² net lettable area. The floor includes:

• Open plan area: 1,400 m² (approximately 140 workstations)
• 6 private offices (12 m² each)
• 4 meeting rooms (15–30 m² each)
• 2 quiet rooms / phone booths (5 m² each)
• Amenities, storage, and circulation: 384 m²

Step 1: Assess Base Building Acoustic Performance

The acoustic consultant conducts a background noise survey with the HVAC system operating at design conditions:

Assessment: The centre position (41 dBA) meets the AS/NZS 2107 recommended level of 40 dBA for open plan... wait — it exceeds 40 dBA by 1 dB. The perimeter and near-core positions are 3–4 dBA above the recommended level.

For NABERS IE 5 Star, the acoustic pillar needs to contribute at the 5-star level. The measured noise levels suggest a 3–4 star acoustic contribution — insufficient.

Step 2: Identify and Address Noise Sources

Step 3: Post-Remediation Measurements

All positions now meet or exceed AS/NZS 2107 'recommended' levels. The tonal component from the lift motor has been eliminated. This positions the building for a 5-star acoustic objective score.

Step 4: RT60 Assessment

Measured RT60 in the open plan area:

The open plan RT60 of 0.54 s falls in the 5-star range (≤ 0.5–0.7 s boundary). The ceiling is a standard mineral fibre acoustic tile (NRC 0.75) installed as a suspended ceiling at 2.7 m with a 400 mm plenum above. The carpet tile floor and office furniture provide additional absorption.

Step 5: Occupant Survey Strategy

The subjective component requires high occupant satisfaction scores. Actions to improve acoustic satisfaction beyond what the objective measurements capture:

1. Sound masking system: Install a ceiling-mounted sound masking system (40–42 dBA pink noise spectrum) to improve speech privacy between workstations. Cost: AUD 18,000 for 1,400 m².

1. Quiet rooms: The 2 existing phone booths are supplemented with 4 additional acoustic pods (prefabricated, free-standing, STC 35) for private calls and focused work. Cost: AUD 32,000.

1. Acoustic protocol: Implement a workplace acoustic etiquette policy — designated quiet zones, mobile phones on silent, headphone provision for collaborative calls. Cost: negligible.

1. Tenant communication: Brief all staff on the acoustic improvements and the NABERS IE rating process before the survey. Informed occupants tend to rate their environment more favourably when they understand the design intent. Cost: negligible.

Step 6: Predicted NABERS IE Acoustic Score

Cost Summary

For a 2,000 m² tenancy with an annual rent of approximately AUD 1,200/m² (AUD 2.4 million per year), the acoustic investment of $124,500 represents 5.2% of one year's rent. Given the 5–8% rental premium associated with NABERS IE 5 Star ratings, the investment pays for itself within approximately 8–12 months through higher rental value or reduced tenant turnover.

NABERS IE vs Green Star vs WELL

NABERS IE is unique in being an operational rating — it measures the building as occupied and operating, not as designed. This makes it the most realistic assessment of actual acoustic quality but also the most challenging to achieve, because design-stage predictions must hold up under real-world conditions.

The Market Impact of NABERS IE Acoustic Performance

Research by the Property Council of Australia and the University of Melbourne has quantified the market impact of NABERS IE ratings:

• Rental premium: 5-star IE-rated buildings achieve 5–8% higher effective rents than comparable non-rated buildings
• Vacancy reduction: IE-rated buildings have vacancy rates approximately 40% lower than the market average
• Tenant retention: Buildings with 5+ star IE ratings have tenant retention rates 25% higher than average
• Green lease alignment: Major corporate tenants (banks, professional services, government) increasingly require NABERS IE ratings as a lease condition

Key Takeaways

NABERS IE provides the most comprehensive and honest assessment of acoustic quality in Australian office buildings. Its combination of objective measurement and occupant feedback ensures that the rating reflects the actual acoustic experience — not just the design intent.

For building owners targeting NABERS IE 5 or 6 stars, the acoustic pillar requires background noise levels at or below AS/NZS 2107 'recommended' targets, RT60 below 0.6 s in open plan areas, and high occupant satisfaction scores. The last component — occupant satisfaction — is influenced by speech privacy, which requires attention to sound masking, partition performance, and workplace acoustic protocols beyond what the background noise measurement alone can capture.

Related reading: Green Star IEQ-4 acoustic guide | AS/NZS 2107 complete guide | Open plan office acoustic design guide

Model your office acoustics: Use the AcousPlan calculator to predict RT60 and noise levels for your NABERS IE assessment.