NCC sound insulation: Class 2 apartments

TL;DR

Class 2 apartment buildings (and Class 3 hotels) are covered by NCC 2022 Volume One Part F7, not the Volume Two rules that apply to duplexes and townhouses. The headline numbers are Rw+Ctr of at least 50 for walls and floors between sole-occupancy units (SOUs), plus Ln,w (impact sound) of not more than 62 for any floor between units (verified 2026-05-09). Field tests use a different metric: DnT,w+Ctr of at least 45. The floor impact rule is the key difference from Class 1 buildings: in an apartment stack, impact noise through concrete slabs or timber floors from the unit above is as much of a compliance risk as airborne speech. Specification 28 lists acceptable DTS construction forms; Performance Solutions require an acoustic engineer report.

In plain English

Class 2 is the building class for residential apartments: a multi-storey block where each unit is a separate residence on a separate title or tenancy. Class 3 buildings (hotels, boarding houses, serviced apartments) carry the same Part F7 sound requirements.

Part F7 of NCC 2022 Volume One is the applicable code section for these buildings, replacing the Volume Two Housing Provisions path that applies to Class 1 houses and townhouses. If you are building a duplex or townhouse, see NCC sound insulation: Class 1 separating walls instead.

The Performance Requirement is F7P1: floors must provide insulation against airborne and impact-generated sound transmission between sole-occupancy units. The deemed-to-satisfy (DTS) compliance path runs through F7D5 (floors) and F7D6 (walls), which set the specific rating numbers, and Specification 28, which lists construction forms that achieve those ratings without separate laboratory testing.

What it requires

Walls between sole-occupancy units (F7D6)

Element	DTS requirement
Wall between two SOUs	Rw+Ctr not less than 50
Wall between SOU and plant room, lift shaft, stairway, corridor, lobby, or different-class space	Rw not less than 50 (Ctr not required)
Door assembly in a wall separating an SOU from a stairway, public corridor, or lobby	Rw not less than 30

The Rw+Ctr rule applies to unit-to-unit walls because low-frequency sound (home theatre, bass, traffic from a balcony) is a significant source of neighbour complaints in apartment buildings. The Ctr adjustment is absent for the wall to-corridor requirement because corridors are not habitable spaces (verified 2026-05-09, NCC 2022 Volume One F7D6).

Walls must be of discontinuous construction where required: a minimum 20 mm cavity between separate leaves (F7D4). The cavity must not be bridged by rigid noggings, shared plasterboard, or services that cross between leaves.

Floors between sole-occupancy units (F7D5)

Element	DTS requirement
Airborne sound	Rw+Ctr not less than 50
Impact sound	Ln,w not more than 62

The floor between two stacked apartments must meet both thresholds simultaneously. This is the major addition compared to the Class 1 rules: Class 1 buildings have no DTS floor impact provision in the Housing Provisions, while Class 2 buildings explicitly require floors to control footstep noise, chair scraping, dropped items, and similar structure-borne impact sound (verified 2026-05-09, NCC 2022 Volume One F7D5).

Ln,w (weighted normalised impact sound pressure level) is measured per AS ISO 717.2 using a standard tapping machine in a laboratory setting. Lower Ln,w means better impact sound insulation (the floor lets through less noise). A value of 62 is the maximum permitted.

Field test verification (F7V1)

If a Performance Solution path is used rather than DTS, in-situ field testing is required. The verification thresholds are:

Airborne (walls and floors): DnT,w+Ctr not less than 45
Impact (floors): LnT,w not more than 62

DnT,w+Ctr is the in-situ equivalent of Rw+Ctr: it accounts for the real room geometry and flanking paths rather than a controlled laboratory chamber. The in-situ value is typically 5 to 8 dB lower than the laboratory rating for the same product. Testing is per AS ISO 16283.

Field testing is not mandatory under the DTS path. However, voluntary post-completion testing of a sample of separating elements is good practice on multi-storey residential projects because flanking failures are common.

What it doesn’t cover

Class 1 duplexes, townhouses, and terraces: governed by NCC Volume Two H4P6 and ABCB Housing Provisions Part 10.7. See NCC sound insulation: Class 1 separating walls.
Internal walls and floors within a single SOU: no NCC sound rating required. AS/NZS 2107 (acoustic design recommendations) is voluntary.
External walls (traffic and rail noise): not addressed by F7P1. AS/NZS 2107 is the reference document; most states apply it via DA planning conditions, not via the NCC.
Class 9c aged care buildings: Part F7 applies with some modifications specific to that class.
Mechanical services noise: Part F7 covers structure-borne and airborne sound between SOUs. Noise from mechanical equipment (lifts, air conditioning, pumps) is addressed separately under F7P2 to F7P4 and typically requires an acoustic engineer regardless of compliance pathway.

Specification 28: acceptable construction forms

Specification 28 of NCC 2022 Volume One lists wall and floor systems that are taken to achieve the required ratings without separate laboratory testing.

Walls (Rw+Ctr not less than 50)

Acceptable forms include (verified 2026-05-09, NCC 2022 Volume One Specification 28):

Two leaves of 110 mm clay brick, 50 mm cavity with insulation
Single 110 mm brick leaf plus independent stud frame with insulation
150 mm or 200 mm concrete panels
Autoclaved aerated concrete panels with steel stud framing
Double steel-stud frames with insulation and multiple plasterboard layers

Floors (Rw+Ctr not less than 50 and Ln,w not more than 62)

Acceptable forms include:

150 mm concrete slab with resilient furring channels and insulation below
200 mm concrete slab with carpet and underlay overlay
75 mm AAC panels with suspended timber joists and isolated ceiling
Timber floors with particleboard sheeting and isolated suspended ceiling

Resilient isolation is the critical element in all lightweight floor systems. Any rigid connection between the structural floor and the ceiling or wall framing below short-circuits the resilient layer and the impact rating drops sharply.

Practical implications

The two-metric floor trap

Every floor between stacked units must satisfy two independent thresholds: Rw+Ctr and Ln,w. A floor system can achieve Rw+Ctr 50 for airborne sound but still fail the Ln,w 62 impact requirement if the resilient isolation layer is inadequate. Check both numbers on the product data sheet before specifying a floor build-up. Specifiers who optimise only for airborne sound are frequently caught out on impact.

Flanking paths in apartments

Flanking is the leading cause of in-situ failures. In apartment buildings the main flanking routes are:

Concrete structural frame: rigidly connected slabs and columns transmit impact and low-frequency sound across multiple floors regardless of the separating element performance.
Services penetrations: pipes and conduit passing through a separating floor or wall create direct transmission paths. Penetration seals must be acoustic, not just fire-rated.
Wall-floor junction: where a separating wall sits directly on a concrete slab, impact energy from the floor travels up the wall. Resilient isolation at the base of the wall (neoprene pads or acoustic resilient strip) reduces this path.
Balconies and external elements: a shared concrete balcony slab connected to both units transmits impact and airborne sound. Detail the junction as a separation, not a shared element.
Ceiling to wall joint: a rigid connection between a suspended ceiling and the separating wall bypasses the wall’s isolation. The ceiling must be independently supported.

Discontinuous construction and the 20 mm rule

F7D4 requires walls between SOUs to use discontinuous construction with a minimum 20 mm air gap between the two leaves. The gap must be:

Free of all bridging material (plasterboard, timber blocks, rigid noggings)
Maintained continuously from slab to soffit or structure above
Not penetrated by services that cross from one leaf to the other

Power points must be offset (not back-to-back). Electrical conduit runs in a single leaf only.

DTS vs Performance Solution

The DTS path (Specification 28 construction form, F7D5/F7D6 ratings) is the simpler compliance route. It does not require post-construction acoustic testing.

A Performance Solution requires an acoustic engineer to demonstrate the design meets F7P1 via calculation or staged field testing (DnT,w+Ctr of at least 45, LnT,w not more than 62 per F7V1). Budget $5,000 to $15,000 for the acoustic report and certifier review on a standard multi-storey residential project, depending on the number of elements and project complexity . The certifier accepts or rejects the report.

Certifier inspection points

For a Class 2 project on the DTS path, the key inspection points are:

Separating walls: confirmed as Specification 28 system, cavity gap maintained, no bridging material
Separating floors: confirmed system type, resilient isolation layer installed without compromise, ceiling suspension isolated from wall framing
Service penetrations: acoustic (not just fire-rated) seals at every penetration through separating elements
Door assemblies: Rw 30 door and frame systems at corridor-to-unit doors

NCC 2025 status

NCC 2025 was published 1 May 2026. ACT, Tasmania, and Victoria adopted it on publication; NSW and QLD adoption is scheduled for May 2027 (verified 2026-05-09, ABCB state adoption page). No specific changes to Part F7 sound insulation requirements for Class 2 buildings have been confirmed as of the verification date. Always check the ABCB’s state adoption page and your state regulator before pricing NCC 2025 changes into a project.

State variations

VIC

Victoria adopts NCC 2022 Volume One Part F7 in full with no state-specific amendments to F7P1, F7D5, F7D6, or Specification 28, so the national thresholds apply unchanged: Rw+Ctr 50 for separating walls and floors, Ln,w 62 for floor impact, and DnT,w+Ctr 45 for field testing (verified 2026-05-09). Victoria also adopted NCC 2025 on 1 May 2026, again without varying Part F7. The legislative framework is the Building Act 1993 and Building Regulations 2018, administered by the Victorian Building Authority. For Class 2 work, a registered building surveyor (RBS) issues the building permit, certificate of final inspection, and occupancy permit, and Cladding Safety Victoria oversight has driven heightened scrutiny of separating elements on apartment projects.

WA

Western Australia adopts NCC 2022 Volume One Part F7 without state-specific amendments to the sound insulation provisions, so Rw+Ctr 50 walls, Ln,w 62 floors, and DnT,w+Ctr 45 field test thresholds apply as per the national text (verified 2026-05-09). The compliance framework is the Building Act 2011 and Building Regulations 2012, administered by Building and Energy within DEMIRS. Every Class 2 apartment project requires a Certificate of Design Compliance (CDC) at permit stage and a Certificate of Construction Compliance (CCC) before occupancy, both signed by a registered building surveying practitioner. WA does not maintain a separate acoustic certifier register: acoustic compliance sits within the building surveyor’s CDC, so the surveyor relies on the engineer’s report for any Performance Solution.

SA

South Australia adopts NCC 2022 Volume One Part F7 with no SA-specific amendments to F7P1, F7D5, F7D6, or Specification 28, so the national Rw+Ctr 50, Ln,w 62, and DnT,w+Ctr 45 thresholds apply unchanged for Class 2 (verified 2026-05-09). The Building Code is given legal force through the Planning, Development and Infrastructure Act 2016 and Planning, Development and Infrastructure (General) Regulations 2017, and SA is staying on NCC 2022 until 1 May 2027 when NCC 2025 is scheduled for adoption. Class 2 buildings require a Certificate of Occupancy issued under the PDI Act before they can be lived in. SA’s Accredited Professionals Scheme registers Building Surveyors at four classes; there is no separate acoustic-certifier class, so the building surveyor signs off on the F7 compliance evidence supplied by the project’s acoustic consultant.

TAS

Tasmania adopts Part F7 from the national NCC text without any TAS-specific variations in Schedule 9 to F7P1, F7D5, F7D6, or Specification 28, so the standard Rw+Ctr 50, Ln,w 62, and DnT,w+Ctr 45 thresholds apply for Class 2 buildings (verified 2026-05-09). Note that NCC 2025 commenced in Tasmania on 1 May 2026 following the Building Amendment Bill 2026 not passing both Houses before the deadline, so any Class 2 project lodged after that date is now assessed against NCC 2025; the Part F7 numbers themselves did not change between editions. Compliance is administered through the Building Act 2016 by Consumer, Building and Occupational Services (CBOS). Class 2 apartments are permit building work: a licensed building surveyor (Open licence, AQF7 plus three years experience) issues the building permit and Certificate of Completion, and there is no separate Tasmanian acoustic certifier class.

NT

The Northern Territory is the outlier: NT Schedule 6 replaces national F7D5 and F7D6 entirely, dropping the spectrum adaptation term Ctr and the Ln,w impact requirement, so NT Class 2 separating walls only need Rw 45 (not Rw+Ctr 50) and there is no DTS impact-sound threshold for floors between SOUs (verified 2026-05-09). Higher-rated walls (Rw 50 plus impact resistance) still apply where one side is a bathroom, kitchen, or laundry adjoining a habitable room. Compliance runs through the Building Act 1993 (NT) and Building Regulations 1993, administered by Building Advisory Services within the Department of Lands, Planning and Environment, with permits and final inspections issued by registered NT building certifiers. Practical implication: a wall design that just scrapes through the NT DTS will not meet the national Rw+Ctr 50 baseline, so any apartment built to NT minimums and later interstate-benchmarked is likely to under-perform on low-frequency noise.

Source link

ABCB NCC 2022 Volume One Part F7 Sound transmission and insulation: https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-one/f-health-and-amenity/part-f7-sound-transmission-and-insulation

ABCB NCC 2022 Volume One Specification 28 Sound insulation for building elements: https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-one/f-health-and-amenity/28-sound-insulation-building-elements

References

Australian Building Codes Board, NCC 2022 Volume One, Part F7 Sound transmission and insulation, F7P1, F7D5, F7D6. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-one/f-health-and-amenity/part-f7-sound-transmission-and-insulation (verified 2026-05-09).
Australian Building Codes Board, NCC 2022 Volume One Specification 28 Sound insulation for building elements. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-one/f-health-and-amenity/28-sound-insulation-building-elements (verified 2026-05-09).
Australian Building Codes Board, Sound Transmission and Insulation in Buildings Handbook (2022 edition). https://ncc.abcb.gov.au/sites/default/files/resources/2023/Sound%20Transmission%20and%20Insulation%20in%20Buildings%20handbook%202022.pdf (verified 2026-05-09).
Australian Building Codes Board, NCC 2025 state and territory adoption information. https://ncc.abcb.gov.au/ncc-2025/ncc-2025-state-and-territory-adoption-information (verified 2026-05-09).

NCC sound insulation: Class 1 separating walls, the Volume Two Part H4P6 rules for duplexes and townhouses
NCC 2022 Volume Two overview, full structure of the residential Volume
Plasterboard, lining system specs and acoustic-rated plasterboard types
Rw+Ctr, the airborne sound metric used in both Class 1 and Class 2 NCC requirements
Flanking, indirect sound paths and why in-situ performance falls below lab ratings
Discontinuous construction, the double-leaf wall strategy required by F7D4
Sole-occupancy unit, what counts as a separate unit under the NCC
Ln,w, the impact sound metric for floors