Sound Insulation Requirements Between Dwellings

What This Requirement Covers

Sound insulation requirements between dwellings in the National Construction Code (NCC) are intended to limit the transmission of airborne and impact noise between separate residential units and between units and certain building services or common spaces. The rules aim to protect occupants from “illness or loss of amenity” caused by undue noise transfer through separating walls, floors and service penetrations. They apply primarily to multi-unit residential situations where sole-occupancy units adjoin or are adjacent to other building parts (for example, Class 2 apartments, Class 3 boarding houses and certain Class 9c residential care buildings).

These provisions set minimum performance outcomes and associated Deemed-to-Satisfy (DtS) verification methods that rely on laboratory or in-situ acoustic measurements referenced to recognised standards (for example, AS/NZS ISO 717.1 and AS ISO 717.2). The requirements address both airborne sound insulation (expressed as weighted standardized level difference DnT,w or weighted sound reduction index Rw) and impact sound insulation (expressed as weighted normalized impact sound pressure level LnT,w or Ln,w). They also require that penetrations for services do not undermine the achieved performance.

Key Requirements

1. Scope and application: Applies to separating elements in Class 2 and Class 3 buildings and some Class 9c residential care buildings where sole-occupancy units adjoin each other or adjoin common spaces, plant rooms, stairways, corridors or similar (see NCC Volume One, Part F7 - Sound transmission and insulation).
2. Airborne sound between sole-occupancy units (in-situ): A separating wall or floor measured in-situ must achieve a DnT,w not less than 40 when determined under AS/NZS ISO 717.1 (as specified in NCC Volume One, Verification Method F7V4 and F7V3).
3. Impact sound for floors (in-situ): A separating floor measured in-situ must achieve a LnT,w not more than 62 when determined under AS ISO 717.2 (NCC Volume One, Verification Method F7V3).
4. Lab-based ratings / alternative Rw values: Where laboratory results are used, forms of construction required to have an airborne sound insulation rating must have the required Rw or Rw + Ctr determined in accordance with AS/NZS ISO 717.1 (NCC Volume One, F7D3). For wall constructions, an Rw of at least 45 is commonly specified in some DtS tables and state variants for laboratory-determined values separating sole-occupancy units (see applicable DtS clauses and Specification 28 where referenced).
5. Walls separating a unit from kitchens, bathrooms or laundries: A wall separating a sole-occupancy unit from a kitchen, bathroom, sanitary compartment (not an ensuite) or laundry must provide insulation against impact-generated sound sufficient to prevent loss of amenity; specific DtS/verification requirements apply in Part F7 and relevant state provisions (see NCC Volume One, F7P4 and jurisdictional schedules).
6. Penetrations and services: The required sound insulation of floors and walls must not be compromised by pipework or other service penetrations - penetrations must be sealed and constructed to retain the rated performance (NCC Volume One, F7P3 and related Verification Methods).
7. Measurement standards: All laboratory or field measurements must be made in accordance with AS/NZS ISO 717.1 (airborne) and AS ISO 717.2 (impact) or comply with NCC Specification 28 where that specification is used (NCC Volume One, F7D3-F7D4 and F7V3-F7V4).
8. Objective and scope references: The Objective and Performance Requirements are set out in NCC Volume One, Part F7 - Sound transmission and insulation (for Class 2, 3 and some Class 9c applications). Always cite the exact clause when confirming compliance with a certifier (for example, F7P1, F7P2, F7P3, F7P4, F7D2-F7D9, F7V3-F7V4).

Residential vs Commercial

1. Residential (Class 1/10): The NCC’s specific sound insulation Part F7 is primarily targeted at multi-unit residential buildings (Class 2 and Class 3). Single detached houses (Class 1) and most ancillary non-habitable structures (Class 10) are generally outside Part F7’s primary DtS provisions for separating sole-occupancy units. However, good acoustic design is still best practice for attached dwellings where occupancy and shared elements create similar amenity concerns.
2. Multi-unit Residential (Class 2 and Class 3): The full Part F7 provisions apply. Requirements are expressed as in-situ performance (DnT,w and LnT,w) or laboratory-derived Rw/Ln,w values and must meet the DtS limits or be demonstrated by a Performance Solution. Refer to NCC Volume One, Part F7 (including F7P1 - F7P4, F7D3-F7D4, F7V3-F7V4).
3. Commercial and other classes (Class 5-9): Where a sole-occupancy unit adjoins a part of another classification (for example, a Class 2 unit adjoining a plant room, lift shaft or public corridor in a mixed-use building) the Part F7 Performance Requirements still apply to protect the residential unit (see F7P2 and Objective F7O1). For purely commercial separations (for example between two office tenancies) other provisions or project-specific acoustic performance targets may be appropriate and often rely on Australian Standards and project specifications rather than Part F7 DtS values.

Exceptions and Exemptions

1. Performance Solution: The DtS values in Part F7 are not the only way to comply. A project may adopt a Performance Solution where it can be demonstrated the objective (prevent illness or loss of amenity) is achieved by alternative means. Performance Solutions require appropriate acoustic testing, modelling and justification in accordance with NCC procedures (see F7P2 and A2G2/A2G4 guidance in NCC Volume One).
2. Class exclusions: Single detached dwellings (Class 1) and many Class 10 structures are not subject to Part F7 DtS requirements for separating sole-occupancy units, though state or local planning controls may impose different expectations.
3. Documented variations and Specification 28: Where the DtS path references Specification 28, compliance can be achieved by meeting the constructions and tested assemblies listed in that specification rather than conducting bespoke lab or in-situ testing.
4. Minor works: Small alterations that do not change the acoustic performance of a separating element may not trigger re-testing, but care must be taken to avoid degrading seals, junctions or continuity of insulation.

State and Territory Variations

1. NCC Schedules: The NCC is a national document but each state and territory may include a schedule that modifies or replaces national provisions. For example, some jurisdictions specify minimum Rw laboratory values for walls or floors (often Rw 45 for separating walls) or adopt additional measurement or verification steps. Always check the relevant state schedule in NCC Volume One (Schedules 4-12) for local amendments.
2. Examples and notes: The Northern Territory’s Part F7 DtS provisions and verification text (F7D3-F7D5 and NT-specific clauses) explicitly state the use of Rw 45 in certain DtS provisions and require Rw/Ln,w values determined under AS/NZS ISO 717 series or comply with NT Specification 28. Other states may follow similar patterns but may have different table values or additional documentation requirements. Confirm the applicable state schedule for your jurisdiction before finalising design or certification.

Practical Compliance Tips

1. Engage an acoustic consultant early - specifying target DnT,w and LnT,w or laboratory Rw/Ln,w ratings at the design stage avoids costly rework. Early tests or laboratory-assessed assemblies reduce uncertainty.
2. Specify tested assemblies - use wall and floor assemblies with laboratory ratings (AS/NZS ISO 717.1/717.2 results) or ones listed in Specification 28 where available, rather than relying on assumed performance of untested constructions.
3. Seal all junctions and penetrations - services, ducts, pipes and electrical penetrations are frequent weak points. Use resilient sealing, acoustic collars and continuous linings to retain the rated performance (NCC Volume One, F7P3).
4. Avoid continuous rigid connections - provide resilient mounts or isolation where floors or walls interface with noisy services or plant rooms to reduce structure-borne noise transmission that can increase LnT,w.
5. Prepare for in-situ testing - if relying on in-situ verification (DnT,w or LnT,w), plan for final commissioning tests with the separating elements completed, sealed and furnished as required by the relevant AS/NZS test method to avoid failed tests.
6. Document Performance Solutions - if you choose an alternative Performance Solution, compile clear acoustic modelling, test evidence and a compliance case tied to NCC Volume One clauses (for example, F7P1-F7P4) and relevant procedures (A2G2/A2G4) for certifier review.
7. Check state schedules and council requirements - always verify local amendments in the NCC state schedules and any council planning conditions; some jurisdictions require higher laboratory Rw values or specific test reporting formats.

Citations used above include NCC Volume One, Part F7 (Performance Requirements F7P1-F7P4; Deemed-to-Satisfy clauses F7D2-F7D9; Verification Methods F7V3-F7V4) and the referenced measurement standards AS/NZS ISO 717.1 (airborne sound) and AS ISO 717.2 (impact sound). For laboratory and in-situ measurement methods also see the NCC references to Specification 28 where that Specification is used as a DtS path.

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