What fire separation is required between residential and commercial in a mixed-use building?

Under NCC 2025, floors between different building classifications in Type A construction typically need an FRL of 120/120/120. Every service penetration through that floor needs a tested fire stop system installed per AS 1530.4, with fire dampers in every duct crossing the boundary (NCC 2025 C3D9, Specification 5).

What acoustic insulation is needed between apartments and commercial spaces?

NCC 2025 Part F7 requires floors between a residential unit and a different classification to achieve Rw + Ctr of at least 50 dB for airborne sound and Ln,w of 62 dB or less for impact sound. Walls between classifications must achieve Rw of at least 50 dB (NCC 2025 F7D5, F7D6).

Should HVAC be separate for residential and commercial in a mixed-use building?

Yes. Commercial spaces need higher cooling loads (100 to 250 W/m² depending on use) and run during business hours. Apartments need 24/7 availability at lower loads (80 to 145 W/m²). A shared system wastes energy and causes comfort problems. Separate systems also avoid strata disputes over running costs.

How do you handle restaurant kitchen exhaust in a mixed-use building with apartments above?

The kitchen exhaust duct must run from the ground-floor kitchen to the roof in its own fire-rated shaft, with grease-rated ductwork and acoustic wrapping. The shaft passes through every residential floor, so it needs fire stops at each level. Plan the shaft from day one because it cannot be added later. AS 1668.2:2024 also allows treated exhaust to discharge horizontally if filtration and odour treatment are installed.

What energy compliance applies to mixed-use buildings in NSW?

In NSW, the Class 2 residential portion follows BASIX for energy and water targets. The commercial portion (Class 5, 6, 7, 8) follows NCC Section J. Both pathways must be met on the same project, and each part is assessed separately against its applicable standard.

Mixed-Use Building Services: Residential Above Commercial

Section 1

What You Need to Know

Mixed-use buildings put apartments above shops, restaurants, or offices. Each use has its own NCC classification, its own fire rules, and its own services. Get the boundaries wrong and you face failed inspections, noise complaints, and costly rework. This memo covers how building services change when residential sits above commercial.

Section 2

The Rules

Each part of a mixed-use building must be classified separately - Class 2 (apartments), Class 5 (offices), Class 6 (retail), and Class 7a (carparks) each follow their own NCC requirements (NCC 2025 Part A6)
Floors between different classifications in Type A construction typically need an FRL of 120/120/120, based on building class and construction type (NCC 2025 C3D9, Specification 5)
Every pipe, duct, and cable through a fire-rated floor or wall between classifications needs a tested fire penetration system, installed exactly as tested (NCC 2025 Part C4, Specification 13, AS 1530.4)
Floors between a residential unit and a different classification must achieve Rw + Ctr ≥ 50 dB (airborne) and Ln,w ≤ 62 dB (impact) (NCC 2025 F7D5)
Walls between a residential unit and a different classification must achieve Rw ≥ 50 dB (NCC 2025 F7D6)
Commercial kitchen exhaust (Type B effluent) must discharge at roof level and must not recirculate - AS 1668.2:2024 allows treated exhaust to discharge horizontally when filtration and odour treatment are installed (AS 1668.2)
In NSW, the residential portion follows BASIX for energy and water; the commercial portion follows NCC Section J - both pathways must be met on the same project (NCC 2025 Part J1, BASIX)

Section 3

What This Means in Practice

A typical mixed-use project has a Class 7a carpark in the basement, Class 6 retail or Class 5 offices at ground and first floor, and Class 2 apartments above. The floor between the last commercial level and the first residential level is the critical boundary. That floor must be fire-rated, acoustically treated, and every service penetration through it needs a tested fire stop.

HVAC systems should be separate for residential and commercial. Commercial spaces run during business hours and need higher cooling loads, typically 150 to 250 W/m² for restaurants or 100 to 150 W/m² for offices. Apartments run around the clock at lower loads, typically 80 to 145 W/m². A shared system cannot serve both schedules without wasting energy or causing comfort problems. Commercial tenants typically get a central plant or packaged rooftop unit. Apartments get split systems or a VRF (Variable Refrigerant Flow) system with individual control.

Restaurant kitchen exhaust is the hardest service to coordinate. The exhaust duct must run from the ground-floor kitchen all the way to the roof, passing through every residential floor. That duct needs its own fire-rated shaft, acoustic wrapping, and grease-rated construction. If the shaft is not planned from day one, it will not fit later.

Section 4

Key Design Decisions

1

Separate vs. Shared HVAC Plant

Run separate systems for residential and commercial. Commercial needs higher capacity, different operating hours, and different controls. Residential needs 24/7 availability and individual tenant control.

Trade-off: Two systems cost more upfront than one, but they avoid energy waste, noise transfer, and strata disputes over running costs.

2

Riser Strategy: Combined vs. Dedicated Shafts

Plan dedicated risers for each service type: mechanical, electrical, hydraulic, and fire. In mixed-use buildings, commercial and residential services often need separate risers because metering, isolation, and maintenance access differ between the two.

Trade-off: Separate risers take more floor area (typically 2 to 4 m² per floor), but they simplify strata boundaries and reduce coordination clashes.

3

Acoustic Isolation at the Classification Boundary

The floor between commercial and residential is the weak point. Use a concrete slab of at least 200 mm with a resilient ceiling system below and a floating floor above to meet the Rw + Ctr 50 dB and Ln,w 62 dB targets. Isolate all mechanical connections: flexible duct connections, resilient pipe hangers, and vibration-isolated equipment mounts.

Trade-off: Acoustic treatment adds 50 to 80 mm to the floor build-up. Factor this into floor-to-floor height early, or the ceiling void on the commercial level will be too tight.

4

Kitchen Exhaust Shaft Planning

If the ground floor includes a restaurant or food tenancy, design the kitchen exhaust shaft from the start. The shaft needs to run from ground to roof, be fire-rated to match the floor FRLs it passes through, and be sized for the exhaust volume (typically 1,500 to 4,000 L/s for a commercial kitchen). Include access panels at each floor for cleaning.

Trade-off: A dedicated kitchen exhaust shaft takes 0.5 to 1.0 m² of floor area per level. Leaving it out locks future tenants out of food-service use entirely.

Section 5

Who Needs to Know What

Section 6

References

National Construction Code 2022, Volume One, Part A6 — Building classification
National Construction Code 2022, Volume One, Part C3 — Compartmentation and separation
National Construction Code 2022, Volume One, Part C4 — Protection of openings
National Construction Code 2022, Volume One, Specification 5 — Fire-resisting construction
National Construction Code 2022, Volume One, Specification 13 — Penetration of walls, floors and ceilings by services
National Construction Code 2022, Volume One, Part F7 — Sound transmission and insulation
National Construction Code 2022, Volume One, Section J — Energy efficiency
AS 1668.1:2015, The use of ventilation and airconditioning in buildings — Part 1: Fire and smoke control in buildings
AS 1668.2:2024, The use of ventilation and airconditioning in buildings — Part 2: Mechanical ventilation in buildings
AS 1530.4-2014, Methods for fire tests on building materials, components and structures — Part 4: Fire-resistance tests of elements of building construction
AS/NZS 3500, Plumbing and drainage (Parts 1-4)
AS/NZS 3000:2018, Electrical installations (Wiring Rules)

Mixed-Use Building Services: Residential Above Commercial

What You Need to Know

The Rules

What This Means in Practice

Key Design Decisions

Separate vs. Shared HVAC Plant

Riser Strategy: Combined vs. Dedicated Shafts

Acoustic Isolation at the Classification Boundary

Kitchen Exhaust Shaft Planning

Who Needs to Know What

Need this engineered for your project?

References

Related design memos

HVAC Design for Multi-Storey Residential Buildings

Understanding NCC Building Classifications for Services Design

Hydraulic Riser Design for Multi-Storey Buildings