What does BASIX require for ventilation in NSW?

BASIX checks whether each habitable room can be ventilated. It scores ventilation as part of the energy category. Natural ventilation through openable windows scores best because it uses no energy. Mechanical ventilation adds to the energy load, so it scores lower unless the system includes heat recovery. All ventilation must also meet NCC minimum requirements.

Do I need mechanical ventilation to pass BASIX?

Not always. Most houses and apartments with good cross-ventilation pass BASIX with natural ventilation alone. You need mechanical ventilation when rooms cannot get openable windows on two faces, when the building is sealed to Passive House standards, or when centralised systems serve multiple dwellings. Bathrooms, kitchens, and laundries always need exhaust ventilation regardless of BASIX.

What is MVHR and how does it affect the BASIX score?

MVHR stands for Mechanical Ventilation with Heat Recovery. It is a ducted system that extracts stale air from wet rooms and supplies fresh air to living spaces, recovering 70-95% of the heat from the exhaust air. BASIX gives credit for the energy recovery, so MVHR scores better than standard mechanical ventilation. MVHR is mandatory if the dwelling is built to the Passive House standard. Installed cost is typically $3,000-$10,000 per dwelling.

How does ventilation affect the BASIX energy score?

BASIX calculates the energy used by ventilation systems and adds it to the total energy score. Natural ventilation uses zero energy, so it does not hurt the score. Exhaust fans use a small amount. Ducted mechanical systems use more. The BASIX tool scores individual fans without ducting as more efficient than centralised ducted systems, because small fans run for shorter periods even though they are less efficient per unit of airflow.

Does BASIX replace the NCC ventilation requirements?

No. BASIX replaces NCC Section J (energy efficiency) for residential buildings in NSW. But NCC ventilation requirements still apply. For Class 2 buildings, Part F6 sets minimum ventilation rates. For Class 1 houses, Part 10.6 (formerly 3.8.5) requires openable windows equal to at least 5% of the floor area of each habitable room. Your design must meet both BASIX energy targets and NCC ventilation minimums.

BASIX Mechanical Ventilation: What It Means for Your Residential Project

Section 1

What BASIX Checks for Ventilation

BASIX (Building Sustainability Index) applies to all residential development in NSW. It covers Class 1 houses, Class 2 apartments, and the residential parts of Class 4 buildings. Every DA and CDC needs a BASIX certificate.

BASIX scores three things: energy, water, and thermal comfort. Ventilation sits inside the energy score. BASIX checks whether each habitable room can be ventilated and how much energy that ventilation uses.

Natural ventilation through openable windows scores best. It uses zero energy. Mechanical ventilation adds to the energy load, so BASIX penalises it unless the system includes heat recovery. The BASIX tool calculates the energy cost of each ventilation option and folds it into the overall energy target.

The energy target for new homes is a 45% reduction in greenhouse gas emissions against the NSW benchmark. Ventilation choices directly affect whether you hit that target.

Section 2

Ventilation Options and BASIX Impact

1

Natural Ventilation (Openable Windows)

Best BASIX score. No energy cost. Windows must meet NCC minimum openable area: at least 5% of the floor area of each habitable room. Works for most houses and apartments with good cross-ventilation. Free to build.

Trade-off: Zero energy cost but depends on window placement. Single-aspect apartments with windows on one face only may not get enough airflow to pass BASIX without mechanical help.

2

Mechanical Ventilation (Exhaust Fans)

Bathroom and kitchen exhaust fans are standard on every project. BASIX scores individual fans without ducting better than centralised ducted systems. Small fans run for shorter periods, which offsets their lower per-unit efficiency. Ceiling fans can also improve the thermal comfort score by reducing the need for air conditioning.

Trade-off: Low energy impact and low cost. But exhaust-only systems do not recover heat from outgoing air. In cold climates or well-sealed buildings, this means losing heat you paid to generate.

3

Mechanical Ventilation with Heat Recovery (MVHR)

MVHR extracts stale air from bathrooms and kitchens and supplies fresh air to bedrooms and living rooms. A heat exchanger recovers 70-95% of the heat from the exhaust air. BASIX gives credit for this energy recovery.

MVHR is mandatory if the dwelling meets the Passive House standard under BASIX. Installed cost is typically $3,000-$10,000 per dwelling, depending on house size and system brand. Running cost is about $100 per year for a 200 m² house.

Trade-off: Highest upfront cost but best energy performance. Makes sense for Passive House builds, cold climate zones, and projects that need to push the BASIX energy score higher to offset other design choices.

Section 3

When You Need a Mechanical Engineer

Apartment buildings with centralised ventilation systems - ducted supply and exhaust serving multiple dwellings needs duct sizing, fan selection, and balancing to AS 1668.2
Passive House projects requiring MVHR design - the heat recovery unit, ductwork layout, and commissioning need specialist input
Projects where natural ventilation alone does not meet BASIX targets - a mechanical engineer can model the options and find the cheapest path to compliance
Mixed-use buildings (residential above commercial) - complex services routing, fire separation of ductwork, and different ventilation codes for each use
Basement car parks below residential - car park ventilation must comply with AS 1668.2 and is a separate system from the residential ventilation above

Section 4

BASIX and the NCC

BASIX replaces NCC Section J (energy efficiency) for residential buildings in NSW. From 1 October 2023, BASIX Version 4.0 or later applies alongside NCC 2025 Section J for Class 2 and Class 4 buildings.

But NCC ventilation requirements still apply separately. For Class 2 apartment buildings, Part F6 sets minimum ventilation rates. For Class 1 houses, Part 10.6 requires openable windows equal to at least 5% of each habitable room's floor area.

Part J6 of NCC 2025 adds another rule: outdoor air supply must not exceed the minimum required by Part F6 by more than 20%, unless the extra air is for free cooling or the system uses an energy recovery device.

Your design must meet both BASIX energy targets and NCC minimum ventilation rates. A mechanical engineer checks both. If the building has an air permeability of 5 m³/hr/m² or less at 50 Pa, NCC 2025 also requires continuous mechanical ventilation.

Section 5

Who Needs to Know What

Section 6

References

BASIX (Building Sustainability Index), NSW Department of Planning and Environment - Ventilation help notes and single/multi-dwelling ventilation guidance
National Construction Code 2022, Volume Two, Part H6 — Energy efficiency (NSW residential provisions)
National Construction Code 2022, Volume One, Part F6 — Light and ventilation (Class 2-9 buildings)
National Construction Code 2022, Volume One, Part J6 — Air-conditioning and ventilation (energy efficiency)
National Construction Code 2022, Volume Two, Part 10.6 — Ventilation (Class 1 and 10 buildings)
AS 1668.2:2012, The use of ventilation and airconditioning in buildings — Part 2: Mechanical ventilation in buildings

BASIX Mechanical Ventilation: What It Means for Your Residential Project

What BASIX Checks for Ventilation

Ventilation Options and BASIX Impact

Natural Ventilation (Openable Windows)

Mechanical Ventilation (Exhaust Fans)

Mechanical Ventilation with Heat Recovery (MVHR)

When You Need a Mechanical Engineer

BASIX and the NCC

Who Needs to Know What

Need this engineered for your project?

References

Related design memos

Natural Ventilation NCC Compliance

HVAC Design for Multi-Storey Residential Buildings

Section J Compliance for Residential Apartment Buildings (Class 2)