Outdated NZ building codes lead to unhappy people and unsafe homes all throughout the country. Based on climate data, these codes are supposed to be in place to make sure homes are protective, safe and comfortable.

The problem is that climate changes are hitting us hard. Global warming alongside high winds, flooding, wildfires and heatwaves mean we’re having to adapt quickly. Climate data is usually updated on a 10-year cycle and the good news is that building guidelines are currently changing to meet modern needs. But are they changing fast enough?

For now, let’s focus on the country’s current building code ventilation requirements, with a focus on how well-ventilated our homes might be. New Zealand has two main sources of building code ventilation requirements, and one optional one:

1. Section G4 of the New Zealand Building Code

2. Healthy Homes Standards

3. NZ Green Building Council's Homestar V5

G4 Building Code and ventilation

If you are wondering about the NZ building code ventilation requirements, G4 is the place to look. The G4 Building Code section represents the minimum standard for ventilation in new builds in New Zealand. It is mainly focused on extraction ventilation, and splits the minimum airflow rates down based on room and ventilation type. See below for a table explaining the extraction ventilation requirements by room type under the G4 building code:

1) Toilets only require ventilation if they have no openable windows
2) Simx recommends 40 l/s for laundries with unvented non-condensing tumble dryers as covered in AS 1668: Part 2 2012

The NZ G4 Building Code does a good job covering the basics of extraction ventilation, but it lets homes get away with simply having openable windows to supply air in each room.

But is that enough? New builds need supply ventilation as well, which goes beyond an open window or door. Often in built-up areas, tenants and homeowners may be faced with noise, security and pollution concerns — not to mention the cold NZ winters and muggy summers full of bugs. Opening a window isn’t always feasible.

Healthy Homes and ventilation

Healthy Homes legislation is a set of standards that aim to improve the standard of living of tenants in rental properties. Healthy homes provides support and advice to landlords and property managers, offering full property audits that make sure homes meet Healthy Homes regulations. Since July 2024, all Kāinga Ora rentals must comply with this standard, and by July 2025, all private rentals must also comply. 

Healthy homes has several ventilation requirements:

• All habitable rooms need at least one door, window, or skylight facing outside, which can be fixed open.

• In each room, the size of the openable windows, doors and skylights must be at least 5% of the floor area of that room.

• All kitchens and bathrooms must have an intermittent or continuous extraction fan that vents air to the outside:

  • Fans installed after 1st July 2019 must also comply with room specific airflow or ducting requirements:

  • Kitchens: either 150mm diameter, or an intermittent exhaust capacity of at least 50 l/s, or a continuous exhaust capacity of 12 l/s.

  • Bathrooms: either 120mm diameter, or an intermittent exhaust capacity of at least 25 l/s, or a continuous exhaust capacity of 10 l/s. 

Much like the G4 Building Code, the Healthy Homes requirements only cover mechanical extract ventilation, not supply. In other words, mechanically extracting old, polluted air (including odours and humidity) from the home to make way for clean air.

However, the main way clean air enters a home that only complies with healthy homes is via the windows. Unfortunately, windows are often insufficient for effectively ventilating a home, either because of physical opening dimensions or lifestyle incompatibility. If air is extracted with insufficient air supply, it can reduce the efficiency of the extraction fan, and lead to moisture and mould building up in areas with little to no airflow.

Homestar and ventilation

A “Homestar rating” takes into account a building’s design, energy efficiency, property management and innovation criteria. Created by the NZ Green Building Council, Homestar exists to make NZ’s homes warmer, drier and healthier. Find out more here.

In 2022, it completed the transition to Homestar v5, making continuous mechanical ventilation a requirement. In V5, Homestar recognised that ventilation is essential for comfort as well as to prevent building damage via excessive moisture. As part of their new version, Homestar laid out a new set of criteria for ventilation:

2 points: Continuous extraction ventilation

3 points: Balanced ventilation

4 points: Balanced ventilation with heat recovery

With an additional point available for ventilation system commissioning. Find out more about how SmartVent can help you achieve your chosen Homestar level here.

The NZ Building Code is undergoing some big changes – what’s next?

Clause H1 of the New Zealand Building Code is currently getting an facelift. Some changes came into effect in May 2023, with more expected over the next couple of years. The idea is to make new buildings warmer, drier and healthier. The knock-on effect here is that less energy is needed to heat them.

Recent H1 NZ building code changes in 2024 (NZBC H1 and Healthy Homes) have drawn attention to the increased need for ventilation as our construction practices and lifestyles have changed over time. We’re expecting to see stricter ventilation requirements in all new builds across NZ, which should eventually bring us closer to international standards. (Right now, we’re falling behind.)

Other than H1, our experts suspect that we'll soon be seeing some supply ventilation requirements, as well as extraction ventilation. Supply ventilation and make-up air will become increasingly important as our homes become more airtight.

Talk to SmartVent to get your property up to scratch

Homeowners, landlords and builders can make sure they’re complying with all ventilation regulations and standards by counting on SmartVent. Our team of highly knowledgeable accredited installers can recommend the best system based on your property’s location, size, layout and materials used, so you, your tenants, and your home are protected from moisture, mould and other airborne threats.

Building new? Get a free home ventilation design from one of our experts.

Looking to renovate? book a free consultation.

Not sure? Give our team a call on 0800 140 150