Why the New Zealand Building Industry is Still Getting H1 Compliance Wrong

For decades, New Zealand housing was notoriously cold, damp, and difficult to heat. In response to this legacy, recent updates to the Building Code—particularly the massive R-value increases in the 5th Edition—sought to address the issue by simply adding more insulation.

But as the industry navigates the updated 6th edition of the H1 Energy Efficiency requirements, this well-intentioned "more is better" mindset is exposing new, equally uncomfortable problems: severe summer overheating and trapped internal moisture. With the 6th edition removing the simplistic tick-box Schedule Method, the days of just adding bulk insulation are over.

At Reshaped Consulting, we consistently see the consequences of treating insulation as a silver bullet. Through our H1 modelling, we prove daily that throwing high R-values at a design without balancing heating and cooling, solar shading, and ventilation creates a compliant but uncomfortable home. The reality is that regulatory compliance does not automatically equal a better build.

Key Takeaways

• The Overheating Epidemic: Relying on the Schedule and Calculation methods often forces unnecessary insulation into homes, turning modern builds into hot boxes.

• Modelling Saves Money: The H1/VM1 Modelling Method evaluates holistic energy profiles, frequently proving that less insulation is needed to pass compliance.

• Joinery Myths: Upgrading to fully thermally broken joinery is not a silver bullet against condensation without a robust, continuous ventilation strategy.

• Smart Design Trumps Brute Force: Simple Passive House principles—like optimizing house orientation and using climate-specific glass on different elevations—often yield better results than maximum R-values.

  
  

Why Are New Zealand Homes Overheating Under the 5th edition H1 Rules?

The biggest misconception in the industry today stems from an over-reliance on the standard Schedule and Calculation methods. These compliance pathways are heavily weighted toward heating and fail to adequately account for cooling.

In Climate Zones 1 and 2—covering areas like Northland, Auckland and Hawke’s Bay —this has resulted in houses stuffed with insulation they simply do not need. When H1 compliance is treated as a late-stage, tick-box exercise, the main downstream consequence is severe summer overheating with high energy bills to cool these houses down. We are seeing this acutely in medium-density builds, particularly north-facing townhouses and apartments, which are effectively becoming thermal hot boxes.

How Can Developers Use the H1/VM1 Modelling Method as a Competitive Advantage?

There is a reality in the current framework that savvy developers can turn into a massive competitive advantage: the system is almost rigged in favour of the Modelling Method (H1/VM1).

Unlike the Schedule or Calculation pathways, the Modelling Method considers a building's holistic energy profile, evaluating both heating and cooling loads. By dynamically modelling the home, we frequently prove that less insulation is required to achieve compliance and optimal thermal performance.

This translates directly to reduced construction costs while actually improving occupant comfort.

Case Study: Optimising a Climate Zone 1 Build in Auckland

We recently completed the H1 modelling for a retirement village project in Climate Zone 2, featuring standard 120sqm dwellings with roughly a 30% glazing ratio. Built on a standard concrete slab without underfloor insulation, the project initially relied on the Calculation Method and was tracking toward highly specified, expensive material requirements.

By taking the project through the H1/VM1 Modelling Method, we were able to optimise the thermal envelope significantly.

Material Reduction via H1/VM1 Modelling

Building Element	Original Calculation Method	Optimised Modelling Method (H1/VM1)
Roof Insulation	R6.0	R3.0
Wall Insulation	R2.8	R2.2
Joinery	Fully thermally broken	Non-thermally broken
Floor	Slab edge insulation	No slab edge or underfloor insulation

The Financial Impact

Across a 120sqm house, the financial payoff of reducing these material requirements is substantial. By downgrading from expensive R6.0 to R3.0 roof batts, swapping R2.8 wall insulation for R2.2, and utilizing standard non-thermally broken aluminum joinery instead of costly thermal upgrades, developers can save an estimated $10,000+ per dwelling in material and installation costs alone.

Multiply those savings across a multi-unit development, and the ROI of early modelling becomes undeniable. More importantly, the modelling ensured the homes would require less energy to run and provide a far more comfortable, balanced climate for residents without the risk of severe summer overheating.

Why Upgrading Joinery Isn't a Silver Bullet

There is a persistent myth that upgrading to fully thermally broken joinery is the ultimate cure for cold, damp homes. The truth is, even top-tier thermally broken windows will experience condensation issues if internal moisture and airflow are not properly managed.

You cannot buy your way out of poor ventilation design simply by upgrading your window frames to thermally broken.

When utilising non-thermally broken joinery, our recommended strategy is to implement an outdoor air supply system or a heat recovery system that does not transfer moisture. By ensuring there is always fresh air being pulled into the home and stale, moisture-laden air being extracted, you actively control the indoor climate, rather than just trapping moisture inside a highly insulated box.

Note: Frame temperature will roughly be the same as the outdoor temperature for non thermally broken frames.

Note: Introducing outdoor air when the temperature outside is low will decrease the indoor relative humidity levels, since cold outdoor air has low humidity.

Adopting Passive House Principles for Free

Creating a high-performance home isn't as difficult or expensive as the general population believes. We already have the tools at our disposal to design highly efficient homes that lean much closer to Passive House principles—often without adding a single dollar to the build cost.

One of the most overlooked, yet easiest principles to implement is house orientation. By simply angling the design to maximise solar gain in winter and provide natural shading in summer, we see massive long-term energy savings.

Moving Beyond the Tick-Box

The upcoming Edition 6 of H1/AS1 and H1/VM1 is poised to phase out the Schedule Method entirely. This is a crucial step in the right direction to combat the overheating issues plaguing our newer housing stock.

But regulatory updates alone won't fix the industry's mindset. We need to stop relying heavily on active heating and cooling devices—like running heat pumps year-round—to compensate for poorly optimised houses.

If you are a developer or architect looking to protect your design intent while dramatically lowering build costs, it requires moving past the basic schedule or calculation method and modelling the building exactly how it will be lived in. Send through your plans today, and let us show you what your building is actually capable of.