Why More Insulation Does Not Always Improve H1 Report Compliance in New Zealand
- Kate Martin
- May 11
- 5 min read
As New Zealand moves further toward performance-based H1 compliance, many designers, builders, and homeowners are discovering that more insulation does not automatically produce a better-performing building.
In fact, under H1VM1 modelling, excessive insulation can sometimes make compliance harder — particularly in Climate Zones 1 and 2, where overheating is becoming increasingly common.
This is one of the biggest shifts occurring within the New Zealand building industry as we move away from the schedule method and toward whole-building thermal performance modelling.
Understanding how insulation, glazing, orientation, ventilation, and thermal bridging work together is now critical for achieving cost-effective and practical H1 compliance outcomes.
Early-stage wall insulation installation to meet updated H1 standards
The Shift Away From the Schedule Method
Historically, many residential projects in New Zealand relied on the H1AS1 schedule method. While simple to apply, the schedule pathway often encouraged blanket insulation upgrades without fully considering how the building would actually perform as a complete system.
As we move toward the phase-out of the schedule method in November 2026, more projects are transitioning to H1VM1 modelling.
This shift is positive for the industry overall.
Rather than simply increasing insulation values everywhere possible, modelling allows designers to optimise the building envelope based on:
climate zone
orientation
glazing ratios
shading
thermal mass
construction detailing
The result is often a building that is not only compliant, but also more comfortable, more energy efficient, and more cost-effective to build.
Why Over-Insulating Can Create Problems
One of the most common misconceptions in H1 compliance is that higher insulation values always improve performance.
In practice, particularly in Climate Zones 1 and 2, overheating is often becoming a larger issue than underheating.
Modern homes are increasingly designed with:
larger glazing areas
improved airtightness
higher insulation levels
reduced uncontrolled ventilation
When these elements are not balanced carefully, buildings can retain excessive heat, particularly in north-facing designs with significant solar gain.
Under H1VM1 modelling, this can actually reduce compliance performance.
This is where whole-building modelling becomes significantly more valuable than relying on prescriptive assumptions alone.
Real Project Example: When Less Insulation Improved Compliance
Recently, we worked on a Napier residential project that had initially been assessed, before they contacted Reshape Consulting, using the H1AS1 calculation method.
The project failed compliance due to a window-to-wall ratio close to 30%, and the original solution proposed was upgrading to expensive PIR insulation boards because there was no additional room available within the roof cavity for thicker insulation products.
Instead of forcing more insulation into the design, we used the H1VM1 modelling method pathway.
The result was that the building achieved compliance using the original architectural design intent — without costly PIR upgrades. In fact, we were able to reduce insulation levels further, down to the Healthy Homes minimum standard requirements for future rental suitability, while still achieving compliance.
This is one of the biggest advantages of modelling-based compliance: the building can be optimised as a complete thermal system rather than simply increasing insulation values in isolation.
Climate Zones Matter More Than Many People Realise
Most of our H1 compliance work is within Climate Zones 1 and 2, where the balance between insulation and overheating becomes particularly important.
In Auckland and other northern regions, H1VM1 Edition 5 modelling has often allowed significantly more flexibility than the traditional schedule method approach.
Rather than automatically increasing insulation, modelling allows the building to be assessed based on how it will actually perform in real-world conditions.
As the industry transitions further into Edition 6 requirements, understanding regional climate behaviour will become even more important.
High Glazing Designs Can Still Achieve Compliance
A common concern from architects and homeowners is whether large glazing areas will automatically create compliance issues.
We regularly work on projects with glazing ratios exceeding 40%, including large north-facing glazing configurations.
In practice, successful compliance usually comes down to balancing:
glazing performance
insulation levels
solar gain
shading strategy
Some of the most effective solutions in Climate Zones 1 and 2 include:
low-e tinted glazing
improved glazing specifications
carefully designed shading and eaves
reducing unnecessary insulation overspecification
We have never had to ask an architect to redesign a project by reducing glazing size or fundamentally changing the architectural intent.
Instead, compliance is achieved through optimisation of the building envelope and glazing performance.
Can You Still Comply Without Thermally Broken Joinery?
Yes — in many situations, compliance can still be achieved using non-thermally broken frames.
Whether this is practical depends on:
climate zone
orientation
glazing percentage
insulation strategy
overall building performance balance
In some projects, compliance can be achieved relatively easily. In others, improved insulation or upgraded glazing specifications elsewhere may be needed to offset the reduced frame performance.
The key point is that H1 compliance should always be assessed as a complete system rather than focusing on a single product or specification.
What the Industry Is Still Getting Wrong About H1
One of the biggest issues still overlooked within the New Zealand building industry is the relationship between compliance, overheating, and condensation risk.
It is entirely possible to create a house that technically complies with H1 requirements while still producing a building that:
overheats
struggles with moisture control
performs poorly for occupant comfort
becomes expensive to cool or ventilate
Compliance does not automatically guarantee a healthy or comfortable home.
As an industry, there is still significant room for improvement in balancing:
thermal efficiency
ventilation
moisture management
occupant comfort
long-term durability
The move toward modelling-based compliance is helping improve this, but there is still a long way to go in creating genuinely healthy and high-performing homes in New Zealand.
Why Early H1 Modelling Saves Money
One of the biggest cost-saving opportunities in any project is engaging H1 modelling early in the design phase.
Early-stage modelling allows optimisation of:
insulation levels
glazing specifications
framing systems
shading strategies
thermal bridging details
This often avoids expensive late-stage changes during consent or construction.
By comparison, late-stage compliance adjustments can become significantly more costly — especially where construction has already started or elements such as underslab insulation have already been missed.
In many cases, early modelling results in:
lower insulation costs
fewer redesigns
reduced glazing upgrade requirements
faster consent processing
better-performing buildings overall
Our Typical H1 Compliance Workflow
Most projects begin with architectural PDF drawings and a window and door schedule.
From there, we:
Calculate construction build-up thermal values
Run H1VM1 modelling simulations
Assess compliance performance
Optimise the design where required
Issue the final compliant report for consent submission
Approximately 80% of projects comply with the first model run.
Where changes are required, they are usually relatively minor and involve:
insulation optimisation
glazing specification adjustments
framing detail refinements
Typical turnaround time is 3–5 working days, although urgent projects can sometimes be completed within the same day where consent timelines are critical.
Most importantly, our goal is always to achieve compliance while maintaining the original architectural design intent wherever possible.
Final Thoughts
The future of H1 compliance in New Zealand is moving toward smarter, performance-based design rather than blanket insulation increases.
The most successful projects are those that balance:
insulation
glazing
orientation
shading
ventilation
thermal bridging
as a complete system.
In many cases, modelling-based compliance can reduce unnecessary construction costs while producing buildings that are more comfortable, more efficient, and better suited to New Zealand’s changing climate conditions.
If you are working on a residential or commercial project and want practical guidance on achieving H1 compliance without unnecessary overspend, early modelling can make a significant difference.
To discuss your project or request an H1 assessment, contact our team with your architectural drawings and window schedules. We can review the project and identify the most practical pathway to compliance.
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