H1VM1 Changes 2025: What You Need to Know

If you design or build in New Zealand, the 2025 update to H1 VM1 affects insulation levels, glazing performance, and how councils expect compliance to be demonstrated.

Because the new H1VM1 is more detailed and more tightly policed, many teams are outsourcing their modelling to specialists. We provide fast, accurate H1 VM1 modelling designed to reduce redesigns, control costs, and keep your consents moving.

If you want to find out more about our H1VM1 services, contact us here.

The new H1 VM1 (Sixth Edition) took effect on 27 November 2025, with a one-year transition period allowing the previous version to be used until 26 November 2026.

From 27 November 2026, all projects must comply with the new H1VM1 requirements.

1. The Modelling Rules Are Stricter 

The new VM1 tightens several assumptions:

• Updated climate data – More accurate temperatures and solar patterns mean your design performs differently than before.

• Clearer shading and solar gain rules – External shading, eaves, and orientation now have a bigger impact on glazing performance.

• Refined internal gains – Occupant and appliance heat loads are modelled more realistically, affecting heating/cooling demand.

• Cleaner ventilation assumptions – Fresh-air rates and passive cooling rules are standardised, so ventilation strategy matters more.

Why this matters: Better accuracy means your glazing, insulation, and layout decisions need clean inputs early—done right, these changes usually give you more flexibility, not less.

2. Multi-Unit + Mixed-Use Projects Just Got Easier

You can now model buildings in one of two ways:

• As a single thermal envelope – treating the whole building as one cohesive energy zone.

• As multiple separate envelopes – allowing each unit, floor, or section to be modelled independently.

What this means for you:

• Simpler modelling for apartments – You no longer need to overcomplicate simulations for each flat; a single envelope approach can streamline the process while still complying with H1.

• Fewer constraints for stacked units – When designing multi-story apartments or townhouses, modelling units separately allows you to account for different orientations, glazing, or construction without unnecessary compromises.

• More options for mixed-use developments – Buildings that combine commercial and residential spaces (e.g., a shop with an upstairs flat) can now be accurately represented in the model, making compliance checks more straightforward.

3. Wall R-values & Thermal Bridging Are Treated More Realistically

VM1 now includes a more accurate method for accounting for framing and thermal bridging, giving a better reflection of how walls actually perform.

Key changes:

• All standard framed walls are now treated as R1.6 for the Reference building, down from the previous R2.0.

What this means from an H1 perspective:

• Standard wall build-ups may show lower overall thermal performance than older models suggested.

• Well-constructed, high-performance walls now earn more credit, rewarding thoughtful insulation and framing choices.

• Optimised walls allow for more glazing flexibility, letting architects place larger windows without compromising H1 compliance.

• Impact on your project

  • Builders will feel this most in material selection

  • Architects will notice differences in glazing allowances, with better-insulated walls giving more freedom in window placement and size.

4. Heated Floors, Ceilings & Walls — Rules Finally Make Sense

This has been a pain point under the old H1 for some time, so it’s great to see it updated. Previously, any heated wet room (bathrooms, toilets, shower rooms) would often require more insulation under floor, even for small spaces. That often caused unnecessary redesigns and extra RFIs and higher costs for your clients. 

What’s changed:

• Heating in wet rooms no longer automatically triggers higher insulation requirements. It will be treated as all other elements with no minimum R-value requirements.

• Under floor heating no longer comes with automatic insulation penalties.

• Practical benefits:

  • Fewer RFIs from councils or certifiers.

  • Fewer surprise redesigns late in the project.

  • Designers and builders can specify heated wet spaces without worrying about compliance headaches and larger costs for your clients.

This change makes H1 compliance more realistic and practical, aligning requirements with actual energy impact rather than blanket rules.

5. All Areas Must Use Internal Dimensions

This is one of the biggest practical changes.

VM1 now requires: 

✔ all roof areas 

✔ all floor areas 

✔ all wall areas

…to be measured using internal dimensions only.

Why this matters:

• More consistent modelling – Calculations now align across rooms, floors, and projects, reducing discrepancies.

• Cleaner consent drawings – Using internal dimensions keeps plans straightforward and easy for councils to review.

• Fewer errors in area take-offs – Reduces the risk of over- or underestimating compliance areas

In theory, measuring all roof, floor, and wall areas using internal dimensions should make modelling more consistent, reduce errors, and simplify consent drawings. 

In practice, however, most existing projects and software still calculate areas using external dimensions, so switching to internal measurements is likely to cause some teething issues and require careful checking of plans and calculations during the transition. 

6. Shading Rules Make Compliance Harder

One of the more practical changes in the updated H1/VM1 is how shading, including eaves, is treated in modelling. Previously, when creating the reference building, designers could often ignore shading from eaves and other fixed features, making compliance calculations a bit easier.

What changed:

• Old H1/VM1: Exterior shading such as eaves, fins, balconies and overhangs had to be modelled in the proposed building but could be ignored in the reference building. Internal shading like blinds or curtains was always ignored.

• New VM1: Exterior shading such as eaves and balconies must now be modelled in both the proposed and reference buildings, except for dedicated features like fins and overhangs, which can still be excluded. Incidental shading from surrounding structures or terrain that significantly affects the building is also considered in both models. Internal shading is still ignored, and trees/vegetation remain excluded.

Why this matters:

• More realistic energy and daylight modelling – The reference building now better reflects real-world shading effects, so calculations are more accurate.

• Impact on north-facing glazing – Shading can reduce solar gains or daylighting more than before, potentially changing compliance outcomes.

• Design implications – Previously “easy pass” designs may now require small adjustments to glazing, eaves, or insulation to maintain compliance.

Overall, the change makes modelling closer to real-world performance, ensuring both proposed and reference buildings are assessed on a comparable basis but will likely make compliance for some areas of the country harder. 

7. New Climate Data Means Some Designs Will Change

The updated climate files in VM1 can shift modelling results, meaning that even familiar designs may behave a little differently.

What to expect:

• North-facing glazing behaves differently – Solar gains and daylighting calculations may change, impacting energy performance.

• Shading plays a larger role – Overhangs, blinds, and nearby obstructions can now have a bigger effect on compliance.

• Some “easy pass” homes move closer to the compliance line – Designs that were previously comfortably compliant may now need a small tweak.

• Some “harder sites” actually gain performance – Cooler or windier locations may benefit from revised climate data.

How These H1VM1 Changes Affect Your Projects

For architects

• Shading devices influence results – eaves, balconies, and nearby structures can change solar gains and daylighting compliance.

• Wall systems now matter – framing, insulation, and thermal bridging affect both energy performance and glazing allowances.

• Modelling reports must justify all inputs cleanly – councils now expect clear, consistent calculations.

• Early engagement avoids redesigns – addressing performance issues before consent saves time and costs.

For builders

• Insulation can often be reduced with proper modelling – no need to over-specify to hit compliance.

• Ceiling R-values don’t need to be extreme – realistic modelling avoids unnecessary material and labour costs.

• High-cost glazing can often be avoided – optimised wall and shading performance allows smarter window choices.

• Mixed-use and multi-unit work is now easier – multiple envelopes and single-envelope options give more flexibility.

For both

• Accurate modelling = lower build cost + fewer council delays + reduced redesign headaches.

Need H1 VM1 Modelling That Saves You Money and Time?

If you want to avoid redesigns, reduce insulation costs, or improve glazing performance (e.g., Thermally broken to non thermally broken) we can help.

Our service gives you:

• Fast turnaround – get results quickly (3 - 5 working days_ so decisions can be made early.

• Clear guidance on exactly what to change – no guesswork, no over-specification.

• VM1 modelling that passes without over-designing – tailored to your project.

• Council-ready documentation – reports formatted for easy approval.

• A team specialising exclusively in H1 – experts who know the rules inside out.

Whether it’s a single home or a full development, we keep your projects moving smoothly, saving you time, money, and stress.

Contact Us today to find out more.