The short answer
H1 compliance is broader than an insulation schedule.
Clause H1 of the New Zealand Building Code covers the efficient use of energy. This guide focuses on one important part of it: demonstrating adequate thermal resistance for the building envelope under H1/AS1.
H1/AS1 Sixth Edition removes the Schedule Method. Its acceptable-solution route for thermal resistance is the Calculation Method; the Modelling Method remains available through H1/VM1. The Calculation Method compares the heat loss of the proposed design with a reference building instead of asking every element to meet one prescriptive schedule target.
The practical change is simple: move from a list of target R-values to a traceable model of areas, construction R-values and whole-building heat loss.
01 · Scope first
Choose the compliance pathway before doing the maths.
H1/AS1 Sixth Edition applies to all housing and to other buildings with no more than 300 m² of occupied space. It does not apply to buildings with foil insulation or curtain walling. Larger non-housing buildings move to H1/AS2 or H1/VM2; curtain walling moves to H1/VM1 or an alternative means of compliance.
| Pathway | Typical scope | What it tests |
|---|---|---|
| H1/AS1 Calculation Method | Housing, and other buildings up to 300 m², within the method's limits. | Proposed envelope heat loss against a climate-zone reference building. |
| H1/VM1 Modelling Method | The same broad size class where modelling is selected or the Calculation Method does not fit. | Annual energy demand of the proposed design against a modelled reference. |
| H1/AS2 or H1/VM2 | Buildings other than housing with more than 300 m² of occupied space. | Calculation or modelling pathways for the larger-building scope. |
Thermly's boundary
Thermly supports the H1/AS1 Sixth Edition Calculation Method. It does not claim to perform H1/VM1 energy modelling, H1/AS2 calculations, HVAC compliance or every requirement contained in Clause H1.
02 · The 2026 transition
The new method changes the evidence, not the performance target.
MBIE published the new H1 documents on 27 November 2025 with a 12-month transition. Previous editions can still be used until 26 November 2026. MBIE says the overall level of energy efficiency and insulation remains unchanged; the changes are intended to improve flexibility, clarity and consistency.
| Topic | Transitional workflow | H1/AS1 Sixth Edition |
|---|---|---|
| Pathway | Fifth Edition can still use the Schedule or Calculation Method. | The Schedule Method is removed; H1/AS1 contains the Calculation Method. |
| Framed walls | Framing assumptions could understate typical thermal bridging. | Assume at least 38% wall framing unless a lower project-specific fraction is demonstrated. |
| Areas | Measurement conventions could differ between workflows. | Net roof, floor and wall areas use overall internal dimensions. |
| Minimum R-values | Expressed partly by reference to scheduled or reference-building values. | Direct minimums apply to roofs, walls and floors other than slabs; the former slab minimum is removed. |
| Thermal bridges | NZS 4214 remained the calculation basis. | H1/AS1 modifies the NZS 4214 bridged-portion rule and makes the expected wall framing treatment explicit. |
This is why changing only the heading on an old schedule is not enough. The Sixth Edition result depends on measured areas, construction R-values and a new whole-building comparison using the current reference equations.
03 · Calculation Method
How the H1/AS1 Calculation Method works.
- 01
Confirm the envelope and climate zone.
Identify the conditioned space, exclude boundaries between adjoining conditioned spaces, and select the building's climate zone from H1/AS1 Appendix C.
- 02
Measure each building element.
Record net roof, net wall and thermal-envelope floor areas, plus wall glazing, opaque doors and skylights. Where an element has different constructions, keep each area and R-value separate.
- 03
Determine construction R-values.
Walls, roofs and non-slab floors use NZS 4214:2006 as modified by H1/AS1 2.1.3.2. Windows, doors and skylights use Appendix D; slabs-on-ground use Appendix E.
- 04
Calculate proposed heat loss.
Each part contributes its area divided by its construction R-value. The proposed building total is the sum across roof, walls, floors, glazing, opaque doors and skylights.
- 05
Compare with the reference building.
H1/AS1 builds a reference heat-loss allowance from the same building geometry, climate-zone coefficients and a reference wall split of 70% opaque wall and 30% glazing.
- 06
Check the method limits and direct minimums.
A pass needs proposed heat loss no greater than reference heat loss, wall glazing no more than 40% of gross wall area, and every applicable element minimum to be satisfied.
Proposed building
HLproposed = Σ (area ÷ construction R)
Pass condition
HLproposed ≤ HLreference
Product R-value is not automatically construction R-value.
A batt labelled R2.8 is only one layer. Framing, cavities, linings, claddings and surface resistances affect the construction result. The Calculation Method needs the R-value of the complete building element.
04 · Standards cross-check
The flexibility has firm boundaries.
The Calculation Method permits trade-offs across the envelope, but it is not an unconstrained heat-loss budget. The following checks come directly from H1/AS1 Sixth Edition and NZS 4214:2006.
- 40% glazing limit
- Wall glazing must be 40% or less of gross wall area for the Calculation Method.
- Direct element minimums
- Roof R2.6, wall R1.0 and non-slab floor R1.3. Slabs have no direct minimum but remain in the whole-building heat-loss comparison.
- 38% framed-wall default
- Use no less than 38% framing unless a lower fraction is demonstrated for the building, including plates, dwangs, corners and opening framing.
- Overall internal dimensions
- Measure the relevant roof, wall and floor areas on the finished internal face, including internal partition thickness where specified.
NZS 4214 and H1/AS1 must be read together
Surface films
NZS 4214 clause 5.2 uses Rsi 0.09 and Rse 0.03 m²·K/W for New Zealand compliance.
Thermal bridges
Clause 5.7 uses the isothermal-planes method to combine the area fractions of parallel heat-flow paths.
Sixth Edition modification
H1/AS1 paragraph 2.1.3.2 replaces part of NZS 4214 clause 5.7.1 when defining the bridged portion.
05 · Schedule-to-Calculation handover
Make the switch without rebuilding the project twice.
Start the Calculation Method while the previous edition remains available, rather than waiting for the transition deadline. Most of the source information already exists in a consent set; the task is to connect it into a reviewable calculation.
| Bring forward | Add for the Calculation Method | Evidence to retain |
|---|---|---|
| Climate zone and project scope | Confirm the current H1/AS1 scope and selected edition. | Project address, zone basis and document version. |
| Insulation and construction specification | Complete assembly R-values including framing and cavities. | Build-ups, framing fraction and product or standard sources. |
| Plans, elevations and schedules | Net envelope areas, glazing, doors and skylights by construction. | Marked-up area take-off tied to the calculation rows. |
| Scheduled element targets | Proposed and reference heat loss plus direct minimum checks. | Equations, inputs, result and assumptions on one review trail. |
Move before the deadline
Build your next H1 project with the Calculation Method from the start.
Connect construction R-values, plan areas, the heat-loss check and source-backed reporting in one Thermly project.
06 · Consent evidence
Make every number easy to trace.
A review-ready result should let another practitioner or processing officer reproduce the logic without reverse-engineering a spreadsheet. Keep the calculation and its evidence together.
- The H1 pathway, edition and project scope.
- Climate zone and the basis used to select it.
- Gross and net envelope areas, with openings clearly separated.
- Construction R-values for every distinct roof, wall and floor build-up.
- Framing fractions and the basis for any value below 38%.
- Window, door, skylight and slab R-value sources.
- Proposed and reference heat-loss workings.
- Glazing percentage and direct minimum-R checks.
- Marked-up plans or another transparent area take-off.
- Manufacturer, BRANZ, MBIE and standards references used.
Common transition mistakes
- Using a product R-value as though it were a complete construction R-value.
- Applying Fifth Edition schedule targets inside a Sixth Edition calculation.
- Using a low stud-only framing fraction without whole-wall evidence.
- Mixing gross and net wall areas or subtracting an opening twice.
- Blending different constructions into one untraceable average.
- Including walls between conditioned spaces in the thermal envelope.
- Leaving slab, glazing or skylight values without a stated source.
- Reporting a pass without the method limits and minimum-R checks beside it.
07 · Primary references
Standards and current guidance used for this guide.
The summary above was checked against the supplied local copies of H1/AS1 Sixth Edition and NZS 4214:2006, then cross-checked against the current public sources below. Always check MBIE for amendments before relying on a compliance pathway.
- 01
MBIE — Clause H1 Energy Efficiency
The Building Code clause, current pathway documents and amendment record. Open H1 Energy Efficiency
- 02
MBIE — H1/AS1 Sixth Edition
Scope, Calculation Method, heat-loss equations, minimums and construction R-value requirements. Open the Sixth Edition PDF
- 03
MBIE — 2025 H1 changes
The transition period and MBIE's summary of the policy changes. Read the change announcement
- 04
NZS 4214:2006
Methods for total thermal resistance, including surface resistances and the isothermal-planes treatment of thermal bridges. Open Standards New Zealand
- 05
BRANZ — H1/AS1 Sixth Edition Calculation Method tool
The current reference implementation and printable calculation workflow. Open the BRANZ tool
- 06
MBIE — H1/VM1 Sixth Edition
The Modelling Method for housing and other buildings up to 300 m². Open the H1/VM1 PDF
Browse the full MBIE H1 Acceptable Solutions and Verification Methods for current and previous editions. This guide is explanatory material, not a substitute for the cited documents or project-specific professional judgement.