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Free NZ H1 Insulation Calculator: Calculation Method (H1/AS1 6th Edition)
This free calculator provides a simplified H1/AS1 Sixth Edition Calculation Method check. It uses the same calculation engine as Thermly's consent reports to compare your proposed building with the reference building and return an indicative PASS or FAIL. To keep the process quick, it uses fewer inputs and generic construction options. The result is intended for early design guidance and cannot be submitted as building consent documentation.
The full Thermly workflow uses the same calculation method with detailed project inputs and documented product provenance. Instead of entering areas manually and choosing generic constructions, you can complete a plan take-off by tracing walls, roofs, floors and openings directly from your plans. You can then model the assemblies you are actually specifying, selecting each layer from Thermly's sourced New Zealand product catalogue with supporting manufacturer and reference information.
This free calculator
- Areas typed in by hand
- Generic constructions, or an R-value you already have
- Whole-building heat-loss verdict, indicative only
- Indicative-only PDF by email
The full Thermly workflow
- Plan take-off: mark up a plan PDF to scale and derive wall, roof and floor areas
- AI assistance: project details, window and door schedules and insulation specifications read off the uploaded plan to pre-fill your inputs, ready for you to check
- Your constructions: built layer by layer to NZS 4214:2006, with real framing fractions
- Sourced products: a catalogue with datasheets, retrieval dates and manufacturer data trails
- Consent evidence: the per-element working and plan extracts behind the verdict
Insulation manufacturer or merchant? This calculator is available white-labelled for your own site.
Enquire1. Location
Look up the H1 climate zone from a postcode, or select your council. The zone is assigned by council (H1/AS1 6th edition), so a postcode is indicative only.
2. Building elements
Pick a generic preset or enter a construction R-value for each element.
Windows, doors and skylights
Either route gives the same answer. The difference is who subtracts each opening from the wall or roof it sits in: you, or the calculator. Choose whichever matches how you measured.
Enter the net area of each wall and roof, with its own openings already deducted, plus one area total per class below. Deduct each opening from the element it actually sits in: where two walls have different R-values, taking it off the wrong one changes the result.
Roofs
Walls
Floor
Slab R-values are computed from your area and exposed perimeter by the H1/AS1 Appendix E area and perimeter method.
Windows & glazed doors
Whole-window R (e.g. 0.46 for double-glazed thermally broken aluminium). Leave blank to use the H1/AS1 default.
Opaque doors
Leave blank to use the H1/AS1 default.
Skylights
R = 1/Uw for the installed skylight.
About the H1/AS1 calculation method
The Acceptable Solution H1/AS1 Sixth Edition took effect on 27 November 2025. It removed the schedule method, the table of fixed minimum construction R-values most designers used to demonstrate compliance. The Fifth Edition, which still contains the schedule method, can be used to show compliance until 26 November 2026 and for building consent applications submitted before 27 November 2026. From 27 November 2026, a new consent application following H1/AS1 must use the calculation method.
The calculation method works by comparison. Your proposed building's total heat loss is the sum, across every envelope element, of its area divided by its construction R-value. The same geometry is then costed a second time using the reference building's R-values for your climate zone. If the proposed building loses no more heat than the reference building, it meets the heat-loss test. That trade-off is the point of the method: a better-insulated roof can pay for more glazing. Some limits are not tradeable. Minimum construction R-values for roofs, walls and floors other than slab-on-ground apply regardless, and wall glazing above 40% of gross wall area puts the building outside the calculation method altogether.
Construction R is not the R-value printed on a bag of insulation. It is the resistance of the whole assembly (lining, insulation, air spaces, cladding, and the internal and external surface resistances) with the framing that bridges the insulation accounted for by the isothermal-planes method of NZS 4214:2006. Framing changes the answer substantially: a 90 mm timber-framed wall with an R2.8 insulation segment computes to roughly R1.7 once the H1/AS1 default 38% wall framing fraction is applied.
What this tool does and does not do. It runs the same calculation engine that produces Thermly's consent reports, so the arithmetic is the same arithmetic, and it gives you an indicative whole-building verdict from generic constructions and entered R-values. It does not capture product-level evidence, per-element working, or the supporting documentation a building consent authority expects. Its output is indicative only and cannot be lodged with a consent application.
Frequently asked questions
- What is the difference between the schedule method and the calculation method?
- The schedule method was a table of fixed minimum construction R-values: meet every figure and the building complied. H1/AS1 Sixth Edition removed it. The calculation method instead compares your whole building against a reference building of the same geometry, so you can trade a better-insulated roof against more glazing, provided total heat loss does not exceed the reference. The Fifth Edition, which still contains the schedule method, can be used to show compliance until 26 November 2026 and for building consent applications submitted before 27 November 2026.
- When does the schedule method stop being available for new consents?
- H1/AS1 Sixth Edition took effect on 27 November 2025 and does not apply to building consent applications submitted before that date. The Fifth Edition remains usable for applications submitted before 27 November 2026. From 27 November 2026, a new building consent application following H1/AS1 must use the calculation method.
- Which H1 climate zone am I in?
- H1 divides New Zealand into six climate zones, assigned by territorial authority (your local council). Zone 1 covers the far north and zone 6 the coldest inland South Island districts. Two districts are split by a geographic line and carry two zones. Selecting your council in the calculator above applies the zone exactly; a postcode gives an indicative zone only, because postcode boundaries do not follow council boundaries.
- What is a construction R-value, and how is it different from the R-value on the insulation?
- The figure on an insulation product is the R-value of that material alone. A construction R-value is the thermal resistance of the entire assembly (lining, insulation, air spaces, cladding, and the internal and external surface resistances) with the timber or steel framing that bridges the insulation accounted for using the isothermal-planes method of NZS 4214:2006. Framing matters a great deal: a 90 mm timber-framed wall with an R2.8 insulation segment computes to roughly R1.7 once the H1/AS1 default 38% wall framing fraction is applied.
- What does "reference building" mean?
- The reference building is a notional building with your building's geometry, but with construction R-values set by H1/AS1 Table 2.1.2.7 for your climate zone. Its walls are treated as 70% opaque and 30% glazing regardless of your actual glazing. Your proposed building complies on the heat-loss test when its total heat loss is no greater than the reference building's.
- Do windows need to be assigned to particular walls?
- For the opening itself, no. For the wall it leaves behind, yes. H1/AS1 Equation 2.1 totals openings by class: one wall-glazing term, one opaque-door term and one skylight term for the whole building, and the reference building splits gross wall area 70/30 without looking at individual walls, so no window needs to know which wall it is in. The wall side is per wall, though. Each wall contributes its net area divided by its own construction R-value, so an opening has to be deducted from the wall it actually sits in: taking 10 m² off an R5 wall rather than the R2 wall it is really in changes the answer. This calculator therefore lets you enter net wall and roof areas alongside one total per class, or gross areas with the openings listed against each element. Both produce the same result for the same building.
- Can I lodge this calculator’s output with a building consent application?
- No. This is an indicative calculation only. The PDF it produces says so on every page, carries no reference number and records none of the product-level evidence or per-element working a building consent authority expects. It is intended for early design decisions. Producing a lodgeable H1 compliance report requires the full Thermly workflow.