What R-value do I need? NZ climate zones explained
- 12 October 2026
- Aaron Davis
"What R-value do I need?" is the most common question we get. The honest answer is: it depends on what you're building, where, and who it's for. Here's how to work it out.
First, what an R-value is
R-value measures how well something resists heat flow. The higher the number, the better it insulates. R-values add up through a wall or roof: two layers of R2 make R4.
There are two kinds, and the difference matters:
- Product R-value is what the insulation achieves on its own, for example R4.05 for a 90mm Eurothane GP board.
- Construction R-value is what the whole wall, roof or floor achieves once framing, linings and air gaps are included. It's always lower than the product R-value, because framing lets heat bypass the insulation.
The Building Code works in construction R-values. Product R-values are what's printed on the packet.
New Zealand's six climate zones
For new buildings, the Building Code splits the country into six climate zones. The colder the zone, the more insulation your design needs. As a guide (Sonder Architecture):
| Zone | Typical areas |
|---|---|
| 1 | Far North, Whangārei |
| 2 | Auckland, Coromandel, parts of Waikato |
| 3 | Central North Island: Taupō, Rotorua, parts of Bay of Plenty |
| 4 | Lower North Island and top of the South Island: Wellington, Nelson, Marlborough |
| 5 | Most of the South Island: Christchurch, West Coast, lower South Island |
| 6 | Central Otago and the alpine interior: Queenstown, Wānaka |
Zone boundaries follow district council boundaries, so check MBIE's H1 documents for your exact site.
New builds: there's no single number any more
Under the 6th edition of H1/AS1, the table of minimum R-values (the schedule method) has gone. Instead, your designer compares your whole building with a reference building for your zone. You can put more insulation in one place and less in another, as long as the total heat loss is no worse and each element meets its own minimum.
In practice that means your designer tells you the R-value needed for each element. What you control is how to achieve it in the space you have. Under the new rules, walls are the hardest part, because the code now assumes at least 38% of a wall is framing. Our post on the H1 changes shows how a continuous PIR layer helps.
Renovations and alterations
New work that needs consent generally has to meet the current rules. Existing parts of the building usually don't have to be upgraded, but the building mustn't end up worse than before. If you're opening up walls, ceilings or floors anyway, it's the cheapest time to insulate well beyond the minimum.
Rentals: the Healthy Homes standards
Landlords have separate minimums, set by the Healthy Homes insulation standard. New ceiling insulation must reach R2.9 in zones 1 and 2, or R3.3 in zone 3, and underfloor insulation R1.3. These use the older three-zone map from the 2008 Building Code, not the six zones above.
Turning R-values into PIR thicknesses
If you know the product R-value you need, this table gives the thinnest Eurothane GP board that reaches it:
| You need at least | Thinnest board | Board R-value |
|---|---|---|
| R1.3 (Healthy Homes underfloor) | 40mm | R1.80 |
| R2.0 | 50mm | R2.25 |
| R2.9 (Healthy Homes ceiling, zones 1–2) | 70mm | R3.15 |
| R3.3 (Healthy Homes ceiling, zone 3) | 75mm | R3.40 |
| R4.0 | 90mm | R4.05 |
| R5.0 | 120mm | R5.45 |
| R6.0 | 140mm | R6.35 |
Remember these are product R-values. Board fitted between framing will give a lower construction R-value; board fixed continuously over framing loses very little.
Not sure what you need? Send us your plans or call 03 540 3003 and we'll help you pick thicknesses. See the price list; we supply nationwide with freight quoted on each order.
See also: NZ Building Code insulation requirements · What is PIR insulation?
A general guide only. Your designer or council has the final say on compliance.