It all depends on how cold it gets where you live. Here are the recommended minimum insulation levels (R-values) for existing homes:
MINIMUM RECOMMENDED R-VALUES FOR EXISTING HOMES
(excluding Central Plateau)
|South Island and Central Plateau|
|Ceilings with 0-75mm of existing insulation||R2.8 blanket or R3.4 segment insulation||R3.2 blanket or R4.0 segment insulation|
|Ceilings with 75-120mm of existing insulation||R1.8 blanket insulation||R2.4 blanket or R2.6 segment insulation|
|Underfloor||R1.4 bulk insulation||R1.4 bulk insulation|
|Walls||Check the thickness of your wall cavity and find the highest R-value product at that thickness|
How important are climate zones?
New Zealand is divided into three climate zones, ranging from relatively warm to cool and frosty during winter.
CLIMATE ZONE 1
All areas north of, and including, Franklin District. Thames-Coromandel is also part of Climate Zone 1.
CLIMATE ZONE 2
All North Island areas not covered by Climate Zones 1 and 3.
CLIMATE ZONE 3
All of South Island and North Island Central Plateau (Taupo and Ruapehu Districts, and north of Rangitikei District).