Recent changes to the New Zealand Building Code have not just tinkered with the insulation requirements for new homes.
They have doubled the ceiling insulation from R 3.3. This is now required to be R 6.6.
That is quite some insulation depth, 350 mm, more than three times the thickness of the R 1.9 standard that was originally made compulsory for new houses back in 1979.
It’s hard to change the insulation in walls much without increasing the depth of the studs to 140 mm. Walls stay at R 2.0.
Timber floors on piles are another substantial change, going from R 1.3 up to R 2.5.
These new insulation regulations in the Building Code were implemented for new homes in May 2023.
You are not compelled to upgrade the accessible insulation in existing homes, but in the long term it is worth considering the new standard when considering a boost in the insulation to an existing home. Many homes with insulation installed in the 1980s or 90s have just R 1.9 in the ceiling.
This suggests a top-up of an R 4.0 or R 4.8 blanket is advantageous to keep you cosy and reduce heating bills in the long term.
That’s about 200 mm extra thickness, although this may need to be reduced in thickness at the edges to allow a minimum 25 mm clearance for ventilation.
All private rentals must comply with the Healthy Homes Standards (HHS). If ceiling insulation was installed prior to 1 July 2016, it only needs to be in reasonable condition with a minimum thickness of R 1.9 (or ~70–120 mm thickness depending on material). Otherwise, it has to be topped up to a minimum of R 3.3 total.