Passive Design

Designing the building and the spaces within it to benefit from natural light, ventilation and even temperatures.

Determining insulation requirements

The minimum levels of insulation required for Building Code compliance can be determined using any of three methods, depending on factors such as construction type and glazing area. Specifying better than minimum is strongly recommended.

On this page:

  • Schedule method
  • Calculation method
  • Modelling method

Insulation for new housing must comply with the New Zealand Building Code (NZBC) clauses H1 Energy efficiency and E3 Internal moisture.

With Acceptable Solution H1/AS1 and Verification Method H1/VM1, the 5th edition amendment 1 is the edition that must be used. See the Building Performance website for more details.

Schedule method
The schedule method specifies minimum R-values for building envelope components – roof, wall, floor and windows and doors – depending on construction type and which climate zone applies.

It can only be used for houses where the area of glazing is less than 30% of the total external wall area and where the combined area of glazing on the east, south and west facing walls is 30% or less of the combined total wall area of these walls (i.e. the north wall may have a greater area of glazing than 30% but this must be offset by reducing the area of glazing on the other three faces).

BRANZ has developed an online tool to help with using the Schedule method under H1/AS1 5th Edition, Amendment 1.

Calculation method
The calculation method uses heat loss calculations to determine the proposed building envelope R-value requirements and compares the results with the heat loss (HL) of a reference building.

Under H1/AS1 5th edition amendment 1, the calculation method can only be used where glazing is 40% or less of the total wall area. Its advantage over the schedule method is that it allows a building with different building elements to be assessed as a whole, with adjustments being made between elements. For example, a wall R-value may be reduced if the roof or floor R-value is increased to compensate or if window R-values are increased. In no situations may R-values for roofs or walls be reduced below the minimum R-values set down by E3/AS1. The construction R-value for roofs, walls and floors in the proposed building must be at least 50% of the construction R-value of the corresponding building element in the reference building. The calculation method cannot be used to reduce the performance of building elements that have embedded heating systems.

BRANZ has developed an online tool to help with using the Calculation method under H1/AS1 5th Edition, Amendment 1.

Modelling method

The modelling method gives designers the greatest flexibility around demonstrating compliance with H1. Modelling is used to demonstrate that energy use of the proposed building does not exceed the energy use of a reference building in the relevant climate zone. The procedure used is set out in Appendix D in H1/VM1 5th edition amendment 1.

There are limits to the use of the modelling method:

  • Where a proposed building includes a heated ceiling, wall or floor, minimum construction R-values apply for that particular element
  • Acceptable Solution E3/AS1 also specifies minimum R-values for walls, roofs and ceilings. The modelling method cannot be used to provide lower values than these


Updated: 13 July 2023