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

NZS 4218:2009 Thermal insulation – Housing and small buildings is cited in H1/AS1 and H1/VM1 as a means of compliance for clause H1 Energy efficiency. It is NZS 4218:2009 that contains the requirements around the schedule, calculation and modelling methods.

Note that significant changes to the Building Code clause H1 Energy efficiency were introduced on 29 November 2021. These will require higher levels of thermal performance in new buildings. The changes will become mandatory in November 2022.

Schedule method
The schedule method specifies minimum R-values for building envelope components – roof, wall, floor and glazing – depending on construction type and one of three climate zones in New Zealand.

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).

The construction types include:

  • non-solid construction, which includes all framed construction
  • solid construction, which includes solid timber, masonry, concrete and earth construction. 

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.

This method may be used where the total area of glazing is 50% 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.

Modelling method

Where the total area of glazing of a building is greater than 50%, a modelling method must be used as an Alternative Solution. R-values are calculated by comparing the energy use of the proposed building with a reference building by means of a computer modelling program such as BRANZ ALF.

BRANZ ALF method

BRANZ ALF (Annual Loss Factor) is a verification method for determining the Building Performance Index (BPI) which can be used to show compliance with NZBC clause H1 Energy Efficiency. It is a software program where the designer inputs information about the project – such as orientation, plan area, wall area, window area, construction types and insulation levels – and the programme calculates the BPI. For Northland and Auckland, however, simulation such as AccurateNZ, SUNREL, IES-VE or Sefaira may give better results than ALF. This is especially important where significant thermal mass effects are being examined.

The software can also be used to assess and improve the thermal performance of existing buildings.

An updated version of the tool, ALF 4.0, was released on 19 February 2019.

Note that under Building Code verification method H1/VM1 5th edition, effective 29 November 2021 with a 1-year transition period, compliance with clause H1.3.2E (“Buildings must be constructed to ensure that their building performance index does not exceed 1.55.”) is no longer  sufficient for demonstrating compliance with clause H1.3.1(a) (“The building envelope enclosing spaces where the temperature or humidity (or both) are modified must be constructed to ­– (a) provide adequate thermal resistance…”). In effect this means that from 3 November 2022, an ALF calculation alone will not be enough to show that a house complies with all the requirements of Building Code clause H1.

Finally, with all discussions around complying with the standard, remember that the minimum figures required for compliance simply define the poorest-performing house you are legally allowed to build. Just meeting the minimum requirements is not the same thing as good practice.



Updated: 13 December 2021