Passive Design

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

Determining insulation requirements

Insulation requirements can be determined using any of three methods, depending on factors such as construction type and glazing area.

On this page:

  • schedule method
  • calculation method
  • modelling method

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

Acceptable Solution H1/AS1 cites New Zealand Standard 4218:2004 Energy efficiency – Small building envelope with modifications as a means of meeting the insulation requirements of the NZBC.

NZS 4218:2009 can be used as an Alternative Solution.

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.

The climate zones are the same as those used by the Window Efficiency Rating System (WERS) for window performance requirements.

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.

Using NZS 4218:2009 as an Alternative Solution

NZBC clause H1 Energy efficiency 3rd edition currently cites NZS 4218:2004 Energy efficiency – small building envelope as an Acceptable Solution. NZS 4218:2009 has been published but at present is not an Acceptable Solution as it is not cited in clause H1. BRANZ recommends that, until it is referenced in Clause H1, NZS 4218:2009 can be used as an alternative solution.

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. BRANZ recommends the use of ALF or modelling methods for effective passive design.