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NZS 4218:2009 calculation method tool


This tool calculates heat loss for the calculation method of NZS 4218:2009. It is not a replacement for NZS 4218:2009, and designers are advised to obtain a copy from Standards New Zealand.

Please read the instructions before using the tool.

What this calculation tool does

Designers need to select the climate zone and wall construction type(s) and accurately enter all area and construction R-values for the various building elements. The tool then applies the calculation method automatically, and pass/fail compliance is determined where possible.

Compliance with NZBC clause H1 Energy efficiency

Only the following designs are eligible to use this tool to demonstrate compliance with NZBC clause H1:

  • Housing (all types, any size).
  • Buildings other than housing with a net lettable area of no more than 300 m².
  • Buildings other than housing with a net lettable area of greater than 300 m² MAY use this tool. However, NZS 4243 is usually used.

This tool is NOT the calculation method of NZS 4243 and MUST NOT BE USED for this purpose.

Refer to New Zealand Building Code clause H1 Energy efficiency (4th edition) for full details.

Measurement of areas

Refer to NZS 4218:2009 Thermal insulation - Housing and small buildings for definitions of element areas and how to measure them.

Construction R-values

Designers must input construction R-values for the roof, walls and floor. This is NOT the same as the insulation R-value. Refer to NZS 4218:2009 for the definition of construction R-values.

The BRANZ House insulation guide gives construction R-values for the most common construction types used in residential construction in New Zealand and can be used with NZS 4218:2009.

Glazing construction R-values must be taken from Appendix C of NZS 4218:2009.

Interpretation of NZS 4218:2009

This tool is implemented according to an interpretation of NZS 4218:2009.

Limitations and liability

BRANZ Ltd accepts no liability for loss or damages resulting from use of this tool. The accuracy of the calculation relies on the designer entering accurate and truthful values.

Restrictions on use

This tool is only to be used in its full unmodified form.

More information on NZS 4218:2009 and NZBC clause H1.

How to use the BRANZ NZS 4218:2009 calculation method tool

Open/print these instructions [PDF, 153KB]

IMPORTANT: Only enter data or select options in unshaded cells. Select options from a drop-down list in cells shaded light blue.

A. Set up the climate and building construction type

  1. Go to the Project Summary worksheet.
  2. Enter the details of the project name, addresses, designer etc. (This is for your own information only.)
  3. Select the climate zone from the drop-down list.
  4. Select the wall construction type from the drop-down list.
  5. If mixed construction (wall construction type option 4) selected, enter the percentages of wall area (excluding glazing) of different types. The ‘Any wall type' percentage is automatically calculated. For example, if the design has 20% wall area solid timber, 30% wall area high thermal mass and 50% other, type in ‘20' for solid timber and ‘30' for high thermal mass, and 50 is automatically calculated.
  6. If solid timber (wall construction type option 2) selected, choose the wall construction details from the drop-down list.
  7. If the wall construction R-values are all the same and the door construction R-values are the same, enter 'yes' in the drop-down list, otherwise leave as 'no'.

B. Enter the areas and construction R-values for all building elements

  1. Go to the Building Elements worksheet.
  2. Enter details for roofs/ceilings, skylights, walls, floors, vertical glazing and doors. (See NZS 4218:2009 for the definitions and measurement details of these building element areas.) For each building element, in the appropriate section:
  • Enter a description for each part of the building element.
  • For each part of the building element, enter the area.
  • For each part of the building element, enter the construction R-value - a message is displayed if the R-value is too low. (Different parts of the same building element with the same construction R-value may be combined into one area.)

3. Check that:

  • all parts of building elements are entered
  • the individual and total areas match the plans
  • the R-values are reasonable.

C. Check the project summary

  1. Go to the Project Summary worksheet.
  2. Check that the climate zone and wall construction type options are correct.
  3. Check that the design has <=50% glazing.
  4. Check that the minimum R-values are not too low.
  5. Check that the design passes. (For wall construction type options 2, 3 and 4, a provisional pass may result as there are some issues that must be checked by the designer and BCA.)

D. Save a copy of the spreadsheet for your design documentation - change the file name as appropriate.

E. Print a copy of the spreadsheet for your consent documentation. Supply all printed sheets with the consent so everything can be checked and include any relevant supplementary information.