H1 Calculation method tool

Please read the instructions before using the tool. Instructions include version update detail.

Compliance requirements for H1/AS1 6th Edition

The use of H1/AS1 6th edition is restricted to housing, and other buildings that are less than 300 m².

Buildings with curtain walling are excluded.

Methods for determining the thermal resistance and construction R-value of building elements are contained within H1/AS1 6th edition and include methods to calculate the R-values for slab-on-ground floors, windows, doors and skylights.

The wall glazing area (windows and glazing in doors) of the building can be no greater than 40% of the gross wall area.

Roof, walls and floors other than slab-on-ground floors must meet certain minimum R-values.

Heated ceilings, heated walls, and heated floors must meet certain higher minimum R-values, except where they are solely installed in rooms with a shower, bath or toilet.

Please refer to H1/AS1 6th edition for full compliance information.

This tool cannot be used for H1/AS2 2nd edition, which deals with larger non-residential buildings that have different requirements.

Using the tool

Select the climate zone and accurately enter all area and construction R-values for each building element.

Data should only be entered into areas that are shaded in blue.

Cells that are shaded in dark blue provide a dropdown list of options. Only options from the dropdown list can be used.

Calculated cells are shown in orange and cannot be selected.

This tool performs a number of checks and calculations and pass/fail compliance determined if appropriate.

This tool will not allow R-values to be entered that are below the minimum permissible for that element.

This tool will also not allow unrealistically high R-values to be entered to reduce the likelihood of data entry errors.

The print area has been set to cover the white area on the Results sheet.

All the entered data will appear on the Results sheet so a printout of that sheet will contain all the necessary information.

The printout will list all of the individual building elements over a number of pages. The output should be scaled to 1 page wide.

Measurement of areas

Refer to H1/AS1 6th edition for definitions of building element areas and how to measure them.

The gross roof area is the net roof area plus the area of skylights in the roof.

The gross wall area is the net wall area plus the area of all vertical windows and doors in the external walls of the building.

For the net roof area, thermal envelope floor area, and net wall area, use overall internal dimensions, measured on the finished internal face of all relevant building elements, including the thickness of any internal partitions.

Construction R-values

The designer must input construction R-values for the building elements. These are NOT the same as the insulation R-values.

Separate verification of the construction R-value should be included with your consent documentation.

Use the BRANZ House Insulation Guide 6th edition to find construction R-values or use the appropriate methods to calculate the construction R-values:

• For walls, roofs and floors other than slab-on-ground floors, use NZS 4214 with changes as per H1 6th edition
• For framed walls, H1/AS1 requires a wall framing fraction no less than 38% be assumed by default
• For windows, doors and skylights, see Appendix D in H1/AS1 6th edition
• For slab-on-ground floors, see Appendix E in H1/AS1 6th edition

Interpretation of H1/AS1 6th edition

This tool is implemented according to an interpretation of H1/AS1 6th edition.

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 values.

Restrictions on use

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

Updated: 3 December 2025