Building Code H1/AS1 Calculation Method

This tool implements the calculation method of the H1/AS1 Fifth Edition - Amendment 1. Please add your building's thermal envelope areas and R-values in the table below. Note that wall and roof areas are 'net' meaning that the area of any windows, doors and skylights must be subtracted.

Additional rows can be added with the button at the top-right.

Please set the territorial authority in which the building is to be constructed below.

The climate zone will be looked up automatically.

Please also tick when the building will be submitted for building consent. The new H1 changes are being phased and this changes the required R-values.

The building is compliant with the calculation method if its heat loss is less than or equal to the reference building heat loss.

For building elements with embedded heating systems, the minimum construction R-values shall be determined through the Schedule method. These apply whenever building elements that are part of the thermal envelope include heating systems and may not be reduced by applying the Calculation method. Refer H1/AS1


R-values are input as construction R-values, NOT the R-value of the batts insulation. Please use another tool (such as the BRANZ Home Insulation Guide available here) to calculate or lookup the R-value of the complete wall, floor or roof assembly.

Continue a saved calculator

If you have previously saved a calculator and wish to continue, please select the 'browse files' button below and upload your calculator CSV file.

Proposed Building Total heat loss (W/K):
Glazing area to total wall area ratio:
Building element type Description Net area (m2) Construction R-value Heat loss (W/K)
Reference Building Total heat loss (W/K):
Building element type Net area (m2) Construction R-value Heat loss (W/K)
Slab-on-ground floor
Floor other than slab-on-ground
Window or door

Click the button below to download your progress and continue at any time.