This tool implements the calculation method of the H1/AS1 Fifth and Sixth Edition for all housing, and for other buildings up to 300 m2. Buildings that are both greater than 300m2 and not housing should use our H1/AS2 calculator available here.

Please set the territorial authority in which the building is to be constructed below. The climate zone will be looked up automatically.

Then add your building's thermal envelope areas and construction R-values in the table below.

Note that:

• only the areas of building elements that form part of the thermal envelope are to be included, but not internal walls and internal floor/ceilings between conditioned spaces
• wall, roof and floor areas must be determined using overall internal dimensions, measured on the finished internal face of relevant building elements, including the thickness of any internal partitions
• wall and roof areas are 'net' meaning that the area of any windows, doors and skylights must be subtracted
• R-values are input as construction R-values, NOT the R-value of the insulation products. Please use another tool (such as the BRANZ Home Insulation Guide available here) to calculate or lookup the construction R-value of the complete wall, floor or roof assembly.

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

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

Heated ceilings, heated walls and heated floors must meet certain minimum construction R-values that may not be reduced by applying the calculation method. They do not apply where heated ceilings, heated walls or heated floors are used solely in bathrooms. Refer H1/AS1 2.1.2.12.