H1 Calculator

Selecting your best route to compliance

There are three routes to H1 compliance, the Schedule method (being removed from December 2025), Calculation method and Modelling method. Our H1 Calculator focuses on the Calculation method, which allows the H1 R-values to flex for an optimised design, while remaining practical and convenient for most housebuilders.

Quickly assess the thermal performance of your build, optimise the design and find your most cost-effective route to compliance with our free H1 Calculator.

Three steps to H1 Compliant Designs

1. Enter your climate zone, date of build and the size of your building.

2. Enter your proposed construction R-values for each building element (incl. ceilings, skillion roofs, walls and floors.)

3. The system compares the heat loss from your proposed building with the equivalent reference building and confirms whether your design would pass or fail H1 compliance.

The calculator also tells you by how much your home would pass or fail. So, you can ensure all aspects of your design are fully optimised.

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Calculation Method

The calculation method uses the H1 construction R-values to calculate the overall heat loss of a 'reference building', with the same dimensions as your proposed home.

The heat loss is then calculated for the proposed home, using R-values specific to your design. These R-values can be individually lower or higher than those set out in H1/AS1* but the overall heat loss must be equal to or less than the reference building. Because compliance depends on the overall thermal performance of the home, not individual R-values, you retain far greater design flexibility, which often results in better cost optimisation.

Modelling Method

The Modelling method builds on the Calculation method by accounting for additional factors like orientation, shading, energy use and heating and cooling loads. While this method provides greater accuracy, it also requires additional design work which can increase costs. Meanwhile, the Calculation method provides a good balance of accuracy and convenience.

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