129: Improving H1 Energy Efficiency

Background

Building Code clause H1 sets the requirements for energy efficiency. This clause requires enclosed spaces where temperature or humidity are modified to provide adequate thermal resistance and to limit uncontrollable airflow in certain buildings. It also sets out physical conditions likely to affect energy performance, and requirements for hot water systems, artificial lighting and HVAC systems.

Significant updates to H1 were introduced in 2021 to improve energy efficiency in new buildings. A review in 2024 identified opportunities to better balance upfront building costs and longer-term benefits, and to improve consistency and certainty of compliance and consenting, while maintaining the required level of energy efficiency.

Since that time, further changes have been made to the acceptable solutions and verification methods for H1 Energy Efficiency to ensure they remain clear, flexible, and affordable for designers, builders and homeowners. The latest targeted changes follow a public consultation from December 2024 to February 2025 and build on the decision to remove the Schedule method as a ‘deemed to comply’ pathway, announced in July 2025.

The Schedule method has been removed

The change that is likely to have the biggest impact for LBPs (especially those holding a Design licence) is the removal of the Schedule method as a compliance option for Building Code clause H1.3.1(a). This leaves the Calculation method and Modelling method as the two ‘deemed to comply’ pathways for H1.

The Schedule method was a relatively quick and simple way to calculate how much insulation was needed in different parts of the country to meet Building Code requirements for new buildings. However, this one-size-fits all approach often proved more expensive than using the Calculation or Modelling methods to determine the appropriate amount of insulation for an individual home.

LBPs who have fully relied on the Schedule method will need to upskill on using the calculation method and may wish to make use of the free online tools available through BRANZ or the New Zealand Green Building Council.

Designers and architects with access to specialised modelling software can continue to use the Modelling method to meet the requirements of H1/VM1 or H1/VM2.

Changes to minimum R-values and thermal bridging assumptions

With the Calculation method in H1/AS1 expected to become the primary way to show compliance for the thermal performance of new housing and small buildings, MBIE have taken the opportunity to adjust some minimum R-values in the Calculation method to avoid costly and complex building requirements. This includes reducing the minimum R-values for roofs from R3.3 to R2.6 and removing the minimum R-value for slab-on-ground-floors as this can be difficult to achieve where the conditioned area above is very small. Despite this, the overall level of energy efficiency required by the Calculation method has not changed.

Another change is requiring thermal bridging from wall framing to be more adequately considered. A recent sample of new residential buildings showed an average framing percentage of 38%, higher than the number assumed by many designers.

Designers will now have to assume a minimum of 38 per cent, unless they can show that a lower percentage is justified. This change aims to provide better consistency of R-values between framed and non-framed walls and provide designers with more certainty in their calculations.

Clarifying that areas of roofs, walls and floors should be measured internally

Internationally, some building regulations require the use of internal dimensions while others require external dimensions. To ensure clarity and consistency, H1 now makes it clear that overall internal measurements should be used when determining dimensions of roof, wall and floor areas.

Improved modelling methods and enhanced tools and tables

The other changes that have been made to the H1 acceptable solutions and verification methods are around improving the usability of the documents and ensuring the modelling methods in H1/VM1 and H1/VM2 better align with modern building practices.

These changes support consistency in how the modelling method is used, and will provide clarity for designers, building consent authorities and building users that buildings have sufficient insulation.

Transition period until 26 November 2026

The updated AS/VMs are already in effect, and designers have until 26 November 2026 to fully adopt the changes. During the transition period designers can choose between the previous and the new editions of the H1 AS/VMs. MBIE will work closely alongside the sector to ensure the changes are well understood and implemented effectively.

Quiz

1. What is the main purpose of Building Code clause H1?
a) Stability
b) Moisture
c) Access
d) Energy efficiency

2. What are the two remaining ‘deemed to comply’ compliance methods for H1?
a) The Calculation method and the Modelling method
b) The Schedule method and the Guessing method
c) The Computation method and the Estimation method
d) The Schedule method and the Computation method

3. What minimum percentage of framing is required to be assumed under the new H1 AS/VMs when working out the R-value of framed walls?
a) 18%
b) 38%
c) 30%
d) 55%