A new report by consultants Aurecon, with costings by quantity surveyors Kwanto, provides a detailed review of the various requirements and specifications to achieve a 6 Homestar v5 rating, and how that compares with the necessary steps to meet NZ Building Code’s H1 Energy Efficiency clause.
The final version of H1, coming into force from 4 November 2023, will require new homes to meet higher levels of insulation throughout the country, particularly in colder climate zones like Christchurch and Queenstown. The updates to the Building Code do not include any improvements to ventilation requirements, nor do they require designers to consider any risk of homes overheating. The new insulation levels do bring the Building Code into closer alignment with Homestar levels of wintertime thermal performance. So, what’s the additional cost of going a step further from H1 and building to Homestar 6?
The report found the cost uptick varied from no additional cost for a 2 bedroom terrace in Christchurch and Wellington, to a maximum of 1.3% extra for a 4 bedroom standalone home in Christchurch.
“For most locations, H1 complaint specifications for both designs required only minor improvements to reach 6 Homestar minimums beyond these mandatory features; typically, in the form of increased ceiling insulation or added wall /ceiling linings. Wellington and Christchurch 2 – Bed designs didn’t require any further improvements to the thermal envelope as both edge insulation and thermally broken glazing was required to achieve H1,” the report found.
It should be noted these costings exclude the cost of land, GST, regulatory costs, and the fees associated with Homestar assessments.
Beyond thermal performance, most of the specifications were kept consistent for both the code compliant and Homestar designs. This reflects a realistic situation where designers can incorporate elements such as water efficient fittings and materials with verified eco-labels, at little or no extra cost.
With the industry set to implement the fundamental improvements to insulation under H1, this report shows the step from a good home to a great home is affordable and important.
Under Homestar, projects benefit from information provided by its Energy and Carbon Calculator for Homes (ECCHO) modelling. This modelling helps optimise design and clarify what areas to invest in for the best health, efficiency and carbon outcomes.
Among the additional requirements Homestar focuses on continuous mechanical ventilation, ensuring homeowners have a good supply of fresh air. The Building Code assumes a reliance on opening windows which has been shown to not always be effective or adequate. Additionally, Homestar rated homes generally perform better for overheating when modelled in ECCHO, with the Building Code failing to even consider it.
The report provides a useful case for those helping clients or who are themselves considering whether to certify to Homestar.
We know lower carbon, healthier homes require far more than adequate insulation. Things like decent ventilation, tackling thermal bridging, robust embodied and operational carbon reduction, indoor air quality, designing out waste to landfill, shading and solar performance are all but ignored in our current regulation, including the updated H1 .
Homestar certification helps fill these critical gaps and provides developers with the tools and knowledge to create better homes for New Zealanders. With the building code expected to change in 2025, forward thinking designers and builders are building to Homestar now, to get ahead of the game. This means they will have experience and be prepared for the coming changes to the building code.
The NZGBC is currently developing a full Homestar v5 design guide which will provide more detail on how to meet various Homestar requirements, and includes input and review by quantity surveyors. This will be available in the coming months.