Buildings influence how we live and how much energy and material we use, and the choices made at the design stage ripple across decades.
Smarter early decisions don’t just cut life cycle costs – they boost comfort and resilience and help meet long-term emissions goals, regardless of shifts in regulatory settings.
Until recently, energy and embodied carbon assessments were seen as specialist territory – complex, time-consuming and out of reach for most designers. That’s changing. New and updated tools are making performance modelling simpler, faster and better integrated with everyday workflows. This shift means designers can embed carbon and energy thinking from the very start, turning sustainability into a practical design advantage.
One newly upgraded tool that’s helping to build a bridge to more accessible modelling is ECCHO – the New Zealand Green Building Council’s Energy and Carbon Calculator for Homes.
‘While ECCHO uses a monthly method and treats the building as a single zone – meaning it can’t capture every nuance such as room-by-room overheating risks – it provides a practical starting point for most projects geared towards stand-alone and terraced properties,’ says Sam Archer, Director of Market Transformation at NZGBC. ‘For more detailed analysis of more complex projects such as apartments that require dynamic zone analysis, other modelling tools may still be needed. Together, these approaches make performance assessment practical and scalable.
ECCHO uses standardised climate and building data to estimate energy use. Internal gains such as heat from appliances and occupants use Homestar defaults or New Zealand Building Code assumptions. The tool also draws on conventions from the Passive House Planning Package for factors like thermal mass and energy balance, but ECCHO is built as an independent web app, meaning it can be accessed from any web browser. Together, these datasets allow ECCHO to provide a broad estimate of heating, cooling, lighting, hot water, plug loads and refrigerant-related energy use for New Zealand homes.
BRANZ embodied carbon dataset gifted to NZGBC
BRANZ’s embodied carbon data now sits at the core of ECCHO, following the gifting of the CO₂RE embodied carbon dataset to NZGBC last year. The CO₂RE dataset provides calculated carbon foot-prints per square metre for typical residential roof, wall and floor constructions, helping designers save time and making embodied carbon assessments faster and more consistent.
As a package, the datasets in ECCHO help designers and architects understand how layout, materials and design affect building performance. Early decisions can then be made that prioritise occupant comfort and health as well as more sustainable and cost-effective outcomes.
‘If you really want to analyse carbon on a home-by-home basis, you need to use operational energy and embodied carbon calculations. ECCHO is a tool that allows you to do that using BRANZ data,’ says Sam.
‘The construction sector contributes a significant share of New Zealand’s carbon emissions, and reducing embodied carbon will be essential for meeting the 2050 net-zero target,’ says BRANZ Principal Behavioural Scientist Casimir MacGregor. ‘However, this shouldn’t come at the cost of operational performance. Heating and cooling and the carbon locked into materials and construction processes both matter – and the balance between them will vary from project to project. In practice, improving one should support the other wherever possible, rather than forcing a choice between them.’
From spreadsheets to smart tools – the evolution of ECCHO
ECCHO’s roots go back to BRANZ’s research, which provided foundational data on building materials and emissions.
‘Our previous calculator didn’t allow changes of the ingredients in a wall assembly. Now, in ECCHO, you can see the buildup and swap things out – change insulation, cladding or timber – and see the effect instantly,’ Sam says.
BRANZ Senior Building Scientist Steve McNeil says it should be noted that, while this flexibility is useful, changing components can also introduce other risks such as moisture issues, which ECCHO is not designed to assess. Those aspects still need to be considered separately.
Flexibility and compliance
Beyond carbon calculations, ECCHO supports compliance with clause H1 Energy efficiency requirements in the Building Code. With the phasing out of the schedule method, designers need to use either the calculation or modelling method. NZGBC says that ECCHO can assess the design against the H1/VM1 modelling method, and users can gain insights into the design in the areas of:
- operational energy performance
- embodied carbon analysis
- single-zone overheating risk assessment.
‘H1 won’t pick you up on overheating, but ECCHO can,’ Sam says. ‘It gives architects an indication of whether a home is likely to overheat, so they can design shading or adjust glazing before it becomes a problem.’
Steve adds, ‘It’s great to see accessible options such as ECCHO getting uptake in the sector. Monthly methods are a good starting point, particularly for simple buildings with small amounts of glazing. However, overheating is a room-by-room issue so, longer term, the industry needs to undertake more detailed modelling that looks at outcomes for occupants using dynamic multi-zone simulation. For maximum impact, design workflows benefit from understanding overheating risk as early as possible – and work is happening to make dynamic simulation more accessible for early design.’
Overheating is influenced by a range of design factors, including:
- shading (or lack of it)
- the number of people in the building
- internal heat gains from activity (for example, lighting and cooking)
- ventilation
- window size, orientation and glazing type/coating
- thermal mass (for example, concrete).
‘Dynamic models enable you to capture these variations across time and space, so you can identify issues – such as over-heating in a single bedroom – that, monthly, single-zone tools cannot,’ Steve says.
The opportunities for industry
The opportunity for many modelling tools is integrating them into designers’ and architects’ workflows.
According to Steve, the industry faces the tasks of improving capability, choosing the right tools for the right stage of design and ensuring that decisions about performance and carbon are made alongside practical considerations such as cost, site constraints and construction methods. As expectations shift, tools will need to support both accessible early-stage guidance and more detailed analysis where required.
Sam says, ‘Two things are helping make energy modelling mainstream in New Zealand – affordable training and strong financial incentives. NZGBC’s Better by Design courses give designers a practical introduction and are currently priced at $10. And modelling opens the door to Homestar certification, which can unlock lower-interest development finance and discounted mortgages – saving developers and homeowners thousands. These benefits are driving a shift towards healthier, energy-modelled homes.’