Wondering how to use energy modelling to inform your home’s design, rather than just tick a compliance box?

Discover why bringing energy assessment into the design phase, not after documentation, will clarify and simplify sustainability design decisions.

Learn the questions to ask your designer and energy assessor so the star rating you achieve reflects the home you actually want to live in.

Listen to the episode now.

Hello! This is Episode 415, and Way #15 of the ‘44 Ways to Create Your Sustainable Home’ series here on the podcast. With this episode, we begin Section Four: Modelling and Measuring Your Sustainability.

Section Four is about the ways you can access data to inform your decision-making, beginning with energy efficiency assessments and modelling of your home’s energy use.

Way #15 is: Use Energy Modelling During the Design Phase.

In most locations, energy efficiency assessment happens after documentation is completed, as part of finalising building approvals prior to construction. 

When left until that point, you’re underutilising the benefit of energy modelling to your project and future home, and it’s potentially costing you money, comfort and sustainability performance every day.

Energy efficiency modelling generally works by calculating how much energy the home will need to maintain thermal comfort across the year. It takes into account the orientation of the building, the climate zone, the construction of the walls, floors and roof, the window sizes and specifications, and the shading design. 

It then runs a calculation based on actual climate data for your site location, and produces a star rating based on the predicted heating and cooling load the home will require.

In Australia, the primary energy modelling tool for residential buildings is NatHERS, the National House Energy Rating Scheme. It produces a star rating from zero to ten on an exponential scale. A 7 star home, the current standard, is around 30% more efficient than a 6 star one. An 8 star is 40 to 50% more efficient than a 6 star one, depending on the climate. A 10 star home requires no artificial heating or cooling to maintain comfort.

Energy standards have only been in existence in Australia since 2003. 

It’s estimated that around 72% of Australian homes average at 1.8 stars, which requires roughly 4 to 5 times more energy for heating and cooling than a 7 star home. 

It’s why Aussie homes are often criticised for their likeness to tents.

Here’s the key to note: whatever system you’re accessing when modelling your future home’s energy efficiency, you have the opportunity to use this modelling as a design tool, not just a compliance check. 

If the energy assessment is done when documentation is almost finished, as part of your building approval process, what are you actually going to do with the results? At that stage, the floor plan is locked in. The window sizes are resolved. The wall construction is specified. The eave depths are set.

If the energy efficiency assessor had been involved six months earlier, during design development, they might have found that a different window-to-wall ratio on the west facade, or a slight pivot of the home’s position on your block, or a bit more shading to one bedroom, would radically improve the home’s energy efficiency and star rating, at very little additional cost.

Best practice looks like an energy assessor engaged during design development, before the key decisions are locked in. Then your energy efficiency assessor can advise you and your design team with modelling data, so decisions are made based on it, instead of treating the model as a checkpoint.

In this Episode, I cover:

• What energy efficiency modelling actually is, and how it calculates a star rating for your home
• The critical difference between using energy modelling as a compliance check at documentation stage, and using it as a design tool during design development
• What some of the failings and opportunities are in energy modelling, especially Australia’s system, NatHERS
• Three specific questions to ask your team so energy modelling is doing real work, including when it will be commissioned, what star rating you’re aiming for, and whether your assessor will collaborate with the design team
• How this all changes if you’re renovating rather than building new, and how the modelling can guide where to invest your budget

Plus a whole lot more.

LISTEN TO THE EPISODE NOW.

RESOURCES:

Episode 208 with Sid Thoo >>> Roof Colour: Dark vs Light (and your home’s energy efficiency)

Episode 263 with Melanie Lupis, Sustainability Certified >>> How to Design and Build an Energy Efficient, Zero Carbon Home

Episode 262 with Melanie Lupis, Sustainability Certified >>> The Residential Efficiency Scorecard for Existing Homes

Episode 293 with Jeremy Spencer, Positive Footprints [NCC Series] >>> 7 Star Homes

Episode 294 with Jeremy Spencer, Positive Footprints [NCC Series] >>> The ‘Whole of Home’ Rating Scheme

Episode 295 with Jeremy Spencer, Positive Footprints [NCC Series] >>> Does Size Matter in Achieving 7 Stars?

Energy Efficiency Assessment and Rating Schemes:

Australia

• Improving energy efficiency and comfort in Australian homes >>> NatHERS, Nationwide House Energy Rating Scheme

USA

• Supporting better comfort, lower running costs, and higher resale value in US homes >>> HERS by RESNET

Canada

• Rating the energy performance of new and existing homes in Canada, backed by the Government of Canada >>> Energuide

New Zealand

• Energy efficiency is governed through the building code
• Voluntary system for further modelling and information >>> Homestar

UK

• Used to monitor the energy efficiency of homes >>> The government’s Standard Assessment Procedure (SAP)
• Changes made in 2026 to UK energy efficiency requirements, with SAP being replaced (transition period applies) >>> Why SAP is being replaced with HEM

Europe / UK

• A labelling system to understand a home’s energy efficiency >>> How to understand Europe’s new energy performance labels

A free e-guide to simplifying sustainability across research, planning, design, materials, and building >>> 44 Ways to Create a Sustainable Home

Access the support and guidance you need to be confident and empowered when renovating and building your family home inside my signature online program >>> HOME Method