Roadmap to Zero Carbon Homes

The Sustainable Builders Alliance is on a mission to make net zero sustainable homes mainstream. Co-founder Jeremy Spencer introduces the free resources they have created to help.

There is no getting around it. Our homes, as important and central to our lives as they undoubtedly are, remain one of the most carbon-intensive things we create.

From the five tonnes of carbon dioxide generated every year by the average Australian home, to the estimated 200 tonnes or more of embodied carbon already released before the keys to a new home are even handed over, the residential building industry is one of the most carbon-intensive industries in Australia.

If we are to meet Australia’s international commitments, all industries will need to figure out how to supply carbon-neutral products by 2050. And the sooner, the better.

The good news is that we already have the knowledge and the technology to produce homes of much lower impact. Producing low-energy, net zero carbon homes – homes that produce as much energy over the year as they use – is possible, but requires that building professionals work together to achieve it. The problem now is one of spreading the know-how and coordinating industry stakeholders.

It’s not enough that a house be designed well for its climate; it must also be built well to achieve the predicted thermal performance in reality.

It’s not enough for a home to perform well thermally; it also needs to be fitted out with energy-efficient appliances to achieve minimum energy use.

It’s not enough to minimise energy demand. With solar panels, batteries, and coming vehicle-to-home (V2H) technology, a house can now be set up to be an energy hub and a net positive contributor to the national grid, supporting its transition to renewable electricity.

And it’s not enough to focus on operational impacts only, when embodied carbon is the lion’s share of the carbon budget on a 2050 timescale – the date when Australia has committed to net zero for carbon emissions.

A carbon-neutral home must consider all of the above. Such a holistic response requires designers, builders, assessors and other building professionals, plus homeowners, to be on the same page, with a basic shared knowledge base of what it takes. That is, they must all be working towards a similar outcome and walking a similar path.

We call this path the ‘Roadmap to Zero Carbon Homes’, and have developed it as a free resource for the industry. It clearly outlines the steps necessary to create net zero sustainable homes, details the key aspects to focus on, and gives practical guidance on how to achieve the goal.

The Roadmap has five steps that serve as an organising scaffold for the myriad principles, practical actions, and useful rules of thumb to employ when creating sustainable, energy-efficient homes. Each step ends with a useful video section to help summarise and consolidate the information presented, and internet links for those who want to delve deeper into topics. Following these steps should guarantee a net zero outcome for the majority of homes.

STEP 1: GOOD DESIGN
Design a house that needs little energy to heat and cool.
Heating and cooling typically account for a quarter to a half of all energy use, so minimising the need for them is the place to start when creating a new low-energy home.

This first step goes through the five fundamental elements of passive solar design – orientation, fenestration (windows), insulation, mass, and ventilation – and explains how to apply them to design for climate, so that heating and cooling needs are minimised.

Designing for climate is also the most cost-effective way to achieve high-Star outcomes under the Nationwide House Energy Rating Scheme (NatHERS). To help with getting started, this step provides a useful ‘Achieving NatHERS 7 Stars Cheat Sheet’ for downloading, full of energy assessor tips that you or your designer can use during the design process to keep design concepts on track for high-Star outcomes.

STEP 2: LOW-IMPACT MATERIAL SPECIFICATION
Build the home with lower carbon, more sustainable materials.
Once you have a design that will perform well in your climate, the next step is to choose the materials for constructing the home. Material choices matter: as electricity grids decarbonise over time, it is increasingly the embodied carbon in the materials we use to build our homes that becomes the main issue.

This step covers ‘Embodied Carbon 101’ and goes through practical strategies to minimise upfront carbon in the homes we build. It also introduces some useful carbon accounting tools and resources to help with this.

Tables of common building materials and assemblies show their typical embodied carbon per square metre, which can be a useful ready reckoner when choosing materials for lower-carbon outcomes. Additionally, there are links to relevant Australian embodied carbon databases, and instructions on how to use Environmental Product Declarations (EPDs) to guide lower-impact product selection.

Step 2 also considers broader environmental concerns when specifying materials, covering environmental timber choice and providing links to further useful web resources on sustainable material selection.

STEP 3: PERFORMANCE CONSTRUCTION
Build the home to operate thermally as designed, so that it performs to its energy rating.
It is no secret that poor thermal construction quality can undermine the NatHERS energy Star rating of a home design. This step looks at where standard construction often fails thermally, and what details and control strategies designers and builders can incorporate on plans and in workflows to minimise these failure points.

There is a useful ‘Builder’s Thermal Performance Checklist’ for downloading. This is a quality assurance document that designers can incorporate into house plans, or homeowners can put in the contract, for builders to follow onsite. It gives project managers a checklist to tick off at each construction stage to make sure common thermal issues don’t accrue in your build as the works progress.

Further important considerations when building energy-efficient homes are health and indoor air quality. This step comprehensively explains condensation theory and control, and provides rules of thumb for selecting healthy materials and ventilation strategies to consider when designing a healthy internal environment.

STEP 4: EFFICIENT APPLIANCE SELECTION
Choose efficient fixed appliances to keep energy demand low.
While passive solar design and a quality build make great starting points, it is the appliances we choose that largely determine how much energy a home uses, what its operational carbon impact will be, and how costly it is to run.

This step on the Roadmap covers the systems and technologies to consider for an energy-efficient outcome, and how to size them to reduce energy bills.

Correct sizing and efficient appliance choices are not only important to keep home running costs down. As Australia increasingly goes all-electric, if we want to minimise expensive infrastructure upgrades, it is important that homes we add to the grid have minimal energy demand when the sun goes down and renewable generation drops off.

This step includes appliance templates that designers can download and add to plans, so that all the relevant performance details energy assessors need for the new NatHERS Whole of Home rating are clearly documented, making the rating process quick and easy.

STEP 5: ENERGY GENERATION & OFFSETTING
Add solar panels for operational net zero and potentially true zero outcomes.
Now that the home is designed and fitted out for minimal electricity consumption, the last step is to add solar generation for that all-electric, low bills, net zero carbon, energy-positive lifestyle!

This step covers what you need to know when choosing, specifying and sizing solar photovoltaic (PV) panels. It includes guidance on PV system sizing for net zero outcomes, how many kilowatts to allow for home car charging, and the roof area requirements to design for.

It also includes construction and safety considerations when planning for battery storage, as well as how to set the home up for future electric vehicle charging and coming V2H integration.

And lastly, for those who want to account for the embodied carbon in the structure, step 5 will very soon include a discussion of offsetting strategies for true zero outcomes – check back soon for this.

Where to find the Roadmap
To access the Roadmap, simply go to the Sustainable Builders Alliance website at thesba.com.au and click the Roadmap tab. You will find the downloadable tools at the bottom of each step. There is also a useful Webinar archive under the Resources tab; a link to our podcast, the Sustainable Builders Yak; and an Events Calendar for those who want to get involved.

Most importantly, when building a net zero sustainable home, you need a team of professionals who all have this knowledge. The Sustainable Building Directory lists SBA members; look out for builders, designers, assessors, tradespeople and other professionals with badges on their profiles. There are five badges to collect, and each one shows that the professional has taken the time to learn and understand the information in the corresponding step of the Roadmap. Build a team who are all talking the same language, and see your net zero home come to life.

Feel free to use the Roadmap on your own projects to create cost-effective, energy-positive, healthy, net zero sustainable homes. And if you find it useful, please let others know about it – especially building professionals!

Let’s get the word out. It’s time to make net zero homes the new normal.