What is it like building a carbon negative home?

It all started with developers from Western Australia who had a vision to create the most sustainable residential community possible.

It took more than 10 years to acquire the land, finalise the design, receive all the required approvals to finally start the construction in March 2021.

The Witchcliffe Ecovillage offers its residents a sustainable lifestyle and the opportunity to be part of a community that is self-sufficient in water, solar energy, fresh food produce, as well as looking after their waste management.

  What is special about this village?


Let’s have a closer look and see what they did differently. A few features of the project that might interest an architect or a builder include:

  • Proof of carbon negativity.

Each house needs to demonstrate that its carbon emissions over 120 years won’t exceed a set specific target of a – 220kgCO2e / occupant / year. Basically, these homes are good for environment. ?

  • Power from the sun.

Houses are carefully designed based on passive solar design principles. Each house needs to install at least 6kW of solar PV panels on the roof. Each cluster is connected to a microgrid and a centralised Tesla Powerpack battery. The connection to the external Western Power grid allows the Ecovillage to sell its excess power and provides power during construction.

  • Water from the rain.

All potable water in the Ecovillage comes from rainwater capture. Each home needs to install a rainwater tank. The water is processed and purified in a closed loop on the site.

  • Food from the garden.

The homeowners of the Ecovillage can use collected rainwater from the communal dam to water their gardens and orchards. It sounds like a dream to have an unlimited supply of fresh vegetables and fruit that everyone can harvest in the Ecovillage.

Image1. U-shaped residential cluster with community garden and open spaces


Why go beyond carbon neutrality?

Carbon neutrality is achieved when a building has zero annual emissions from energy use. This is not a hard task especially with solar passive principles and use of renewables.  Having an extensive solar system helps to neutralize some additional emissions.

The idea to go beyond carbon neutrality came from the need to also neutralise the embodied energy, or emissions caused by materials and their maintenance over the life of the building.

Using low carbon materials can have a positive effect on air quality and health, but also help the building to last longer.  After consulting with sustainability experts to understand which materials to use and which to avoid, it became clear that life cycle assessment (LCA) should be incorporated into the design and review process of each building.

Image2. A beautiful example of a strawbale home in Margaret River

Every parent’s dream is a child coming back home.

Looking at materials is important to make the picture holistic and to make sure the house you are building will last longer and can be passed on to future generations. For those who know LCA, it’s clear that carbon reduction will result in reduction of energy and water bills, cost of future repairs and maintenance, and will have the lowest long-term impact on nature.

It’s a simple equation:

Lower carbon = Lower cost.


How to measure carbon neutrality?

It may surprise many that most new homes could achieve 50-70% CO2 reduction without large investment. In fact, the City of Vincent in Western Australia requires all new houses to achieve at least 50% C02 reduction for design approval. It is a huge mind shift and step forward towards sustainable housing.

Each Ecovillage home needs to demonstrate that its whole of life carbon emissions won’t exceed a set specific target of -220kgCO2e / occupant / year.  It can be also expressed as a percentage of CO2 saving versus a benchmark residence, the target being a 105% carbon saving. Once future homebuyers have completed the concept and materials to use in their new homes, they need to confirm that their home is meeting the set targets in the Witchliffe Ecovillage Sustainable Building Design Guidelines.

To measure carbon, you need a tool that is easy and robust enough to calculate future home emissions. It also should be flexible and non-prescriptive, so that designers can be creative and explore different options of sustainable design and remain within their budget.

To support this effort, the Ecovillage team commissioned software company eTool to develop a new tool, which needed to be intuitive to use and provide the necessary confirmation. eTool is an LCA software provider and passionate environmentalist and has always had a soft spot for residential projects trying to lower their carbon footprint and their energy bills.

The first prototype was called eTool Turbo, then Lifecycle.House, but we ended calling it RapidLCA.


RapidLCA App for Low carbon HOMES and more…

The eTool team was inspired to be involved with such an iconic project as the Witchcliffe.

The process for RapidApp users is simple:

  • Download the app and find your lot or address
  • Spend 20-30 minutes to input data
  • Generate a compliance report showing your home’s carbon footprint and required targets are met
  • Submit for design approval, build permit, or even green loan.







Future of the RapidLCA App

As of early 2021, about 100 homes have undergone an LCA using the RapidLCA app and no-one was struggling to meet the metric of 105% CO2 reduction. In fact, many were exceeding the target, which proved that LCA is not hard and can be done by anyone, even without an architectural or engineering degree.

eTool is now working on enabling the one-off assessments for single use and extra features for interested developers.









Get in contact with US if you would like to know more.


NCC 2022 and NatHERS Star Ratings – eTool Position Statement

NCC 2022 are proposing some dramatic improvements in residential energy use. This is, in principal a fantastic development and one that eTool very much supports. We do however feel that mandating 7 star NatHERS performance carries some risk and isn’t the most effective deployment of available capital for rapid decarbonisation. The reason is simple, there is much lower hanging fruit available in areas not covered by the NCC proposed changes.  It’s also highly likely that the 7 Star requirements will lead to net-negative outcomes for the planet.

See below examples of the life cycle impacts (Global Warming Potential) of three detached residential buildings designs in each capitol city (averaged) selected because of their ubiquity (the homes selected are very standard display home products), plus an overall national population weighted average. Due to their relatively large size (and hence large thermal loads in comparison to other impacts) they represent a somewhat “best case” scenario of what improving thermal performance can achieve. The charts below indicate that moving from 6 to 7 stars doesn’t significantly move the needle on life cycle global warming impacts.  Although moving from 6 to 7 stars delivers a 25% (average) saving in heating and cooling energy requirements, it only results in an average 2% reduction in life cycle impacts.

Life Cycle Impacts of 7 Star NatHERS NCC 2022

While this change could make sense for particularly hot or particularly cold climates, such as Darwin, Hobart and Canberra, it makes significantly less sense for the more temperate areas of Sydney, Melbourne, Brisbane, Adelaide and Perth.  So, the question is, can Australian new home buyers get better bang for buck elsewhere?  The “Other Impacts” are broad (see below for a breakdown for the population weighted average example), but the two largest categories are outside of the proposed scope for NCC 2022.  So, while eTool are supportive of improved thermal performance of buildings, we also see inherent risk associated with targeting this strategy in isolation.  That is because, for homes to “rate” 7 stars in many temperature climates they require a lot of thermal mass (e.g. brick and concrete), so what the 2022 NCC may end up doing is discouraging the use of low carbon materials such as timber in preference of brick and concrete for thermal mass.  This will in turn result in higher life cycle material impacts and ultimately higher net impacts, working against the intended goals of the amendments (to reduce greenhouse gas emissions).

Likewise, plug loads are another area – currently outside the NCC – that requires attention.  Solar PV most certainly should play a role in reducing the impacts of the building, energy monitoring, and possibly other policy levers the government can pull to improve the energy efficiency of appliances.  There’s other easy wins that should be addressed, higher efficiency HVAC, lower GWP refrigerant gases are good examples.  Ultimately, life cycle assessment should be the cornerstone of any policy for reducing the environmental impacts of Australian residential and commercial buildings.

Life Cycle Impacts Australian Residence