Zero-Carbon Buildings

To be considered zero-carbon, a building must achieve net-zero status for both Operational Carbon and Embodied Carbon.

Operational Carbon – refers to the carbon (or more precisely greenhouse gas – GHG) emissions released as a result of energy consumed in the day to day operation of a building.

• Industry refers to these emissions in terms of scope, as either scope 1 or 2 depending on where and how they originate. 
• Scope 1 emissions are GHGs released directly from sources that an entity owns or controls. For instance, fugitive emissions from refrigerants used in central air conditioning, plant, or fossil fuels burnt on site.
• Scope 2 emissions are the indirect GHG’s released in the generation of the energy which the entity purchases.

Embodied Carbon - on the other hand refers to the total carbon emissions (GHGs) released as a result of constructing a building, including:

• Producing the materials used in the initial construction, repairs and renovation over the life of the building;
• Transporting the materials to site; and
• The direct energy use on site during construction and repairs or renovation over the life of the building.

Currently in Australia when industry refers to zero-carbon or carbon neutral outcomes for buildings, it is typically referencing Operational Carbon only. Operational Carbon is now a mainstream concept actively embedded within corporate Environmental, Social and Governance (ESG) frameworks; but for carbon neutrality to be properly impactful, industry must work towards a combined measure which takes account of both Operational and Embodied Carbon.

In Australia there is currently no universally accepted definition for this combined measure, however the term ‘net zero whole life carbon’ is becoming widely used.

Net zero is a target or goal to eliminate and or compensate for all human generated greenhouse gas emissions. The ‘net’ status is achieved by utilising offsets to account for unavoidable carbon emissions.

Offsets are generated from an activity that prevents, reduces, or removes greenhouse gas emissions from being released into the atmosphere and are typically third party validated.

Offsets however should be considered a last resort once all other physical and operational opportunities to prevent emissions being generated or reduced in the first place have been exhausted.

In the discussion surrounding emissions both are correct – carbon is widely used but Greenhouse Gas Emissions (GHG) is more precise.

Greenhouse gases (GHG) refer to several types of gases that trap heat in the atmosphere. These gases include carbon dioxide, but also other gases such as methane and nitrous oxide.

Carbon dioxide (CO2) is the most potent greenhouse gas contributing about 80% of the overall warming effect of current emissions (GHG Protocol). For this reason, CO2 is used as the reference gas when measuring the Global Warming Potential (GWP) of the various greenhouse gasses. The GWP is a unit of measure of the radiative effect of a given GHG over a chosen timeframe relative to CO2, (usually over a 100 year time frame), and is measured in units of carbon dioxide equivalent (CO2e).

One kilogram of carbon dioxide has a GWP of 1kg CO2e, compared for example, to one kilogram of methane which is approximately 28kg CO2e.

Failure to limit global warming average temperature to less than 1.5 degrees Celsius will have a catastrophic impact on the World’s ecosystems.

According to the World Green Building Council (WGBC)

“The landmark 2018 special report from the UN Intergovernmental Panel on Climate Change (IPCC 2018 report), Global Warming of 1.5ºC, presented a stark picture of the dramatically different world we will inhabit if global average temperatures rise by 2ºC compared to a 1.5ºC scenario. The catastrophic breakdown of climate associated with the difference between these two scenarios is likely to result in entire eco-systems being destroyed….The consequences will be long lasting and, in some cases, irreversible.” (Adams et al., 2019)

Australia is a signatory to the 2015 Paris Agreement on Climate Change which aims to reduce greenhouse gas emissions and limit global temperature increase to 1.5 degrees above pre-industrial levels by 2050. The recently released Sixth Assessment Report from the Intergovernmental Panel on Climate Change (IPCC - 2021), which states that human activities have warmed the climate ‘at a rate that is unprecedented in at least the last 2000 years’ further focuses our attention on the challenges ahead for Australia in meeting our international commitment to climate goals.

Australia’s federal government has now passed legislation and is committed to cutting carbon emissions by 43% by 2030 and to meeting net zero emissions by 2050.

Constructing, operating, maintaining and demolishing buildings (the building sector) accounts for 39% of the total global carbon emissions, so there are real opportunities to make significant reductions are through design, material selection, and construction techniques.

According to the WGBC (2019) the building sector globally accounts for 39% of carbon emissions with 11% attributed to embodied carbon of materials and construction and the remaining 28% from operational emissions.  In Australia the embodied carbon emissions of materials used in construction is similarly estimated between 5 to 10% of total national greenhouse gas emissions. (Edge Environment Pty Ltd).

…and it is unlikely we are going to construct less buildings, as the WGBC states:

“By 2060, the total global floor area of buildings will double, with more than 50% of this anticipated within the next 20 years. The growth in new buildings will be particularly rapid in Asia and Africa’.”

A significant step-change in the building and construction sector is required to meet our carbon commitments.

As Australia’s electricity grid decarbonises the impact of operational carbon in building sector emissions will reduce relative to the impact of embodied carbon.

In 2019 Operational Carbon accounted for 74% of Australia’s built environment emissions, but by 2050 the Green Building Council of Australia estimates this figure will be around 15%.

Meeting Australia's ultimate net-zero goal will require a greater focus on Embodied Carbon in the building and construction sector.