Embodied carbon in residential construction: LCA, materials and the NCC pathway

What it is

Embodied carbon is the greenhouse gas emitted to extract, manufacture, transport, install and eventually dispose of every material that goes into a building. It sits next to operational carbon, the energy used to run the building once people move in. On a 7 star NCC compliant house the operational carbon falls every year as the grid greens and the appliances improve, while the embodied carbon was spent on day one when the slab was poured and the frame went up. That makes embodied carbon a much larger share of the total impact than it used to be.

Embodied carbon is measured through life cycle assessment, almost always shortened to LCA. LCA tallies the kilograms of carbon dioxide equivalent across the material life cycle, from raw extraction through to end of life. The output is usually quoted in kilograms of CO2 equivalent per square metre of gross floor area.

TradeLens reads specifications, structural schedules and supplier declarations to surface high carbon material choices, missing environmental product declarations and projects that claim a low carbon outcome without the LCA evidence to back it.

What LCA actually measures

A residential LCA usually covers the modules defined under EN 15978 and ISO 14040. The product stage covers A1 to A3, which is raw material extraction, transport to factory and manufacture. The construction stage covers A4 transport to site and A5 installation. The use stage covers B1 to B7, including replacement and maintenance over a 50 year reference period. End of life sits at C1 to C4.

For a residential build the heavy lifting sits in A1 to A3. Structural materials, the slab, the frame, the roof and the cladding usually represent 60 per cent or more of the upfront emissions. The fit out matters but is smaller, and the use stage on a 7 star home is much smaller than the upfront stage on a per year basis.

Inputs come from environmental product declarations, or EPDs, which are third party verified statements that report carbon impact per declared unit of product. EPDs are voluntary today but are the basic input LCA software relies on.

Concrete, steel and timber

Three materials dominate the upfront footprint of a residential build.

Concrete

Concrete is the largest contributor on most slab on ground homes. Standard 25 to 32 MPa mixes sit around 250 to 350 kilograms of CO2 equivalent per cubic metre, driven by the Portland cement clinker. Supplementary cementitious materials such as fly ash and ground granulated blast furnace slag can cut that figure by 20 to 50 per cent.

Steel

Reinforcement, structural sections, roof sheeting and brickwork ties. Australian primary steel sits around 2.0 to 2.5 tonnes of CO2 equivalent per tonne of finished product. Steel made from electric arc furnaces using scrap input sits much lower, often near 0.5 to 0.7 tonnes per tonne.

Timber

Timber is the lowest impact major structural material on a per kilogram basis and stores biogenic carbon while it remains in the building. Plantation softwood for framing carries a small upfront footprint and a long storage period. Engineered products like LVL, CLT and glulam add manufacturing energy but allow longer spans and less concrete in the substructure.

Where the NCC is heading

NCC 2025 publishes embodied carbon provisions for residential as voluntary ABCB guidance rather than a mandatory clause. Building Ministers agreed in 2025 that the residential code would not carry mandatory provisions in this cycle.

Commercial buildings did get a voluntary pathway in NCC 2025 using the NABERS embodied carbon rating tool. For residential, the ABCB has been asked to investigate a minimum standard for NCC 2028. The materials industry is rolling out EPDs and lower clinker mixes ahead of that date because the lead time on a verified product declaration is long.

What a builder can do now

Four moves do not need to wait for NCC 2028. First, ask suppliers for EPDs on the largest line items, starting with concrete and steel. Second, specify a clinker replacement floor on concrete pours. Most ready mix suppliers will quote 25 to 30 per cent fly ash or slag without changing the structural design. Third, scope a basic upfront LCA on signature projects. The result becomes a marketing asset and a head start for the 2028 transition. Fourth, track the gap between any low carbon claim made in tender or marketing material and the evidence that supports it. Builders carry that risk under Australian Consumer Law.

How TradeLens uses this

TradeLens flags residential contracts that reference low carbon outcomes without EPD evidence, structural schedules that lock in high clinker concrete on signature builds and tender documents that promise an LCA result the build cannot deliver. It also tracks supplier EPD coverage across a builder portfolio against the NCC 2028 horizon.