“Net zero” appears on a growing share of architecture-firm websites, developer brochures, and corporate sustainability reports. The phrase suggests a building that puts back as much as it takes out — a clean ledger. The reality is that “net zero” can mean four or five different things depending on who’s using it, and most of them aren’t the version the brochure implies.
This is the short decoder.
Net zero what, exactly
The phrase needs a noun. There are three main ones:
Net zero energy. The building produces, over a year, as much energy on site as it consumes. Usually achieved with rooftop solar plus a very efficient envelope. Doesn’t address embodied carbon.
Net zero carbon — operational. The building’s operational emissions over a year — heating, cooling, hot water, plug load — net to zero. Onsite generation, electricity from a clean grid, and offsets all count.
Net zero carbon — whole life. Operational emissions plus the embodied carbon of the construction materials and the eventual demolition. The hardest version, and the one most aligned with what climate science actually requires.
When someone says a building is “net zero,” the right next question is: which definition?. The answer matters significantly.
The offset problem
Most “net zero” claims in the construction industry rely partly or wholly on carbon offsets — the purchase of certificates that represent emissions reductions or carbon sequestration elsewhere, used to balance the building’s own emissions on paper.
The offset market has a credibility problem. Multiple investigations — including detailed analyses by The Guardian and academic work in Science and Nature — have documented that a substantial fraction of the offsets in the voluntary market represent reductions that didn’t happen, weren’t additional, or weren’t permanent.
The reasonable position, supported by groups like the Science Based Targets initiative and the UN Race to Zero: cut your own emissions as much as possible first, then only use high-quality offsets — ideally permanent carbon removal rather than avoided-emissions credits — for the residual.
A “net zero” building that’s 80% operational emissions plus 20% verified carbon removal is meaningfully different from a building that’s 20% reduction plus 80% cheap forest-protection certificates of doubtful permanence.
What the credible standards require
The honest definition, as set out by the World Green Building Council:
- Highly energy-efficient envelope and systems — reduce demand before generating
- Powered entirely by renewable energy — onsite where possible, contracted clean grid where not
- Embodied carbon measured, disclosed, and reduced — from extraction through demolition
- Any residual emissions offset only with credible removal credits, not avoided-emissions credits
A building that meets all four points is genuinely net zero whole-life carbon. A building that only meets the first three but uses unmeasured high-embodied-carbon concrete construction is net zero operationally and not whole-life.
The operational-vs-embodied shift
For most of the last two decades, building sustainability focused on operational carbon. As envelopes have gotten more efficient and grids have decarbonised, the operational share of a building’s lifetime emissions has shrunk. Embodied carbon — the carbon released during manufacturing, transport, and construction — has become a larger share of the total.
In 2026, embodied carbon is roughly 50% or more of the whole-life emissions of a new building. A net-zero-operational building that’s built from high-carbon materials is, increasingly, an incomplete answer.
This is why this Journal keeps returning to embodied carbon in material choices — see the carbon inside a square meter of floor, on reclaimed wood, on cork. The materials are most of where the emissions live.
How to read a net-zero claim
When you next see a project marketed as “net zero,” the three questions to ask:
- Net zero of what? Energy, operational carbon, or whole-life carbon
- Verified by whom? A self-declaration, or an external standard with audited methodology
- Offsets — what share, and what kind? A small share of high-quality removals, or a large share of cheap avoided-emissions credits
The answers don’t need to be perfect — the standards are evolving, and a project that’s most-but-not-all-of-the-way there is meaningfully better than a project that isn’t trying. But the answers should exist. A “net zero” project whose team can’t answer those three questions is selling a feeling.