In Switzerland, “CO2-neutral living” is no longer a slogan. It is a claim you must be able to prove.

Picture this: a developer presents twelve luxury apartments on the shore of Lake Geneva on its website. On the home page, in large letters: “CO2-neutral living”. The heat pump and the solar panels are real. So are the concrete, the steel and the glass of the façade, whose emissions were produced on the building site before anyone moved in. The rest is offset with certificates bought from a private provider. Nobody at the developer has lied. But nobody could prove the sentence either.

In Switzerland, since 1 January 2025, anyone making a claim about the climate has to be able to prove it. And in 2026 the Federal Office for the Environment, FOEN, explained what it means by proof. For a property website, that changes more than it seems.

What the law says.

While debating the CO2 Act for the period after 2024, adopted on 15 March 2024, Parliament added a letter x to Article 3(1) of the Federal Act on Unfair Competition. Since 1 January 2025, anyone who makes claims about themselves, their goods, works or services relating to the climate impact they cause, where those claims cannot be substantiated on an objective and verifiable basis, acts unfairly. The same act, in Article 23, makes intentional unfair competition punishable, on complaint, by up to three years’ imprisonment or a monetary penalty.

Letter x is about the climate. Other green words, such as “eco-friendly” or “sustainable”, are not exempt: they remain subject to the general ban on false or misleading claims, and the Swiss Commission for Fairness in Advertising, which only issues recommendations, expects solid evidence for them.

What the FOEN guidance says.

The implementation guide UV-2561, dated January 2026, makes several things clear. The law reverses the burden of proof: whoever makes the claim must be able to substantiate it in a dispute. There is no obligation to have it audited beforehand, but the company carries the risk of having no proof. And the information needed to understand the claim must be easy to find and right next to it; the detail can sit behind a link or a QR code.

On offsetting, the guidance is categorical. Climate claims about a product, and services count as products, cannot rely on offsets. According to the guidance, “climate neutral” cannot currently be proven, because it covers effects beyond CO2 and other greenhouse gases. “CO2 neutral” is effectively ruled out for products. “Net zero” denotes a future target, which must be presented as such and be backed by a reduction pathway consistent with Swiss targets and an accessible roadmap. And certificates under private standards that do not meet certain requirements only support a contribution claim, not the netting of tonnes.

The guidance mentions buildings explicitly. It refers to the cantonal building energy certificate GEAK, to the cantons’ model energy regulations and to Minergie for net-zero buildings. And it notes that FOEN offers a CO2 calculator for property portfolios that covers emissions from heating and hot water and from electricity and district heating, and gives a first estimate of those from building materials.

What I do not know.

The guidance is not law: it guides authorities and businesses, and in a dispute a court decides. I have not found any published judgment applying letter x. I do not know whether a court will treat an apartment for sale as a product, or the home-page sentence as a claim about the company, and the guidance says this is decided case by case. I am not a lawyer. What your development may claim, and on what evidence, is a question for your legal counsel.

The blind spot: the sentence is not only on the home page.

A climate claim turns up in places nobody reviews together: the sales brochure in PDF, the listings on property portals, the project name, the captions on the renderings, the sales team’s presentation and what the agent says on the viewing. The guidance adds that a label can also be a climate claim. And there is the qualifier that is missing: “CO2 neutral in operation” and “CO2 neutral” do not say the same thing, because the construction emissions have already happened. If the qualification is not next to the sentence, in every language on the site, the sentence misleads even if nobody intends it to.

If you cannot show the calculation, do not write the sentence.

Where I stand.

I believe a luxury development needs no general green words at all. People buying a home worth several million read, compare and ask. A certificate with its number, the GEAK class, the expected consumption per square metre or exactly what the heat pump covers are more convincing than a drawn leaf, and they can be proven. I would put those figures on each apartment’s page, next to the claim they support, with a link to the detail. If the proof is not next to the sentence, the sentence has to go.

What I would check.

• Every word about the climate. On the website, in the PDFs, on the portals, on site hoardings and in presentations, in every language.
• The proof behind each one. Which calculation or certificate supports it, who holds it and whether it is up to date.
• Offsetting. Whether any claim about an apartment or a service relies on purchased certificates.
• Net zero. Whether the company presents it as a target, whether it names the year and whether the roadmap is public.
• Proximity. Whether the explanation sits next to the claim, not three clicks away.

Where to start.

1. This week

   Make the list

   Every climate claim on the website, in brochures and on portals, with its page and language.

2. This month

   Gather the proof

   Certificates, calculations and their dates, and remove whatever cannot be supported.

3. This quarter

   Rewrite with figures

   With your legal counsel: precise sentences, with their scope and the link to the detail beside them.

4. Before every launch

   Check again

   The new brochure, the new listing and the new website go through the same list.

Choose the sentence about climate you like most on your website. Now imagine a buyer copies it, forwards it to their adviser and asks: “Can this be proven?”

How long would it take you to send the proof? Do you have it in the same language you make the promise in? And a doubt to leave open: what weighs more in a luxury development, a modest figure that is well proven or a beautiful sentence that cannot survive a simple question?

If you would like me to review what your website claims about climate today, with what evidence and where it shows it, start with the Strategic Diagnostic. What your development may claim is for your legal advisers to decide, not a designer.