Swiss ISOS Reform 2026: What Changes for Property Projects

Switzerland has adopted its ISOS reform, with revised heritage and spatial-planning rules taking effect on 1 November 2026. The decision matters for property owners, developers and selected solar installations. It is not a blanket permission to demolish or build. OWNY.CH examines the adopted rules and the questions they raise for investment decisions.

Adopted, but not yet in force

On 18 September 2026, the Federal Council adopted amendments to the ISOS Ordinance (VISOS) and the Spatial Planning Ordinance (RPV). They take effect on 1 November 2026. This is no longer merely a consultation proposal. However, as of this article's information date, 26 September, the new provisions are not yet in force. The federal authorities plan to evaluate their practical effects by the end of 2028.

For a purchaser or developer, adoption and commencement are different milestones. A property acquired today does not come with a guaranteed permit because a regulatory announcement sounds favourable. The analysis below distinguishes the adopted provisions from OWNY.CH's practical interpretation for project planning and investment assessment.

Four changes to understand

First, the new exception concerns projects inside building zones where a federal task arises solely from a federal-law permit and the element assessed under that permit has no effect on the townscape. In that situation, the specified ISOS requirement for an assessment by a federal commission does not apply.

Second, Article 11 paragraph 3 VISOS expressly recognises that cantons and municipalities may depart from preservation objectives in their planning when other interests prevail following the required balancing exercise. Third, the definitions of preservation of substance, structure and character are clarified. Fourth, Article 32b RPV provides special treatment for certain solar installations built alongside new or replacement buildings. Each change has conditions; the word simplification is not a substitute for checking them.

An ISOS area is not simply a list of listed buildings

The Federal Office of Culture describes ISOS as a basis for balancing townscape protection with other public tasks. It covers approximately 1,200 townscapes. Relationships between buildings, open spaces and groups of structures matter, rather than only the significance of individual houses. Federal tasks and cantonal or municipal tasks engage different legal mechanisms.

A buyer should therefore avoid two shortcuts. An assurance that a house is not individually listed does not settle the ISOS question. Conversely, inclusion in an inventory does not by itself prove that every alteration is impossible. Ask for the relevant layers of planning and protection to be documented together for the parcel. That is more useful than relying on a brief verbal description in a sales conversation.

The practical example: a basement and groundwater permission

The explanatory report discusses below-ground elements requiring water-protection permission as an important example. The connection between the permitted element and the townscape is decisive. Other permit conditions remain applicable. The exception is limited to building zones, not construction outside them, and does not remove other federal-task triggers such as certain federal financial assistance.

Our practical interpretation is that project records should identify which element requires which permission and why that element does or does not affect the townscape. A basement parking level and its visible access ramp are not interchangeable concepts. Simply describing a development as underground cannot replace drawings or the competent authority's assessment. Early clarification can focus design work on the actual issue before substantial costs are committed.

Solar installations: building type and timing matter

The official explanations limit the special treatment to new and replacement buildings during construction. An alteration retaining substantial parts of a building is not automatically a new building. Solar installations must meet the relevant adaptation requirements, and cantonal permit reservations can still apply. The special treatment ends at formal acceptance by the authority; later replacement of an installation requires its own assessment.

OWNY.CH recommends bringing energy planning into the design process early. Coordinate the roof, facades, installation and submission route rather than treating solar equipment as a late addition. Ask whether notification is sufficient or a permit is required. Easier treatment of the installation does not authorise demolition of the previous building or approve the replacement building itself. Those decisions need their own legal and planning basis.

Why Zurich owners should pay attention

The City of Zurich states that ISOS preservation objectives cover approximately 75 per cent of its settlement area. It identifies development locations including Altstetten, Zurich West, Oerlikon and Schwamendingen where direct application can be relevant. This is area coverage, not the percentage of blocked applications or individually listed houses. The city information page still refers to consultation; we therefore rely on the newer federal documents for adoption and commencement.

For owners in Zurich, the reform is a reason to revisit specific development assumptions, not to mark up every property valuation. An extra floor, change of use or replacement building remains a project-specific proposition. When assessing potential rental income or resale proceeds, treat additional space as an assumption until the essential planning conditions are credibly documented. A location's general development appeal does not settle the feasibility of one scheme.

What this means for valuation and funding

In our assessment, a clearer procedural boundary may reduce uncertainty. The decision does not, however, provide a defensible universal figure for time savings or a nationwide property-price uplift. Effects will differ between projects. We therefore avoid inventing percentages for extra value, shorter procedures or additional homes resulting from the reform.

When buying with a development idea, separate the existing property's income from the development scenario. What works without alteration? Which costs arise before an authority decides? What reserves remain if the schedule slips? Our apartment-building purchase checklist sets out the documents relevant to due diligence. Our Zurich UBS bubble-index analysis also explains why an attractive location cannot replace a property-specific assessment. Together these questions create a more robust basis than pricing a building solely on hoped-for future permissions.

A working checklist before 1 November

The following is an editorial planning aid, not a permit prediction. For a particular project, planning specialists and, where appropriate, a construction-law adviser should review the records with the competent authority.

• Obtain the current ISOS record, preservation objectives, zoning plan and local or cantonal protection documents.
• List federal-law permissions separately and explain each element's relationship to the townscape.
• Compare retention, alteration and replacement options with their assumptions clearly identified.
• Plan solar installations alongside the building and check acceptance timing and cantonal requirements.
• For pending proceedings, clarify the applicable transitional rules and relevant decision date; do not let deadlines expire.
• Base price, budget and programme on documented conditions rather than a headline.

What remains uncertain – and our conclusion

The consultation record shows that broad support did not mean agreement on every detail. Solar boundaries, formal acceptance and pending proceedings were among the issues raised. A request made in a consultation response is not itself law. Nor does the adopted decision promise that an existing dispute will simply disappear.

OWNY.CH sees the reform as a targeted clarification of the procedural framework. Its economic opportunity lies in better project assessment and more realistic design alternatives. Successful infill development still needs a convincing proposal, reliable documentation and a reasoned balancing of interests. Greater clarity is valuable, but it is not the same thing as a guaranteed permit. Owners should use the coming weeks to improve their evidence, not to replace uncertainty with optimistic assumptions.

Frequently asked questions

Is the ISOS reform already in force?

No. It was adopted on 18 September 2026 and takes effect on 1 November 2026. This article reflects information available on 26 September 2026.

Can a building in an ISOS area now be demolished freely?

No. The decision creates no general entitlement to demolition, replacement development or extra floors. The project and other applicable protection and building rules remain decisive.

Will all solar installations be permit-free?

No. The special rule concerns certain installations constructed alongside new or replacement buildings. Conditions, timing and cantonal requirements must be checked.

Published by Matthias H. Römer · OWNY.CH