Swiss Federal Supreme Court clarifies
the calculation of primary and secondary
usable areas under the Second Homes Act
("Lex Weber")

On 11 August 2026, the Swiss Federal Supreme Court handed down a decision in cases 1C_317/2025 and 1C_319/2025, ruling for the first time that wellness and leisure facilities – including fitness rooms, saunas, indoor pools with Jacuzzis, and game rooms – qualify as main usable surfaces (MUS) under Art. 11 para. 2 of the Swiss Second Homes Act (SHA; "Lex Weber"). This decision clarifies a long-disputed question and has significant practical implications for property owners and developers in Swiss mountain resorts.

Background

Under Art. 11 para. 2 SHA, dwellings created under the former law (i.e. lawfully existing or approved before 11 March 2012) may be renovated, converted or even demolished and rebuilt without use restrictions, but the main usable surface may only be increased by a maximum of 30% of the MUS existing on 11 March 2012. The SHA refers to the SIA 416 standard for the definition of MUS, distinguishing it from secondary usable surfaces (SUS) such as laundry rooms, cellars, garages and civil protection shelters. Until this ruling, no Federal Supreme Court decision had addressed whether wellness and leisure facilities fell within the MUS or SUS category under the SHA, leading to diverging views among scholars, cantonal authorities and the Federal Office for Spatial Development (ARE).

Facts

The case concerned a chalet in Val de Bagnes (Valais) comprising two dwellings created under the former law. The construction project included extensive wellness and leisure areas on the ground floor – a changing room, shower area, wellness space with indoor pool and Jacuzzi, a sauna, and fitness room – as well as a game room at basement level. These spaces covered over 100 m², featured large windows opening onto a terrace of approximately 50 m², and were shared between both dwellings. The Cantonal Court annulled the building permit, finding that these spaces constituted MUS and that the projected total MUS of 340.36 m² far exceeded the permitted maximum of 258.80 m² (199.08 m² + 30%).

Federal Supreme Court Analysis and Practical Implications

• Wellness and leisure facilities qualify as MUS subject to the 30% cap. The Federal Supreme Court confirmed that fitness rooms, saunas, indoor pools with Jacuzzis, and game rooms cannot be equated with the ancillary premises typically classified as SUS under the SIA 416 standard (laundry rooms, cellars, garages, storage rooms, civil protection shelters, waste disposal rooms), which are not intended for prolonged occupation by persons. The Court relied on Annex A to SIA Standard 416/1:2007, which expressly lists "recreation rooms" and "communal rooms" under the MUS category of "dwelling and living," as well as on the commentary to the Intercantonal Agreement on the Harmonization of Building Terminology (IVHB), which classifies premises "intended for leisure activities" as MUS. Accordingly, any such facility intended for prolonged use must henceforth be counted toward the 30% extension cap, significantly curtailing the scope for luxury amenities in renovated or rebuilt chalets.

• Shared facilities do not provide a means of circumvention. The fact that the wellness and leisure facilities were shared between the chalet's two dwellings was held to be immaterial. Having regard to the objectives of the SHA – to limit second homes and the surface they occupy, in implementation of the constitutional mandate for the protection of nature and the landscape (Art. 75b Federal Constitution) – shared recreational facilities must be included in the MUS calculation. Developers may not, therefore, structure such facilities as common or shared areas in order to exclude them from the cap.

• A uniform federal standard prevails, displacing divergent scholarship and cantonal practice. The Federal Supreme Court expressly departed from the view of Professor Zufferey (Droit public de la construction, 2024), who had classified indoor pools, saunas and steam rooms as SUS not subject to the 30% cap. It further held that a divergent practice of the Graubünden authorities (in particular, the Administrative Court's decision R 15 18 of 2015, rendered prior to the entry into force of the SHA) was not binding upon it. The SIA 416 standard must henceforth be interpreted uniformly across all cantons, and developers should no longer rely on local precedents classifying such facilities as SUS.

• The 2024 legislative amendment does not alter the analysis. While the amendment to Art. 11 SHA that entered into force on 1 October 2024 extended the possibility of demolishing and rebuilding dwellings created under the former law with an increase of up to 30% of the pre-existing MUS, it did not modify the 30% cap itself or the definition of MUS. The Federal Supreme Court rejected the appellants' argument that this legislative relaxation warranted a different assessment.

Property owners with ongoing renovation projects involving wellness facilities should reassess their MUS calculations without delay following this decision.

For the French version, see here: Le Tribunal fédéral clarifie le calcul des surfaces utiles principales et secondaires au sens de la loi sur les résidences secondaires (Lex Weber)