Background
#A Switzerland-wide solar obligation exists only for new buildings with more than 300 m² chargeable building area: they need a solar system on the roof or facade (Art. 45a EnG).
Federal law sets no obligation for existing houses. Cantons may go further – Bern requires solar systems on all new buildings, and Lucerne, Thurgau, Schaffhausen and Valais also on roof renovations. What applies to your building is therefore decided by the canton.
What roof and planning dictate
#Federal law: when constructing new buildings with a chargeable building area of more than 300 m², a solar system such as a photovoltaic or solar thermal system must be installed on the roofs or facades (Art. 45a para. 1 EnG, in force without time limit since 1 January 2025). Cantons may extend the obligation to smaller buildings and set the exemptions – for example when a system is technically impossible, economically disproportionate or conflicts with other regulations.
Cantons that had already introduced rules on on-site generation for new buildings under the MuKEn 2014 model regulations by 1 January 2023 are exempt from the federal rule (Art. 45a para. 4 EnG). Cantonal law applies there – in Canton Zurich, for example, at least 10 watts per m² of energy reference area, with PV coverage of at most 70% of the chargeable building area required (§ 10c EnerG, § 47b BBV I).
Bern goes furthest: all new permanent buildings and extensions must be fitted with solar systems, suitable roof areas as completely as possible; roof areas below 50 m² are exempt, and owners whose solar costs exceed 5% of the other construction costs are released (Art. 39a KEnG). A comprehensive roof renewal triggers a reporting duty, and new public, managed car parks with 80 or more spaces need solar canopies (Art. 39d and 39e KEnG).
Duty on roof renovation: Lucerne requires half of the new-build requirement or a replacement levy of CHF 1,000 per kW not installed when a roof is re-covered or re-sealed (§ 15 para. 1bis KEnG, §§ 13–14 KEnV). Thurgau requires the solar potential of suitable roof areas to be used in a comprehensive roof renovation (§ 4c ENV), and Schaffhausen at least 30 W per m² of energy reference area when the roof skin of buildings from 300 m² chargeable building area is comprehensively renovated (§ 26h EnerV). In Valais, a building with a new roof covering must generate part of its electricity or heat itself (Art. 43 kEnG), and in Geneva suitable areas must be fitted with a solar system during roof renovations (Art. 14A LEn).
Aargau applies the federal solution: new buildings with more than 300 m² chargeable building area need a photovoltaic or solar thermal system whose module or collector area amounts to at least 20% of the chargeable building area (§ 26a EnergieV). In Canton Zurich, the government proposed on 6 January 2026 that suitable roofs over 300 m² be fully covered and existing buildings retrofitted during roof renovations – this is a bill before the cantonal parliament, not yet law.
Outlook: the new MuKEn 2025 model regulations of the cantonal energy directors recommend at least 20 W per m² of energy reference area for new buildings and an obligation on roof renovations affecting at least 50 m², with at least 10 W per m². They are a recommendation to the cantons with implementation targeted by 2030, not directly applicable law.
The process in four steps
#Tick off for your project
Classify the project
new build, extension or roof renovation? For new builds, the chargeable building area counts (federal: more than 300 m²); for roof renovations, the cantonal definition, such as a new covering or sealing.
Check the cantonal rule
your canton’s energy act and ordinance or the energy office provide information on minimum capacity, exemptions and any replacement levy. The cantonal guides on this site summarise the details.
Assess the roof early
suitability (for example via sonnendach.ch), structure and orientation determine whether the obligation can be met sensibly or an exemption can be requested. The earlier this is clear, the more cheaply the system fits into the roof planning.
Provide proof in the procedure
compliance with the solar obligation is usually documented by form in the building permit or notification procedure. Plan size, layout and any exemption justification before filing.
Checked for your roof, not just read up on
Once the framing is clear, a property-specific check with roof, grid and documentation is worthwhile.
Frequently asked questions
#Sources
#The responsible authorities are decisive. Always verify binding details – amounts, deadlines and conditions – for your specific property against the current status of the respective authority.