Background
#In Canton Aargau, the solar obligation is not a general retrofit requirement for every existing roof, but applies to new buildings with a total chargeable building area of more than 300 m².
For such building applications, a photovoltaic or solar thermal installation must be planned on the roof or facade. The cantonal energy ordinance requires a minimum solar area of 20 percent of the chargeable building area; the total building area of one building application is decisive, including relevant small buildings and extensions. Exemptions are narrowly defined and must be justified, for example where the installation would be inadmissible for townscape or landscape protection reasons, or where economic viability is not demonstrated by the cantonal calculator. Builders should therefore coordinate solar area, roof structures, facade options, energy proof and building submission early.
For your roof
New build: size the system right
For solar obligations what counts is output per area. With your address or postcode we size output, yield and cost for your new build.
Free and non-binding · no unsolicited calls
Rather talk directly? +41 78 615 90 58
What matters in the canton of Aargau
#The 300 m² threshold is the first determinant: new buildings are affected when the chargeable building area per building application totals more than 300 m². Not only main buildings matter, but also small buildings, extensions and parts of underground structures that project above the relevant terrain and are covered.
The minimum size is area-based: photovoltaic modules and glazed, selectively coated solar thermal absorbers must together reach at least 20 percent of the chargeable building area. Whether this area is implemented on the roof, facade or in combination is a planning question and should not be decided only after the energy proof.
Aargau does not treat technical impossibility as a simple standard exception. The fact sheet assumes that implementation is generally possible when roof and facade areas are considered; economic proportionality therefore becomes the central exemption argument.
Anyone claiming economic disproportionality must provide evidence using the cantonal calculation aid. Relevant factors include amortisation over 25 years or proof that the required energy yield cannot be achieved despite including permissible roof and facade variants.
Townscape and landscape protection can justify an exemption, but not automatically. An exemption is only possible where, based on specialist assessment, the installation is inadmissible in zones with elevated requirements; partial implementations or alternative facade solutions should therefore be considered early.
The solar obligation and the building-law notification procedure are separate topics. The obligation under § 26a EnergieV determines whether solar area must be planned; the solar notification form and permit question determine how the concrete installation is submitted procedurally.
The process in six steps
#Tick off for your project
Calculate building areas in the preliminary project
combine all buildings in one building application and check whether the chargeable building area exceeds 300 m². Splitting simultaneously constructed buildings into several applications should not be planned as an avoidance strategy.
Derive the minimum solar area
determine the 20 percent requirement from the chargeable building area and check whether roof, facade or a combination of PV and solar thermal can sensibly accommodate the area.
Coordinate roof and facade planning with the architecture
clarify roof structures, parapets, terraces, railings, access, fire protection, maintenance and shading early so the solar area does not later conflict with ventilation, technical equipment or design.
Bring energy proof and building submission together
the obligation to use solar energy belongs in the building project documents. Since April 2025, energy proofs in Aargau are submitted electronically via EVEN; PV planning should therefore be consistent with the proof documents.
Prepare exceptions only with evidence
obtain specialist assessment for protection conflicts; for economic viability use the cantonal calculator with the required standard values. Without traceable evidence, an exemption is not robust.
Clarify the procedure for the concrete installation separately
in addition to the solar obligation, check whether the planned roof or facade system is subject to notification or a full building permit. This affects timing, documents and the realistic installation start.
Checked for your roof, not just read up on
New build: size the system right
For solar obligations what counts is output per area. With your address or postcode we size output, yield and cost for your new build.
Free and non-binding · no unsolicited calls
Rather talk directly? +41 78 615 90 58
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.