Short answer
Must I green a flat roof with PV in Basel-Stadt?
In Basel-Stadt, a PV system on a green flat roof is permitted, but must satisfy greening, structural and building-law requirements at the same time. From 10 m², new builds and conversions are subject to the greening duty; for PV planning, the decisive points are 15 cm of substrate, the 40/60 alternative and, for notifiable systems, the 1 m height and 45° setback.
Important
As of July 2026, the 40/60 split is not a freely selectable optimisation model: according to Basel’s guidance, it is the alternative where a full-area combination of greening and raised PV is not possible. Whether structural capacity, drainage, fire safety and maintenance routes allow the specific layout must be assessed separately for each roof.
At a glance
Key figures: PV green roofs Basel-Stadt
| Metric | Value |
|---|---|
| Greening duty | from 10 m² for new builds and conversions |
| Standard substrate | at least 15 cm, with at least 20 cm on 1/3 |
| Area alternative | 40% greening / 60% PV |
| Low structural capacity | below 120 kg/m²: special build-up required |
| Notifiable flat roof | maximum 1 m height and 45° setback |
Decision points
What determines the right path.
The greening duty sets the framework first. Under section 72 BPG and section 9 NLG, flat roofs in new builds and conversions from 10 m² must be extensively greened; PV layout must therefore not start from an area incorrectly assumed to be free.
Substrate depth drives build-up height and load. Basel-Stadt generally requires a 15 cm compacted vegetation layer and at least 20 cm across one third of the area; these values belong in the structural preliminary assessment before racking is selected.
There are two clearly defined area logics for PV and greening. The City Gardener accepts a full-area combination with raised panels or, where that is not possible, a split of 40% greening and 60% photovoltaics across the theoretically greenable area.
The area below and in front of modules needs its own layer logic. For the combined option, the guidance specifies 15 cm of substrate between panels and 7 cm in a 40 cm strip in front of them, so that plant choice, maintenance and shading work together.
Low load capacity is not a detail to address after the quote. Below 120 kg/m², the former “Basler Dachsubstrat leicht” is no longer permitted; the City Gardener requires adapted substrate with reduced layer thicknesses or a suitable alternative substrate.
The building-law layout runs alongside roof planning. For a notifiable flat-roof PV system, the top edge may rise no more than 1 m above the roof edge and must be set back so it is not visible from below at 45°; protected zones or listed buildings require a building permit.
Sequence
How the project stays cleanly managed.
- 1
Classify the roof and projectfirst establish whether it is a new build or conversion and whether the flat-roof area is at least 10 m². This determines whether Basel’s greening duty is part of the project scope.
- 2
Document structural capacityhave the roof build-up, existing load reserves and capacity in kg/m² assessed by the responsible specialist before the PV layout. Below 120 kg/m², do not specify the superseded lightweight option.
- 3
Set the area strategyin the preliminary design, draw either the full-area combination with raised panels or the 40/60 split. Technical areas, drainage, escape routes and maintenance paths must not be squeezed between modules later.
- 4
Coordinate substrate and planting with PVfor the combined option, include the 15 cm between panels and 7 cm in the 40 cm strip in front of them in the build-up. The City Gardener requires low-growing native plant species, not a pure sedum planting.
- 5
Check the notification or permit routereconcile the PV drawing with the 1 m height limit, 45° setback and low-reflection construction. If the building is in a protected zone or listed, schedule the building application before execution.
- 6
Coordinate renovation and incentives only where there is a genuine combined project: if the roof is being energy-refurbished, the Action Solar Power Plant Basel grant application must be filed before construction starts. For roof areas, the action requires 90% of the good and best solar-cadastre suitability or the technically feasible PV potential.
Checklist
Questions to settle before the quote.
- From 10 m² of roof area, check whether an extensive green roof is mandatory for a new build or conversion
- Clarify load capacity before assigning modules: below 120 kg/m², the substrate build-up is subject to special requirements
- Show clearly in the layout whether green roof and PV are combined across the full area or separated at a 40/60 ratio
- For flat-roof PV, check the 1 m height and 45° setback before the notification procedure
FAQ
More questions: PV green roofs Basel-Stadt
Sources
Official sources & references.
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.
- Promoting urban nature: green roofs and photovoltaicsCanton Basel-Stadt, City Gardener
- Green flat roofs: updated checklist, April 2026Canton Basel-Stadt, City Gardener
- Solar installations: notification and permit requirementsCanton Basel-Stadt, Building and Hospitality Inspectorate
- Action Solar Power Plant BaselCanton Basel-Stadt, Office for Environment and Energy