Background
#For a PV green roof in Basel-Stadt, the green-roof duty, structural capacity and module racking on a flat roof must be planned as one coordinated concept.
For new builds and conversions, extensive greening is mandatory from 10 m² of roof area; the City Gardener generally requires at least 15 cm of substrate and 20 cm across one third of the area. A raised PV system can be combined with greening across the full area or, where that is not possible, split the theoretically greenable area into 40% greening and 60% photovoltaics.
For a roof with a low load capacity below 120 kg/m², the former lightweight solution is no longer accepted; the build-up needs a suitable alternative substrate or reduced layer thicknesses. In addition, notifiable flat-roof systems must meet the 1 m height limit and the setback for 45° visibility.
For your roof
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What roof and planning dictate
#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.
The process in six steps
#Tick off for your project
Classify the roof and project
first 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.
Document structural capacity
have 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.
Set the area strategy
in 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.
Coordinate substrate and planting with PV
for 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.
Check the notification or permit route
reconcile 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.
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.
Checked for your roof, not just read up on
What does a system on your roof cost?
With your address we calculate price range, incentives and payback for your roof from federal data. We email the report straight away.
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.