New rainwater ordinance 2023

New rainwater ordinance 2023

For whom?

The main changes

1. Mandatory rainwater collection tank and increased capacity Rainwater pits are always mandatory for new construction, reconstruction, or expansion, or when renovating an existing building with drainage works (except when the cadastral plots belonging to a single property are collectively smaller than 120m²).

   How big should the rainwater harvesting tank be?

   • Roof surface <80 m²: min. 5,000 l
   • Roof area 80 – 120 m²: min. 7,500 l
   • Roof area 120–200 m²: at least 10,000 liters
   • Roof surface >200 m²: min. 100 l/m², unless the application shows that the potential uses are disproportionate to the specified volume
   • Multiple residential units: at least 100 l/m²; for each 5,000-liter increment exceeded, at least one residential unit must be connected.
   • Buildings other than dwellings: min. 100 l/m², unless it appears from the application that the potential uses are disproportionate to the established volume.

2. Expansion of the infiltration area and volume: The infiltration area must be 8% of the total draining area. The infiltration volume must be equal to 33l/m² of the draining area.
3. Application The collected rainwater must be used to the maximum extent for applications that do not require drinking water quality, including toilet flushing, cleaning water, washing machines, and outdoor use.
4. Increase of buffer volume drainage area The buffer volume for large paved areas is increased when, for technical reasons, an infiltration system cannot be installed. The total drainage area is determined by the sum of various elements:
   • Paved surfaces: New construction/reconstruction/expansion (except for permeable pavements with a slope of <2%).
   • Roof Area

   If a rainwater pit and/or green roof is present, these can be subtracted from the draining surface:

   • Rainwater cistern: deduction of 30 m² per connected residential unit.
   • Green roof: for green roofs, connection to a rainwater tank is not mandatory. If you do connect to a rainwater tank and the green roof has a buffering capacity of at least 50 l/m², the area of the green roof may be halved when calculating the draining surface area for the infiltration facility.

5. Construction of the infiltration facility The infiltration facility must be constructed above ground, unless the permit applicant demonstrates with reasons that underground construction is unavoidable. Up to a depth of 50 cm, the soil is considered to be located above the average highest groundwater table. If the depth is > 50 cm and the draining surface is > 1,000 m², additional tests will be required. Furthermore, it should be noted that the emergency overflow is located at a depth of less than 30 cm below ground level.
6. Collective infiltration facilities The possibility of collectively assuming obligations regarding rainwater is being introduced.

Eleven solutions

Do you also have questions about the new regional rainwater ordinance 2023?

Which rainwater cistern do we need to place [it], when is [it] infiltration or buffering necessary? At Deschacht we know all about it, our people are already fully up to speed. Don't sit with your questions and contact us for a solution tailored to your project!