Flood risk plans and extensions: what counts as an extension of an existing building

In areas covered by a flood risk prevention plan (PPRI), where the rules do not set the size of “extensions”, these must remain smaller than the existing building and be physically and functionally connected to it.

In a case in Versailles (a 105 m² extension to an existing 54 m²), the planning permission was annulled: this was a new building, not an extension.

This is consistent with case law and with the national planning glossary.