Building in the Thames Floodplain

A staggering percentage of the high-value residential real estate in the London Borough of Richmond upon Thames is situated directly within the Thames floodplain, heavily concentrating in areas such as Kew, Mortlake, Barnes, and Twickenham. Developing property in these zones—whether executing a massive ground-floor rear extension, digging a basement, or constructing an entirely new riverside dwelling—is subjected to the absolute, unforgiving authority of the Environment Agency.

In standard boroughs, the local council holds ultimate planning power. In Richmond’s Flood Zones 2 and 3, the council is legally subservient to the Environment Agency's dictates. If the EA issues a statutory objection against your architectural proposal, Richmond planners cannot override them. The application is dead upon receipt.

The Sequential and Exception Tests

For any major development creating new, self-contained dwellings within high-risk flood zones, the applicant must pass the grueling Sequential Test. This dictates that you must mathematically prove there are no alternative, safer sites within the entire borough where the development could be located instead. For individual homeowners extending existing properties, the focus shifts to the Exception Test.

The Exception Test demands irrefutable architectural proof that the development provides wider sustainability benefits to the community that outweigh the inherent flood risk. More critically, it demands a site-specific Flood Risk Assessment (FRA) proving the development is safe for its lifetime (calculated at 100 years, factoring in severe climate change allowances) without amplifying flood risk elsewhere along the river.

Safe Egress and Finished Floor Levels

Architectural floorplans in riverside Richmond are dictated by the "Finished Floor Level" (FFL). The EA mandates that the FFL of any new habitable extension must be set a minimum of 300mm above the modeled 1-in-100-year flood event plus climate change. This frequently forces extensions to be built on elevated, stepped plinths, which subsequently triggers massive planning friction with the council regarding excessive height and overshadowing of neighbours.

Furthermore, the design must legally guarantee a "safe route of egress." Occupants must be able to entirely evacuate the property above the predicted flood level and reach safe ground outside the flood warning zone. If the route to the public highway dips below the flood line, the application fails.

Official Richmond upon Thames Council Resources

Before committing to any major architectural project, we strongly advise cross-referencing your ambition directly with the local authority. The following links provide direct access to Richmond upon Thames Council's live planning portals and heritage registries:

• Richmond upon Thames Planning & Building Control Portal
• Search Live Richmond upon Thames Planning Applications
• Richmond upon Thames Heritage, Conservation Areas & Article 4 Directions

How We Can Help

If you are considering a major refurbishment, extension or basement in Richmond upon Thames, our in-house architectural and construction teams are highly experienced with the specific constraints and policies of this council. Do not leave your planning application to chance—our Planning & Permissions and Architecture services are explicitly designed to handle strict London authorities from initial conceptual design through to final, legal consent.

Once permission is secured, our Refurbishment & Interiors division carefully manages the execution, guaranteeing the design integrity is maintained throughout the build phase.

*Published in the Hampstead Renovations Planning Guide Collection — delivering expert design and build strategies for London's most heavily guarded conservation boroughs.*