A flood risk assessment for your London extension, £359 fixed
If your house is in Flood Zone 2 or 3, the council expects one with your application. We prepare the report: the flood level, the floor heights and what you are doing to keep water out. £359.
- £359 fixed, no survey fee
- Levels and resilience set out
- Free redraws until approval
What does a flood risk assessment cost?
The fee is £359, with no survey fee and no VAT to add. It is the assessment for a minor householder scheme, such as an extension under 250 m² in a flood zone. Larger or more complex sites, and any scheme that needs a sequential test, are quoted before we start.
This report is written up in full on our sister site fixedfeeplans.co.uk. Our fixed fee below still applies if you order through us. Read it on fixedfeeplans.co.uk.
What the £359 covers
- The flood zone and the flood sources for your address, checked against the national map
- The estimated flood level and your proposed finished floor level, given to Ordnance Datum
- The resistance and resilience measures for the extension, with a short explanation
- How surface water and groundwater will be managed, in the words the council expects
- The report, ready to submit with the planning application, and answers to the officer’s questions
Is my house in a flood zone?
The Environment Agency’s flood map for planning shows river and sea flooding in three zones. Zone 1 is low probability, under 1 in 1,000 a year. Zone 2 is 1 in 1,000 to 1 in 100, and Zone 3 is 1 in 100 or greater (planning guidance).
A zone is not a refusal. It is a requirement to show the council you have thought about it. For a minor extension that is a short, specific report.
What the standing advice asks
For a minor extension in Zone 2 or 3, the government’s standing advice asks for floor levels at least 600 mm above the estimated flood level, and flood-resistant materials to the same height (standing advice). With a high level of certainty about the flood level, 300 mm may do. If you cannot raise the floor, the report sets out extra resistance and resilience measures to protect to 600 mm.
The report also gives levels relative to Ordnance Datum, and says how surface water and groundwater are dealt with. We prepare all of that from your survey and the flood data.
- Floor level against estimated flood level
- Materials and details below the flood line
- Surface water and groundwater routes
- Any consent for work near a main river
Where it fits in your application
The assessment goes in with the planning drawings, so build the two together: planning drawings for the design, and a constraints report if you want to check the zone first. If the work is a basement, the flood issues are bigger, and we say at the quote whether the standard report is enough (basement drawings).
When an assessment is required
- Zone 2 or 3
- A flood risk assessment is needed for development, including minor development and changes of use, in Flood Zone 2 or 3. gov.uk, Flood risk assessment for planning applications
- 1 hectare
- In Flood Zone 1 an assessment is needed on a site of 1 hectare or more. gov.uk, Flood risk assessment for planning applications
- Surface water
- It is also needed in Flood Zone 1 where the site is at risk of surface water flooding now or in future. gov.uk, Flood risk assessment for planning applications
- 250 m²
- A minor extension is a householder or non-domestic extension with a floor space of no more than 250 m². gov.uk, Flood risk assessment: standing advice
- 600 mm
- The recommended minimum is for floor levels at least 600 mm above the estimated flood level, with flood-resistant materials to the same height. gov.uk, Flood risk assessment: standing advice
- 300 mm
- This can be reduced to 300 mm where there is a high level of certainty about the estimated flood level. gov.uk, Flood risk assessment: standing advice
- 20 m
- Works within 20 m of a main river may need a separate permit or consent. gov.uk, Flood risk assessment: standing advice
Flood risk questions
Do I need a flood risk assessment for an extension?
If the house is in Flood Zone 2 or 3, yes, including for minor development. In Zone 1 only for larger sites or where surface water is a risk.
Source: gov.uk, Flood risk assessment for planning applications
How high must the floor be?
The standing advice recommends at least 600 mm above the estimated flood level, or 300 mm where the level is certain.
What if I cannot raise the floor?
Then the report sets out extra flood resistance and resilience measures that protect to at least 600 mm above the estimated level.
Does £359 cover a large extension?
It covers a minor householder scheme, which the guidance defines as no more than 250 m². Larger schemes are quoted before we start.
Will the Environment Agency object?
For a minor extension that follows the standing advice, the advice is the Agency’s own guidance. We cannot promise any consultee’s reply.
Other services people book with this one
In a flood zone? Get the report in with the application
Send the address and the extension size. We reply with a fixed fee.