Guidance

Preparing a flood risk assessment: standing advice

Find out if you need to follow standing advice when completing a flood risk assessment and what to do.

From:
Environment Agency
Published
1 April 2012
Last updated
23 August 2024 — See all updates

Applies to England

Local planning authorities (LPAs) should use flood risk standing advice for local planning authorities to check when to consult the Environment Agency or use standing advice.

Planning applicants should start by referring to flood risk assessments if you’re applying for planning permission, to check that this standing advice applies to their development.

Planning applicants and LPAs should use this guide to make sure flood risk assessments (FRAs):

  • contain the correct information
  • follow the standing advice

If your site is in flood zone 1 but will be at increased risk of flooding from rivers or the sea during the development lifetime, you should:

  • complete a flood risk assessment (FRA)
  • apply this guidance as if the site were in flood zone 2

Check if your site will be at increased risk of flooding from rivers or sea in future. Do this by referring to the LPA’s strategic flood risk assessment (SFRA).

When to follow standing advice

Follow standing advice for vulnerable developments for developments (including change of use) in flood zone 2 that have a vulnerability classification of:

  • ‘more vulnerable’ - except for landfills, waste facility sites, caravan or camping sites where the Environment Agency should be consulted
  • ‘less vulnerable’ - except for waste treatment sites, mineral processing sites, water treatment plants and sewage treatment plants where the Environment Agency should be consulted
  • ‘water compatible’

You should use the advice for minor extensions to complete an assessment for a minor extension in flood zone 2 or 3. A minor extension is a householder or non-domestic extension with a floor space of no more than 250 square metres.

Also follow local flood risk standing advice for development (including change of use) if your site is in an area with critical drainage problems. These are currently only designated in Devon and Cornwall. Contact the LPA for a copy of the local standing advice.

If your development is not covered by the standing advice in this guide:

LPAs should also consult the Environment Agency as set out in the flood risk assessments: standing advice for local planning authorities guidance.

Advice for minor extensions

For all relevant minor extensions (see When to follow standing advice), you should follow the standing advice for: 

  • what to include in your FRA 
  • floor levels 
  • extra flood resistance and resilience measures 
  • other permissions or consents

What to include in your FRA

Your FRA should be: 

  • appropriate to the scale, nature and location of the development 
  • proportionate to the degree of flood risk 

It should contain the information set out in the site-specific flood risk assessment check-list.  

For all development covered by this standing advice, your FRA should include: 

  • your site address 
  • a description of your development 
  • the estimated flood level for your development, taking into account the impacts of climate change over its lifetime 
  • details of the finished floor levels 
  • details of your flood resistance and resilience plans 
  • any supporting plans and drawings 
  • any other information the relevant standing advice tells you to include 

The estimated flood level is the depth of flooding anticipated on your development site.

For a river flood, this is a 1 in 100 annual probability event plus an allowance for climate change. For a tidal flood, this is a 1 in 200 annual probability event plus an allowance for climate change.

You may be able to get the estimated flood level and information about residual risks from the Environment Agency’s Flood Map for Planning. If not, you will need a flood risk specialist to calculate this for you. 

You should state all levels in your assessment in relation to Ordnance Datum (the height above average sea level). You may be able to get this information from the Ordnance Survey. If not, you will need to get a land survey carried out by a qualified surveyor.

Check with the LPA to see if your minor extension is in an area with increased flood risk because of multiple minor extensions. If it is, you need to include an assessment of the off-site flood risk. 

Check table 2 of the planning practice guidance if your proposed minor extension is in flood zone 3b (functional floodplain). It states that development should not be permitted in flood zone 3b if its vulnerability classification is: 

  • ‘highly vulnerable’ 
  • ‘more vulnerable’ 
  • ‘less vulnerable’

Floor levels

We recommend floor levels are set at least 600 millimetres (mm) above the estimated flood level. You will also need to use flood resistant materials up to at least 600mm above the estimated flood level. 

You may be able to reduce this to 300mm if there is a high level of certainty about your estimated flood level. If there is a particularly high level of uncertainty it may need to be increased. 

Flood water can put pressure on buildings, causing structural issues. If your design aims to keep out a depth of more than 600mm of water, you should get advice from a structural engineer. 

If you cannot raise the floor levels in this way, you will also need to include extra flood resistance and resilience measures. These measures should protect the property to at least 600mm above the estimated flood level. 

Your plans also need to show how you are going to make sure the development is not flooded by surface water or groundwater.

This could be by: 

  • diverting water away from buildings but safely managing it within the site
  • raising floor levels above the estimated flood depths of surface and groundwater flooding

Extra flood resistance and resilience measures

Follow the guidance in this section where you cannot raise the finished floor levels to the required height. Your building design should:

  • prioritise excluding flood water where possible
  • speed recovery in case water gets in

Make sure your flood resilience plans follow the guidance in the Construction Industry Research and Information Association (CIRIA) Code of Practice for Property Flood Resilience. 

Standards are available for: 

Other permissions or consents

You may need a separate permit or consent if the development or any associated works such as site preparation or construction: 

  • is within 20 metres of a main river (including culverted main rivers), a flood defence or flow control structure 
  • directly affect a watercourse that is not a main river 
  • involve activity in the floodplain of a main river which could divert or obstruct floodwaters, damage any river control works or affect drainage, and potential impacts are not controlled by a planning permission 
  • are covered by regional flood defence and land drainage byelaws, where these are applicable 

Check if you need permission to do work on a river, flood defence or sea defence. Do this as soon as possible to make sure you can get the necessary permissions. 

You can check if your development activity and location are covered by regional flood defence and land drainage byelaws by referring to this statutory guidance. 

If there is a watercourse (including culverted watercourses) on or next to your site, read owning a watercourse and your watercourse: rights and roles. They will help you understand your responsibilities and the rules you need to follow. A culvert is an underground structure that water can flow through. 

Flood risk permits or consents are often needed as well as planning permission. Getting planning permission does not guarantee you will also get a flood risk permit or consent.

Standing advice for vulnerable developments

For all relevant vulnerable development (see When to follow standing advice), you should follow the standing advice for: 

  • what to include in your FRA 
  • sequential and exception tests 
  • floor levels 
  • extra flood resistance and resilience measures 
  • access and escape 
  • surface water management 
  • other permissions or consents

What to include in your FRA

Your FRA should be: 

  • appropriate to the scale, nature and location of the development 
  • proportionate to the degree of flood risk 

It should contain the information set out in the site-specific flood risk assessment check-list.  

For all development covered by this standing advice, your FRA should include: 

  • your site address 
  • a description of your development 
  • an assessment of the flood risk from all sources of flooding for your development, plus an allowance for climate change 
  • the estimated flood level for your development, taking into account the impacts of climate change over its lifetime 
  • an assessment of the residual risks resulting from the breach or overtopping of any flood defences 
  • details of the finished floor levels 
  • details of your flood resistance and resilience plans 
  • any supporting plans and drawings 
  • any other information the relevant standing advice tells you to include 

The estimated flood level is the depth of flooding anticipated on your development site in a: 

You may be able to get the estimated flood level and information about residual risks from the Environment Agency’s Flood Map for Planning. If not, you will need a flood risk specialist to calculate this for you. 

You should follow guidance in Using modelling for flood risk assessments to check: 

  • when you may need to use modelling  
  • what standards to follow 
  • how to get modelling advice 
  • what information you need to provide

Sequential and exception tests

Before you start a FRA, check if your development needs to satisfy the sequential test. The sequential test steers development to areas with the lowest flood risk. It compares your proposed site with other available sites to show which one has the lowest flood risk. The LPA may refuse planning permission if other, lower risk sites are identified. 

When the sequential test is needed

A sequential test is required for major and non-major development (refer to check the development class) if any proposed building, access and escape route, land-raising or other vulnerable element will be: 

  • in flood zone 2 or 3
  • in flood zone 1 and the LPA’s SFRA shows it will be at increased risk of flooding during its lifetime
  • subject to sources of flooding other than rivers or sea

A development is not exempt from the sequential test just because a FRA shows it can be made safe throughout its lifetime without increasing risk elsewhere. See What is the aim of the sequential approach?.

When development is exempt from the sequential test

Development is exempt from the sequential test if it is a: 

  • householder development like residential extensions, conservatories or loft conversions
  • small non-domestic extensions with a footprint of less than 250 square metres
  • change of use (except changes of use to a caravan, camping or chalet site, or to a mobile home or park home site)

Development is also exempt from the sequential test if it is a development on a site allocated in the development plan through the sequential test and: 

  • the proposal is consistent with site’s allocated use
  • there have been no significant changes to the known level of flood risk to the site, now or in the future, which would have affected the outcome of the test

You may not need a sequential test if development can be laid out so that only elements such as public open space, biodiversity and amenity areas are located in areas at risk of any source of current or future flooding.

How to apply the sequential test

You should speak to the LPA early to discuss the sequential test and to determine an appropriate area of search for the test. The LPA should consider whether the test is passed, with reference to the information it holds on land availability. 

Also include information with your application to identify any other ‘reasonably available’ sites not already identified by the LPA within the area of search. This should include sites such as those currently available on the open market. The LPA may also require you to check on the current status of alternative sites to determine if they can be considered ‘reasonably available’. Refer to guidance on Applying the sequential test to individual planning applications. Speak to the LPA to find out what further information may be needed on the sequential test. 

If the sequential test is satisfied you need to check if the exception test also needs doing.

When the exception test is needed

The exception test is needed for development with a vulnerability classification of: 

  • ‘highly vulnerable’ in flood zone 2 
  • ‘more vulnerable’ in flood zone 3a 
  • ‘essential infrastructure’ in flood zone 3a or 3b 

If it does, you need to satisfy both elements of the exception test before the LPA can permit the development.

Floor levels

You need to provide the: 

  • average ground level of your site 
  • ground level of the access road(s) next to your building 
  • finished floor level of the lowest room in your building 

Finished floor levels should be a minimum of whichever is higher of 600mm above the: 

  • average ground level of the site 
  • adjacent road level to the building 
  • estimated river or sea flood level 

Where there is a high level of certainty about your estimated flood level, it may be appropriate to reduce this to 300mm. If there is a particularly high level of uncertainty it may need to be increased. 

You should also use construction materials that have low permeability up to at least the same height as finished floor levels. 

Your plans also need to show how you are going to make sure the development is not flooded by surface water or groundwater. This could be by: 

  • diverting water away from buildings but safely managing it within the site 
  • raising floor levels above the estimated flood depths of surface and groundwater flooding 

Standards for the installation and retrofit of resistance measures are available in British Standard 851188-1:2019+A1:2021.  

State in your assessment all levels in relation to Ordnance Datum (also known as height above average sea level). You may be able to get this information from the Ordnance Survey. If not, you will need to get a land survey carried out by a qualified surveyor. 

If you cannot raise floor levels to meet the minimum requirement, you will need to: 

  • raise them as much as possible 
  • consider moving vulnerable uses to upper floors 
  • include extra flood resistance and resilience measures 

Internal flooding of new vulnerable development like residential dwellings is unlikely to be considered appropriately flood resistant and resilient. 

When considering the height of floor levels, you should also consider any additional requirements set out in the SFRA. Flood water can put pressure on buildings causing structural issues. If your design aims to keep out a depth of more than 600mm of water, you should get advice from a structural engineer. They will need to check the design is safe.

Extra flood resistance and resilience measures

Follow the guidance in this section where you cannot raise the finished floor levels to the required height. Your building design should:

  • prioritise excluding flood water where possible
  • speed recovery in case water gets in

Make sure your flood resilience plans for the development follow the guidance in the CIRIA Property Flood Resilience Code of Practice. Note that the code of practice uses the term ‘recovery measures’. In this guide we use ‘resilience measures’. 

Only use resistance measures that will not cause structural stability issues during flooding. It may not be possible to safely exclude the full estimated flood level. If this is the case, you will need to exclude it to the structural limit then allow additional water to flow through the property. The design should be appropriately flood resistant and resilient by: 

  • using flood resistant materials that have low permeability to at least 600mm above the estimated flood level 
  • making sure any doors, windows or other openings are flood resistant to at least 600mm above the estimated flood level 
  • using flood resilient materials (for example lime plaster) to at least 600mm above the estimated flood level 
  • raising all sensitive electrical equipment, wiring and sockets to at least 600mm above the estimated flood level 
  • making it easy for water to drain away after flooding such as installing a sump and a pump 
  • making sure there is access to all spaces to enable drying and cleaning 
  • making sure that soil pipes are protected from back-flow such as by using non-return valves 

Standards are available for: 

You will also need to comply with relevant Building Regulations in Part P. They set minimum and maximum heights for certain electrical infrastructure. 

Temporary or demountable flood barriers are not appropriate for new buildings. Only consider them for existing buildings when: 

  • there is clear evidence that it would be inappropriate to raise floor levels and include passive resistance measures 
  • an appropriate flood warning or other appropriate trigger is available 

If proposals involve the development of buildings constructed before 1919, refer to Flooding and Historic Buildings guidance produced by Historic England.

Access and escape

You need to provide details of your emergency access and escape plans if any part of your development is below the estimated flood level. This includes access and escape routes. Follow the Flood Risk Emergency Plans for New Development guidance. 

Make sure your plans show: 

  • a safe route of access and escape which is set above the estimated flood level and connects the site to an area away from flood risk 
  • that any single storey buildings or ground floors without access to upper floors can access a safe refuge above the estimated flood level 
  • that any basement rooms have clear internal access - for example a staircase to an upper floor above the estimated flood level 
  • how the development could be evacuated before an extreme flood – this is an event with a 0.1% annual probability of flooding plus an allowance for climate change

You will also need to comply with relevant Building Regulations in Part B. They require you to provide suitable access for the fire service.

Surface water management

You need to include a sustainable drainage strategy if your application is for: 

  • major development involving surface water drainage 
  • development involving surface water drainage in areas at risk of flooding 

If sustainable drainage systems (SuDS) are required but are not included in the development, provide the LPA with evidence of why SuDS would be inappropriate. 

Even where the National Planning Policy Framework does not require SuDS, we recommend their consideration on all development types, including changes of use, wherever appropriate. 

Your SuDS will need to provide benefits for: 

  • water quantity 
  • water quality 
  • biodiversity  
  • amenity  

You should include all the information set out in Sustainable Drainage Systems. You can put it in a separate document or in the FRA. 

In major development your SuDS should also provide multifunctional benefits where possible. More information on multifunctional benefits can be found in What are sustainable drainage systems and why are they important? 

Your plans for the management of surface water need to meet any requirements set out in your local authority’s: 

  • local plan or supplementary planning documents 
  • local flood risk management strategy 
  • surface water management plan where available 
  • SuDS guidance where available 
  • SFRA 

They also need to meet the requirements of the planning practice guidance and the approved building regulations Part H: drainage and waste disposal. Read section H3 rainwater drainage. 

Refer to the non-statutory technical standards for guidance on the design, maintenance and operation of SuDS. Further guidance on how to design SuDS to maximise their benefits is in the CIRIA Suds Manual. 

You can follow Water UK’s Design and Construction Guidance to design and construct SuDS. This should make sure they qualify for adoption by the relevant water and sewerage company. 

You need planning permission to surface more than 5 square metres of a front garden using a non-porous material.

Other permissions or consents

You may need a separate permit or consent if the development or any associated works such as site preparation or construction: 

  • is within 20 metres of a main river (including culverted main rivers), a flood defence or flow control structure 
  • directly affect a watercourse that is not a main river 
  • involve activity in the floodplain of a main river which could divert or obstruct floodwaters, damage any river control works or affect drainage, and potential impacts are not controlled by a planning permission 
  • are covered by regional flood defence and land drainage byelaws, where these are applicable 

Check if you need permission to do work on a river, flood defence or sea defence. Do this as soon as possible to make sure you can get the necessary permissions. 

You can check if your development activity and location are covered by regional flood defence and land drainage byelaws by referring to this statutory guidance. 

If there is a watercourse (including culverted watercourses) on or next to your site, read owning a watercourse and your watercourse: rights and roles. They will help you understand your responsibilities and the rules you need to follow. A culvert is an underground structure that water can flow through. 

Flood risk permits or consents are often needed as well as planning permission. Getting planning permission does not guarantee you will also get a flood risk permit or consent.

Submit your flood risk assessment

You should submit your completed FRA with your planning application to your LPA. 

The LPA will review your FRA and tell you if it is satisfactory. Planning applications that do not have a satisfactory FRA may be refused.

Updates to this page

Published 1 April 2012
Last updated 23 August 2024 + show all updates

  1. Added 'where the Environment Agency should be consulted' to the 'When to follow standing advice' section.

  2. Added link to 'your watercourse: rights and roles' under 'other permissions or consents' section.

  3. Removed 'researching the development site' section to avoid duplication. Updated and provided more clarifications on all other sections.

  4. Clarity improved to reflect the latest National Planning Policy Framework, historic buildings guidance, the CIRIA Property Flood Resilience Code of Practice and relevant British Standards and Building Regulations. Improved links to strategic flood risk assessments. Greater clarity on the need for flood risk assessments, sustainable drainage information and sequential and exception test information. Highlight the need to check the compatibility of the proposed use with the flood zone. Clearer approach to flood risk mitigation. Highlighting that some developments may also need a flood risk activity permit.

  5. Guidance reviewed and no changes made.

  6. Clarity improved and links updated. Clarified status of advice for minor extensions and advice on climate change. Added ‘extra resistance and resilience measures’ section from 'Flood risk standing advice for local planning authorities' guide. Included advice for areas of flood zone 1 that will be at future risk.

  7. Changed URL for Find out what flood zone your development is in, to the new Flood Map for Planning service. Changed URL for Check if your development is within 20 metres (m) of a main river, to the Main River map

  8. First published.

Sign up for emails or print this page

Contents

Related content