Flood risk assessment: standing advice
Find out if you need to follow standing advice when completing a flood risk assessment and what to do if so.
You need to follow the Environment Agency’s standing advice if you’re carrying out a flood risk assessment for a development classed as:
a minor extension (household extensions or non-domestic extensions less than 250 square metres) in flood zone 2 or 3
- ‘more vulnerable’ in flood zone 2 (except for landfill or waste facility sites, caravan or camping sites)
- ‘less vulnerable’ in flood zone 2 (except for agriculture and forestry, waste treatment, and water and sewage treatment)
- ‘water compatible’ in flood zone 2
This includes developments involving a change of use into one of these vulnerable categories or into the water compatible category.
Find out what flood zone your development is in.
Read the guide on flood risk assessment for planning applications if this doesn’t apply to your development.
Contact the Environment Agency for advice if your development is:
- classed as ‘more vulnerable’ and is a landfill or waste facility site, or a caravan or camping site
- classed as ‘less vulnerable’ and is for agriculture and forestry, waste treatment, mineral processing, or water and sewage treatment
Research your development site
For all developments covered by standing advice, you should do the following research before starting your flood risk assessment.
Contact the Environment Agency for information about flood risk in your area.
Contact your local planning authority or check the planning section of their website for their strategic flood risk assessment if one has been adopted as part of the local plan. Refer to the strategic flood risk assessment in your flood risk assessment.
Check if your development is within 20 metres (m) of a main river. Ask the Environment Agency for advice if it is.
Check if you need to do a sequential test
Before you start a flood risk assessment, check if you need to carry out a sequential test. A sequential test compares your proposed site with other available sites to show which one has the lowest flood risk.
You need to carry out a sequential test if one hasn’t already been done for the type of development you plan for your proposed site - check with your local planning authority.
What to include in your assessment
For all developments covered by standing advice, you must put together a flood risk assessment which includes:
- your site address
- a description of your development
- an assessment of the flood risk for your development (consider all sources of flooding not just rivers and the sea and include an allowance for climate change
- the estimated flood level for your development, ie the 1 in 100 year river flood level or the 1 in 200 year tidal flood level
- details of your flood resilience and resistance plans
- any supporting plans and drawings
- any information the relevant standing advice tells you to include
You may be able to get the estimated flood level from the Environment Agency or your local planning authority. If not, you’ll need a flood risk specialist to calculate this for you.
Your written flood risk assessment can be in any format, but must include the relevant plans, surveys and assessments. Check with your local planning authority if they have any specific software requirements, eg for producing detailed hydraulic models.
Minor extensions standing advice
You need to provide a plan showing the finished floor levels and the estimated flood levels.
Make sure that floor levels are either no lower than existing floor levels or 300 millimetres (mm) above the estimated flood level. If your floor levels aren’t going to be 300mm above existing flood levels, you need to check with your local planning authority if you also need to take flood resistance and resilience measures.
State in your assessment all levels 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’ll need to get a land survey carried out by a qualified surveyor.
Your plans need to show how you’ve made efforts to ensure the development won’t be flooded by surface water runoff, eg. by diverting surface water away from the property or by using flood gates.
If your minor extension is in an area with increased flood risk as a result of multiple minor extensions in the area, you need to include an assessment of the off-site flood risk. Check with your local planning authority if this applies to your development.
Make sure your flood resistance and resilience plans are in line with the guidance on improving the flood performance of new buildings.
Vulnerable developments standing advice
For all relevant vulnerable developments (ie more vulnerable, less vulnerable and water compatible), you must follow the advice for:
- surface water management
- access and evacuation
- floor levels
Surface water management
Your plans for the management of surface water need to meet the requirements set out in either your local authority’s:
- surface water management plan where available
- strategic flood risk assessment
They also need to meet the requirements of the approved building regulations Part H: drainage and water disposal. Read section H3 rainwater drainage.
You need to get planning permission to use a material that can’t absorb water (eg impermeable concrete) in a front garden larger than 5 square metres.
Access and evacuation
You need to provide details of your emergency escape plans for any parts of a building that are below the estimated flood level.
Make sure that your plans show:
- single storey buildings or ground floors that don’t have access to higher floors can access a space above the estimated flood level, eg higher ground nearby
- basement rooms have clear internal access to an upper level, eg a staircase
- occupants can leave the building if there’s a flood and there’s enough time for them to leave after flood warnings
You need to provide both the:
- average ground level of your building
- finished floor level of the lowest habitable room in your building
Ground floor levels should be a minimum of whichever is higher of:
- 300millimetres (mm) above the general ground level of the site
- 600mm above the estimated river or sea flood level
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’ll need to get a land survey carried out by a qualified surveyor.
If you can’t raise floor levels above the estimated flood level, you need to consider extra flood resistance and resilience.
Submit your flood risk assessment
They’ll review your flood risk assessment and tell you if it’s satisfactory. Planning applications that don’t have a satisfactory flood risk assessment may be refused.
Contact the Environment Agency
PO Box 544
Monday to Friday, 8am to 6pm 0370 8506 506
From outside the UK +44 1709 389 201