GovWire

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 LPAs 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
• less vulnerable - except for waste treatment sites, mineral processing sites, water treatment plants and sewage treatment plants
• 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:

• read flood risk assessment for planning applications and the flood risk assessment check-list
• consider asking the Environment Agency for pre-application advice on flood risk

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 Agencys 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 F

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