Flood Risk Assessment to support a change of building use

The Town and Country Planning act categorises land and buildings into a range of groups known as “use classes”. It is important to be aware of what class any building that is in line for a change currently sits in. These classes are also updated quite often so it is wise to check before taking a change of use any further.

Planning Permission to Change “Use Class”

In almost all cases planning permission is needed to change a building from one use class to another. There are some instances where it is not needed but these are in the minority. An example would be changing from A3 to A1; Restaurant or Cafe to a Shop. There are some building that do not fall into any class, examples would be things like Petrol Stations, Car Showrooms, Scrap Yards and even Launderettes. These building types are considered “sui generis” which is the term used to losly group anything that doesn’t fit into the use classes structure.

Use Classes

Below is a list of the different classes. The final decision lies with the planning authorities and it is important not to assume one class or another until it has been officially categorised.

Part A

  • A1 Shops –  retail warehouses, shops, travel and ticket agencies, undertakers, hairdressers, post offices, showrooms, pet shops, sandwich bars, domestic hire shops,  funeral directors, dry cleaners, and internet cafes.
  • A2 Financial and Professional Services – Financial services including banks and building societies, professional services (this does not include health and medical services)  including employment and estate agencies.  Betting offices and pay day loan shops are not included here – they are now classed as “sui generis” uses.
  • A3 Restaurants and cafés –  Restaurants, snack bars and cafes.
  • A4 Drinking establishments – Public houses, wine bars or other drinking establishments, this does not include night clubs. This class does include drinking establishments with expanded food provision.
  • A5 Hot food takeaways – For the sale of hot food for consumption off the premises

Part B

  • B1 Business – Offices that are not included in A2, light industry that is suitable for a residential area and research and development businesses.
  • B2 General industrial – Buildings used for industrial process that do not fit within class B1. This excludes buildings used incineration purposes, chemical treatment, landfill or hazardous waste.
  • B8 Storage or distribution – This includes  land and buildings used for open air storage.

Part C

  • C1 Hotels – Hotels, boarding and guest houses. These are places where no significant level of care is provided so does not include hospices and the like.
  • C2 Residential institutions – Residential care homes, nursing homes, hospitals, residential colleges, schools and training centres.
  • C2A Secure Residential Institution – This class is for secure residential accommodation. This includes prisons, young offenders institutions, detention centres, custody centres, short term holding centres, secure training centres,  secure hospitals, secure local authority accommodation or use as a military barracks.
  • C3 Dwellinghouses – this class is made up of 3 sections:
    • C3(a) covers use by a single person or a family this includes a couple married or not, people related to each other  with members either persons family being treated as the same family, an employer and certain domestic employees like nannies, gardeners, drivers etc. This class also includes use by a carer and the person receiving the care and a foster parent and foster child.
    • C3(b): this covers up to six people living together as a single household and receiving care
    • C3(c) this covers groups of people (up to six) living together as a single household. These groups do not fit into the C4 definition, but which fell within the previous C3 use class, to be provided for. An example would be a homeowner who is living with a lodger.
  • C4 Houses in multiple occupation – small shared houses occupied by between three and six unrelated individuals, as their only or main residence, who share basic amenities such as a kitchen or bathroom.

Part D

  • D1 Non-residential institutions –health centres and clinics, crèches and nurseries, schools, museums, art galleries (other than for sale or hire),  libraries, places of worship, church halls, halls, law courts. Non residential education and training centres.
  • D2 Assembly and leisure –  Music and concert halls, Cinemas, bingo and dance halls (but not night clubs), swimming pools, Ice skating rinks, gymnasiums and areas for indoor or outdoor sports and recreations (except for motor sports, or where firearms are used).

Planning Permission

In many cases planning permission is not needed. For example changing a shop of one sort into a shop of another doesn’t not require planning. However, there are a number of changes that do require prior approval and flooding is one of these. As the case study below states, in areas whee flooding has been deemed an issue it is crtical to get a flood risk assessment done before moving forward with any kind of change of use.

Examples of changes that do need planning include

  • Office to Residential
  • Storage and Distribution to Residential
  • Agricultural to Residential – different rule apply to different sized buildings.

If you would like more information on your planned change of use development then get in touch today. We are able to produce Flood Risk Assessments for planning applications and we have years of experience in doing this for change of use applications.

Case Study: Flood Risk Assessment to support a change of building use.

Project Outline:

Unda was approached by a regular client who was overseeing the development and subsequent change of use of a 3 storey commercial building to residential flats. As the development would lead to people habiting the building on all 3 floors the regulator requested a Flood Risk Assessment as the building was located in flood zone 3 (an area recognised as having a risk of flooding).

Benefit to client:

Unda was able to demonstrate through their Flood Risk Assessment that whilst the development was in flood zone 3 the area was protected by effective and maintained flood defences. Within the report an evacuation strategy was included. Planning permission was granted.

Unda’s approach:

Unda’s flood risk assessment was prepared to assess the potential significance of flood risk to a development which consisted of a vacant commercial being adapted for residential purposes. The site was located in flood zone 3 as classified by the Environment Agency.

The development’s location was highlighted as being at potential risk of flooding from surface water, river, coastal and reservoir flooding. Unda’s flood risk assessment demonstrated that although the building was located in a flood zone, the area’s defences were suitable to mitigate against potential flooding. Based on being able to quantify the mitigation measures in place were adequate, the overall risk rating of low was given to the site within Unda’s completed report.

Unda’s specialist flood risk consultant conducted a detailed review of the data and assessed the on-site and off-site flood risk. The proposed development did not involve changes to the existing buildings footprint and concrete car parking area. Unda was able to identify that there would be no increase in impermeable surfaces or loss of flood plain storage within the site boundary following the building’s conversion.

Run-off from the development remained unchanged indicating that there would be no increase of flood risk from the site to any local receptors.

As part of the flood risk assessment Unda include an escape route should the site become inundated with water in the unlikely event there was a barrier breach.

If you have concerns about flooding issues to a property which you are looking to purchase, sell or secure flood insurance for, please contact Unda. Our flood risk consultants will quickly be able to advise how they can assist and will provide a fixed price quotation to understand your issues and provide solutions where possible. For prompt attention Tel: 01293 214 444 or send your details via our contact form.


CS1 image 1

Main Side Bar Form


Become a Member