Change of Use for C3, C4 & Sui Generis in HMOs

Updated October 2024

If you are planning to convert a residential property into an HMO, knowing about change of use classes is important in understanding planning requirements for your HMO investment. Depending on the number of occupants you are looking to host, as well as the size and location or your property, different planning processes can be required.

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Use Classes Explained

C3 (Residential)

The C3 use class covers properties or houses that are primarily used as single-family houses or as residence for a single household. A single household generally will refer to a group of people who are related, either through marriage or blood, or are living together as a family. These groups can include couples, parents and children, or other individuals living together as a family, such as grandparents.

C3 properties can include various property types, such as bungalows, maisonettes, houses and apartments. However, the layout tends to be consistent with the exclusive use of a single household and not that of an HMO.

C4 (HMO)

Contrary to a C3 use class, C4 constitutes an HMO property where there are three or more unrelated tenants living together who share facilities such as the bathrooms, kitchen and living areas. This use class refers specifically to smaller HMOs that have six occupants or less.

To convert a C3 to a C4 HMO, you might need to apply for planning permission to meet the criteria for an HMO that is set out by your local planning authority – i.e. your local council. This includes various considerations that are not required for C3 use class, such as the size, layout and facilities available within the property.

Sui Generis (Large HMO)

The planning category known as “Sui Generis” is a planning use class that is used when the property does not fall under any specific category or use class. It is generally used for unconventional uses and as far as HMOs are concerned, for large HMOs over 6 occupants.

The planning process for Sui Generis properties tends to be more complex and involves some additional considerations compared to C4. For example, a comprehensive assessment of factors such as the potential impact on the local area, noise pollution, traffic impact, and other considerations related to the particular use.

Take the complexity out of Sui Generis planning with HMO Designers.

We help landlords and HMO developers create stunning, compliant large HMOs.
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C3, C4 & Sui Generis Summary

Use ClassOccupancyTenant TypeProperty Type
C3Up to 6 occupantsSingle householdResidential
C43 – 6 occupantsSeparate householdsHMO
Sui Generis7+ occupantsSeparate householdsHMO
large hmo sui generis

Planning Requirements for C3 to C4 Change of Use

The planning permission requirements from C3 to C4 can vary depending on the location of the property and the requirements outlined by your local planning authority. A C3 to C4 change of use often falls under what’s known as permitted development rights, which allows you to change the use class of the property without requiring a full planning application. However, other areas may require full planning, such as those with an Article 4 direction.

To determine the specific requirements in your area, you should speak to your local council for the most up to date and accurate information. If you find that you can convert the property under permitted development, it’s worth noting that converting your residential property to an HMO is still subject to certain limits and criteria, such as HMO licensing regulations and building regulations.

c3 to c4 change of use diagram

Planning Requirements for C3 to Sui Generis Change of Use

Converting a residential property to a large HMO with over 6 occupants will constitute Sui Generis use class and therefore requires a full Sui Generis planning application. Sui Generis properties are effectively a lot closer to commercial use than residential use, and therefore the requirements are stricter.

Some specific documentation that you need for your Sui Generis planning application includes:

  • Existing and Concept Drawings – As part of your application, you must submit drawings of both what the building currently looks like (Existing) and what the building is proposed to look like after development work (Concept).
    These drawings must be detailed and high quality with the correct scale and level of detail. They should also take into account HMO licensing requirements and standards such as room sizes, fire safety requirements and other safety features.
  • Ordnance Survey Map (OS Map) – This is required by the council and represents the location of the property within the neighbourhood on a scale of 1:1250.
  • Design and Access Statements – A design and access statement is another requirement, and this document outlines your reasoning for your design choices. This usually includes considerations such as an analysis of the area, material selections, Article 4 considerations, diagrams of the development and more.
  • HMO Management Plan – Some councils may request a management plan as part of your application. This includes items such as the number of bedrooms, tenancy agreements, waste management and maintenance.
  • Transport Statements – Although not required, a transport statement can strengthen your application and includes a study on parking provision of the area, produced by a transport consultant.

In addition to the above, your local authority will be looking for evidence that you have fully considered the impact on your local area, the community and the occupants as part of your planning application. Therefore, additional requirements for your planning application can often include factors such as:

  • Detailed project descriptions & plans
  • Impact assessments on traffic, noise and parking
  • Development justification
  • Legal & policy compliance
  • Public consultation such as neighbours or community groups

Sui Generis planning can be a complex area of property legislation that is often difficult to navigate. Speaking to an HMO expert, such as HMO Designers, can help you get to grips with Sui Generis planning and submit a successful planning application.

c3 to sui generis change of use diagram

Planning Requirements for C4 to Sui Generis Change of Use

In most cases, converting a small HMO (C4) to a large HMO (Sui Generis) will constitute the same full planning required for C3 to Sui Generis. Therefore, a planning application is required for this change of use class. The requirements for such a change of use will of course depend on the specific circumstances and local planning regulations enforced by your local council.

The application requires:

  • Existing and Concept Drawings
  • Ordnance Survey Map (OS Map) 
  • Design and Access Statements
  • HMO Management Plan 
  • Transport Statements
  • Other additional requirements listed under C3 to Sui Generis

Change of use from C4 to Sui Generis is a fairly common planning application, and some of the most common reasons these planning applications can be rejected is due to applicant not fully taking into account all of the requirements set out by the council and legislation, commonly the impact on the living conditions and amenities of the occupiers and neighbours.

The planning application process for C4 to Sui Generis can be very similar to C3 to Sui Generis. However, this does vary from council to council and as always, we recommend speaking to an HMO expert or local planning authority.

c4 to sui generis change of use diagram

Can You Change Use Within Sui Generis?

No.

If you want to change the use of the Sui Generis property (for example, you are converting a theatre into a large HMO), you must submit a full planning application.

Planning Requirements for C3, C4 and Sui Generis Summary

Conversion TypePlanning Requirements
C3 to C4Allowed under Permitted Development unless in Article 4 area.
C3 to Sui GenerisFull planning application required
C4 to Sui GenerisFull planning application required
Change of Use within Sui GenerisFull planning application required

HMO Designers Planning Applications

Here at HMO Designers, we’ve been delighted to work with a number of landlords and HMO investors to create stunning HMOs that fall under the Sui Generis use class. This means we’re specialists in large HMOs, from HMO architecture to planning, and have extensive knowledge of the planning application process required for C3 to Sui Generis and C4 to Sui Generis.

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