Upward Extension Services

Maximise your existing house by building upwards

  • Need more roof space?
  • Planning a loft extension?
  • Building new flats?

Extend upwards and gain additional living space – without waiting for planning permission.

or call us for advice today!

Upward extensions don’t always need planning permission

Whether your proposed upward extension is for:

  • A detached house

  • Semi detached houses

  • Terraced buildings

Under new “Permitted Development” rights, no planning permission is needed for homeowners, landlords, and property developers to build additional storeys and obtain more space for their residential dwellings.

Prior approval applications

Since August 2020, a permitted development England amendment (new Class AA) simply requires a ‘prior approval application’ to be submitted – NOT a full planning application.

The new legislation means you still cannot start any upward extensions to an existing building without the approval of the council or local authority.

External appearance

The council will need to assess if and how your planned upwards extension of an additional storey will significantly affect the external appearance of your existing house.

The local planning authority will want to ensure the new storeys, and new roof, conform to the look, design and materials of the host building. Many councils will provide guidance and instructions.

Typical examples:

  • Front of the house (principle elevation) – including all design and architectural features.
  • Rear and side extensions – and any side elevation which faces a highway. New floors and the new roof will need to look identical, or as similar as possible to the existing building.
  • Neighbour’s natural light – one of the most common obstacles when building upward extensions in a densely populated suburban area is a neighbour’s loss of adequate natural light.
  • Neighbour’s privacy – an equally challenging issue is the potential breach of an adjoining neighbour’s privacy when an additional storey may overlook their property.

Prior Approval Application – key items you must include

In your house extension planning system, the ‘prior approval application’ should be easier than applying for planning permission.

To help with the approval process, it’s important to ensure that your council/ local planning authority receives all the key items required, as follows:

  • Detailed description of proposed upwards extension.
  • Written statement to include:
    • Proposed number of dwellings
    • Number or pre-existing dwellings
  • Proposed elevations.
  • Existing elevations.
  • Size, dimensions and position of any newly-installed windows.
  • Direction ‘North’ indicated on plans, to-scale.

Prior Approval Application – additional conditions you need to know

Your eligibility for building upwards also rests upon meeting the following conditions:

Date your property was built

For extending homes

Property was built:

  • After 1st July 1948*

  • Before 28th October 2018

For adding new flats

Property was built:

  • After 1st July 1948*

  • Before 5th March 2018


You must be able to:

  • Clearly show that the entire property was built after 1948 – and not just a part of the building.

  • Provide documented proof in the form of title deeds, historic maps, or other building records.

If your property was built outside of the above dates – you are required to apply for planning permission to build upwards.

Prior Approval Application – what happens next

Your local planning authority will notify each adjoining home / building owner or occupier of the application details including, maximum height of additional storeys proposed.

Your neighbours are given 21 days in which to respond.

For a prior approval to be granted an application must also meet the following conditions:

  • All upward extension work must be completed within 3 years from the prior approval date.
  • A building management report must include details of safety compliance measures to reduce impact of ‘noise, dust and vibration’, and use of materials.

Want to discuss extension options?

Upward Extension for a Bungalow

A bungalow can offer significant potential for creating more space and installing other ancillary facilities. However, an upward extension can often present a challenge.

Bungalows from the 1960s onwards can often be built without any structural support, such as internal load-bearing walls. In most cases, the professional services of structural engineers will be needed from the initial planning stage.

Adding an extra storey

Under ‘permitted development’ you may be planning to build an extra storey. It is strongly recommended for a structural engineer to check your foundations to ensure the existing building can support the weight of the extra floor level.

A structural engineer’s survey will also determine the absence of internal load-bearing walls. If this is the case, a structural steel member will need to be installed to support the weight of the additional, planned floor.

Alternatively, the upwards extension of a bungalow can often be achieved by using a timber frame rather than a masonry construction. This type of extension may not require an alteration of the foundations or intensive underpinning of an existing building.

Maximum Height of Upwards Extensions

Each of the above 6 classes of upward extension for existing buildings has its own, individual specification for constructing additional storeys.

These will clearly translate to the maximum height for a building extended upwards and, therefore, the maximum height of the new roof.

Under the new permitted development rights a new roof must not exceed the height limit for the following typical residential properties:

Detached house – 1 storey

  • 3.5 metres (11.48 feet) at the highest point of existing house.

Detached house – 2 storeys

  • 7 metres (22.96 feet) at the highest point of the existing house.

Terrace house

  • 3.5 metres (11.48 feet) of the next tallest house.

Semi-detached building

  • 3.5 metres (11.48 feet) of an adjoining premises.

What happens if a maximum height is to be exceeded?

If during the planning process the number of additional storeys looks set to exceed the maximum allowed height you will need to make an application for planning permission.

Surrounding streets

The overall impact upon surrounding streets and local environment is all-important in a local planning authority approval process.

The definition and consideration of an ‘adjoining property’ may not always be limited to an immediate neighbouring premises. Nor any further impact upon an adjoining property beyond issues of loss of privacy and natural light.

In addition to the front of a house facing the highway, the extended area surrounding a property may also be considered in a local authority assessment of ‘external appearance’

It cannot be assumed permission for your prior approval application will be guaranteed.

Your Permitted Development Rights

Permitted development rights for upward extensions was introduced against a backdrop of the UK’s ongoing housing shortage – currently around 5 million homes. And as an acceptable alternative to building on ‘green belt’ land, conservation areas or national parks.

Town and Country Planning Act 2020

Under the The Town and Country Planning (General Permitted Development) (England) (Amendment) (No. 4) Order 2020:

  • A maximum of 2 storeys are allowed to be built on 6 classes of property without planning permission.
Class AA:

Detached, free-standing building – in commercial or mixed use (residential).

Up to two storeys may be added, above ground level.

Class AB:

Terrace building – including semi-detached buildings – in commercial or mixed use (residential).

Two storeys can be added, but only if:

  • Building currently consists of 2 or more storeys.


One storey only can be added if:

  • Building currently consists of 1 storey.

Thinking of extending upwards?

Class AC:

Terrace dwelling house – includes semi-detached houses.

Two storeys may be added, but only if:

  • Building currently consists of 2 or more storeys.


One storey only can be added if:

  • Building currently consists of 1 storey.

Class AD:

Detached dwelling house

Two storeys can be added if:

  • Building currently consists of 2 or more storeys.


One storey only can be added if:

  • Building currently consists of 1 storey.

How many prior applications are actually approved?

Since the introduction of permitted development rights in August 202o, the number of prior applications for upward extensions made by homeowners, landlords and developers up to the end of 2021 has continued to increase.

  • Class AA (Detached building) – up to 2 additional storeys – 49 per cent approved.
  • Class AB (Terrace building/ semi detached) – either 1 or 2 additional storeys – 21 per cent approved.
  • Class AC (Terrace dwelling/ semi detached) – either 1 or 2 additional storeys – 56 per cent approved.
  • CLASS AD (Detached dwelling) – either 1 or 2 additional storeys – 63 per cent approved.

Other considerations for adding storeys

Town and Country Planning (General Permitted Development) Order 2015.

  • PART 1 Article 2(3) land

Under the Order, a building should not be located on PART 1 Article 2 (3) categories of land, including :

  • Conservation area.

  • Area of outstanding natural beauty.

  • National park.

  • A World Heritage site.

  • Site of ‘special scientific interest’.

  • Change of Use

Under the Order, no previous permission was granted for a change of use including:

  • Class M – which allows for 150 square metres of building to be converted for residential use.

  • Under ‘Class AA permitted development’  no previous additional storey (s) were extended upwards above the original house.

  • Property must continue use as a house after upward extension completed.

Single residential dwellings extended upwards cannot be changed for use as a small-size HMO (house in multiple occupation).

Under permitted development rights, if you intend to build additional storeys, and create a small-scale HMO, you will need to apply for planning permission.

  • Additional storeys


  • Contain no windows installed in the wall or roof slope of a side elevation.

  • Follow the ‘pitch’ (angle) of the roof on the existing building.

  • Additional works

Under a ‘permitted development’ for an upward extension, you are only allowed:

  • Additional works to strengthen existing walls and foundations of the property within the “curtilage” – i.e. immediate surrounding land only, including any closely associated buildings and structures.

IMPORTANT: You are not allowed to include any other type of “engineering operations”.

Is the height of your existing accommodation 18 metres (50.05 feet) or above?

 the above 6 classes of existing residential properties, the new general permitted development rights for upward extensions also requires:

  • A structural engineer’s report for prior approval application.

The report for the local planning authority must confirm that the building’s external existing walls comply with B4(1) of Schedule 1 contained within Building Regulations 2010 (S.I. 2010/2214).

B4(1) of Schedule 1 states:

“The external walls of the building shall adequately resist the spread of fire over the walls and from one building to another, having regard to the height, use and position of the building”.

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AC Design Solutions offer competitive prices along with quality service. You can be assured that your application will be dealt with professionally and efficiently by our dedicated and knowledgeable team.

or call us for advice today!