loft extensions and Conversion London Planning Permission

What is “permitted development” Class B – additions to the roof?
Permitted development rights allow householders to improve and extend their homes without the need to seek a specific planning permission from Local Authority either for loft extensions or ground floor rear extensions. This means works can start as soon as the building owner is ready provided contractor and building control documentation has been acquired. It is advised to seek neighbour written approval before undertaking any construction that’s would affect adjoining structure and foundations, between properties. The guidance set out below gives an explanation of the rules on permitted development for householders, what these mean and how they should be applied in particular sets of circumstances. Permitted development rights for householders Technical Guidance can be found here.

How can I apply for a loft extension planning permission?
You can appoint an Architect to draw out the plans of the existing building to then proceed to work on proposal. At some point a Structural Engineer will also be consulted before planning submission or during Building regulations stage,
Once plans are submitted to the planning department of Local Authority, the case officer may request changes or alterations to meet the council standards and policies in order to grant approval to loft conversion as well as additional reports such as design and access statements. It can take approx. 8 weeks for an application to be approved and can vary on the Local Authority Borough workload.

When do I need loft conversion planning permission?
In order to be permitted development, a proposal must meet all the limitations and conditions under each Class A to H relevant to the proposal. It is therefore essential that any proposed household development is considered in the context of the permitted development rules as a whole in order to determine whether it benefits from permitted development rights and therefore does not require an application for planning permission.

Many loft conversions are covered by permitted development rights and don’t require planning permission. However, if you live on designated land or have a certain style of property that's tricky to convert, you may not be covered by permitted development. Refer to the Planning Portal for more information or you can also contact us to discuss further.

If your house is in a conservation area any alterations to the roof should preserve or enhance the special character or appearance of that particular area. This may mean that the possibility for acceptable schemes is much more limited. It will depend on the type of roof you have, the amount you want to alter it and how visible that alteration will be.  The SPG Guidelines in most local councils for Loft extensions were adopted in 1996, which aimed to ensure that the aspects listed below were taken into account in the planning of the proposed loft conversion.

Lofts For Planning Permissions


Lofts For Planning Permissions 3D


Example above of Dormers to rear roof under planning permission


Lofts For Planning Permissions Mansard

Example above to Mansard roof extension under planning permission

It is important to note that a local planning authority is allowed to remove permitted development rights in some or all of its area by issuing what is known as an Article 4 Direction; or may have removed those rights on the original, or any subsequent, planning permission for the house. Where permitted development rights have been removed in either of these ways a planning application will be needed for development. Before undertaking any development, checks should be undertaken with the local planning authority to determine whether any such restrictions on permitted development have been made

How can someone tell if their loft is suitable for conversion? 

• Look for other conversions on your street

• Measure the head height - hint, if it's 2.2m or more, your loft should be tall enough to convert.

• Check what type of roof you have

 Roof Types

How to make sure my loft is designed under “permitted development”? see below which are extracts from the Householder Technical Guidance 2017

Development is permitted by Class B

  • if any part of the dwelling house would, as a result of the works, exceed the height of the highest part of the existing roof
  •  any part of the dwelling house would, as a result of the works, extend beyond the plane of any existing roof slope which forms the principal elevation of the dwelling house and fronts a highway
  • the cubic content of the resulting roof space would exceed the cubic content of the original roof space by more than -
    • 40 cubic metres in the case of a terrace house, or
    • 50 cubic metres in any other case

 Lofts Volumes


  • the materials used in any exterior work shall be of a similar appearance to those used in the construction of the exterior of the existing dwelling house
  • other than in the case of a hip-to-gable enlargement or an enlargement which joins the original roof to the roof of a rear or side extension –
    • the eaves of the original roof are maintained or reinstated
    • the edge of the enlargement closest to the eaves of the original roof shall, so far as practicable, be not less than 0.2 metres from the eaves, measured along the roof slope from the outside edge of the eaves; and
    • other than in the case of an enlargement which joins the original roof to the roof of a rear or side extension, no part of the enlargement extends beyond the outside face of any external wall of the original dwelling house
  • any window inserted on a wall or roof slope forming a side elevation of the dwelling house shall be -
    • obscure-glazed, and
    • non-opening unless the parts of the window which can be opened are more than

 Roof Descriptions

Building Regs

Building regulations approval is different from planning permission and you might need both for your project.

The statutory framework for building control is regulated by The Building Act 1984 and the Building Regulations 2000. There are two methods of control, by appointing the local authorities or an Approved Inspectors, licensed to operate under the Act.

Building regulations are minimum standards for design, construction and alterations to virtually every building. The regulations are developed by the UK government and approved by Parliament. The Building Regulations 2010 cover the construction and extension of buildings and these regulations are supported by Approved Documents. Approved Documents set out detailed practical guidance on compliance with the regulations.

How much does an Architect charge?

Architectural fees are based on the requirements of the project, the skills set of the architect, experience, overheads, and the resources needed to undertake the work, profit and competition. Before the fee can be agreed, both architect and client should establish; the project details and services to be provid­ed, the procurement method, an approximate construction cost, and the project timetable.

If you plan to extend your loft conversions in London please contact us at your convenience and we will arrange a free phone call meeting.

Click here to see a selection of completed loft conversions and rear extensions in London