loft conversion

In most circumstances you will not need planning permission for a loft conversion, as the development will be covered by GPDO (permitted development). However, you should also check if your permitted development rights are restricted or have been removed (see below)*


Roof extension pictured above by Ben+Eoin, architect from Southwark, London. Click here to see more and shortlist them for your home project.


Planning permission for a loft extension or loft conversion?

A straight loft conversion should not usually require planning permission as you are not altering the external shape of your house. Adding rooflights or skylights also be covered GPDO (permitted development) rules, so don’t require planning permission. However, you should also check if your permitted development rights are restricted or have been removed (see below)*

If you intend to extend your roof space as part of your loft conversion, planning permission may be needed.

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Does a mansard roof extension need planning permission?



If you have a valley (aka butterfly or London) roof as in the diagram below, it will usually require a mansard roof extension, which will require planning permission.

Mansard roof extensions


Does a rear dormer loft extension need planning permission?



A rear dormer extension will usually be acceptable under GPDO (permitted development), and so not requiring planning permission. See the rules in the box below. However, if the dormer is on the principle elevation (i.e. fronts the road/path) it will need planning permission (see the box below for the rules). However, you should also check if your permitted development rights are restricted or have been removed (see below)*


dormer loft extension


Permitted development rules for loft conversions

1. An extension beyond the plane of the existing roof slope of the principal elevation that fronts a highway is NOT permitted development.

2. Materials to be similar in appearance to the existing house.

3. Cannot extend up beyond the existing highest point of the house.

4. No verandas, balconies or raised platforms.

5. Any side-facing windows must be obscure glazed and non-opening unless the parts which can be opened are more than 1.7 metres above the floor of the room in which it is installed.

6. Must not exceed 40 cubic metres for terraced houses and 50 cubic metres for detached and semi-detached houses.

7. Roof extensions, apart from hip to gable ones, to be set back at least 20cm from the original eaves. The 20cm distance is measured along the roof plane (fig.1)


Permitted development rules loft conversions


Summarised from information provided by the Planning Portal. Please consult with your local planning department directly before undertaking your extension.


Does a HIP TO GABLE loft extension need planning permission?



A hip to gable extension will usually be acceptable under GPDO (permitted development), and so does not require planning permission – see the rules in the box above. However, you should also check if your permitted development rights are restricted or have been removed (see below)*

Hip-to-gable roof




*Have your permitted development rights been restricted/removed?

There are certain situations to be aware of where permitted development rights do not apply in your area or to your property:

  1. Your permitted development rights have been removed or restricted due to:
    • local restrictions
    • covenants
    • your property is listed
    • being in a conservation area or other protected area in the UK (AONBs, national parks, SSSIs, World Heritage sites, etc.)
    • an Article 4 direction
    • a previous planning application (e.g. your roof extension area allowance may have already been used up!)
  2. The property is a flat or maisonette.
  3. You don’t own the whole property.


Do you need to apply for permitted development?

You are not required to apply for permitted development for a loft conversion.

Certificate of Lawful Development

To be completely sure that your project meets permitted development guidelines and that permitted development rights apply for you, It is usually a good idea to obtain a certificate of lawful development (ideally prior to construction). Not only will this provide peace of mind, it will also provide proof for a future buyer of your home that the development is lawful.


Do you need building regs approval for a loft conversion?

Yes.  It’s a legal requirement and without approval your local council could force you open up or re-build sometimes significant aspects of the project. It could even lead to prosecution and fines.

There are a few ways of obtaining building regulation approval detailed in our other recent post here but for a loft conversion, the most common route is to submit a building notice to the council before the work starts. Make sure you consult with your builder and/or architect and agree who will be responsible for this notice.

We’d strongly recommend working with an architect as you will need to be confident that the work will comply with building regulations, otherwise you might have to demolish/re-do any work that does not comply.

If you’d like some help finding the right architect for a loft extension visit our home page to find out more or use the form below.


Here are some more helpful articles to help you plan your loft conversion:


How to plan a loft conversion – the dos and dont’s – advice from the experts

Loft conversion plans – where to start – building regulation requirements

What is the average and minimum ceiling heights in a house?

How much does a loft conversion cost?



Emily  Design for Me

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