Planning Permission

Planning permission is not normally required. However, permission is required where you extend or alter the roof space and it exceeds specified limits and conditions. You are viewing guidance for England.

A loft conversion for your house is considered to be permitted development, not requiring an application for planning permission, subject to the following limits and conditions:

  • A volume allowance of 40 cubic metres additional roof space for terraced houses*
  • A volume allowance of 50 cubic metres additional roof space for detached and semi-detached houses*
  • No extension beyond the plane of the existing roof slope of the principal elevation that fronts the highway
  • No extension to be higher than the highest part of the roof
  • Materials to be similar in appearance to the existing house
  • No verandas, balconies or raised platforms
  • Side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor
  • Roof extensions not to be permitted development in designated areas**
  • Roof extensions, apart from hip to gable ones, to be set back, as far as practicable, at least 20cm from the original eaves
  • The roof enlargement cannot overhang the outer face of the wall of the original house.
[NOTE: For an explanation of how to apply the 20cm set back condition please see pages 34-35 of ‘Permitted development for householders – Technical guidance‘.]

*Bear in mind that any previous roof space additions must be included within the volume allowances listed above. Although you may not have created additional space a previous owner may have done so.

**Designated areas include national parks and the Broads, Areas of Outstanding Natural Beauty, conservation areas and World Heritage Sites.

Loft conversions mini guide

Check out our interactive mini guide to loft conversions. loft conversion Loft Conversion loft grab

Access our interactive guide to the planning permission and permitted development regimes for loft conversions.

Please note: the permitted development allowances described here apply to houses not flats, maisonettes or other buildings. View guidance on flats and maisonettes here.

Permitted Development for householders – Technical Guidance

You are strongly advised to read a technical guidance document produced by the Government to help understand how permitted development rules might apply to your circumstances.

Download ‘Permitted development for householders – Technical guidance’

Protected Species

Work on a loft or a roof may affect bats. You need to consider protected species when planning work on this type. A survey may be needed, and if bats are using the building, a licence may be needed.

Building Regulations

Building regulations approval is required to convert a loft or attic into a liveable space.

This section provides guidance for making alterations to the loft space of an existing house which is no more than two storeys high. Requirements for alterations to an apartment or other dwellings like maisonettes, or houses over three storeys, will be similar but may be more extensive and possibly extend to other parts of the building.

The regulations will be applied to ensure, for example:

  • the structural strength of the new floor is sufficient
  • the stability of the structure (including the existing roof) is not endangered
  • safe escape from fire
  • safely designed stairs to the new floor
  • reasonable sound insulation between the conversion and the rooms below.

You may wish to make these alterations to enhance the storage facilities available or to increase the living space of the home.  If you plan to make the loft space more accessible or more habitable by, for example, installing a stair to it and improving it by boarding it out and lining the walls / rafters etc, more extensive work is likely to be required and the Building Regulations are likely to apply.

It is recommended that you contact Building Control to discuss your proposal and for further advice and you must also find out whether work you intend to carry out falls within The Party Wall etc. Act 1996.

Boarding-out for storage

In most homes, the existing timber joists that form the “floor” of the loft space ( i.e. the ceiling of the rooms below) will not have been designed to support a significant weight (known as “load”). The joists tie the pitched members of the roof together to prevent them spreading and support the ceiling lining of the rooms below.

An excessive additional load, for example from storage, it may mean that the joists are loaded beyond their design capacity. If you decide to lay flooring boards over the existing joists in the loft space, then this may require a Building Regulations Application to Building Control. Your local Building Control body will be able to advise you on this issue.

Creating a liveable space

If you decide to create a liveable space (a ‘livable space’ is where you intend to use the room as a normal part of your house, this includes spare bedrooms which may be used infrequently) in an existing loft space of a home it is likely to require a range of alterations.

Many of these could have an adverse impact on the building and its occupants if they are not properly thought out, planned and undertaken in accordance with the requirements of the legislation.

Further Information

The following pages give an indication of some of the elements normally required to satisfy the requirements of the Regulations when converting a loft:

The following common work sections give an indication of several other elements normally required to satisfy the requirements of the Regulations when converting a loft:

Existing walls & foundations

Load bearing walls

With regard to the structural stability of the existing walls when undertaking a conversion of a loft space, consideration will need to be given as to how the new loads will be supported.  For example, if new floor joists are provided and they are to be supported by an existing wall, the wall will need to continue all the way down through the house to a foundation or alternatively the wall will need to be provided with an adequate intermediate support.

Existing openings

Some houses have through lounges on the ground floor where the existing load-bearing wall that did take a load down to the foundation has been removed, or it may have originally been built as a through lounge, with a steel/timber beam installed over the opening.  This beam should be checked that it is strong enough to carry any new loads from the loft conversion are added.

Existing foundations

Generally the additional load (weight) from construction and use of the new loft room(s) does not mean a significant increase on the load being transferred to the foundations.

However, in some cases, the increase in load could be significant and the adequacy of the existing foundations to carry this extra load will need to be checked. It may be necessary for the capability of the foundations to be increased by underpinning them. A structural engineer or your Building Control Body will be able to advise you.

New Dormer

A dormer is generally constructed from timber.  The main parts that form a dormer are the roof, side walls (cheeks) and front wall which faces the garden.  The cheeks can be supported in one of two ways:

  • The rafters can be doubled and bolted together with the cheeks then constructed off the rafters.
  • If the dormer width means the cheeks are at the edges of the roof then the cheeks can be taken down to the floor and supported of the floor joists (which are doubled) or on a beam, or in some cases by the party or external walls.

Dormer Walls

The front wall of the dormer can be supported off the external wall, or if it is to be set back from the external line of the house, it can be supported off the new floor joists, which should be designed to cater for the extra load of this wall (see also external walls).

The dormer may well need to be constructed so as to give resistance to a fire spreading to or from a neighbouring property – the nature and extent of the construction to give this fire resistance will be dependant on the size of the dormer cheek and its proximity to the boundary.

Removal of rafters

To enable a window, rooflight or dormer to be installed when creating new room(s), it is normally necessary to cut an opening in the existing rafters.

The remaining sections of the cut rafter(s) can be supported by the new dormer  or, in the case of a new window/rooflight, will need to be supported by installing new timbers (known as trimmers) across the head (top) or sill of the new opening.

Depending on the size of the new opening, these may need to be two timbers fixed together (double trimmer) so that they can adequately transfer the load to the existing rafters on either side of the new opening.

It generally good practice to strengthen the rafters on both sides of the opening as they are now taking more load. This can be achieved by bolting another rafter of the same size and length to the existing.

New internal elements

The new elements which help to form the new loft room(s) are broadly:

  • Floor & beams
  • Walls
  • Doors

Floor & beams

It is unlikely that the existing ceiling joists will be adequate to support the weight (loads) that arise from the construction, contents and use of a typical habitable room developed in a loft.

To overcome this problem new floor joists would need to be installed to take these new loads.  These can normally be placed between the existing ceiling joists and will probably be larger than the existing joists. If the existing walls are adequate then the new floor joists may be supported on them.

Otherwise additional support – such as steel or timber beams – should be introduced which in turn will be required to be adequately supported and provided with fire resistance.


New walls will contribute to the perimeter of the new room(s) and will help support the existing and new roofs where existing roof supports have been removed.  Such new support for the roof will normally take the form of low level walls towards the eaves of the premises, helping to reduce the span (unsupported length) of the existing rafters.  Other walls, typically loadbearing, will separate the new room(s) from other areas of the home.  These walls may need to be fire resisting.

Sound Insulation

Sound insulation is required between habitable rooms.  With a terraced or semi-detached house, the building control body may also ask for sound insulation between the converted loft and the neighbours loft to be improved.  If they think it is necessary the building control body also ask for a test to be carried out, but this will depend on the neighbours allowing access for the testers.  The existing party wall will need to be upgraded to provided sound insulation between the properties.

Fire safety

Loft Conversions

When converting an existing roof space into a room or rooms the provisions for escape need to be considered throughout the full extent of the escape route. This often means that additional fire protection will be necessary in the existing parts of the house.

For example, a typical loft conversion to a two-storey house will result in the need to provide new fire-resisting doors and sometimes partitions to protect the stairway (see Approved Document Part B Volume 1 FAQ bullet points). This is because it is too dangerous to escape via windows from floors above first floor level.

Mains powered, interlinked smoke alarms will also need to be provided within the stairway at each level.

It may also be necessary to upgrade the fire protection to some parts of the structure of the house such as the floors.

You may also wish to consult ‘Approved Document B (Fire safety) – Volume 1: Dwellinghouses (2006 Edition)‘ .


Fire & general safety

To ensure adequate fire safety for the dwelling a new stair serving the new room(s) will be needed.  Where there is not enough room for a full traditional stair, it may be possible to use a “space saving” stair.  Retractable ladders or stairs are not normally acceptable.

For general safety reasons, there are specific criteria that a stair should be designed to.

Opening for new stairs

This would normally be formed by cutting away some of the existing ceiling joists between the existing habitable areas of the home and the loft-space.  As these joists support the existing ceiling and restrain the pitched roof from spreading, replacement support should be provided.  This would normally take the form of timber “trimmers” around the opening, most likely to be at least two timbers fixed together (double trimmer) to ensure the load is transferred to remaining timbers.


This is an introductory guide and is not a definitive source of legal information. Read the full disclaimer here.

This guidance relates to the planning regime for England. Policy in Wales may differ. If in doubt contact your Local Planning Authority.