Loft conversion

If any of the following occur then the works are considered to be a loft conversion and an application will be required, irrespective of the proposed use of the room:

  • Permanent fixed stair (not retractable ladder)
  • Installing a floor
  • Lining of walls/rafters

If any of the following occur then the works are considered to be a structural or material alteration or other controllable works and an application will be required:

  • In all cases the installation of rooflights would constitute building work and a Building Regulations application would be required
  • Any alterations to the existing roof structure, e.g. removal of purlins / struts is a structural alteration and a Building Regulations application would be required

A limited area of boarding on the floor in the loft space is permitted for access/maintenance, light storage. However if there are any doubts about the ability of the structure to support the additional loading you are advised to seek guidance from a competent person.

If you are unsure about any aspects of building work then please consult your local Building Control department who will be happy to advise you.

Guidance notes for construction professionals on when work to a loft area is controllable under the building regulations 

This guide only applies to the conversion of lofts within single occupancy bungalows and two storey houses. Additional and different criteria apply to other buildings.

The aim of this guidance is to provide you with an idea of what is required before you submit an application under the Building Regulations for proposed works involving the conversion of the roof space of a dwelling.  It is not intended to provide comprehensive details of the associated regulations but highlights the most important matters that you need to consider. Such works can be more complex than other extensions and we recommend that you seek professional assistance before submitting a Building Regulation application for us to check.

Structural considerations

Most ceiling structures are not strong enough to serve as a floor.  Upgrading the structure will involve the installation of new floor joists and in some cases steel or timber beams to carry the floor and roof loads. Existing walls, lintels and beams may need to be assessed for adequacy to carry additional loads. In some cases foundations may need to be exposed and checked.

The involvement of a Structural Engineer is normally needed to calculate the sizes of new structural members.

Fire safety

For the conversion of the attic of a single storey dwelling (bungalow), it may only be necessary to provide escape windows to the new habitable rooms at first floor and mains interlinked smoke detectors/alarms in the circulation spaces on the ground and first floor.

(Escape Windows Each habitable room at first floor should be provided with an escape window having a clear opening area of at least 0.33m2 and a minimum dimension (height or width) of 450mm (e.g. 750mm x 450mm) and positioned between 800mm and 1100mm above the finished floor level.

If a pass door is provided between the two rooms and both rooms open onto the new stairway, then only one escape window need be provided.

The formation of a room in the roof of a two storey house creates a potentially increased risk to occupants of the new floor in the event of a fire.  As a result of this the regulations require that a protected escape route be formed from the new rooms at second floor level to a final exit at ground floor level such as the front door. The structure forming this enclosure must have 30 minute fire resistance and the doors must be fire doors. Existing floors separating rooms from landing areas may need to be upgraded to achieve a 30-minute fire rating.

Fire safety - smoke detectors

Smoke alarms should be fitted at every floor level.  These should be mains powered with a battery back up supply and conform to BS.5446.  Optical type detectors (rather than ionisation type) are less prone to false alarms.  They should be fitted in hallways and landings ensuring that manufacturers’ guidance on location and maintenance is followed.  They should also be linked so that a single unit activating will set off all the sounders in the dwelling.

Fire safety - enhanced fire detection option

In certain circumstances it may be appropriate to compensate for an escape route that does not meet the above standards of fire protection by including an enhanced automatic fire detection and alarm system.  It may be that an owner would prefer not to change internal doors for fire doors. The designer should discuss and agree this in advance with their Local Authority Building Control service provider.

This option is applicable in the case of typical loft conversions forming up to two new rooms at second floor level with a total floor area not exceeding 50 square metres and no one floor level in the property exceeding 200 square metres.

In such cases Building Control may accept the provision of a Grade D LD1 standard fire alarm system as described in BS 5839 Part 6 in lieu of fitting replacement fire doors to rooms off an enclosed stairway.

Such a system will have smoke detectors sited in hallways and landings at all floor levels. They must also be sited in all habitable rooms and areas where a fire might start that communicate with the stair enclosure. Heat alarms should be used in place of smoke alarms in kitchens and other rooms with a use that may trigger false alarms. Any cupboards containing potential ignition sources that are off the stair should also be provided with a detector or should be fitted with a FD30 fire door.

Hard-wired or radio-linked systems are acceptable. All detectors link to central control and indicating equipment as below. Mains power should be sourced from a regularly used local lighting circuit with lithium type rechargeable batteries giving a 72 hour back up supply.

In adopting this fire safety strategy it is essential that the owner and occupiers are made aware of the above information and of the need for regular testing and maintenance. They should also be informed about the importance of the equipment in providing essential early warning in fire and hence an adequate means of escape. Contact your local office for further information on this option.

Fire safety - escape routes

It is usually necessary for the stair enclosure to lead directly to a final exit to external air (i.e. via a ground floor hallway) without passing through a room (as in fig 1).  If this cannot be achieved then it is permissible to form two alternative routes to exits that are separated from each other by fire resisting construction and fire doors. (as fig2).

Achieving the above requirements can be difficult and undesirable to clients in houses with open plan ground floor layouts. Recognising this, the regulations allow an alternative arrangement incorporating a sprinkler system. Using this option, the ground floor is separated from the upper floor by a fire resisting partition and fire door at either ground or first floor level. A residential sprinkler system to BS 9251:2014 is fitted to cover the ground floor only with any kitchen being separated from the space by fire resisting construction with . This allows a viable alternative emergency escape route from the new loft rooms via suitable escape windows at first floor level. This option requires the i


A retractable ladder is not a permitted means of access to a loft conversion. The three types that can be considered are:

  • A standard staircase
  • A spiral staircase
  • An alternating tread (‘space saver’) staircase

The last type is only acceptable where serving a single room (and a bathroom) and where it is not possible to create sufficient space for a standard or spiral stair.

The pitch (steepness) of the stairs and the dimensions of steps and balustrades must comply with the appropriate Building Regulations contained in Approved Document K.  A full 2.0metre headroom is normally required over new stairs although a reduced dimension is sometimes acceptable under sloping ceilings if this is not achievable. Most local authorities will accept a reduced stair width of 600mm where it only gives access to one or two new bedrooms.

In situations where it is impractical to install a standard stair in a loft conversion, a designer may alternatively follow the guidance for ‘limited access’ stairs in BS 5395-4:2011. This permits steeper pitches of up to 50o and smaller going (tread) dimensions although it includes the requirement to provide stair gates at the top and bottom in the interests of the safety of very young children.

Sound insulation

With conversions in attached properties, the sound insulating properties of party walls within the loft space need to be considered. The Local Authority may require parts of walls to be upgraded where they are of a lesser standard than walls at habitable floor levels. Where no party wall exists in the loft, a new wall must be constructed up to the underside of the roof finish with appropriate fire-stopping measures. The specifications of this wall should comply with Approved Document E that deals with sound insulation.

Thermal insulation

A loft conversion creates new ‘thermal elements’ i.e. walls and roofs that separate the heated space from an unheated space or outside air. The thermal insulating properties of such elements need to be upgraded to comply with Building Regulations. 

Electrical installation

This must comply with Part P of the Building Regulations. Design, installation, inspection and testing should be carried out by a contractor who is a member of a competent person’s scheme for electrical wiring approved by the Secretary of State. If this is not the case then you should check with your local Building Control department for advice on their procedure for checking this part of the work.

The Party Wall Act 1996

The Party Wall Act places a legal responsibility on building owners to give notice to adjoining owners when carrying out works affecting a wall separating dwellings.

This is often applicable for loft conversions in semi detached and terraced properties. The Act is civil legislation that is not enforced by your Local Authority and planning permission and Building Regulations approval does not remove the need to comply with it. Further information on the Act is available on the websites mentioned below

Planning permission

Some loft conversions require planning permission and you are strongly advised to check with the Local Authority’s Development Control section before starting work.

Extra information may be found on the Planning Portal website.