Loft Extensions – Electrical Installation

Loft Extensions – Electrical Installation

If you are planning on doing most of the work on your loft extension yourself one of the major obstacles you’ll be faced with is the electrical installation. Any kind of electrical work can be daunting for even the most experienced DIY’er and it is often an area where poor planning at the outset can result in serious problems and delays as the work nears completion.


Any extension to your home will be classed as new building work and must be carried out in accordance with the Building Regulations 2010 and this includes any new electrical installations.

New electrical installations in England and Wales are covered by The Building Regulations Part P1 which require that the installation is designed and installed so it does not pose a danger. To comply with Part P the work must be carried out in accordance with BS 7671 which requires that a new electrical installation must be designed, suitably enclosed and separated by appropriate distances to protect against the risk of electric shock, burn or fire injury.


New installations need to be inspected and tested during installation and before they are taken into service to ensure they comply with Part P and any other relevant parts of the Building Regulations.

Electrical work on dwellings (domestic properties) falls into two categories – notifiable and non-notifiable. A project is classed as notifiable where there will be new circuits back to the main consumer unit or where there are extensions to existing circuits in special locations.

If you are employing a contractor to carry out the work he will need to be

  • Registered in accordance with a self-certification scheme, in which case he can issue a BS 7671 installation certificate; or, 
  • Be qualified to carry out inspection and testing, although Building Control will still need to be notified prior to the work starting and they may require further testing to be carried out before a certificate is issued.

If you plan to do all the work yourself you will need to inform your local council’s Building Control department before starting work and they will decide on the level of testing and inspection required. They may carry out the inspections themselves or designate a third-party.


Before starting any work you’ll need to think about what you actually need in terms of electrical outlets and how they will be supplied?

RCD Devices

All sockets and outlets will need to be protected by a Residual Current Device (RCD) in accordance with BS 61008. RCD protection will also be needed where a cable is installed near metal parts (for instance, if you are using metal section stud walling); or where a cable is installed in a wall at a depth of less than 50mm – unless protected by steel conduit or trunking (in both instances).

Electrical Outlets and Fittings

The requirements and positions for electrical fittings and outlets such as lights, power sockets, smoke detectors, phone/network outlets, etc. will need to be decided early on so that provision can be made for cable runs within stud walls, partitions and floors.

The planned use of the room will have a bearing of the number and type of outlets you’ll need. However, in accordance with NHBC guidelines, a main bedroom will require 6 x 13A outlets and any other bedroom 4. For a landing 2 outlets will be required and a for hallway 2 outlets (a double socket counts as 2).

(Source: NHBC Standards: Part 8 Services and Internal Finishing)

The number of light fittings you’ll need will depend on the intended use. However, the Building Regulations Part L (Conservation of Fuel and Power) require that low energy lighting is installed in a reasonable number of locations and to comply with this in a loft conversion you should fit one energy efficient light fitting per 25m² or one in every four fixed light fittings, whichever is greater.

Loft extensions typically have low ceilings and the use of halogen lighting can cause over-heating. It is worth bearing this in mind and avoiding the use of halogen lights wherever possible.

Also, lighting in stairways is important, especially where non-standard flights are in use. Ideally you should provide lighting so it falls on the treads and not the risers and so the top and bottom of the flight are clearly lit. Two way switches should be provided at the top and bottom of the stairway.

Wall-mounted sockets and switches should be located so they are reachable. As a guide sockets should be mounted 450mm from the floor and light switches or consumer units no more than 1200mm from the floor.

If the loft is to be used as a living space then you’ll be required to fit a mains operated smoke detector in circulation spaces of each floor of the building – interlinked so that when one is triggered the alarm is sounded on every floor. The detector needs to be fixed within 7.5m from the door of any habitable room and at least 300mm away from any light fitting. The power should be supplied through a dedicated circuit, unless there is a battery back-up in which case you can connect to the lighting circuit.

Any bathroom/toilet or shower room must be provided with an extraction unit. Although this could be a passive stack system it is likely you’ll opt for a mechanical system which will need a source of power.

For heating controls the minimum requirements are set out in the Domestic Heating Compliance Guide for the particular type of appliance and heat distribution system:


Cables without special protection should be positioned vertically or horizontally from the socket being served , not less than 50mm below the surface of a wall and not less than 50mm from the top or bottom of a timber joist or batten in a floor or ceiling.

Safety services (smoke alarms) need to operate for as long as possible in the event of a fire so cabling needs to be fire-resistant.

Cables shouldn’t be placed within or over thermal insulation material unless they have been appropriately sized as the presence of insulation can reduce the current carrying capacity of electrical cables.

For domestic installations harmonised cable core colours can be used – the same as those used for domestic appliances – i.e.: green/yellow – earth; blue – neutral; brown – live.

Stay up to Date

All information is for guidance only and is not exhaustive. Legislation is constantly being updated so it is important to check that you are working to the latest revision. The Planning Portal is a useful source of up to date information and your local council’s planning and building control department can provide further guidance if you need it.

References and further reading:

NBS Shortcuts – Lofty Aspirations

BRE Good Building Guide GB8 69 pt.2 – Loft Conversion: Safety, insulation and services

BRE Digest DG525 Domestic Smoke Alarms

BRE Thermal Insulation: Avoiding the risks

NICEIC Part P Fact Sheet

A Practical Guide to the 17th Edition of the Wiring Regulations Christopher Kitcher

Planning Portal Guide to Electrical Work

British Standards

BS 5446-2:2003 Fire detection and fire alarm devices for dwellings. Specification for heat alarms

BS 5839-1:2002 Fire detection and alarm systems for buildings. Code of practice for system design, installation and servicing

BS 5839-6:2004 Fire detection and fire alarm systems for buildings. Code of practice for the design,

installation and maintenance of fire detection and fire alarm systems in dwellings

BS 7671:2008 Requirements for electrical installations.

BS EN 61008-1:2004 Residual current operated circuit-breakers without integral over-current protection for household and similar used (RCCBs).

Building Regulations

Approved Document B: Fire Safety (volume 1) – Dwellinghouses
Approved Document L1A: Conservation of fuel and power – New dwellings
Approved Document L1B: Conservation of fuel and power – Existing dwellings
Approved Document P: Electrical safety – dwellings