Last edited 12 Nov 2020



[edit] Introduction

Rewiring older buildings can be necessary to prevent fire or injury.

When renovating a property, it is important to ascertain as early in the process as possible, whether rewiring will be required, as the fabric, décor and fittings of the building are likely to be disrupted.

Rewiring will usually be necessary if a building has not been rewired within the last 25-30 years. It may also be appropriate if major remodelling work is being undertaken such as building extensions or conversions.

Such works may fall within the requirements of the Building Regulations Part P: Electrical Safety. This requires that:

Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.

Approved document P: Electrical safety, dwellings, provides guidance for how Part P can be satisfied in common building situations in dwellings.

[edit] Has the building been rewired?

It is usually possible to determine whether a building has been rewired recently by inspecting parts of the wiring that are exposed, as well as the electricity meter and fuse box (consumer unit).

Old and out-dated round-pin sockets or dolly switches will be an indication that rewiring is required. The colour and style of cabling is another indication of rewiring. Modern installations are wired in PVCu insulated cable and are grey or white, while older wiring may be rubber, fabric or lead insulated. PVCu cables should be inspected, as older installations may not have twin-earthed cabling (i.e. a second earth cable running within the outer sleeve). A modern consumer unit will be fitted with miniture circuit breakers (MCBs) and residual current devices (RCDs).

Partial rewiring can usually be identified by the presence of different socket and switch styles in the building, as well as by surface-mounted wiring along skirting boards and walls.

[edit] Rewiring process

[edit] Planning stage

It is important to have a general idea of room layouts before rewiring a building, so that lights, plugs and other electrical items can be positioned appropriately. The purpose of the rooms in terms of lighting, tasks, fire safety, security, and so on, should be considered at this stage. Having to make additions and amendments later is often costly and time-consuming.

It is also sensible to consider ‘futureproofing’ the installation to a certain extent. Will likely technological developments place additional demands on the building, such as Ethernet cables in every room to accommodate uninterrupted WiFi for new smart appliances? Are the requirements of the building occupants likely to change in the future?

For hallways, landings and rooms with more than one access, there may be a requirement for two- or three-way light switching. Other modern features that can be planned for might include automated lighting, home network cabling, speaker cabling, security cabling, heating controls, sensors, door bells, telephone and data, TV aerial sockets, and so on.

If the mains connection and meter need to be moved, the local electricity utility company must carry out this work, with advance notice given and charge paid.

If the building is older or uses materials, such as timber panelling, cob or solid stonework, this should be communicated to the electrical contractor before work begins, as it can impact upon the techniques adopted and procedures followed.

[edit] Time and cost

The average cost of rewiring a three-bed semi-detached house in the UK is around £3,500. Although this price will differ depending on location, property size, accessibility, complexity, and so on.

The time taken will also vary, although the same size house might take around four or five days.

[edit] Works

Rewiring work is categorised as first fix and second fix.

First fix is generally taken to mean the works before plastering. Running new cabling will involve lifting floor coverings, floorboards and possibly skirting boards, as well as routing out channels in the walls. First fix work also involves fitting new back boxes for sockets and switches.

Second fix takes place once the building has been re-plastered, flooring replaced, ceilings filled and made good, and so on, and might include:

[edit] Earth bonding

Earth bonding (also known as cross bonding) ensures that if a fault occurs which causes metal components (such as plumbing, boiler casing, radiators and so on) to become live, they do not pose an electrocution hazard.

Underneath sinks or baths, metal clamps will often be placed around the copper pipes with green-and-yellow striped earth cables. All pipes leading to and from the boiler and heating systems need earth bonding. Buildings using plastic instead of copper pipes require the mains stopcock to be earthed rather than appliances.

[edit] Rewiring in wet areas

Wet areas offer the greatest risk of electrocution and so extra precautions are necessary. Sockets for shavers are permitted away from bath and shower splash zones, but no other power sockets. Switches should be pull-cord operation or battery-powered IR-type switches.

Electrical appliances, including showers, lighting fittings and ventilation fans, must be appropriately protected from moisture, with an appropriate Ingress Protection (IP) number.

There are mandatory requirements for areas containing a bath or shower, as specified by the I.E.E. Wiring regulations (BS 7671: 2001 Section 601). Safety standards are measured in zones, with the perceived risk of electric shock being the basis of each zone’s requirements. The zone categories are as follows:

  • Zone 0: Inside the bath or shower. Any fittings must be SELV (max 12V) and rated IPX7 (protected against water immersion).
  • Zone 1: Above the bath or shower to a height of 2.25 m. Minimum rating IPX4 required.
  • Zone 2: Area reaching up to 0.6 m outside the bath or shower. Minimum rating IPX4 required.
  • Zone 3: Area outside above zones. General rules of BS 7671 apply.

[edit] Electrician or DIY

Part P of the building regulations covers electrical works. While minor repairs, replacement and maintenance work are not notifiable, more significant works, and work in wet areas may be require a Building Regulations application, with the work inspected before and after completion by a qualified electrician. The electrician will check compliance and issue a part P certificate.

Approved document P makes clear that after the works are complete, the installation should be no more unsatisfactory that before the work was started. When extending or altering and installation, only the new work must comply with the building regulations, unless:

Attempting electrical works as a DIY job, can be a false saving, and can result in dangerous defects. A common DIY fault is running the cable at angles across walls. This is in contravention of wiring regulations which require all cables buried in walls to run vertically or horizontally from sockets.

Qualified electricians often work to a fixed price on a supply-and-fix basis. This means that they provide both labour and materials. The price will be calculated according to:

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