Whole-House Rewiring in a London Renovation: Scope, Specification, and What to Expect

When a Full Rewire is Required

A full rewire — replacing all fixed wiring, consumer unit, and associated accessories throughout the property — is required in most London townhouses built before 1970 and in many built before 1990. The indicators that trigger this requirement are:

Wiring age and type: Original rubber-insulated wiring (black rubber sheathing, present in houses wired before the 1960s) is brittle with age, the insulation cracks and may expose conductors, and it does not comply with modern wiring regulations. It must be replaced. Early PVC-insulated wiring (from the 1960s and 70s) is more durable but typically lacks an earth conductor in older circuits and is sized for the appliance loads of its era — insufficient for modern use. Wiring of this age should be replaced as part of any comprehensive renovation.

Consumer unit: Original fuse boards with rewirable fuse wire (common up to the 1980s) do not provide the protection offered by modern RCD-protected consumer units and should be replaced. A modern split-load consumer unit with RCD protection on all circuits is required by the 18th Edition Wiring Regulations (BS 7671) for new installations.

Insufficient circuits and sockets: A property wired in the 1960s or 70s will have far fewer socket outlets than is practical for modern use — a bedroom with two double sockets was standard; a kitchen with four or five sockets was generous. Modern usage requires far more: a kitchen needs twelve or more outlets for appliances, a home office needs dedicated circuits, and the proliferation of USB-charged devices means socket provision that was adequate twenty years ago now feels immediately inadequate.

Lack of documentation: If there is no electrical installation certificate or periodic inspection report for the existing installation, its condition cannot be assessed without intrusive investigation. A rewire provides a clean baseline with full documentation.

Design and Specification

A rewire for a prime London property should begin with a design stage that establishes:

Circuit layout: The number and type of circuits (lighting, ring final power, dedicated appliance circuits, bathroom shaver sockets, EV charging, outbuildings) and their allocation to the consumer unit. For a four-storey townhouse, a minimum of 20–30 ways in the consumer unit is typical; larger properties or those with extensive smart home or AV systems may require a second consumer unit.

Consumer unit specification: A split-load consumer unit with dual RCDs or RCBO protection on all circuits. RCBO (residual current circuit breaker with overcurrent protection — a combined MCB and RCD in one device) protection per circuit is the premium specification: it isolates only the affected circuit on a fault, rather than tripping an RCD that takes out half the house. For properties with home automation, a dedicated consumer unit for smart home circuits may be appropriate.

Cable routing: In a London townhouse, electrical cables must be routed from the consumer unit (typically in the basement or ground floor) to every room on five or six floors. Routes should be planned to minimise the length of cable runs, to avoid structural elements that cannot be chased (particularly concrete floors or load-bearing walls that require structural engineer approval for chasing), and to allow future access. Cable management in voids (floor and ceiling voids, service ducts) is preferable to chasing into masonry wherever possible.

Socket provision: For a prime residential property, the socket schedule should specify every socket outlet in every room: the number of outlets, their position on the wall (height and horizontal position), whether USB-A or USB-C charging outlets are to be integrated, and whether any sockets are to be fused connection units for specific appliances (under-counter refrigerators, dishwashers, boiling water taps). A typical prime residential kitchen will have 14–20 socket outlets; a bedroom 6–10; a home office 8–12.

Lighting circuits: Each floor should have at least one dedicated lighting circuit (two for larger floors). All lighting circuits should be specified to accommodate dimming — this requires confirmation that the specified LED drivers are dimmer-compatible and that the dimmer types are compatible with the LED loads.

Data and communications: The electrical specification should be developed in conjunction with a data cabling specification (structured cabling for networking — Cat6A to every room, with a central network patch panel), telephone, and any audio-visual infrastructure (HDMI or speaker cables to specific wall positions). These low-voltage systems are installed by a separate specialist contractor but their cable routes and back boxes must be incorporated into the first fix electrical programme.

Smart Home Pre-Wiring

For a property where home automation is planned or contemplated, the rewire is the critical opportunity to install the infrastructure. The incremental cost of installing KNX bus cable, Lutron conduit, or CAT6 data cable during first fix electrical — when walls are open and cable runs are straightforward — is minimal compared with the cost of retrofitting it after plastering and decoration.

Minimum smart home pre-wiring for a prime London property should include: - Multi-core cable (typically KNX or Lutron Homeworks specification) from every switch position to the nearest distribution board, allowing retrofitting of smart switches and dimmers - Data cable (Cat6A) to every room, to a central patch panel in a comms cabinet - HDMI and audio cable to intended AV positions in principal reception rooms, bedrooms, and kitchen - Conduit in concrete or inaccessible floor constructions where additional cables may be required in future

First Fix and Second Fix

Electrical work proceeds in two stages separated by the plastering programme:

First fix: All cable routing, back box installation, and conduit. Cables are run from the consumer unit position to every outlet, switch, and luminaire position and left with sufficient tail for connection. Back boxes (metal or plastic mounting boxes set into the wall or ceiling) are installed and set to the correct depth for the specified accessories. All cables are labelled at both ends. At the end of first fix, the wall and ceiling surfaces are ready for plastering.

Second fix: Installation of accessories (sockets, switches, dimmers, data outlets), luminaires, and consumer unit after plastering and before decoration, or after decoration depending on the finish sequence. Connection of all circuits to the consumer unit. Testing and commissioning of the complete installation to BS 7671.

Testing and Certification

On completion, the installation must be tested by the installing electrician and an Electrical Installation Certificate (EIC) issued. The EIC records the installation details, test results for every circuit (insulation resistance, earth loop impedance, RCD operating times), and confirms compliance with BS 7671. The EIC should be retained with the property documentation — it is required for buildings insurance claims involving electrical faults and for any future Part P notification work.

For properties being sold, a valid EIC or an Electrical Installation Condition Report (EICR) less than five years old is increasingly expected by solicitors and mortgage lenders.

Programme and Disruption

A whole-house rewire of a four-storey London townhouse takes 4–8 weeks for first fix and 2–3 weeks for second fix, with a testing and commissioning period of 2–3 days at the end. This is one of the most disruptive trades on a renovation project — it requires access to every room, involves chasing into walls and ceilings (generating significant dust and debris), and must be coordinated with plastering (which follows first fix) and decoration (which follows second fix).

The rewire should be programmed as an early trade, immediately following any structural works and demolition, so that first fix can be completed before plastering begins. Attempting to introduce a rewire into a programme after plastering has been completed — as sometimes happens when an inadequate existing installation is discovered late — is extremely expensive and disruptive.