Full Rewire vs Partial Rewire

If you've been told your house "needs rewiring", it's reasonable to ask: all of it? Sometimes the answer is yes. Often it's no, and replacing a few circuits, or simply the consumer unit, will make the house safe at a fraction of the disruption. This guide explains the difference.

What each one means

A full rewire replaces every circuit in the property: lighting, sockets, cooker, shower, immersion and any outdoor supplies, plus the consumer unit and earthing arrangements. Nothing old is left in service.

A partial rewire replaces some circuits and keeps others. Typical examples are rewiring the ground-floor sockets and kitchen while leaving recently rewired upstairs circuits alone, or replacing old lighting circuits that have no earth.

How to tell which you need

The clues tend to fall into two groups.

Pointing towards a full rewire

• Rubber-insulated, fabric-covered or lead-sheathed cable anywhere in the house. Where it's found in one place, it's usually elsewhere too.
• Insulation resistance tests showing breakdown across most circuits.
• A house about to be gutted for renovation anyway.

Pointing towards a partial rewire

• Most of the wiring is modern PVC cable and tests well, with problems confined to one or two circuits.
• An extension or kitchen was wired off an old circuit that can't cope.
• Lighting circuits lack an earth but the socket circuits are sound.

What an EICR shows

An Electrical Installation Condition Report is the most reliable way to decide. It records the type of wiring, tests insulation on each circuit, checks earthing and bonding, and codes every problem by severity. A report showing insulation breaking down on every circuit is a strong case for a full rewire. A report with problems on two circuits points to a partial one. Without a report, any recommendation is partly guesswork.

Disruption compared

A full rewire affects every room. Floorboards come up, walls are chased and the house will need plastering and decorating afterwards. A partial rewire limits that to the rooms involved, though cables still have to get back to the consumer unit, so a few other areas may be touched. In both cases, making good and decorating are usually separate from the electrical work unless agreed.

Cost drivers compared

For either job, the main factors are:

• The number of circuits being replaced.
• How many sockets, switches and lights you want, especially if you're adding more.
• Access: solid floors, finished ceilings and tight lofts take longer to route cables through.
• Whether the property is empty or lived in.
• Whether a new consumer unit is included, which it almost always is on a full rewire.

A partial rewire costs less overall, but the cost per circuit can be higher because of the work needed to connect new to old neatly.

When a consumer unit upgrade alone is enough

If the wiring itself tests well and the main issue is an old fuse box with no RCD protection, replacing the consumer unit may be all that's needed. It brings modern protection to every circuit without disturbing walls. The catch is that a new board's RCDs will expose any hidden leakage, so the circuits must be tested first. See our page on consumer unit upgrades.

For more on the practical side of rewiring, see our house rewires page.