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Home extensions are one of the most common large home improvement projects in Aberdeenshire. A new kitchen, a side return, a loft conversion, or a single storey rear extension all add living space and usually add electrical demand: more lighting, more sockets, sometimes a new bathroom, often a heat pump or upgraded heating circuit. The consumer unit is at the centre of how this electrical work is planned and delivered. For most Aberdeenshire extensions, a consumer unit upgrade is part of the project. This guide explains how the upgrade fits into the wider build, what it costs, and how to coordinate the electrical work with the extension programme.
Why extensions usually trigger a consumer unit upgrade
Three factors typically push an extension project toward a consumer unit upgrade:
Spare ways are exhausted
An existing 8 or 10 way consumer unit fully populated with the existing circuits has no spare slots for the new extension circuits. A typical extension adds 2 to 5 new circuits (lighting, ring main, fixed appliances, possibly a dedicated heating circuit). The consumer unit needs to expand to accommodate them.
RCD coverage requirements
The new extension circuits must meet current Wiring Regulations including comprehensive RCD protection. If the existing unit does not provide RCD protection on the bank where the new circuit would land, either the new circuit gets a separate RCBO or the unit needs upgrading to provide consistent protection.
Building Standards notification
Adding new circuits is notifiable work under Building Standards. The notification covers the new circuits and the consumer unit. If the existing unit no longer meets current standards in some respect, the notification process is cleaner if the unit is upgraded as part of the project rather than left as a known limitation.
Typical extension circuits added
For a typical Aberdeenshire single storey rear extension or kitchen extension, the new circuits typically include:
- Lighting circuit: Lighting for the new room, often with switching at multiple points.
- Ring main: A new socket ring providing power outlets in the extension.
- Cooker or hob circuit: If the kitchen is being relocated to the extension, a new dedicated circuit for the cooker or induction hob.
- Oven circuit: Where the oven is separate from the hob, a second dedicated circuit may be needed.
- Fridge or freezer circuit: Sometimes a dedicated circuit for refrigeration where the kitchen layout requires it.
- Bathroom or utility room circuits: Where the extension includes a bathroom or utility, typically a fan, lighting, and shower or immersion circuits.
- Heating circuit: Where the extension is heated by an electric boiler, electric underfloor heating, or a heat pump, dedicated heating circuits.
- External lighting and sockets: Patio lighting, outdoor sockets, garden circuits.
A modest single storey extension may add 3 to 5 new circuits. A larger two storey extension or a major renovation may add 8 to 12 new circuits.
When in the extension project does the consumer unit upgrade happen?
Timing matters. The consumer unit upgrade typically happens at one of three points:
First fix electrical stage
Most extensions follow a standard build sequence: foundation, structure, roof, weatherproof shell, first fix services (electrical, plumbing, HVAC) within the open structure, plastering, second fix services (sockets, switches, accessories), decoration, completion. The consumer unit upgrade is best done at the end of the first fix stage, just before plastering. The new cables for the extension are run during first fix and terminated at the new consumer unit; the cables to existing circuits are also reterminated at the new unit at this point.
Before the first fix electrical stage
For some projects (typically where the existing consumer unit needs replacing for safety reasons regardless of the extension), the upgrade is done before the first fix electrical work begins. This gives the contractor working in the extension a clean unit to terminate the new cables at, but it means the existing house has new cables running to the new unit early in the project.
As a separate project after the extension is complete
Where the existing consumer unit can accommodate the new extension circuits without immediate replacement (some spare ways available, RCD protection adequate), the extension is wired into the existing unit and the consumer unit upgrade is deferred. This is the lowest cost option but typically just defers the upgrade to a later date.
Faithful Spark advises on the right timing for your specific project at the survey stage based on the existing unit’s condition, the extension scope, and your overall project programme.
Cost of consumer unit upgrade as part of an Aberdeenshire extension
Pricing for a consumer unit upgrade aligned with an extension project:
- Standard 12 way unit (typical for a 3 bedroom home with a single storey extension): £600 to £800.
- Larger 14 to 18 way unit (for a 4 bedroom home with a substantial extension): £700 to £950.
- 20 way or larger unit (major extension or two storey extension with multiple new circuits): £850 to £1,200.
- Hybrid full RCBO unit on a larger property: £80 to £150 above the standard unit price.
The cost is usually slightly higher than a like for like consumer unit replacement because the new unit has more ways and accommodates additional protective devices for the extension circuits.
Adding the new circuits themselves is a separate cost line, typically £180 to £350 per circuit depending on cable run length and accessory specification. For a typical single storey rear extension with 4 new circuits, the new circuit cost is approximately £800 to £2,000 alongside the consumer unit upgrade.
Coordinating the electrical work with the main contractor
Most Aberdeenshire extensions are managed by a main contractor who subcontracts the electrical work to a specialist firm. Faithful Spark works with main contractors in two ways:
Direct engagement by the homeowner
Some homeowners prefer to engage Faithful Spark directly for the electrical work, with the main contractor coordinating but not subcontracting the electrics. This puts the homeowner in direct control of the electrical specification and pricing.
Subcontract to the main contractor
For larger projects, the main contractor often subcontracts the electrical work to Faithful Spark as part of the overall project quote. The homeowner deals only with the main contractor on commercial matters.
Either approach works. The choice depends on the homeowner’s preference and the size of the project. Faithful Spark coordinates with the main contractor on programme, sequence, and on site working as standard.
Building Standards notification
Most extension electrical work is notifiable under Building Standards. The notification covers the new circuits, the modifications to the existing installation, and the consumer unit changes. Faithful Spark is NICEIC registered and self certifies the work through the NICEIC competent person scheme. The homeowner does not need to engage with Aberdeenshire Council Building Standards directly for the electrical element.
For new build extensions or where structural changes are part of the project, separate Building Warrant approvals are required for the structural elements. The electrical notification sits alongside but does not replace the broader Building Warrant process.
Common extension electrical considerations specific to Aberdeenshire
Granite property cable routing
Aberdeen and Aberdeenshire have a substantial stock of granite properties. Routing new cables through granite walls is more challenging than through brick or block. Faithful Spark identifies cable routes during the planning stage so the main contractor can plan structural openings appropriately.
Heat pump installations in extensions
Many Aberdeenshire extensions include a heat pump installation. Heat pumps need a dedicated circuit, often three phase for larger units. The consumer unit upgrade may need to accommodate a three phase distribution element where the heat pump requires it. Faithful Spark advises at the heat pump specification stage on the consumer unit implications.
Solar PV with extensions
Where the extension includes solar PV (often on a new south facing roof), the solar inverter connects to the consumer unit. The new unit accommodates the solar import and export protection alongside the existing and new circuits.
EV charger circuits in larger extensions
If the extension includes new garage or driveway space, an EV charger circuit is often included. The new consumer unit accommodates the Type A or Type B RCD protection required for the EV charger.
Smoke and heat alarm upgrades
The 2022 Scottish smoke detection standards require interlinked mains powered alarms throughout the property. Adding an extension typically requires the alarm system to be extended to cover the new spaces, which is usually done at the same time as the consumer unit upgrade.
Frequently asked questions
Can the existing consumer unit be reused if it has spare ways?
Possibly. If the existing unit has comprehensive RCD protection, accepts the appropriate brand of RCBO for the new circuits, has spare ways for the extension circuits, and is in good condition, it can stay. Faithful Spark assesses this at the survey stage. For most older units, the upgrade is more cost effective than working around the existing unit’s limitations.
When in the build programme should the consumer unit be upgraded?
End of first fix electrical, just before plastering. This is the most efficient point because the new cables can be run, terminated at the new unit, and tested before the walls are closed up. Doing the upgrade later requires more cable accessibility work and risks delays to the plastering programme.
Will the extension need its own separate consumer unit?
Most extensions add circuits to the main consumer unit, not a separate unit. A separate sub board may be appropriate where the extension is self contained (a granny annex, a converted outbuilding). Faithful Spark advises on the right approach at the design stage.
Can my main contractor do the electrical work?
Only if the main contractor includes a NICEIC or SELECT registered electrician in their team. Some main contractors have an in house electrician; many subcontract to a specialist firm. Either route works provided the electrician is registered and certifies the work.
Will I need an EICR after the extension is complete?
Not strictly. The new electrical work is documented in an Electrical Installation Certificate covering the additions and the consumer unit. A full EICR of the wider installation is typically not needed unless one is otherwise due (5 year cycle for landlord properties, 10 year recommendation for owner occupiers). For more on EICRs see our companion guide on EICR services in Aberdeen.
Book an extension electrical survey
Faithful Spark works with Aberdeenshire homeowners and main contractors on extension electrical projects. Free survey at the planning stage, fixed price quote, and coordinated delivery aligned with the main contractor’s programme. See our pillar guide on consumer unit upgrades in Aberdeen for the full picture.
Faithful Spark Electricians. NICEIC approved. Local Aberdeen team. Consumer unit upgrades, extension wiring, and Electrical Installation Certificates for Aberdeen, Peterhead, Ellon, Fraserburgh and across Aberdeenshire.
