An annexe charger follows the supply it is attached to. If the flat runs off the main house consumer unit, the car, the main kitchen and the annexe kitchen share one cut-out. If the annexe has its own meter, the charger should sit on that supply and that bill. Planning permission may also matter if the annexe is, or will be, a separate dwelling rather than a room for a family member. Sort the supply and the planning story before you mount anything.
One meter or two
Look at the meter, not the estate agent's floorplan. A submain to a small consumer unit in the annexe is still the house supply. A second MPAN and a second bill means the network already treats it as its own connection. The charger belongs on the supply of the person who will pay for the miles.
A long submain across a garden is a cable job in its own right. Voltage drop, protection and where the isolation sits should be in the quote. A family member in the annexe should not have to knock on the main house to reset a breaker they cannot reach.
Ancillary room or separate home
Councils distinguish accommodation that is ancillary to the main house from a self-contained dwelling you let or sell. Using an outbuilding as a separate home can need planning permission even when the walls are already there. This guide is not a planning decision. Ask the council before you wire a charger into a flat you intend to rent.
Listed buildings and homes in conservation areas can need consent for the box on an outbuilding even when the use is only ancillary. A timber garden room and a brick coach house are not the same mounting job.
The load is the whole site
A 7kW charger draws about 32 amps for hours. An annexe with its own oven, and a main house with an electric shower, can already sit close to an older 60 or 80 amp cut-out. The survey has to see both boards. Load management can pause the car when the site is busy. It cannot invent capacity the network has not provided.
If the annexe is on its own supply, do not casually feed the charger from the main house because the Wi-Fi is better there. You will put the energy on the wrong bill and the wrong certificate.
Letting the annexe
A tenant needs written consent, a clear bay, and a rule for the electricity. Landlord grant routes and occupant grant routes are different, and many owner-occupied annexes qualify for neither. Check GOV.UK on the day you apply. Do not install first.
Private rented electrical safety rules can apply to a let annexe. Keep the charger certificate with the inspection record. Agree whether the unit stays if the tenant leaves.
- Photo of the meter that will pay for the car
- Whether the annexe is ancillary or a separate dwelling
- Bay location and lead route that does not cross a shared path
- Who holds the app login and the isolation key
New rooms are not automatically Part S
Approved Document S is about chargepoint infrastructure for certain new residential buildings and some major renovation, not a promise that every granny flat must leave the site with a 7kW charger. A retrofit annexe is usually a survey and a dedicated circuit, plus planning if the use is changing.
VAT on electrical work to an existing building is normally 20%. Zero-rating is a narrow rule for chargepoints incorporated in qualifying new dwellings. An outbuilding in the garden of a house you already live in is unlikely to be that case. Ask the contractor to show the rate on the quote.
Frequently asked questions
Can the annexe share the house charger?
Only if the lead reaches the annexe bay without a trip hazard, and everyone accepts whose bill pays. A dedicated point on the right supply is usually clearer.
Does a garden room need its own fuse at the street?
Not if it is fed from the house and the house supply can take the load. A separate dwelling with its own address may already have, or may need, its own connection. The network operator decides new supplies.
What if the annexe is off-grid for broadband?
The electrical design is unchanged. Scheduling may need a charger that still works with poor signal. That is a specification line, not a reason to skip earthing.
Can I claim a grant because a relative lives there?
Only if a live OZEV scheme fits the tenure and the parking. Family use of an owner-occupied house is often outside the household grants. Check GOV.UK.
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How this guide was prepared
This guide was written by the Local EV Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.