List what the building will power
A light and battery charger create a different brief from a garden office with heating or a workshop with larger tools. Write down equipment that may operate together and provide manufacturer requirements for significant loads.
Include likely future equipment, marking what is confirmed and what is still optional. That helps the electrician consider a useful first installation without assuming every detached building needs the same supply.
Describe the route, not just its length
Describe the route, not just its length
Mark the possible route between the house and building. Include driveways, paving, planting, walls and shared or restricted land. Access and reinstatement can affect the work as much as the approximate distance.
HSE guidance on underground services stresses planning and locating services before excavation. Do not dig a route in advance on the assumption that a sketch identifies buried cables or other services. Agree groundworks and responsibilities with the project team.
Have the existing installation assessed
Have the existing installation assessed
The existing supply, earthing, protection and circuit arrangements need consideration alongside the addition. A working socket at the house does not establish that it is the right source for a detached building.
A consumer unit, cable size or earthing arrangement must follow the equipment demand and site assessment. The building’s name or size alone does not provide enough information to choose them.
Coordinate the room and the route
Coordinate the room and the route
For a garden office, mark desks, heating and lighting. For a workshop, mark benches, storage and tools. Share the building supplier’s electrical requirements and identify where the electrician’s work meets another contractor’s installation.
Agree testing, handover and the applicable certification and notification route. In England, a new circuit is notifiable; being outdoors does not by itself make every alteration notifiable.
Your planning checklist
- Building layout and intended use
- Equipment list, heating and future demand
- Approximate distance and route sketch
- Paving, landscaping and other services
- Who provides groundworks and reinstatement
Questions answered
How much does distance affect the cost of electricity to an outbuilding?
A longer route can affect materials and labour, but distance does not explain the full price. Equipment demand, the existing installation, access and reinstatement also matter. A route across a finished drive can involve different work from a similar distance through an accessible garden.
Ask Max about thisCan an old cable to my garage be reused for a garden office?
It needs assessment against the new use and its actual condition, route and protective arrangements. The fact that an existing light works does not establish suitability for office equipment and heating. Provide any records you have and a realistic equipment list before assuming the old supply will remain.
Ask Max about thisShould I dig the trench myself before the electrician visits?
Do not start excavation on an assumed route. Agree the design and groundworks responsibilities first, including precautions for buried services. Plans alone do not establish the precise position of existing cables or pipes. The electrician and whoever undertakes excavation need a coordinated approach before digging begins.
Ask Max about thisDo I need to decide on garden-office heating before arranging power?
Yes, include the proposed heating and other significant equipment in the initial brief. A supply intended only for lights and charging may not suit later sustained loads. If the product is undecided, explain the likely use and separate confirmed requirements from possible future additions.
Ask Max about thisDoes every garden building need its own fuse box?
Not always. The equipment demand and existing supply and protection determine the design. A separate board should be included because the arrangement needs it, rather than simply because the building is called a garden room or garage.
Ask Max about thisFurther reading
These references explain the relevant safety and building guidance. Building Regulations guidance here applies to England.
Updated 24 October 2026.