Permitted development for outbuildings
Most garden rooms are built under permitted development, meaning a separate planning application usually isn't needed, but the rules depend on the building's height, position relative to boundaries, and how much of the garden is already covered by other outbuildings. Horsham District Council's planning pages, GOV.UK's guidance on when permission is required, and the Planning Portal's outbuildings guidance all cover this in more detail.
Ancillary use versus a self-contained space
A garden room built under permitted development is generally treated as space that supports the main house, an office or a gym, rather than as an independent dwelling. If you're considering something closer to a self-contained annexe, it's worth raising this with the council directly, since the planning position can differ.
Foundations, drainage and power
Ground conditions vary considerably across the villages this site covers, from heavier clay to more free-draining soil, and a sloping garden is common in some of the more rural spots. A local installer will usually want to see the plot, or good photos and dimensions, before confirming the right base and how power will be run out to it.
Insulation for year-round use
For daily, year-round use, proper insulation in the walls, roof and floor, along with double or triple glazing, matters far more than it would for a basic garden shed. Any mains electrical connection should be carried out and tested by a qualified electrician.
Frequently asked questions
Do I need planning permission for a garden room?+
Many garden rooms fall under permitted development, subject to size, height and position, but this depends on your specific property. Horsham District Council's planning pages are the place to check.
Can a garden room be used as a bedroom?+
One built under permitted development is generally treated as ancillary to the main house rather than a self-contained dwelling. Raise your intended use directly with the council if you're considering something more independent.
Will I need an electrician?+
Yes, any connection to the mains electricity supply should be carried out and tested by a qualified electrician.
Useful local links
- Crawley Borough Council – Planning — The planning authority for Crawley, which sits outside the Horsham district boundary.
- GOV.UK – Planning permission: when you need it — Government guidance on when planning permission is required in England and Wales.
- GOV.UK – Party Wall etc. Act 1996 guidance — Government guidance on notifying neighbours and resolving disputes over shared or boundary walls, relevant to attached garage conversions.
- Planning Portal – Garage conversion — National guidance on when planning permission is needed for a garage conversion in England.
- Planning Portal – Extensions — National guidance on permitted development rules for single-storey house extensions.
- Planning Portal – Outbuildings — National guidance on permitted development rules for garden buildings and outbuildings, including height and coverage limits.