Do I Need Planning Permission for a Garden Annexe?
Very often, yes. Being modular or in a garden does not make an annexe permitted development. Planning depends on size, position and especially use: a self-contained annexe is treated very differently from a garden room used incidentally to the house.
Adacon Technical Team · Published
Incidental, ancillary or independent
A garden room for hobbies or an office is usually 'incidental' to the house. An annexe with a bedroom, kitchen and bathroom used by a member of the household is usually 'ancillary'. One used as a separate, independent home is effectively a new dwelling. Each is assessed differently.
Building Regulations
Accommodation for sleeping generally brings Building Regulations into play, covering matters such as fire safety, insulation, ventilation and drainage. Building control confirms what applies.
Council tax
A self-contained annexe may be assessed separately for council tax, although discounts or exemptions can apply in some family situations. Check with your council.
What to do first
Ask your local planning authority about your site, or apply for pre-application advice. Share the intended use honestly — it shapes the answer.
Worth knowing: Planning, Building Regulations and council tax depend on your site and how the annexe will be used. Confirm with your local planning authority and building control before ordering.