What is the difference between a garden office and an ADU?

A garden office is an ancillary outbuilding used for work purposes — it has no sleeping accommodation, kitchen, or bathroom and is legally part of the main dwelling's curtilage. An ADU (Accessory Dwelling Unit) or granny annexe is a self-contained dwelling with its own entrance, kitchen, bathroom, and sleeping accommodation.

A garden office is an ancillary outbuilding used for work purposes — it has no sleeping accommodation, kitchen, or bathroom and is legally part of the main dwelling's curtilage. An ADU (Accessory Dwelling Unit) or granny annexe is a self-contained dwelling with its own entrance, kitchen, bathroom, and sleeping accommodation. The distinction matters for planning (ADUs usually need permission; offices may not), Building Regulations (ADUs must meet full dwelling standards), council tax (ADUs may attract separate liability), and mortgage/insurance (ADUs need separate consideration).

Why this matters

This question relates to Prefab Timber Cabins: Garden Offices, ADUs & Granny Annexes, which covers the broader topic in detail. Understanding this specific aspect helps architects, builders, and timber dealers make informed specification decisions.

For full context and additional technical detail, see our comprehensive guide:

→ Prefab Timber Cabins: Garden Offices, ADUs & Granny Annexes

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About this answer

This answer is part of the PuurModulair Knowledge Base — comprehensive timber specification guidance for architects, builders, and dealers across the UK, EU, and Scandinavia.