accessory apartment
C1Formal, Technical, Urban Planning
Definition
Meaning
A secondary, self-contained housing unit created within or on the same property as a single-family home.
A legal residential unit that exists in addition to the primary dwelling, typically to provide additional rental income or accommodate extended family members.
Linguistics
Semantic Notes
The term combines 'accessory' (subordinate or auxiliary) with 'apartment' (a self-contained living unit). It is a specific technical term in housing and zoning law, not a general synonym for any small apartment.
Dialectal Variation
British vs American Usage
Differences
In American English, 'accessory apartment' is the standard term in zoning and real estate. In British English, 'granny annexe' or 'granny flat' is more common in everyday speech, with 'ancillary dwelling unit' used in formal/planning contexts.
Connotations
US: Neutral to positive, associated with urban density solutions and affordability. UK ('granny flat'): More familial, informal, sometimes implying a smaller or less permanent structure.
Frequency
Much more frequent in American English due to its status as a formal legal/jargon term. In the UK, the concept is common, but the specific phrase 'accessory apartment' is rarely used.
Vocabulary
Collocations
Grammar
Valency Patterns
The city permits [accessory apartments] in single-family zones.They added [an accessory apartment] to their property.The [accessory apartment] includes a kitchen and bath.Vocabulary
Synonyms
Strong
Neutral
Weak
Vocabulary
Antonyms
Phrases
Idioms & Phrases
- “[No specific idiom. The term is technical.]”
Usage
Context Usage
Business
Used in real estate listings and property development proposals.
Academic
Found in urban studies, housing policy, and sociology papers.
Everyday
Used by homeowners discussing renovations or rental possibilities.
Technical
Precise term in municipal zoning codes, building permits, and architectural plans.
Examples
By Part of Speech
verb
British English
- The council allowed them to ancillary-dwell.
- They decided to granny-flat their garage.
American English
- They plan to ADU their basement.
- The city incentivizes homeowners to accessory-dwell.
adverb
British English
- [Not typically used adverbially]
American English
- [Not typically used adverbially]
adjective
British English
- The granny-flat conversion required planning permission.
- They built an annexe-style dwelling.
American English
- The accessory-apartment ordinance was updated.
- They obtained an ADU permit.
Examples
By CEFR Level
- Their house has a small apartment inside.
- They built an extra apartment in their garden for rental income.
Learning
Memory Aids
Mnemonic
Think: An ACCESSORY is an extra item. An ACCESSORY APARTMENT is an extra living unit added to a property.
Conceptual Metaphor
A HOUSE AS A CONTAINER with a smaller, separate box inside.
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Do not translate as 'дополнительная квартира' which implies a separate, full apartment elsewhere. Closer concepts are 'пристройка', 'второстепенная жилая единица', or the calqued term 'аксессуарная квартира' in professional contexts.
Common Mistakes
- Using it to refer to any small apartment not physically attached to a main house.
- Confusing it with a 'studio apartment', which is defined by layout, not legal relationship to a primary dwelling.
- Spelling as 'accessary apartment'.
Practice
Quiz
What is the primary purpose of an 'accessory apartment' in most contexts?
FAQ
Frequently Asked Questions
Essentially, yes, but 'accessory apartment' (or ADU) is the formal American legal and planning term, while 'granny flat' is a more informal British term emphasizing use for family.
Yes. It can be attached (like a basement conversion), within the main house, or detached (a separate small building in the garden), as long as it's on the same lot as the primary residence.
They increase housing density gently, provide rental income for homeowners, create more affordable housing options, and make use of existing infrastructure without requiring large new developments.
Zoning. Many residential areas were historically zoned only for single-family dwellings, so creating a second unit was illegal. Modern reforms are changing this in many cities.