property & types
Duplex apartment
A duplex apartment is a single flat spread over two floors and connected by an internal staircase. In UK listings the term overlaps with maisonette, and it is not a formal legal category.
In simple terms
A duplex apartment is a flat on two levels with an internal staircase. Agents use the word loosely, so check the entrance and tenure.
Example
A two-level flat at the top of a purpose-built block is advertised as a duplex apartment. It is reached through a shared entrance hall and lift, with the bedrooms upstairs. The title and lease, not the advert, show it is a leasehold flat with a service charge and a share of the building insurance.
If you're buying
Usage varies. Some agents use maisonette for a home with its own external door and duplex for a two-level flat reached through a shared lobby, and others treat the words as near-synonyms. Because there is no legal definition, rely on the floor plan, the title plan and the lease rather than the advert. Ask whether the stairs suit you, how sound travels between floors and to neighbours, and whether the lease restricts changes to the layout. Confirm tenure, lease length, ground rent and service charge, and ask your lender whether it has any criteria on the building. Compare the price per square metre with ordinary single-level flats nearby rather than assuming a premium is justified. (Sources read 30 October 2026: Designing Buildings penthouse entry, which notes that top-floor apartments can span two levels; Whitegates maisonette guide. Duplex is not defined in UK law and there is no official definition.)
If you're selling
Describe the layout and entrance accurately, because the duplex label can mean different things to different buyers. Prepare the lease, service charge accounts and building insurance details before listing. A floor plan that shows both levels and the staircase helps buyers who cannot view straight away and avoids queries late in the sale.
Related terms