Duplex

In the UK, the term ‘duplex’ refers to an apartment (not a house) that includes two floors of accommodation, joined by an internal staircase.

Historically, this would have been referred to as a maisonette, but the term duplex has become increasingly popular because of its perceived Americanism, and is generally applied to apartments with a more modern design, whereas a maisonette might be more traditional.

An apartment with three floors can be referred to as a triplex. There is some dispute about whether an apartment with a mezzanine level should be referred to as a duplex. Where a duplex is on the top floor of a high-rise building, it might also be referred to as a penthouse.

Strangely however, and rather confusingly, in the USA, a ‘duplex’ is a dwelling comprising two apartments with separate entrances, whether the apartments are side by side, or one above the other.