Is there a word to refer specifically to the people who live in the other part of a duplex (two-family house, side-by-side)? Not neighbor, i think, as that's more generic.

  • What's a duplex? It's not a term in general use in the UK. Is it a maisonette (basically a house divided into a flat upstairs and downstairs)?
    – Andrew Leach
    Oct 26, 2014 at 11:29
  • 2
    @AndrewLeach: A duplex is typically divided into left and right parts, not by floor.
    – Drew
    Oct 26, 2014 at 20:25

4 Answers 4


Following Kris's advice, I searched for a definition.

A duplex house plan is a multi-family home consisting of two separate units but built as a single dwelling. The two units are built either side-by-side, separated by a firewall, or they may be stacked. Duplex home plans are very popular in high-density areas such as busy cities or on more expensive waterfront properties. The two units of a duplex floor plan are usually a mirror image of one other, but are also available with attached units varying in size and layout. An example of this would be: unit A has two bedrooms and one bathroom and unit B has three bedrooms and two bathrooms.

Family Home Plans

For semi-detached houses which are side-by-side, the person in the other half is your next-door neighbour. For a maisonette where the building has two single-storey flats on different floors, that person is your upstairs (or downstairs) neighbour.

Next-door neighbour does include the properties on both sides of yours, so as well as referring to the person in the other half of your building, it also refers to the person on the other side, whose house yours is not joined to. In the UK, there isn't a standard term distinguishing those, although "through the wall" might be conveniently used to refer to the neighbour you share the building with.

In a terraced house, where more than one house is joined together along a street, even "through the wall" isn't particularly helpful, as that really only works for the end-of-terrace house (which are often sold as "semi-detached").

  • 1
    But there's nothing there that tells us about the common single structure or the space-sharing. Nothing to set it apart from the usual NDNs.
    – Kris
    Oct 26, 2014 at 13:01
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    I'm struggling to see how a side-by-side "duplex" is different from a semi-detached house (or maybe they are the same thing). In British English there's no special word for such a relationship but maybe I'm missing something. There seems to be no "space-sharing" going on that I can see. For upstairs and downstairs lawyers use the term "superadjacent" and "subadjacent" neighbours, but that is a rather technical usage. Oct 26, 2014 at 13:48
  • Me too, which is why @Scimonster needs to define how he's using duplex. The definition I found doesn't involve space-sharing.
    – Andrew Leach
    Oct 26, 2014 at 13:49
  • @AndrewLeach a duplex is slightly more generic than semi detached. You can use a duplex for flats too. Also it's rare IMO to see end-of-terrace houses sold as semis. They'd be referred to as "end terrace".
    – sksamuel
    Oct 26, 2014 at 16:51
  • I'm referring to what you call a "semi-detached" house.
    – Scimonster
    Oct 26, 2014 at 17:46

Roofmates is a term commonly used in my neighborhood.

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    What part of the States do you live in? Is this term recognized elsewhere? Are there differences? Thanks.
    – Mari-Lou A
    Oct 26, 2014 at 15:18

I don't think there is a distinction between separate houses and attached units. When I lived in a house, the people on the next property were my next-door neighbors. I now live in an apartment building. The person in the unit next to mine is my next-door neighbor, the person in the unit beneath is my downstairs neighbor. (Of course, we hope they don't call us the "people who stomp around on our ceiling".) As far as co-tenant, I don't think that would be accurate, as that (to me) indicates someone sharing the exact same unit, not the one next door. The two separate units in a duplex can be the property of two separate owners and so not be property held jointly.


I don't believe there is a well-understood special word for the people occupying the other half of the duplex you live in. Probably "co-tenant" or something similar is technically correct, but I imagine you would be misunderstood by many people if you tried to rely on that word alone.

In casual contexts I'd use something like duplex neighbour. I think almost everyone would understand that correctly.

In a formal context, like a police report, I would spell it out with a long phrase -- the occupant of the adjoining duplex apartment or something like that.

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