flatmate

kämppis, asuinkumppani, kämppäkaveri A person with whom one shares a flat.
2002, Elaine Lally, At Home with Computers, http://books.google.com.au/books?id=kFtsXqhlCGkC&pg=PA149&dq=%22flatmate%22 %22flatmates%22+flat+-intitle:%22%22+-inauthor:%22%22&hl=en&sa=X&ei=ci1ST6mYNcWviQfu563aCw&redir_esc=yv=onepage&q=%22flatmate%22|%22flatmates%22%20flat%20-intitle%3A%22%22%20-inauthor%3A%22%22&f=false page 149,

Yet when both Regine and her flatmate are at home they tend to spend their time in their rooms, although Regine (and probably the flatmate too) tends to spend more time in the communal areas of the flat when the other is not at home.

“So, it would probably be best if we could find another flatmate and go for a flat of five, and if old Chip does pull out, at least we can then drop down to a flat of four. What do you reckon?”

Kamal moved Fathi′s things into his own room, and the two became flatmates.

The apartment in which Kamal lived was spacious, with several large rooms and various flatmates.

It had been weeks since all the flatmates had sat down together for a meal. Communication was breaking down. Written notes had begun to appear all over the house; please don′t touch this food, I bought it especially for Hermione(..).

One night, one of the flatmates (the one who owned the house) was ranting and raving all night about her girlfriend.

The position may have been different when your client was living in the house with the flatmates.