This is a container clue combined with charade - one word goes around (accommodates) other elements, and separate word parts are joined together in sequence.
Look for a word meaning 'chum' that can accommodate 'one relation' inside it. Then add a word meaning 'not gross' (think financial terms). The phrase 'accommodating' tells you which word contains the others.
Answer: MAISONNETTE | MATE (chum) contains I SON (one relation), giving MAISON, then add NET (not gross, as in net profit) = MAISONNETTE (type of apartment)