ignoring is the least of your problems, you have yet to meet inconsiderate housemates that blast loud music, or those who make the electricity bill go sky high yet you have to evenly pay for electricity.

in my opinion, when a housemate starts ignoring you, it's most probably cause you did something to annoy them but they do not want to tell you about it cause they don't know how, or, they don't want to hurt your feelings or get into arguments. that's what happened with me and my previous housemate and in the end, i moved out, and friendship was ruined (which is kinda a pity actually cause we were secondary school mates).

but i guess that's just how life is... best thing to do is to cooly confront ur housemate, but just be prepared to not have things go back to how they previously were.