This topic is directly related to this:
https://interpersonal.stackexchange.com/questions/8301/how-to-sooth-relationship-between-roommate-and-my-sister-who-lives-with-us

Tensions between my sister/dependent and our roommate have continued to get worse, and have finally escalated to a point in which I feel we have to move. The problem that I am having now is if I should tell him that I am looking for a place even before a place is secured. He can be very impulsive, and I worry that if he knows I am looking he will take it upon himself to initiate our 30 days notice before I am ready. 

So my question for you all is: How do I tell my current roommate/landord that I am looking for another place to live?