In a screenplay if you're in a house and move rooms do you have to make a slug like INT. KITCHEN when you were just in the bathroom?

Hey, Peyton. Screenwriter here. Let me give you the CORRECT answer.

First, let me explain what sluglines are for so you will understand the logic behind the answer. Then get used to thinking from that POV - that's part of your job.

Sluglines (aka headings) are for the production crew and their purpose is to help plan shooting days and times, locations, wardrobe, cast, etc. Therefore, they're hardly for the actors.

Now. Since the production crew NEEDS to know where to shoot, when, what to prepare etc., it's important that you do your job - and make sure everything is SUPER clear AND according to the industry standard format. The industry standard is the industry standard because it's like a universal language. If you don't mention that the location is different, everything will stay in the first location - that's how the production crew (or readers at production and representation companies, way way way before the production stage, for that matter) will see it; they won't know they're supposed to move to another room.

With that established, you have a couple of options:

You could write a full heading and end it with CONTINUES or you could write a mini-heading. The latter is a great option if you keep moving from room to room inside the same house or if you go back and forth or when it's an action scene which requires quick pacing. If you feel like you need that second option, then you simply write KITCHEN (or THE KITCHEN). That's probably what you saw in some scripts.

This way or another, yes - you MUST.

Of course not. The actors AUTOMATICALLY KNOW what room they are in and what they are supposed to be doing at all times. You are just writing it down so, if the movie becomes a big Oscar winner...then you can turn the screenplay into a book and make money.