Can I disable automatic home area ?

[Dovahkiin]

so when i set the 'home' area , to be more restrictive so colinists don't go around cleaning the dirt outside of structure for example, after a little bit of time the area appears to go back to what it was before, i.e. overly large. is there a setting to disable that ?

[Astasia]

Yes, it's one of the buttons on the lower right of the screen, near the colonist bar and area visibility toggles.

[Jamaican Castle]

FYI - the home area automatically expanding has nothing to do with time. It expands when a building or zone is placed down (which includes a lot of spurious situations like graves or dumping stockpiles that are outside your actual "home"). As long as you aren't building in an area, your un-designations should stick.