Huh, that's interesting. Just out of curiousity, was the house underground?Not about nighttime or raining.
You can try make a house floor using dungeon brick,
and let an NPC live in,
you will see him "shocking" at house in daytime on the map.
Huh, that's actually a bug then. It does have some use though, I suppose. You could build a house in a dangerous area and your NPCs can't get themselves killed by drowning or something.No, it's in surface.