Shadows through the ceiling

So, I've made some rooms inside castle walls, and for reasons that i cannot seem to figure out, the shadows that should be only on the roof of this room are actually showing through the ceiling to the floor of the room.

now, obviously if i disable my skylight from casting shadows then this doesn't happen, however I will want it casting shadows, and if i disable the walls beyond from casting shadows, then i wont get shadows being cast on the roof.

the ceiling/roof is a whitebox floor, because there is a second level above so i needed a floor, and the whitebox floor allows me to put materials on both sides so it also acts as a ceiling to the room below. i have tried several other objects to use (as i use just a cube for the foundation/floor of the room) as the ceiling, apparently it doesn't matter what object i use, it does the same thing either way.

And i can disable shadows on the whitebox, which does in fact fix the walls casting the shadows in the room, but then i get this strange light shining in from somewhere outside of the room:

but i dont even want light shining through to the room, because its a room i feel like the ceiling should block outside light either way.

so, what am i doing wrong here?

Strange that you are getting shadows inside with the roof. Would it be possible to upload a template containing the problem? You can create a template from the objects, sun, sky etc, and export it as a png.

To make the room appear darker without changing the outside lighting, use adjustment volumes.

Is that in the skylight?

I'll have to look when I get home