Have you ever wonder why the NPCs mostly just stay at the same floor, even though the cell (regardless where at) has multiple floors?

Do you have a nice custom home that has multiple floors in the same cell (i.e. no loading doors), and you want your NPCs to move up- and downstairs more?

This http://www.nexusmods.com/skyrim/mods/57376/? should address that need.

What does sandboxing mean?
Sandboxing is just a term describing NPCs' auto behavior in a given location, like walking around, sitting down, drinking, eating, etc. Keep in mind that NPCs cannot roam outside of this location.

Why don't NPCs go up and down the floors in a cell (a single loaded area) with multiple floors?
In Skyrim, NPC's sandboxing behaviors are defined to a specific location in 3d (a spherical shape). The global game settings GMST fSandboxCylinderTop and fSandboxCylinderBottom restricts that location to a more flat shape (imagine chopping the top and bottom of an orange off, so it's flat on top and bottom).
The default value for fSandboxCylinderTop is 150 and fSandboxCylinderBottom -100, which is too flat for the NPC to notice things the floor above or below (a floor is 288 unit tall).

What this does:
This is a little tweak to change the global game settings GMST fSandboxCylinderTop from 150 to 576, and fSandboxCylinderBottom from -100 to -576. As a result, the NPC can detect things (markers for various actions) roughly 2 floors above and below during their sandboxing behavior within their sandbox radius, so they will go up or down the floors to use those things (furnitures, markers, etc.).

Requirements:
None, just Skyrim the base game.

Compatibility:
Should be compatible to everything.

How to Install:
NMM: simply download with NMM and install it with NMM

Manual Install: simply extract sandboxcylinderheight.esp to Skyrim\Data

Load order doesn't matter. You can place it anywhere within your mod list, as I have yet know of any mods that make the same changes.

Other Notes:
This is a little side thing that came off when brainstorming with the Vilja team to improve companions' sandboxing behavior in custom player homes. So please do check out the wonderful mods the Vilja team offers (they have more, I am only listing out a couple):
http://www.nexusmods.com/skyrim/mods/26393/?
http://www.nexusmods.com/skyrim/mods/48470/?

Please let me know if you have any questions, but due to real life schedules, I might not be online on Nexus/gamesas Forums as frequently. You will be more likely to catch me on http://emmates.proboards.com/.

Well done, can't wait to try it out. Thank you!

Thank you, I hope you like it.

Cool. Thanks for the info. I'm going to add this to my personal catch-all mod.

With the current events going on, I want to share a very small piece of my mind. Right from the beginning of this little tweak (I am no modder, and I never think this is a mod, it's just a setting tweak), I have shared what I learned from it. So I hope many of you had or will find the information helpful, but I also hope I have demonstrated in the little way that I can what my ideal modding community should be, one that shares files, knowledge, skills, and methods openly and selflessly with the sole intention of improving modding as a hobby without violating anyone's intellectual properties.