Hello! I've been making a home and duplicated solitude's jail. Everything seems to look fine in the creation kit but when I go to test out the jail these blue-ish "planes" appear on certain doorways and arches. These planes not only block the view of the entrances but also weird glitches such as these: (apparently I don't have permission to post links to the pictures, so if you want pictures I could probably message them)

Any help is greatly appreciated!

Sounds like a room bound issue. A lot of vanilla cells use room bounds and portals to help with performance. So if you copy and paste or duplicate a vanilla cell such as the Solitude Jail01 which has several portals and rooms you are coping the room bounds also.

First make a backup of your esp and place it somewhere safe. Go into the CK and load your file. Make sure markers are activated ( M key) then click view on the task bar select Show/Hide and tick Portals and Rooms and you will see what I'm talking about (Big Blue Boxes). You can either add new rooms and Portals or delete the existing ones if not sure how to do this see here http://www.creationkit.com/Bethesda_Tutorial_Optimization

Hope that answers your question.

johng58 is likely on the right track. The 'bluish planes' are actually the skybox, as the level beyond that point is being culled (not rendered).