Here it is applied to both the front and back wall perhaps incorrect to do so. Anyway, when I bring them into your file they go whack. My thought is, take these bits that work and get your other geometry. So I did that and then stripped out the other material that didn't seem to work. I inserted that geometry, and it botched some of your face normals on the way in, however a quick 3drotate command righted that. I needed to do that as I was getting some strange rendering issues with 'force 2 sided' turned on. You may have a different graphics card and this might not be required, otherwise flipping them 180 about an edge was all that was required, I left the other floors for you to do.
Yes it was really bugging me, and I STILL don't know what was fluxxing it up in your file, however use the attached FWIW