light shining through cracks in a dungeon tile modules, and I don't know how to fixit

[nightowl79a]

I’m trying to make sort of a dungeon tile set that I can hook together to make a dungeon, like something found in the creation kit for Skyrim. I used snapping for everything and adjusted the vertices so that they were as even as possible, but light still shines through the cracks in the roof and floors. They really need to be interlocking and seamless with no light shinning through and I’m stumped. Can’t find anything on Google related to making dungeon tiles in blender.

dungeon.blend (636 KB)

[JA12]

I’m not getting the same result on 2.69 nor 2.70RC. Those objects are separate and what I understood, that what is wanted.
The only thing I noticed was wrong is object scale on some of the objects. That should be 1,1,1. Select objects, ctrl+A -> scale to apply it.

Here what those looked like when I rendered (didn’t apply scale for these)