One sided single polygons (probably what your wall is made of) don't normally do well to keep light out, no matter how many of then you fit together (and thru) each other. I used to stack cubes around the outside of my sets like this to keep light from coming in - basically building a room around the outside of the walls....light won't go thru objects that have thickness, like cubes. Of course you can't do it with everything (because of windows and doors, but you CAN do it just along all the corners and it still works :).

FWIW, in this day and age of realistic render engines especially, walls with thickness (and window panes too) are essential.

Laurie