Lighting???

Hello,
I had a question about lighting and posted it in the Game Design section but was told I should post it here. I was given an answer to how I could set up a directional light both inside and outside of a building so that light can be seen both inside and outside. I noticed the problem I have with using point lights and spot lights is that my floor textures tend to flicker because I use several cubes that overlap each other to make up my floors (causing z-buffer flickering), but when I use a directional light, I don't seem to have that problem.

The person suggested that I set up a directional light so that no shadows are cast (for my outside light), but I notice when I use 2 directional lights (one for the inside, and one for the outside). I get the 'z-buffer flickering problem' again. Is there any way around this? Thank you.