Texture Interference / Layering Meshes

[SurfThug]

I have a question about overlapping meshes in Blender (and then to Unity and KSP). I'm overlapping to add decoration to larger, tiled faces. Specifically, I'm creating buildings for the KerbTown plug-in / Kerbin City. Here's an example where I've overlaid a plane with a door texture on top of a wall that uses a tiled texture (ignore the fact that the door is upside down :-) ):

Here's the same situation in another part of the scene where the textures are interfering with one another:

I run into two situations with this modeling. Either the meshes are too close together and I get interference from some perspective or distance (rounding in rendering) or I move the overlaid mesh far enough away that there is no texture interference, but it is clear when you get close that there is a gap between the two meshes.

Is there a minimum distance of separation to avoid texture interference? (or is there not because the rounding errors vary with distance?)

Is the only way to avoid this to make a "cut out" in the underlying mesh and then fit the overlaid mesh in the resulting "hole?"

Is there a completely different technique someone could point out to me?

Thanks!

[Dispatcher]

I've experienced similar things. Some things I've done which have improved my results: separate the meshes by a short distance (a few cm in Blender) ... or ... experiment with different shaders in Unity ... or ... flip the normals of a problem mesh. There are probably other things but this is what I've experienced. As to cutting meshes, I've not needed to do that, although I've joined meshes. Good luck!

[SurfThug]

I did some research and found the answer to my question. The problem I tried to describe is commonly called "z-fighting." You can google that term to read more. Basically, when two meshes are co-planar, the render engine doesn't know which mesh to draw, so it picks one. If it picks a different one every few render cycles, you get flickering. "Co-planar" is hard to nail down in a game like KSP because you can zoom anywhere from right against a texture to kilometers away. What was not co-planar within a few meters becomes co-planar at distance, because the range of numbers is limited and becomes coarser. The only solution in this situation is to remove the mesh you don't want to render. So, I'll have some geometry editing to do...

[sumghai]

The other solution to z-fighting is to slightly offset the two layers - much easier to do then deleting faces.

[Dispatcher]

Actually, another thing I've done is ADD yet another mesh. (It was for translucency effects.) But sumghai has a good suggestion. One way to offset the planarity is to ever so slightly rotate one of the meshes. I've not needed to do that but its good to know just in case.