I am done some models for my map and now i kinda bumped into a problem.

When a model got some invisible parts in Zero edit does this mean its inviseble in the game to?

And does the game render both sides of a polygon?

show us a picture of it.

if some of the vertices are placed too close to each other they'll sometimes merge into one if I'm not mistaken, and/or make the polygons project the texture inverted.

That problem usually happens for people who believes a model needs EVERY single little model-detail

show us

Yeah, that means it's too high-poly in whatever section it goes invisible.

nah - just that there's some vertices which are too close to each other