As driven has said, unticking export two sided faces should handled this situation.
So i did some more tests and i have found out that my problem is my sketchup, or version of sketchup. I'm using the 2014 version and no matter what i do it messes up my export file.
I installed the 2105 and it works perfectly. I don't have a clue on why this happens, but at least i have found a way to solve my problem.
Thank you so much for your fast replies! It helped me alot.