"Half Slabs"

Hi! I'm working on a game that is made out of blocks and I want my players to be able to walk up automatically if they encounter something that is a bit smaller then the blocks they encounter normally. You might have heard of Minecraft. It has half slabs that allows you to simply walk up half a block. I need that too in my game. So, if anyone knows how I could do this, please tell me. (I also think there is a big issue. I import all my maps in one mesh and that makes it harder for the game to find the half blocks. But still just a guess) Thanks