NavMesh generated on opposite side

Is there a way to stop a navMesh from generating on the non normal side… a box only want it generated on top of the box NORMAL side (top) but it also generates on the inside of the box (bottom)

I think I see what you mean. It’s possible but it depends on your scene. If you set the walkableHeight to a high value, the inner of the box becomes unwalkable and you won’t get a navmesh polygon inside.
But it will also influence all the navmesh so this can be an issue.

ok that is what I assumed, but yes I can’t ues that as the meshes are at different heights and restricting mesh heights to max hight will not work.

I also would like to add a wall mesh in the middle of a floor and not calculate the navmesh around the wall… also have a 2nd floor over the 1st floor.

Can a custom mesh be used as navmesh?

Yes and no.
You can create a mesh in your DCC and then load it and compute a usable navmesh. With the appropriate parameters it will almost be similar to the mesh you created.
But it’s not possible to use any mesh as a navmesh directly.