Runtime NavMesh for VR navigating

Unity Engine
1

I am working on an archviz project for cardboard where the user can download custom cad buildings and afterwards explore them in VR with cardboard.

So far everything works fine.
The challenge now is the navigation in this runtime generated mesh environment:

I do not want to have collliders on all imported 3d-objects due to memory usage.
But for the player not to fall through the scene I need colliders at least for the floors.

But how will I know what objects are floors?

My idea is to use the latest implementation of NavMesh, which allows runtime baking.

BUT:

How could this NavMesh help me (and not any NavMeshAgents) to navigate through the scene?
For example, is it possible to generate a raycastable colliderobject out of the generated NavMesh?

2

I found out that many users try and fail to raycast directly against a NavMesh, will this ever be possible?

(To generate a mesh from NavMesh is very easy…

NavMeshTriangulation triangles = NavMesh.CalculateTriangulation();
Mesh mesh = new Mesh();
mesh.vertices = triangles.vertices;
mesh.triangles = triangles.indices;

…but adding a MeshCollider to a GameObject with that mesh ends in an inaccurate result due to that convex issue…)

Maybe raycasting without colliders could help here…