I personally take all my flat wall modular parts and on the edge i extrude in for a tiny lip. It stops tiny holes and even helps cull whats behind better.
For added work… if u want tesselation to work with this method u would have to copy the normals from the last visible vert to the end vert that u noramlly wouldnt see… it makes it like a smooth transition but keeps the vert normal pointed in teh correct direction so that the tesselation will go in that direction and be totaly seemless.