About fine meshing near small cracks
 

I built a model in gambit, I started with creating many volumes, and created those "doors" and "windows" and "cracks" by spliting different volumes with each other, so I have the openings left. Since the cracks are really small, I created some volumes surrounding these window and door cracks just to get a much finer grid around them, of'coz these volumes are split from each office, and I didn't set their surface BCs so as a default their surfaces will be INTERIOR, just the way I want them to be.
Then when I mesh the model, I started with each surrounding volume of the window, creating finer grid, then the volumes around the door cracks. After that, I mesh the six offices one by one, with a coarser grid. I then mesh the left whole domain with a even coarser grid. I always use tet/hybrid to mesh my model.

I can see, for example, at the interface of the surrounding volume a window, the mesh size of the surrounding volume and that of the whole domain is different, and the latter large tetrahedron doesn't seem to have a multigrid nice transition of grid size. I'm a little worried about this, is this OK? Is the way I model this model in gambit OK? I mean, do I have to set the surfaces between surrounding volumes of windows and doors with offices and whole domain as INTERFACE so that FLUENT can connect the surfaces for me and make the grid size transition smoothly? I actually tried it, but gambit said it didn't work.

What about the size difference between the surrounding volumes and say, the whole domain? can I just neglect that? Is there some other way to work this out?

pictures would help to understand.
I assume you have connectivity problem