I would strongly recommend a very careful reading of the BFC spec. The Rendering Engine Guidelines section points the above out, and proper BFC handling has some other gotchas.
Note that any geometry that isn't BFC-certifed will probably have to be added to your threejs model twice, with the same geometry for each copy, but reversed winding of the vertices. And if you look closely at the BFC Spec, you will see that a culling can be enabled and disabled at any time inside a file, so fully proper handling requires BFC tracking on a line-by-line basis, not file-by-file. (See the NOCLIP and CLIP commands in the BFC spec.)
Note that any geometry that isn't BFC-certifed will probably have to be added to your threejs model twice, with the same geometry for each copy, but reversed winding of the vertices. And if you look closely at the BFC Spec, you will see that a culling can be enabled and disabled at any time inside a file, so fully proper handling requires BFC tracking on a line-by-line basis, not file-by-file. (See the NOCLIP and CLIP commands in the BFC spec.)