I made a village after studying village mechanism in wiki.
I placed some doors, built roofs on one side, and placed villagers on 2 blocks above the roofs.
After making village, I built roofs on both sides of the doors.
The doors seemed not to be houses, but they remained houses.
The villagers have continued to increase forever.

I checked this phenomenon using MOD which can judge weather doors are counted as houses, and took schreenshot, which is attached.
The doors were no longer houses, after killing villagers or breaking and replacing doors.