I am creating a village to encourage Villager breeding, but have noticed something. There are doors in the building that I know are not considered 'houses' by the algorithm, as there is no sky on the outside of the door (Minecraft Wiki). However I have seen some Villagers use these doors, even as it does not help them get to a real house; I thought they only opened doors to get inside the house. Will Villagers open and close doors that aren't considered parts of valid houses? Or are these really being considered houses and I've made more than I thought?
If I remember correctly, the algorithm deems a door a house and therefore eligible for breeding if there is sunlight within five blocks of it on either side and if one side has more overhead blocks than the other. Ie. if you have 3 blocks on the side A and 4 blocks or more on side B it is valid.
In my experience, villagers will always randomly interact with doors regardless of whether they view it as a valid house.