Quote from mcon1
I am having problems getting an npc village to grow. What I did is added multiple doors to existing houses. Does that add to the total number of houses?
I am playing in superflat mode, and under the town, I made long tunnels with doors every 4 blocks, would those count as houses, or should I replace the 'dirt' roof with wood/cobble?
Adding doors to existing houses does work, but you need 3 extra doors for 1 extra villager.
Also, I'm not sure if I'm misunderstanding you, but if you build houses underground they will not register as houses. Each door needs "access" to the open sky within 5 blocks of it, and a "roof". The roof type doesn't matter, as long as its not glass.
Here's an example of a "house" with multiple doors, each door has a roof within 5 blocks(the line of double slabs in the middle) and is open to the sky on the other side within 5 or less blocks:

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The ability link several maps together
Palm trees
treasure crafting
ship crafting
volcano biomes, rocky desert biome
Colored glass
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A tower attached to a house helps as well. Two or three will stay up there away from the mobs
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Maybe they are too crowded. Mine sometimes die out if I have too many in a small area.