Additional huts are required in order to grow the population of your village. For example, if you have 7 villagers and haven't built the first new hut, the villagers will refuse to breed because there isn't enough housing. Each time a new hut is completed, your villagers will once again be willing to make babies (instead of complaining that there isn't enough housing), up to the next limit (as explained above). Your builders will start construction on a new hut when it's needed, but you may run into temporary housing shortages if your population grows to the next limit before the new hut is completed.
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Barbara
Unicorn
Last Day of Work