The Boarding House is meant to house Nomads when they are accepted into your village but before they move into houses. Nomads will not move directly into empty houses, they move into the Boarding House AND they gather the needed resources (firewood, food, clothing, etc.) needed for the people there. They will slowly move out and into available houses but you need to have space there for the Nomads. Even though the game Help section says that Nomads will not arrive until the Town Hall, Market and Trading Post have been built, my experience is that building the Town Hall and either the Market or Trading Post will trigger Nomad events and make the Boarding House a necessity. Based on your question my sense it that you built the Boarding House way too soon - perhaps thinking that it would provide general use housing for your day-to-day population.
Building new houses for the youngsters move into speeds the population growth of the village. Your housing works best if (again, based on my experience in the game) the average number of house occupants is 3-4. When the average number of occupants in your houses goes above 4 it is time to build some more housing.