Well sort of. Consider a couple in a 4 bedroom house who's kids have moved out, but don't move into a smaller place (say 2 bedroom condo) because they would have to pay a bigger tax bill. So there are two bedrooms not being used because of taxes.

> Consider a couple in a 4 bedroom house who's kids have moved out, but don't move into a smaller place (say 2 bedroom condo)

This would theoretically deal with the problem of having young couples with many children who can only afford to live in a 2-bedroom condo, because all the bigger housing is occupied by old people with empty nests and the only new housing is 2-bedroom condos or smaller. But, if you're not interested in forcing the old people to leave, it doesn't solve the problem of housing supply -- you'll still need some housing for the old couple and some more, separate, housing for the new large family, and if you don't build additional housing to accommodate the incoming people you'll end up with a housing shortage, regardless of whether old people shift from their existing homes into smaller ones or not. As long as you're building housing for the people who move in, you might as well build it in the sizes they demand.