Some difficulties that many real estate professionals anticipate in investing in single-family houses for rental purposes include an increased risk, since you require 100% occupancy to earn any income, or you have zero percent occupancy, and therefore receive no return on your investment. Single-family rentals are heavily dependent upon maintaining a successful landlord-tenant relationship, and may expose the landlord to more liability, since rental houses typically include tenants with children who are prone to accidents, for which the landlord may incur legal responsibility. And the individual unit cost of a single-family house is much higher than the individual unit cost of a multi-family apartment building.