When a landlord retains control of a portion of the premises for common use by multiple tenants, he must exercise ordinary care to keep that common area in a condition reasonably safe for its intended use. Since the landlord incurs no liability when the premises are under the exclusive control of one tenant, the prerequisites of liability for an injury resultig from a defective condition in a common area are that the landlord must have reserved the area for common use for himself and the tenants, and that he must have retained control of the area himself rather than have vested it in one tenant or the tenants in common.