A multi-dwelling unit (MDU) (multifamily residential building; multifamily residential structure; multifamily residential unit; multi-family house) is a structure consisting of multiple separate residential units that are contained within one or more buildings within one complex. All of the units may be owned by a single landlord with each unit leased to the resident tenants, as in an apartment complex, or owned separately and occupied by the owner or leased to a tenant, as in a condominium, who may sublease it to a subtenant.
Multi-dwelling units of larger than a fourplex are commonly considered commercial real estate. The reason for this is generally the need for property management of the real estate and for the property owners.
MDUs can take various forms, including:
- Apartment complex – An individual housing unit in a multi-unit building leased from the apartment building owner with boundaries generally defined by a perimeter of lockable doors;
- Townhouse – A number of single or multi-unit buildings in a continuous row with shared walls and no intervening space;
- Condominium – Building or complex where the multi-dwelling units are typically owned individually, rather than leased from a single apartment building owner, with common grounds and common areas within the complex owned and shared jointly;
- Cooperative (co-op) – A type of multiple ownership of a multi-unit housing complex in which the residents hold shares in the cooperative corporation that owns the property, while each resident receives the right to occupy a specific housing unit.