How To Make A Non-Conforming Minneapolis Duplex Unit Legal

Every now and then I run into a duplex in Minneapolis with a really nice non-conforming unit in the basement or attic.

They always inspire buyers to dream of easily converting the property to a legal triplex.

The trouble is, when a property goes from a duplex to a triplex, the building code it’s required to adhere to changes. Any property with two units must conform to International Residential Building Code (IRC). Properties with three or more units must conform to the International Building Code (IBC), essentially a commercial designation.

The two codes are completely different animals. For example, a duplex owner who wants to add a third unit in the attic must now install a sprinkler system throughout the property, as it is more than two stories tall. Or, if someone has or wants to add a unit in the basement, under residential code it must have a ceiling height of 7 feet. IRC code mandates a height of 7 feet 6 inches.

If a duplex owner decides to forego converting the building to a legal triplex, an Accessory Dwelling Unit (ADU) may be an option. In Minneapolis, there are three types of ADUs: internal, attached and detached.

An internal ADU is located within the walls of the duplex. An attached ADU is an addition to the original property. A detached ADU is a freestanding structure on the same lot.

In the case of a non-conforming ADU, registering the property as an internal ADU with the city may be the easiest option.  Doing so maintains the property’s status as a duplex, which means it remains governed by IRC building requirements.

The most important thing to know is the property owner must live in one of the building’s units (not necessarily the ADU), and the restriction is recorded on the deed.

The ADU must be at least 300 finished square feet, and not more than 800.  It cannot exceed the area of the first floor in size, and must also be on one level.

The city’s application process is fairly detailed. It may well be worth the effort, however, as the alternative is a loss of revenue from the non-conforming unit or worse yet, the city dictating its removal.