How tall can an ADU be in Ferndale, and what setbacks apply?

An accessory dwelling may be up to 25 feet tall, with side and rear setbacks of 5 feet each (Section 5.01.C). It may not sit in the front yard.

That 25 foot cap is notably taller than the 20 foot limit for ordinary accessory structures like garages and sheds (Section 3.02), which gives room for a two-story unit or a dwelling above a garage.

A few related placement rules:

• The footprint may not exceed the principal structure's footprint or 20 percent of the lot, whichever is less (Section 5.01.C). The published text has a typo here, so confirm the figure with Community and Economic Development at 248-336-4370.
• The unit may share a roof with the house but not walls, under the Article 20 definition of an accessory dwelling.

Review is administrative through the Building Department (Section 9.07).