Permit costs and time required to build a duplex, triplex, or accessory dwelling

Adding another dwelling to your home? Here’s what the permits will cost (and how long they might take to get).

We get calls every week from people who want to turn a single-family home into a duplex, convert a garage to turn a duplex into a triplex, or add an accessory dwelling unit to their property. Inevitably, these clients want to know about the permit process and costs for adding to their existing structures. Effectively, these are all the same from a design and building perspective, but the permit process varies quite dramatically. No matter which path you choose, permitting can take anywhere from 4–12 months and in some specific cases even longer.

The information below is specific to Berkeley, California, but most cities have permitting processes that are very similar.

Consider these scenarios:

1. You own a single-family home and want an accessory dwelling unit (ADU)

   • If you keep the design under the height limits and are willing to sign a deed restriction promising to owner-occupy one of the two units for eternity, then you can skip the planning permits with a “by right” planning approval. Then you get your building permit, which takes four or more months.

   • If you want a design that is over the height limit of 14′, you can apply for an AUP planning permit, which costs about $4,000 and takes four or more months. Then you get your building permit, which is another four months or longer.

2. You own a single-family home and want a duplex.

   • If you are zoned for two units, then the city may allow this. The designer has to check at the planning desk.

   • Planning will require a use permit that has neighbor review. Planning permits take about six months. Building permits will follow.

3. You own a duplex and want to add a third unit.

   • The zoning situation here is the same as in Scenario 2 above. You might want to just make a big addition to the duplex and keep it as two units, or you might want to permit the third unit. Again, this requires the designer to visit the city.

In each of these cases, the cost is about $6,000 for a planning use permit. When adding a new unit utility hookups come into play, so that can run an additional $15,000 or more. And finally, there are the Building permits which are based on building costs. In Berkeley, CA, for a $400,000 project you can anticipate permit fees of approximately $18,818.08 (info from the permit fee calculator below).

Need to know more about permit costs in Berkeley, CA? Try the city’s permit calculator: