Permit costs to build a duplex, triplex, or ADU
Adding an accessory dwelling unit (ADU) to your home? Here’s what the permits will cost (and how long they might take to receive).
We get calls every week from people who want to turn a single-family home into a duplex, convert a basement into living space in order to turn a duplex into a triplex, or just add a small accessory dwelling unit to their property. Inevitably, these clients want to know about the permit process and costs for adding to their existing home.
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 6–12 months. This is specific to Berkeley, but most cities are very similar.
Consider these scenarios:
You own a single-family home and want to add a rentable accessory dwelling unit.
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, then you can skip the planning permits with a “by right” planning approval. Then you apply for your building permit, which takes five or more months to be issued.
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 five or more months. Then you apply for your building permit, which is another five months or longer until it is issued.
You own a single-family home and want a duplex.
If your property is zoned for two units, then the city may allow this. The designer has to check at the planning department during the pre-design phase.
Planning will require a use permit that has neighbor review. Planning permits take about six months. A building permit application will follow.
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 any case, the cost of the permit is variable depending on the scope of work and anticipated value of the project. For a $300,000 residential project you can expect Berkeley, California to assess approximately $14,000 in permitting fees. A $500,000 project would incur about $23,500 if permitting fees.
Berkeley provides a great tool to check what the fees on your project may be based on project type and budget: Permit Fee Calculator
