• Daniel Saloner

The Real Costs of Building an ADU

“How much is this going to cost?”

The simple answer is that no two ADU’s are the same, which means your total cost will vary with each project that you complete . Whether it is total square footage, finishing touches, or location, every ADU will have a different total bill. However, a good rule of thumb is that your structure will cost between $230-370 per square foot when factoring in all requirements. Roughly 70%-85% of your ADU cost is for the actual structure of the building. The remaining percentage is allocated to design, permitting, sitework, etc.

A breakdown of your expected costs:

Design & Engineering

This includes a full set of construction drawings for your ADU project. Design and Engineering costs will also include Title 24, structural engineering, building code review, and permit processing. Design and Engineering is the phase when you are in connection with the architect or draftsman and getting ready to submit the plans to the city. This phase can also include the cost for a survey, if required on your property.

Permits & Fees

These are the costs you pay to the city for planning and building checks. A good rule of thumb is to account for $10-12/sqft in fees. The fees that you may encounter are submittal fees, school fees, building fees, etc.

Site Work

This phase entails preparing the site for construction and is dependent on your property’s specific conditions. For a particularly level lot, you can expect typical sitework to cost around $15,000. If you need to alter the property more substantially and start moving dirt, putting in retaining walls, installing a new septic system, etc., expect your sitework costs to rise.

Building Construction

As the name says: this is the actual building of your ADU, including finishing materials like fixtures, cabinets, countertops, etc. This is where we measure the cost by square foot and can estimate it costing between $220-370 per square foot.


Standalone ADU’s are now required to have solar panels installed, unless the primary dwelling already has solar panels. Although this is an added initial cost, you will save on utility costs over the life of your ADU.

Other Costs

There may be additional costs that come up such as additional structural engineering, civil engineering, or soils engineering. You may also need to upsize your utilities, including the electrical panel and water line.

Potential Cost Breakdown:

Building Construction: $140,000-300,000

Design & Engineering: $8,000-12,000

Permit & fees: $6,500-14,500

Site Work: $10,000-15,000

Solar: $8,000-10,000

Other Costs: $2,500-6,500

While an ADU can seem expensive, it is important to remember that you are making an investment in your property, not just a purchase. So, when you find yourself asking “how much is this going to cost?” make sure you also ask the follow up question, “how much is this going to make me?”