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Accessory Dwelling Units (ADUs)
Accessory Dwelling Units (ADUs) are known by many names like granny units, in-law units, second units, and backyard cottages. An ADU is a small dwelling unit that may be established in addition to single-family or multifamily dwellings in residential, mixed-use, or agricultural zones. An ADU may be detached, attached to the primary dwelling or other accessory structure, or located within a main dwelling and may involve new construction or conversion of an existing structure (such as a detached garage or other accessory structure, or a portion of a dwelling). Read more about Second Dwelling Units.
Approximate Building Fees for ADU Units
Review the Building Check List of the preparation that will be required and then complete our Residential Permit Application.
Try the Sonoma/Napa Accessory Dwelling Unit Calculator (Note: Calculator works in Firefox and Chrome)
The valuation tables below are only estimated cost for the various types of accessory dwelling units in Napa County. You can also print the ADU Estimation tables below from the PDF.
| Rebuild based on $200,000 valuation - 500 Sq. Ft. | Fees |
|---|---|
| Inspection – Fire Standard Fee | 453.64 |
| Plan Review – Fire Fee | 294.87 |
| Plan Review – Environmental Health Fee | 154.00 |
| Plan Review – Engineering Fee | 493.00 |
| Inspection – Engineering | 187.00 |
| Residential – New Dwelling – Planning Fee | 1724.00 |
| Plan Review – Public Works | 93.00 |
| Plan Review -Energy | 256.61 |
| Plan Review -Standard | 1796.29 |
| Inspection -New Dwelling -Plumbing | 318.20 |
| Inspection -New Dwelling -Mechanical | 228.39 |
| Inspection -New Dwelling -Electrical | 207.86 |
| Imaging Plan Retention - Residential | 15.00 |
| State Strong Motion Residential | 26.00 |
| State Building Standards Surcharge | 8.00 |
| Permit Issuance ($32.70) | 71.00 |
| Building Inspection Fee - Standard | 2566.13 |
| Certified Access Specialist Program: Fund | 4.00 |
| General Plan Surcharge | 292.35 |
TOTAL |
|
| *Fees are estimated only, actual fees may change |
| Rebuild based on $500,000 valuation - 1200 Sq. Ft. * | Fees |
|---|---|
| Inspection – Fire Standard Fee | 942.04 |
| Plan Review – Fire Fee | 612.33 |
| Plan Review – Environmental Health Fee | 154.00 |
| Plan Review – Engineering Fee | 493.00 |
| Inspection – Engineering | 187.00 |
| Residential – New Dwelling – Planning Fee | 1,724.00 |
| Plan Review – Public Works | 93.00 |
| Plan Review -Energy | 347.81 |
| Plan Review -Standard | 2,434.69 |
| Inspection -New Dwelling -Plumbing | 431.29 |
| Inspection -New Dwelling -Mechanical | 309.55 |
| Inspection -New Dwelling -Electrical | 281.73 |
| Imaging Plan Retention - Residential | 15.00 |
| State Strong Motion Residential | 65.00 |
| State Building Standards Surcharge | 20.00 |
| Permit Issuance | 71.00 |
| Building Inspection Fee - Standard | 3,478.13 |
| Certified Access Specialist Program: Fund | 4.00 |
| General Plan Surcharge | 381.96 |
TOTAL |
|
| * May be subject to Housing Impact fees | |
| *Fees are estimated only, actual fees may change |
| Rebuild based on $300,000 valuation - 750 Sq. Ft. | Fees |
|---|---|
| Inspection – Fire Standard Fee | 616.44 |
| Plan Review – Fire Fee | 400.69 |
| Plan Review – Environmental Health Fee | 154.00 |
| Plan Review – Engineering Fee | 493.00 |
| Inspection – Engineering | 187.00 |
| Residential – New Dwelling – Planning Fee | 1724.00 |
| Plan Review – Public Works | 93.00 |
| Plan Review -Energy | 287.01 |
| Plan Review -Standard | 2009.09 |
| Inspection -New Dwelling -Plumbing | 355.90 |
| Inspection -New Dwelling -Mechanical | 255.44 |
| Inspection -New Dwelling -Electrical | 232.48 |
| Imaging Plan Retention - Residential | 15.00 |
| State Strong Motion Residential | 39.00 |
| State Building Standards Surcharge | 12.00 |
| Permit Issuance | 71.00 |
| Building Inspection Fee - Standard | 2870.13 |
| Certified Access Specialist Program: Fund | 4.00 |
| General Plan Surcharge | 322.22 |
TOTAL |
10,141.40 |
| *Fees are estimated only, actual fees may change |