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

9,189.34

*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

12,045.53

* 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