Unincorporated Land in Napa County

A detached guest cottage may be developed with a building permit if the following conditions are met:

A.The lot contains an existing, legal single-family dwelling unit;

B.The proposed building site complies with the requirements of Chapter 18.108 (Conservation Regulations);

C.The square footage of the living area of the guest cottage does not exceed the square footage of the living area of the main dwelling unit. However, in no event shall the living area of the guest cottage exceed one thousand square feet as measured from the inside of the exterior walls.

The guest cottage shall be a separate stand-alone structure, within five hundred feet of the main or secondary residence. The planning director may waive the five hundred foot limit if the applicant presents substantial evidence that an environmental or agricultural constraint prevents meeting this requirement and/or if a greater distance is required to meet the standards of the department relating to private water or sewer systems. The planning director may waive the requirement that the structure be stand alone if an alternative design (such as a single level to be built on top of an existing structure) provided by the applicant includes design features which preclude future expansion of the structure beyond the allowable living area of the unit.

Examples of such features include:

  1. use of external staircases rather than internal staircases to access a second floor unit;
  2. exclusion of common walls which could be penetrated to create additional living space; or
  3. exclusion of attached areas that can be easily converted to additional living space (such as substantially enclosed porches). Guest cottages legally constructed prior to the date of adoption of the ordinance codified in this chapter which are attached to other structures are to be considered legally conforming and may expand up to the one thousand square foot limit;

D.Any construction shall conform to height, setback, lot coverage, site plan review, fees, charges and other zoning requirements applicable to residential construction in the zone in which the property is located;

E.County building code requirements which apply to single-family dwellings shall also apply to the guest cottage;

F.Approval by the county department of environmental health where either a private sewage or disposal system or private water system is to be used.

REF: https://library.municode.com/ca/napa_county/codes/code_of_ordinances?nodeId=TIT18ZO_CH18.104ADZODIRE_18.104.080GUCORIES