The following information is provided by the County of Monterey Health Department.

There are many requirements that need to be considered before having plans drawn up and applying for an Accessory Dwelling Unit on your property. The following information is not all inclusive but will give you an idea of the things the Environmental Health Bureau (EHB) evaluates during the permit application process.

EHB recommends that you inquire with the Housing and Community Development Planning Department first to determine if an Accessory Dwelling Unit (ADU) would be allowed based on your property’s zoning. Such development may be restricted as described in Title 20 and/or Title 21 of the Monterey County Zoning Ordinance, or prohibitions specified by the Monterey County General Plan. 

"Accessory dwelling unit" or ADU means a permanent residence, secondary to an existing main dwelling, which provides complete independent living facilities for one or more persons. It shall include permanent provision for living, sleeping, eating, cooking, and sanitation on the same parcel where the single-family dwelling is situated.

"Guesthouse" means an attached or detached living quarters of a permanent type of construction lacking internal circulation with the main dwelling, without kitchen or cooking facilities, clearly subordinate and incidental to the main structure, on the same lot, and not to be rented, let, or leased, whether compensation is provided or not.

Conversion of existing structures to ADUs or “Junior ADUs” are processed as ministerial permits per Government Section 65852.2(b) but still must meet EHB requirements as described below. All existing EHB requirements are as described in Monterey County Code (MCC), Monterey County Local Agency Management Program (LAMP) and the most current edition of the California Plumbing Code. 

Onsite Wastewater Treatment System (Septic System):

• Nitrogen loading from the OWTS shall not exceed the proportionate quantity of 40 grams Nitrogen per acre of land (called the nitrogen limit). When estimated nitrogen loading exceeds the nitrogen limit for the property, a supplemental treatment unit shall be incorporated into the OWTS. (LAMP Table 5-2 – Minimum Lot Size for New Development and for Additions to Single Family Dwellings)

• EHB recommends that each dwelling unit be served by a dedicated OWTS. The Accessory Dwelling Unit shall have its own septic tank but may share the dispersal field with the primary dwelling. Septic tank capacity shall be in accordance with LAMP Table 5-3 – Minimum Capacity of Septic Tanks and dispersal system sizing shall be in accordance with LAMP Section 5.9 – Site Evaluation and Soil Characteristics.

• All horizontal setback distances shall be met (LAMP Table 5-8 – Minimum Horizontal Setback Requirements for Conventional OWTS)

• The onsite wastewater treatment system (OWTS or septic system) that serves the first dwelling shall be in good working order, as demonstrated by an OWTS Performance Evaluation, and an acceptable set aside area(s) for a future dispersal field repair shall be available for each OWTS (MCC, Section 15.20.060.D).

Potable Water to Supply to Project:

• The proposed water source must demonstrate adequate source capacity is available to add a new water service connection.
  • New and existing 2-4 service connection water systems must demonstrate at least 3 gallons per minimum per proposed service connection.
  • For larger water systems, or if all homes will be on the same parcel, contact EHB’s Drinking Water Protection Services, for details on the minimum source capacity requirements.

• The proposed water source must meet all bacteriological and primary drinking water standards, and any secondary drinking water standards that exceed notification levels. If such information does not exist, recent water quality testing will be required to be completed prior to approval of the associated project.

• Source capacity testing results and water quality analysis shall be current within 5 years, with limited exceptions as approved by EHB. Contact EHB’s Drinking Water Protection Services – Water Systems to inquire about the validity of testing completed 5 years ago or more.