Appendix BC Accessory Dwelling Units (ADU)

Accessory dwelling units (ADUs) proposed for existing residential construction shall be in accordance with this appendix and other applicable requirements in this code, and the existing building together with the ADUs shall not exceed the scoping limitations of Section R101.2.

ADUs shall be permitted without requiring a change of occupancy where in compliance with all of the following:

1. 1.

   An ADU shall be permitted within an existing single-family detached dwelling or within an existing townhouse unit that is within the scope of the International Residential Code.

2. 2.

   Only one ADU shall be permitted for each primary dwelling unit.

3. 3.

   The owner of a property containing an ADU shall reside in either the primary dwelling unit or the ADU, as of the date of permit approval.

4. 4.

   An ADU shall have a separate house number from the primary dwelling unit.

5. 5.

   ADUs shall be secondary in size and function to the primary dwelling unit and shall comply with all of the following limits:

   1. 5.1.

      Not less than 190 square feet (17.65 m²) in area.

   2. 5.2.

      Not more than 50 percent of the area of the primary dwelling unit.

   3. 5.3.

      Not more than 1,200 square feet (111 m²) in area.

6. 6.

   An ADU shall be provided with a separate entrance from that serving the primary dwelling unit, either from the exterior of the building or from a common hallway located within the building.

7. 7.

   An ADU shall have a maximum number of two bedrooms.

8. 8.

   The location of a detached ADU shall comply with Section R302.

9. 9.

   An ADU shall be provided with adequate provisions for electricity, water supply and sewage disposal.

The following words and terms shall, for the purposes of this appendix, have the meanings shown herein:

ACCESSORY DWELLING UNIT (ADU). An addition or alteration that is an additional, subordinate dwelling unit on the same lot, and is entirely within a dwelling unit, attached to a dwelling unit or in a detached structure.

Any owner or owner’s agent who intends to construct an ADU within an existing or proposed building or structure shall first make application to the building official and obtain the required permit.

Except as modified by this section, building planning shall be in accordance with Chapter 3 and building structure shall comply with the International Residential Code.

The path of egress travel from an ADU to a public way or to a yard or court that opens to a public way shall be independent of, and not pass through, the primary dwelling unit.

For ADUs adjoining the primary dwelling unit, the 1-hour fire-resistance-rated wall and floor assembly provisions of Section R302.3 shall not be required, provided that both of the following conditions have been met:

1. 1.

   The interconnection of smoke alarms per Section R310.4 activates the smoke alarms in both the primary dwelling unit and the ADU.

2. 2.

   The interconnection of carbon monoxide alarms per Section R311.5 activates the carbon monoxide alarms in both the primary dwelling unit and the ADU.

For ADUs adjoining the primary dwelling unit, the interconnectivity of smoke alarms and carbon monoxide alarms may be independent for the primary dwelling unit and the ADU, provided that a 1-hour fire-resistance rating is provided for walls and floor assemblies in accordance with Section R302.3.

A primary dwelling unit and an ADU shall be provided with:

1. 1.

   A separate heating system.

2. 2.

   Separate ducting for heating and cooling systems. Return air openings for heating, ventilation and air-conditioning shall not be taken from another dwelling unit.

3. 3.

   Separate climate controls.

A primary dwelling unit and an ADU shall be provided with:

1. 1.

   Ready access to the service disconnecting means serving the dwelling unit.

2. 2.

   Ready access for each occupant to all overcurrent devices protecting the conductors supplying the dwelling unit in which they reside.

A primary dwelling unit and an ADU shall be provided with:

1. 1.

   Ready access for each occupant to shutoff valves serving the dwelling unit in which they reside.

2. 2.

   Ready access for each occupant to appliance shutoff valves serving appliances in the dwelling unit in which they reside.

A primary dwelling unit and an ADU may share a common potable water system, provided that there are separate, accessible main shutoff valves allowing the water to be turned off on one side without affecting the other.