Accessory Dwelling Units Construction: Fire and Sound Separation

Seattle DCI has recently clarified its interpretation of the Seattle Residential Code (SRC) requirements for accessory dwelling units (ADUs). (ADUs are separate living spaces within a house.).  Our code requirements are different, depending on whether the ADU is in a new construction project, or it is a remodel of an existing space within a single-family residence.

For new construction, such as an addition built to be used as an ADU or an entire new house with an ADU, the construction needs to meet the requirements for a two-family dwelling.  These requirements include one-hour-rated fire and sound separations, including portions of the building that support any fire-rated construction (such as walls that support fire-rated floor-ceiling construction).  For more detail, these requirements are in SRC Section R302.3.

Seattle DCI has revised the interpretation for ADUs being created within existing buildings.  If an existing space (such as a basement) is being remodeled for use as an accessory dwelling unit, no sound or fire separation is required.

For more information, contact:

Cindy Hoover
(206) 233-2554
cindy.hoover@seattle.gov