Substantial Alterations Projects for Single-Family Residences

When alterations or additions to single-family residences and duplexes are extensive enough, the Seattle Residential Code (SRC) requires updates to important life safety and structural systems. These projects are called “substantial alterations” and there are six definitions of these types of projects in section R107.8.1 in the Seattle Residential Code. The main definitions (or “triggers”) are:

  • Repair of buildings with a damage ratio of 60% or more
  • Remodeling or additions that substantially extend the useful physical and economic life of the building
  • Changes of use of the structure

A project that extends the physical and economic life of a house or duplex (or a significant part of the building) usually involves reconfiguring the rooms in the house, possibly adding a story or partial story, replacing or upgrading systems (electrical, plumbing, and/or heating),  and “repositioning” the house in the market. If you have to move out of your house during your remodel because the house is “uninhabitable” then your project is likely a substantial alteration.

If a single-family or duplex project is a substantial alteration, the Seattle Residential Code requires specific upgrades to the building (described in section R107.8). These upgrades include bedroom egress windows, exiting requirements, smoke alarms, carbon monoxide alarms, separation between dwelling units, and seismic strengthening of the building. These projects require plan review, as there are too many issues that need checking for the project to be eligible for a subject-to-field inspection permit. So please plan on having your drawings screened and scheduling an intake appointment for your substantial alteration projects.

If you need help in determining whether or not your project is a substantial alteration, please visit DPD’s Applicant Services Center for technical assistance. If your project is not a single-family residence or duplex, you may need a pre-submittal conference to make this determination.

For more information, contact:

Cindy Hoover
(206) 233-2554