Navigating Substantial Alterations for Office-to-Residential Conversions

The City of Seattle has a unique Substantial Alteration code provision that is triggered by an existing building’s change of use to a more hazardous occupancy, such as from commercial to residential. When a project is determined to be a substantial alteration, the entire building needs to be upgraded to specific code requirements regarding:

• Fire
• Life safety
• Accessibility
• Energy conservation
• Structure and seismic

Although these requirements can seem intimidating, fear not! Remember: These office-to-residential conversions are being upheld by the SEBC and not to new building standards. This means the code provisions aren’t as strict, and the Seattle Department of Construction and Inspections (SDCI) can provide some wiggle room. SDCI encourages people to set up pre-submittal meetings to discuss how these code requirements can be addressed, as well as any impracticalities to following these stipulations.

Our combined experience with multi-unit residential buildings and historic renovation projects sets us up for success with office-to-residential conversions. We’ve designed over 78 million square feet of multi-unit residential buildings—from high-rise to podium and garden-style housing. We’ve also designed over 11 million square feet of historic renovation projects. Our deep knowledge of both markets allows us to seamlessly blend the old with the new, breathing new life into repurposed structures.

Our experience reveals that many concrete buildings from the 1920s are configured well for residential adaptive reuse due to their letter-shaped floor plans. E-, F-, and L-shaped buildings contain multiple wings that can be efficiently configured as double-loaded corridors, allowing daylight to flood apartment units on both sides of the hallway. In contrast, most rectangular office buildings have floor plates that are too deep for residential use, so it becomes harder for natural light to reach the depths of apartments. Many of the letter-shaped buildings from the 1920s were also designed for future vertical expansion which can make adding a rooftop amenity deck straightforward from a structural standpoint.

The right team for transforming a commercial building for residential use understands how to take advantage of such challenges and turn them into opportunities. We have an extensive archive of historic building scans from several city- and portfolio-wide building studies — well over 1,000 buildings in our archives at our fingertips. This makes it easy for us to quickly assess any building that is being considered for conversion.

Once the project’s goals are negotiated and set with the city, we work hard to minimize seismic upgrades and cost. We maximize the inherent capacity of the existing building. We tailor surgical solutions to address only what is deficient, often avoiding costly new seismic interventions such as concrete shear walls or steel braced frames.

As office-to-residential conversions become more commonly considered in Seattle, we’re happy to walk a building with anyone interested in taking on these adaptive reuse projects and share our insights based on experience.

Interested in learning more? Check out our selection of renovation, adaptive reuse, and substantial alteration projects below. And feel free to contact me directly with any questions.