Converting grandfathered duplex to SFH to add ADUs

[Eugenia K.]

There appear to be a handful of grandfathered duplexes with non-conforming AADUs on the market! I was wondering if people had experience with and/or perspectives on legalizing the 3rd unit by converting the duplex to a SFH (which then would have 2 AADUs)?

Wondering how this might impact:

- Appreciation and buyer desirability 

- Financing (after buying with a 2-4plex interest rate initially)

- Cost to legalize

Example listing: https://www.redfin.com/WA/Seat...

[Michael Haas]

@Eugenia K. - since this one is zoned SF5000 it would be possible to convert it back to single family with 2 ADUs. Since its an older building, you would likely have the second ADU setup under the "low income housing" requirement, not the "built green" requirement, unless you were doing a significant and studs out remodel.

Like almost every question worth asking, the answer to your question about costs is "it depends". 

My question for you would be: why are you looking to do this conversion? 

In my experience, folks that want fully legal units should buy fully legal units. Folks that are ok with non-conforming or illegal units should buy non-conforming or illegal units. Legalizing an exiting illegal unit can be as cheap as $15,000 and a 12 week wait for permits if most of it is built to code as-is, or as much as $200,000 (as much or more than it would cost to build from scratch) if the work is sub-par and needs to be ripped out.