SMC 11.72.070 Commercial and large size vehicles.
No person shall park a vehicle on any street or alley, except in a Manufacturing or Industrial Zone as defined in the Zoning Code of Seattle (Ordinance 86300 as amended) between the hours of midnight and six (6) a.m. if the vehicle is a truck and/or trailer or other conveyance which is over eighty (80) inches wide.
After calling around, and with some more helpful research by the viewer, to the best of our knowledge we were able to determine that there are many areas in Ballard where 80"+ wide RV overnight parking is not allowed. We recommend if you are concerned about a vehicle doing this in your neighborhood, that you call the Seattle Police and alert them to the violation.
Here is a PDF map showing the various zones. Basically any Single Family areas (yellows) are off limits to overnight 80"+ wide RV street parking. Seattle Zoning PDF
