Seattle Public Library literally wrote the book on researching house history and as such has an enormous wealth of resources and finding tools for the subject. Holdings include guides for house history research, maps (Baist, Sanborn, Kroll), and city directories (including Polk). Ask for the Local History Resources Binder at the Humanities desk on the first floor. SPL also does workshops on house history research; check their website for schedules.
The link below for Local History Resources includes an incredible range of tools, collections, and other resources for researching local history, including house histories and genealogy. A small selection of those resources have been duplicated here as particularly relevant, but viewing the full list is highly recommended.
The Puget Sound Branch of the Washington State Archives holds pre-1974 records from the King County Assessor's Office as well as other relevant materials. These records include photographs of houses and building improvements from approximately 1937 to 1971. In addition, the archives houses property record cards and tax assessment rolls.
Contact the archives for an appointment to view records. You will need your parcel number in order to access property records.
The King County Assessor's Office offers a variety of online resources for property assessment, including sales and tax records as well as parcel maps. Use the Assessor's Office for house information after 1973. If the property is not found in the below online resources, consult the Assessor's Office for hardcopy/microfilm records.
Pre-1974 records from the King County Assessor are housed at the Puget Sound Branch of the Washington State Archives.
The Seattle Municipal Archives retains the records of city agencies and officials for public use. As such, they are particularly useful for resources on public works projects and urban planning. In addition to city records, the archives also have Kroll and city zoning maps as well as city directories.