It happened around 11:20 Tuesday morning on the 400 block of West 7th Street.
Authorities say the third floor roof collapsed onto the second floor, in the back of the building.
The building was vacant at the time and no one was injured. The collapse caused structural damage and brought down several interior walls.
Several adjoining properties have been deemed unfit for habitation by L&I.
Nearby apartments were also evacuated as a precaution.
No word what caused the collapse.