Police spokeswoman Shannon Haigh says the search Monday is a precaution after one transient was arrested on the roof Sunday as the building burned.
Haigh says he told police he was asleep when he was awakened by the crackling sound. He said he was alone and did not have a cooking fire. He was released after questioning.
Investigators are looking for the cause of the fire in the former Alf Christianson Seed building. It has been vacant since 2011.
Haigh says the fire burned an office area. The building sits next to a rail line, and trains were delayed when fire hoses crossed the tracks.