Firefighters say when they arrived shortly after 4 p.m. Sunday there was just light smoke showing. But once inside a unit, they found the fire running between the walls.
Crews quickly tore open the sheetrock to get at the flames.
"Oh it's very dangerous because there isn't the sense of urgency, but that's completely untrue. We can have fire that's actually running in the attic space - that was our fear today," Lakeside Fire Protection District Chief Andy Parr said.
The damage was confined to three units. No one was hurt.