Fire crews are investigating what caused a blaze to break out at a boarded-up, vacant house in Innisfil.
Officials say crews were first called to the empty house on 6th Line near Emberton Way and Saint John's Road Saturday for a fire.
They say battling the flames was difficult because of all the "hidden voids" in the old construction.
Fire officials say the fire sparked back up on Sunday and was likely a "continuation" from the day prior, adding the construction may have kept a small area of the blaze hidden from the crews.
There is no damage estimate.