There are a couple of different theories on what caused the spectacular fire at a 3.5-million dollar mansion in Burlington on Lakeshore Road last week.
The Ontario Fire Marshall is investigating whether a construction worker accidentally left some equipment on after he was done for the day.
But Fire Investigator James Gillespie says he hasn't ruled out other possibilities.
The fire is believed to have started in a double garage attached to the two-storey mansion.
It took firefighters six hours to extinguish the blaze.
The mansion was almost finished and was close to having a final inspection by the City of Burlington's building department.