Firefighters were called to reports of an explosion at 79 Markham St., near the intersection of Bathurst Street and Dundas Street was.
Firefighters arrived to find the back of the house blown out.
There are no reported injuries but the building has extensive damage.
Tony Duggan lives in the building next to the site of the fire and said this is the third time firefighters have been called to the address in the past year.
"Come round to the third time we're certainly worried," he told CBC News. "There's only a narrow alleyway between our building and this one."
Click on the Soundcloud file below to hear CBC overnight reporter Tony Smyth's interview with Duggan and his son James.