Investigators cannot determine the exact cause of the fire that killed a Toronto family of four at their cottage last Christmas Eve, but said Thursday that the blaze appeared to start in the living room — and the placement of smoke alarms likely played a role in preventing the victims from escaping.

The Office of the Fire Marshal has completed its investigation into the Dec. 24, 2016, fire that killed Geoff Taber and Jacqueline (Jacquie) Gardner and their sons Scott, 15, and Andrew, 13. The fire broke out at their cottage on Hamilton Drive North in Douro-Dummer Township near Peterborough, Ont., around 4 a.m. The two-storey cottage was largely destroyed.

The damage to the home was so severe that the ignition source of the fire could not be isolated "and therefore the cause of this fire is classified as undetermined," Scott Evenden, Fire Investigations Services operations manager with the Fire Marshal's Office, told reporters on Thursday.

Several potential ignition sources were found, Evenden said, including a wood-burning fireplace, electric baseboard heating and propane-powered kitchen appliances.

But after conducting a fire pattern analysis, and looking at the home's utilities and appliances, investigators were only able to determine that the fire originated in the living room on the main floor.

There was nothing to suggest the fire is suspicious, Evenden said.

The home was an open-concept style, Evenden said. The living room had a vaulted ceiling, and a stairwell close to the living room led to the upstairs, where the bedrooms were located.

The home had multiple wall-mounted smoke alarms, but they were located some distance from the vaulted ceiling and stairwell.

"We believe this may have played a role in the late detection and notification in terms of sounding the alarm," Evenden said.

Smoke inside a home will rise to the highest point, Evenden explained. In this case, that would be to the top of the vaulted ceiling.

"[The smoke] would have to progress down to a point where ultimately it would spread horizontally across the structure and then come in contact with the smoke alarms," he said. "This regretfully, I believe, ultimately played a role in the inability of the victims to escape safely from the structure."

Taber and Gardner were registered lawyers. Taber was a partner at Osler, Hoskin & Harcourt LLP. Gardner was with Altamira Investment Services Inc.

Friends described the family as vibrant.

"They were lovely, open, giving and social," Anne Donald, who described herself as a close friend of the family, told CBC Toronto last year. Donald said the cottage was a gathering spot for the family, and that they were "really excited" to spend Christmas there.

The boys were remembered as sports lovers and avid hockey players.

On Thursday, investigators said that, due to the destruction caused by the blaze, they weren't able to determine whether the smoke alarms were working. But Evenden said the tragedy was a reminder to everyone to ensure that their residence has smoke alarms on each floor and outside every bedroom. Smoke alarms should be checked once a month, he said, and batteries replaced once a year.

Smoke alarms should also be replaced when they expire, he said.

Families can also practice fire escape plans, he added.