TORONTO -- A house fire that killed a family of four last year started in the clogged vent of a clothes dryer on the main floor where there was no smoke alarm, an investigation by Ontario's fire marshal has found.

The late detection of the fire by the family, which was trapped on the second floor of the house, in turn resulted in the delayed arrival of emergency services, said the report released Wednesday.

The early morning blaze on March 29, 2013 claimed the lives of Kevin Dunsmuir, 55, his wife Jennifer, 51, and their sons Cameron, 16, and Robert, 19. A third son was away in university at the time of the fire.

Fire marshal Tadeusz Wieclawek said the house in East Gwillimbury -- a small town north of Toronto -- was equipped with a smoke alarm on the second floor, but by the time it was activated, escape down the central staircase was no longer possible.

One member of the family also had mobility issues, which added to the complexity of the situation, he said.

"We are now confident that fire conditions were such that it made survival by the occupants and rescue by the emergency responders untenable," he said.

A timeline of the incident showed that it took over 12 minutes for the East Gwillimbury volunteer firefighters to arrive on scene after the emergency call was made at about 5:30 a.m.

After the fire, there were questions about why the Newmarket fire department, which had a house of professional firefighters within a 10-kilometre radius of the fire, was not called in.

But Wieclawek said the investigation found no issue with the training or equipment of the crews that did respond.

"I want to emphasize that in this case it's pretty clear that due to the delay in the detection of the fire and notification, response time was not an issue."

He said that when emergency crews arrived on scene, it was already too late to mount a rescue. The "extreme" conditions of the fire forced crews to focus on "an exterior defensive attack," he said.

"This was a tragic fire and it is difficult to express the impact it has had on family, friends, local first responders, the community and our own investigative team," he said.

Wieclawek said his office is now conducting an evaluation of their education programs, which focus on how to plan a home escape and how to properly use smoke alarms.

He added that his team is working on a public service announcement about the proper installation and maintenance of dryers.

"The fact is that fire protection is a shared responsibility between the individual, the community and municipalities," he said.