Investigators have pinpointed where a fire that significantly damaged a Gravenhurst home started.

The fire ignited in an unoccupied bedroom inside the Kilworthy Road home on Thursday morning. A smoke alarm alerted the sleeping woman and she was able to escape without injury.

Before firefighters arrived flames had already consumed the bedroom and had spread to a nearby kitchen and dining room.

The house sustained extensive fire and heat damage which is preliminarily estimated at $75,000.

The cause of the fire is still under investigation, but it is not considered suspicious.