This week in Findon, a third house fire has been caused by a discarded cigarette butt.

Apart from a pet cat, no humans were injured in the Thaine Ave fire.

The southern end of the house was seen on fire as firefighters were called to the scene shortly before 11pm.

Damage worth $100,000 was estimated due to the fire and the firefighters took about 30 minutes to control the blaze.

A Metropolitan Fire Service spokesman said, "An occupant had been smoking in the carport and improperly discarded the cigarette ... the occupants were alerted when the power was cut to the house as the fire extended into the roof."

Later in the evening when the results could have been far more tragic, it was fortunate to not have taken place.

He said in a week, caused by smoking materials, which had not been extinguished, fire cause investigators were concerned that this was the third house fire.

Discarded cigarette butts were also the cause of a $200,000 house fire in Sellicks Beach early Boxing Day morning and a $60,000 shed fire in McLaren Flat on December 27.