The Arson Squad is investigating a Greenfields house fire suspected to have been deliberately started on Friday night.
A Department of Fire and Emergency Services spokesman said the WA Police Arson squad was investigating the Lakes Road fire, which started at 11pm and caused about $200,000 damage.
The spokesman said the house was "fully engulfed" with flames and was suspected to have been deliberately lit.
It took Mandurah Fire and Rescue, Mandurah volunteers and Falcon volunteers one hour to extinguish the blaze.