Fire crews from Acomb and York were called at 9.51pm on Wednesday (December 10) to the house on Rosebery Street in the Leeman Road area of the city.
A 33-year-old woman was treated by an ambulance crew at the scene after breathing in smoke but didn’t go to hospital. A boy aged nine got out of the house unharmed.
The blaze started in the timber frame extension, before spreading to the kitchen and downstairs bathroom. As a result the extension was destroyed.
Fire crews used a hose reel jet to put out the flames. They said the bathroom suffered 50% fire damage and the kitchen 20%. Much of the house was smoke damaged.
The fire is being blamed on an electrical fault in the washing machine.