The blaze started at a house in London Road in Fletton at 2.46pm.
Crews from Dogsthorpe, Stanground and the multistar, Yaxley and Whittlesey attended the scene, and closed London Road for a number of hours to tackle the flames.
All crews left the scene by 5.15pm yesterday, before being reinspected at around 7.30pm.
Today, a spokesman for Cambridgeshire Fire and Rescue said an investigation had revealed the fire was started deliberately.
Anyone with information is asked to contact Cambridgeshire police on 101.
Pictures: David Lowndes, Leigh Johnston and Isaac Ellard
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