Arsonists set fire to two cars in Farcet in the early hours of Saturday.
Cambridgeshire Fire and Rescue Service crews from Yaxley and Stanground were called to a blaze in Straight Drove at about midnight.
A spokesman for the fire service said: "Crews arrived to find two cars well alight that had spread to a building. Firefighters used two hose reels to extinguish the fires and one positive pressure ventilation fan to clear the smoke."
An investigation determined that the cause of the fire was deliberate, and the incident comes less than a week after a van was torched in nearby Sawtry by arsonists.
Anyone with information should contact police by visiting www.cambs.police.uk to submit an online report or call Crimestoppers, anonymously, on 0800 555111.