North Yorkshire Police is appealing for witnesses and information about the arson, which happened off Blueberry Way at some time between Sunday 6 August and 1am on Monday 7 August 2017.
A spokesman said: "Two building site vehicles were set on fire causing extensive damage.
"We are appealing for information about anyone that was seen acting suspiciously in the area at this time."
Email [email protected] or call 101, select option 2, and ask for Peter Beard.
Information can also be passed on via Crimestoppers, in confidence, on 0800 555 111.
Please quote the North Yorkshire Police reference number 12170139096.