Emergency services attended, and the Scottish Fire and Rescue Service extinguished the fire safely. No one was injured in the incident.
Detective Constable Adam Gow, of Livingston CID, said: “Thankfully nobody has been injured as a result of this reckless act.
“We are treating the fire as deliberate and are asking anyone with any information to come forward and speak to officers.
“I would ask if you noticed anyone acting suspicious in the area to get in contact with police and I would also appeal to anyone who has possible dashcam or CCTV footage that may be able to assist us with our enquiries.”
Anyone with information should contact police on 101, quoting incident number 4053 of 15 May. Alternatively, Crimestoppers can be contacted anonymously on 0800 555 111.