Police officers are appealing for witnesses following the wilful fire-raising at Blythewood House in Port Elphinstone at the weekend.
The incident happened at around 1.45pm on Sunday, April 22, and resulted in an extensive fire.
Detective Constable Richard Barnwell said: "We are treating this fire as suspicious and would urge anyone with information or who saw anything unusual or suspicious in the days leading up to the fire to contact us.
"This was an extensive fire which required the attendance of the fire service for several hours. Police also attended and there were numerous road closures in the area while the incident was dealt with.
"We would ask that anyone who saw people at the building or in the area on Sunday or in the days leading up to the fire to contact police on 101 using reference number 2314 of 22 April. If you wish to remain anonymous you can contact Crimestoppers on 0800 555 111."