As reported previously, the blaze happened at around 5am today and some internal furnishings had been set on fire.
This caused damage to the furnishings and to three rooms of this derelict building.
Officers are appealing for anyone who saw suspicious activity or vehicles at the site.
If you can help, call 101 quoting incident 45 of July 30.
You can also make a report by emailing [email protected], quoting incident 45 of July 30 in the subject box.
Alternatively, you can call the independent charity Crimestoppers on 0800 555 111 or online at crimestoppers-uk.org.