Detectives said the blazes, at two properties in the village of Brookfield, near Johnstone, were being treated as "wilful".
Firefighters from the Scottish Fire and Rescue Service went to properties in Merchiston Oval at about 7.20pm on Friday and extinguished the flames.
Police Scotland, who also attended, confirmed no-one was injured as a result of the fires - but said approximately £500,000 worth of damage has been caused.
Detectives from the force are following a positive line of inquiry as they appealed for anyone who saw anything suspicious to get in touch.
Detective Sergeant Karen Boyd, of Paisley CID, said: "Our enquiries into the incident are ongoing and anyone who may have seen anything suspicious in the area around that time is urged to get in touch.
"Anyone with information is asked to contact Police Scotland via 101 quoting incident number 3242 of May 6."