A Canberra man, who suffers from multiple mental illnesses, was sentenced to 20 months in jail by the ACT Supreme Court for burning down a massage business because he claimed it "smelt of semen".

Key points: The Canberra man was arrested for arson in August 2018

The Canberra man was arrested for arson in August 2018 Police believe an object was set on fire and thrown through a window of the massage parlour

Police believe an object was set on fire and thrown through a window of the massage parlour The 20-month jail sentence could be suspended in December

Andrew John Richardson, 37, was arrested after he was identified in CCTV footage outside the Phillip business, Jenn's Magic Massage, in August 2018.

The fire caused significant damage to the building.

At the time, ACT police said they believed an object had been set on fire and then thrown through a window, sparking the blaze.

Justice Michael Elkaim noted Richardson appeared to have no particular reason to target the business in Dundas Court, but said clues could be found in comments he made, which were detailed in a pre-sentence report.

"I was having a bad night, not hearing voices, was not sleeping," Richardson reportedly said.

"I was agitated, walked in there one time and it smelt bad, of semen."

Justice Elkaim said that showed a degree of premeditation, but he also noted Richardson suffered from mental illnesses, including schizophrenia and Tourette's.

In handing down the sentence, Justice Elkaim said his goal was to deter Richardson from further criminal conduct.

"Without knowing why he committed the crime it is difficult to know if he is likely to reoffend," he said.

"One can only assume that the crime was precipitated by his mental health issues."

The court recognised that Richardson had been complying with his medication regime in prison.

The sentence will be suspended in December if Richardson is willing to comply with strict conditions.