A "damaged" and homeless man who had been smoking bath salts has no memory of starting a fire which ripped through two commercial premises, damaging buildings and destroying a truck.

Wade Bernard O'Malley, 48, pleaded guilty to arson only after being shown a security camera video of him starting the fire at the Wineworks bottling plant at Flaxmere, Hastings, in September last year.

He tried three times to use a lighter to set fire to plastic wrapping on a loaded pallet of packaged wine in the Wineworks yard, the Napier District Court was told on Friday.

When he succeeded, the resulting fire destroyed a truck and a curtain-side trailer, damaged a container, and jumped a fence to the Bostock yard next door, damaging orchard workers' accommodation and an ablution block.

Before sentencing O'Malley to 30 months in prison on Friday, Judge Gordon Matenga asked the Crown and defence lawyers to clarify how much damage had been done.

Crown prosecutor Lara Marshall and defence counsel Will Hawkins compared notes and agreed on the figure of $354,778.

However, Judge Matenga said there was other damage that could not be quantified, including delays and disruption to the businesses and management time in dealing with the aftermath.

He said Wineworks had been unable to operate at the site for some time.

The judge also said that although no one was injured in the blaze, "danger to occupants and firefighters is inherent in any fire".

O'Malley had been sleeping rough in the Flaxmere industrial area in the days before lighting the fire one evening, and had twice been found dossing down in the unoccupied Bostock workers' accommodation.

After lighting the fire at Wineworks, he went into an apple packhouse nearby and made himself a coffee in the smoko room, before being found and arrested by police.

O'Malley was convicted on one charge of being unlawfully in a building, one of being in an enclosed yard, and two of arson.

Judge Matenga said that before lighting the fire, O'Malley had been smoking bath salts and had taken a pill. O'Malley did not know what the pill was.

"As a result of smoking the bath salts and taking whatever drug it was … you have no memory," the judge said.

O'Malley has a previous conviction for arson, in 2014.

Judge Matenga said that a cultural report on O'Malley made "grim reading" and described him as a "damaged man" who had suffered childhood violence, trauma and mental health issues.

"You coped with the situation by using substances, which … drive your offending."

The judge but did not order any reparation.

"Reparation, in a word, is unrealistic," the judge said. "You are not someone who has any ability to pay."

Judge Matenga said O'Malley had expressed remorse, especially to the workers whose lives were affected.

He hoped they had not lost their jobs.