"It was lucky it was during the day and a few people noticed it. We managed to knock it before it got too extreme," he said.
Firefighters had to remove part of the roof after the fire spread into the eaves.
On Sunday, the Kaikohe brigade responded to another blaze, in bushes on Thorpe Rd about 5.10pm.
Police had spoken to a number of children about that fire.
The past few weeks has seen a series of fires lit in paper or rubbish bins pushed up against buildings.
Mr Hutchinson urged business owners not to leave bins, paper or other flammables close to their buildings, and to empty outdoor rubbish bins daily.
The Kaikohe school opened as usual yesterday.