"I don't think anyone will be running around with a ruler to see if it is 3cm or not. It can grow longer than a stubble but we are not looking for full-on old man beard," he said.
Paterson said the school received a positive response for the trial.
"We expected if anyone was upset they would be getting in touch but we haven't really had any of that," he said.
The trial is expected to run until the end of next year when it will be reassessed.
"It is a trial period so we are not tied to it forever, but if it works well it is great," Paterson said.
Principal Kathy Paterson said she was happy with the process the school went through to make the decision.
An earlier survey of staff, students and parents at the school found many supported allowing facial hair.
But Paterson said she did not see the need to release the survey.
"We have used the student voice, we co-constructed the outcome with the students. There is no need at all. There is a very strong voice for the students to be tidy and well represented," she said.
- Star.kiwi