"We're building a brand new science facility and we're going to be demolishing our existing facility," Grinter said.
He said the school was working towards having the building done in 2019 and the new block open in 2020.
Plans for the facility include eight teaching spaces.
"It's been a project in the making for many years. It started when there were some concerns around the structural integrity of the existing science block. These have been set aside, it's really now more about modernising," he said.
"We're really replacing an old facility with a wonderful new facility that's going to present science teaching and learning at the highest possible level. This is appropriate for us because science is the fastest growing subject in the school."
The project is the first step in what Grinter calls a master plan to totally rework the school site over about 20 years.
The master plan covers everything from music and performing arts to sport, Maori and a new library.
"It brings all our building in under the one roof generally, which is going to be quite a radical change," Grinter said.
"It's really exciting. I'm hopeful one day it will come to fruition and this old school that was built in 1927 will be a highly modernised environment ... it's a plan for the future."
The 20-year timeline isn't set in stone as the works are subject to funding but for now, the plan for the science block is ticking along.
The planning process is expected to be completed by the end of the month. Ministry of Education sign off will follow, as will a tender process.
Grinter said the new blocks would look drastically different to the existing main block to keep with its "splendour".
The ministry's head of education infrastructure services, Kim Shannon, said the ministry was working closely with the school and the board of trustees to ensure that the master plan met its educational, cultural and physical design priorities.
Shannon said the ministry spent just over $377,000 on capital works projects in Rotorua in 2017.
This was on top of the 5ya funding.
She said the additional spending was in response to population growth.
"The end goal is to ensure all schools are safe and inspiring learning environments that meet the needs of both students and teachers."
The biggest project further afield is the redevelopment of Te Kura o Te Whanau-a-Apanui, east of Opotiki, following the closure of three nearby schools.
Te Kura o Omaio, Te Whanau-a-Apanui Area School and Raukokore School closed in January 2016.
Detailed design work for Te Kura o Te Whānau-a-Apanui is scheduled to begin later this year.
