The project, which has been in the pipeline for about five years, involves the expansion of the five-building hostel block for male pupils via new bedrooms and a bigger common room.
Female pupils, who board on a site next to the North Otago Netball Centre opposite the Tamar St school, will join male boarders - on the same block but in separate buildings- from 2020.
A historic red-brick building on the school's grounds will undergo minor work, including fire protection, and would house female year 13 boarders from 2021.
There are about 80 boarders at the school.
College hostel manager Justin Fowler said the project, funded by school owners the Christian Brothers, reflected the changing nature of boarding schools.
"A lot of co-ed boarding schools have them (dormitories) quite close together now, so we are catching up to that trend. It's pretty exciting.
"We're future-proofing the hostel for the next 20 or 30 years. That's got some huge benefits."
Benefits included easier access to the school's facilities, improved wireless internet access for pupils and the opportunity for more social activity.
It could also potentially encourage more boarders, he said.
The hostel building would still be maintained after it was vacated by the end of this year.
Mr Fowler said the school would consider renting the space out more permanently, as it did during school holidays, which was a "big part of the hostel business".
