The library and administration buildings have had enough problems. They were extended in 1999 and 2001, then found to have serious leaky building issues. Temporary repairs have been carried out, says Mr Havill.
"Whether these buildings are to be replaced too will be influenced by weathertightness reports."
But it's safety concerns for the classrooms that have triggered the decision to demolish. A site-renovations programme found steel casings eroding around concrete in the foundations of the school's art and technology buildings.
"Inevitably that led to similar assessments of the main two-storey blocks. So B C D E and F blocks are going to be demolished and replaced. Consultants looked at the whole site, under the buildings as well, and that's what has led to this building replacement," says Mr Havill.
He was initially surprised by the extent of work the school grounds face. "I'd thought it would be just about maybe sorting out the drainage, because pipes come apart."
Sewage is already run through pipes above ground rather than below, to reduce the number of pipe breakages.
"I thought it would be about primarily dealing with chronic undulation," he says.
The school has been plagued by subsidence issues since it was built nearly 50 years ago.
"If you go for a walk around the school you'll see a lot of the walkways are tiled, and the movement becomes quite evident. Two years ago you would have been struck by the undulating driveways and walkways and lawns. Too often students and teachers are tripping and falling - that's part of life here at a college built on a landfill site."
When Mr Havill began as deputy principal in the 1990s, truckloads of stone chips would be brought in to fill subsiding areas.
Talk of moving the school has come up in the past, but a suitable site has never been established.
"When I first came here I dealt with a Ministry official who was firmly of the view that the school should be shifted, because there were just so many problems associated with the subsidence. But I think the reason it never happened was because there just weren't the alternative sites for a secondary school in this northwestern sector of the isthmus."
Architects are now waiting on final geo-tech reports before completing options for the Ministry of Education. It is anticipated the school, with a roll of almost 1300, will be rebuilt to accommodate 1450 students by 2015.
Depending on the fate of the gym, library and administration blocks, the school will either be rebuilt in its current place or moved to another site within the school grounds.
"To be able to build on a new site means we can continue on in old buildings, then transfer into the new school once it's completed."
Meanwhile, buildings scheduled for demolition are being strengthened temporarily. "The Ministry is commissioning some temporary safeguarding strengthening to all existing blocks, because they've been assessed as a serious risk.
"There's certainly a post-Christchurch heightened awareness."
A Ministry spokesperson says while its consultants are deciding which parts of the school site are most suitable for construction, it isn't 100 per cent sure of the best solution.
"It is necessary to identify a solution that minimises disruption to the school's operations during construction. The costs of repairing the school's existing buildings are similar to those that would be incurred replacing them and, given rolls are expected to increase significantly over the next three to five years, a rebuild is considered the most effective option."
Mr Havill hopes Western Springs will become a sustainable school.
"It's a school that will have to last and serve the community in 60 or 70 years. We have to get ourselves very future-oriented and look at what education is going to be like in 10 to 40 years time.
"Will we have a whole lot of single-cell classrooms? It's about creating flexible spaces that better facilitate the way students learn these days. Not like in my day when it was sit down, shut up and listen."
Despite the work ahead, Mr Havill is excited by the prospect.
"This is not an opportunity that comes along very often. It's a special opportunity and one we intend to make the most of. We will be consulting not just the school community but the wider community. The community stands to benefit hugely from this opportunity to recreate the school."
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