Building a new home under one huge roof

Project Detail

Project Team

The lessons learnt

Marian College was opened in 1982 when two Catholic secondary schools for girls were merged, one of which had been founded in 1893. Following the February 2011 earthquakes when the college was destroyed, the school was temporarily hosted by brother school St Bede’s College, which then reopened in Barbadoes Street in early 2012. It was clear Marian needed its own dedicated space, however, and the hunt finally ended in 2019 with the announcement that a 3.15-hectare site had been acquired in Papanui, close to St Bede’s College and adjoining St Joseph’s Primary, allowing a Catholic education hub to develop. 

The new land already had one of the largest distribution centres in the South Island on it (at 17,500m²), and the question became how to most cost-effectively build a college for a current roll of 430 students, with the potential to increase to 600. 

Shaun Mitchell, Principal Project Manager at the Catholic Diocese of Christchurch, explains the process.

“Along with the design team, we’d considered three options for the site,” he says. “Would we knock the existing building down and build a brand new school, knock most of it down but keep some for indoor sports or similar – or find a way to make use of the existing structure? Whatever we chose, it would have to be extremely cost-effective.”

Using the bulk of the existing warehouse in a unique way became the preferred approach.

A brand new, built-for-purpose timber school would be housed inside just over half the original steel building. With a footprint of 9,600m² and including some rooms on a second level, this option delivered a total school area of 13,000m².

Using as much timber as possible within the steel structure also spread the seismic loadings on the “poor quality” soils, and met the economic demands of the Diocese. Like many projects, the budget has been under significant pressure as a result of Covid, material supply and labour availability issues. 

While Covid restrictions stopped work on the site completely for a time, the cost and availability of engineered timber remained a problem, as did some materials such as gib. Supply was less of an issue for the lightweight timber framing used between classrooms, but as with the rest of the industry materials’ costs continued to increase. 

Sustainability and achieving a 4-star Greenstar rating was an important consideration for the college. Glulam, LVL beams, the Potius® flooring and roofing, and Strandboard® linings sequester more carbon than concrete and steel. Repurposing the existing warehouse also contributes towards a highly sustainable project. It’s hoped that such a sustainably built learning environment will become a learning tool in itself for pupils now and in the future. 

The college consists of six classroom blocks plus a central, free-standing chapel. Block 1 houses administration facilities, Block 2 the library, technical laboratories, including a food lab and kitchen, Block 3 the cafeteria, Block 4 mathematics, social sciences and technical classrooms, Block 5 the arts and sciences rooms, and Block 6 contains the double-height performing arts and sports facilities.

Outside are landscaped grounds and a full-sized sports field. 

For a fly-through of the completed concept, go to https://www.ournewhome.nz/flythrough

How do you convert a steel structure so big at least three jumbo jets could fit inside into a modern girls’ college in earthquake-prone Christchurch? The myriad problems that could cause were solved with true Kiwi innovation and brought to life by Sheppard and Rout Architects. Spokesperson Jonathan Kennedy describes the issues involved.

“This was a real jigsaw puzzle,” he said. “Keeping strict control of the budget was critical.”

The original steel warehouse was constructed in the early 1960s and added onto across the decades as demand for warehouse space increased. This led to a variety of materials used, but predominantly Colorsteel® and tilt-slab concrete, although the gabled roof design was basically retained throughout the process. Expansion finally stopped in the 1990s, however, changes in material and structural systems over the years had made it challenging to construct something with standardised unit sizes and heights within.

• After brainstorming approaches to the challenges, timber emerged as the obvious choice for the major construction material for the college. Not only was this a sustainable solution, but its other advantages meant costs could be contained as far as possible, especially when a whole-of-life approach was considered.
• Foundations required less strengthening than if the new build was constructed in steel and concrete, because timber delivers a significantly lighter structure overall with similar strength and arguably better seismic performance.
• Normally, claddings specified by the Ministry of Education are based on the assumption that schools are external structures, not sitting inside another building. Retaining part of the original warehouse to shelter the college meant a significant saving on those costs.
• The Potius™ panel system of cross-banded LVL box beams delivered the structural spans the architects were hoping to achieve for the large open plan teaching spaces. These beams were also known by and acceptable to the Ministry of Education for use in a school, following the firm’s prior school projects’ experiences with them. 
• However, it was found that smoke could collect between the beams themselves, and so the architects needed to work through specific architectural detailing to enable alarms and sprinklers to function as required.
• Rain noise inside the warehouse “umbrella” could have been a problem, but is blunted with acoustic material between the roof purlins over the double-height atrium and sports areas. Additional noise minimisation between individual rooms was managed through staggered studs and other high performance architectural detailing materials and methods.
• “Completing a design of this scale with timber presents many design difficulties,” said Jonathan. “Selecting the right consultant team, including those with prior experience and knowledge in timber technology, has enabled the realisation of a wonderfully warm and sustainable set of spaces within an otherwise uncompromising existing warehouse shell.” 

How to rise to the challenge of rebuilding a college warehouse following the Canterbury earthquakes? While panels are often prefabricated in the factory then trucked to a site, in the case of Marian College the 17,500m² former distribution centre has now been partly dismantled and encases a 9,600m²,modern girls’ school constructed mostly in timber. Powell Fenwick Consultants Ltd are the engineers for this innovative project, and Isaac Williams outlines some of the challenges they encountered.

“We design many timber framed buildings across the country,” he says, “but this one was a bit different.” 

The weights associated with conventional steel and concrete structural systems required deep foundations and proved cost prohibitive. A lightweight timber solution was proposed which utilised a Potius® cassette floor system with spans up to 10m and lightweight Strandfloor® sheathed shear walls for lateral resistance. 

With sustainability being one of the project’s key deliverables, an exposed timber structural system met the brief while creating a strong and unique aesthetic. Ultimately, using these lightweight timber systems made the project feasible.

Christchurch’s liquefiable soils typically present challenging environmental considerations. When building on this site in particular, structural engineers Powell Fenwick worked closely with the geotechnical engineers (ENGEO) to ensure the stiffness of the of the soils and mat raft foundations could accommodate the building demands, Isaac said.

The existing warehouse had been constructed in multiple stages and generally had separate structural systems. For the most part, the building structure and envelope was retained and strengthened to 100 percent NBS (IL3) seismic recommendations for schools, providing the weathertightness elements. By preserving the building structure, significant volumes of steel and concrete demolition rubble were avoided and given a ‘new life,’ adding to the sustainable outcomes for this project.

Construction of a timber building inside a weathertight, but well ventilated, warehouse was hugely beneficial as it made moisture and water management a relatively minor consideration and essentially removed weather delays from the construction risks.

Staggered stud, timber framed walls were typically used for acoustic treatment. “I was surprised at just how many services had to run through some of these walls. We quickly had to establish typical details and rules of thumb for the tradesmen on site to follow, which did cause some coordination headaches.” The use of double walls and 140x45 staggered studs significantly reduced these challenges.

As with most projects in construction over the pandemic, supply of timber was challenging and required the contractor to be incredibly resourceful. Over this period, Powell Fenwick worked closely with the contractor to make substitutions of engineered timber products to suit availability. 

Where the Potius® and LVL system came into its own was when the structural layout was consistent and regular. This made the details relatively simple and effective. When steps in diaphragms and misalignment of walls are introduced, this presents complexity and cost. 

“Utilising knowledge gained from this project, I believe this system can be implemented cost-effectively moving forward,” says Isaac.

While it’s not unusual to build transportable homes inside a factory or warehouse, it’s quite another to build a two-storey multifunction complex school to fit inside 9,600m² of the original 17,500m² former distribution centre – the largest in the South Island at one time. Damian Leary is the project manager representing lead contractor Armitage Williams Construction Ltd, and he explains.

Damian believes the Canterbury earthquake sequence of 2010-11 put a lot more focus on the resilience of buildings that have a large component of timber in their construction. “Building large projects in timber or engineered timber wasn’t much of a thing before then,” he says. “It was more common to build large projects in steel and tilt-slab concrete, but the earthquakes showed how heavy and rigid they are compared to timber ones - and with the advances in timber engineering, how much better and more cost effective timber ones actually are.”

The overall weight of a building is an important consideration in Canterbury because fine soils don’t like being shaken about and this quickly affects the stability of a structure. “In the case of Marian College, the original factory was built in 1960 and added to over the years using a variety of materials and construction methods, so we had to do a lot of seismic re-strengthening before we actually started building,” he says. “However, this also meant we were able to simply lay 300mm concrete slabs and key them onto the existing ones - using 2,500m³ of concrete. So even that was a comparatively big job.^1.”

Multifunction buildings deliver everything needed in a modern girls’ college, from administration to technology labs, including food and other sciences to arts, maths, sports, relaxation areas and general classrooms. As well as structural considerations, building the structure in timber softens any “industrial” feeling within the college, and a timber chapel with its high level of finishing sits front and centre.

The increasing use of BIM (building information modelling) across all aspects of a build proved more of a challenge than expected, however. “Ideally, all architectural, engineering and construction aspects of a project are overlaid to allow designers to put the right services in the right place, first time,” Damian explains. “But if all the disciplines don’t overlay their work with each other’s, it can end up being a lot simpler to as-build the services on site with various consultants involved, saving the complexities of changing the models.” 

One example was with the timber framing that formed the vertical walls between rooms, which carry services like electricity and water. Careful placement of services and strict guidelines meant the timber framing was only allowed to be drilled in specific locations to each wall throughout.

Craning the prefabricated timber panels for floors and walls should have been a simple job, too. However, in a restricted space, even a double-height one, getting long-span and engineered timber elements into position was no easy task. Slew cranes didn’t work in such a confined space, and hiring a Hiab unit was an unexpectedly large expense. In Block 6, the performing arts and sports centre, however, chains had to be used to safely place the last of the units as there was zero room for a Hiab. 

¹By comparison, a single-storey building under construction next to the college will require 18 metre-deep screw piles