Cathedral College New Classroom Block

PROJECT DESCRIPTION

This technical modular building for Christchurch’s Cathedral College is a three-storey classroom and administration block with a 1,500m² gross floor area. The ground floor level includes offices and staff areas,while the upper two levels include classrooms and collaboration spaces. The building comprises full height rocking Cross Laminated Timber (CLT) shear walls with CLT suspended floors, on a shallow concrete foundation.

CLIENT BRIEF/PROJECT CHALLENGES

The project had a tight budget and required an approach which prioritised resilience and sustainability. The design process also highlighted archaeological risk associated with pre-1900 historic activity within the project area. WSP sought authority from Heritage New Zealand to modify the archaeological site before construction commenced, to avoid delays or additional costs.

OUR SOLUTION

WSP utilised a Future Ready approach, using their in house knowledge to ensure a design that followed international best practice with sustainable outcomes. A large portion of the building was manufactured off-site in a modular fashion, while full height wall panels ensured a high degree of buildability, requiring less time on-site.

The panels were designed to improve user safety, a key consideration for our client. The WSP team also studied the environmental sustainability of the final structure and found that the design used 330 tonnes less CO2 than a traditional steel building, equivalent to the CO2 emissions of 110 cars in one year, or 890 return flights for a single person to Auckland. WSP investigated the use of alternative structural systems during design, however due to the poor ground conditions at the site a lightweight timber solution was determined to be the best.

This performance-based approach resulted in reduced foundation loads which did not require costly deep-piled foundation solutions. The building also features a heat recovery mechanical ventilation system, low energy lighting and elevator, and a high rated thermal envelope reducing the energy use of the building when in operation.

OUTCOME/CLIENT BENEFITS

The use of full height CLT panels resulted in an accelerated construction timeframe. The rocking mechanism used by WSP has also ensured a resilient low damage system should the building be subjected to seismic activity in the future.

The lightweight solution and panellised system mean reduced construction programme timeframes and costs savings. In addition, the primary structure realised higher seismic resilience and exceeded the New Zealand Building Code minimum requirements. The mass timber construction also realised sustainable benefits through reduced CO2 emissions.

LIST OF PRIMARY SERVICES

• Structural Engineering
• Building Services Engineering
• Fire Engineering
• Architecture
• Civil
• Geotechnical
• Planning, MEH
• Project Management
• Geotech
• Archaeology

KEY FACTS

The building also marked the first use of innovative resilient slip friction joints (RSFJ) by Tectonus in a CLT shear wall building of this type. This incorporated working with University of Auckland on delivering this innovative structural solution.

Archaeological remains encountered during construction included rubbish pits, a latrine pit, drains and an old boundary fence line. Analysis of the material samples from the rubbish pit and latrine fill indicated previously undocumented residential domestic activity on the property during the 1860s, prior to the formation of college. This information has now been formally documented and contributes to our ongoing understanding of the history of New Zealand.