Specialist engineers from WSP were commissioned to design the fire safety system for what is now Auckland’s tallest timber construction. Led by Auckland-based fire and life safety manager Biswadeep Ghosh, fire work on the Mission building involved design assessments, fire severity calculations, independent peer reviews and plenty of inspections.
While the two lowest levels are constructed with standard concrete and steel, the rest of the 10-storey building uses the latest in cross laminated timber – including all floors, walls and ceilings. Biswadeep says this posed a challenge in calculating the building’s fire severity rating.
"These calculations tell us how long a fire will last in a building until everything burns out. Calculations developed for steel and concrete structures can’t be used with accuracy for timber structures, so we spent two weeks calculating based on the all-timber design of the building.
“The risk of a timber building catching fire is the same as for a steel or concrete building. But timber buildings will burn for longer if the worst was to happen. That’s why getting the numbers right was so important.”
Other challenges in the fire design included the tight site - sandwiched between other buildings and next to two main roads. Plus, with parts of the building designed as wellbeing and detox spaces, the design had to be sensitive to the Mission’s security requirements and open architectural vision.
The new building has all the latest in fire safety features, including passive fire protection – barriers designed to stop the spread of fire from one area to another. Designed to the letter of the Building Code, it’s fully sprinklered, alarmed and has dynamic exit signs, which change colour depending on the location of a fire. All stairwells and corridors with exposed timber have been coated with fire retardant paint.
“There weren’t many passive fire design solutions available for cross laminated timber when we started – meaning this project was a real learning and research experience,” says Biswadeep.
With much of the focus in the construction industry now shifting to lower carbon building materials, he expects WSP will be involved in more timber-only fire designs. The learnings from the Mission building have shown how well it can work and just what’s possible.