Overloading primary cause of Dunedin balcony collapse

  • Nick Smith
Building and Housing

An investigation by the Ministry of Business, Innovation and Employment into the collapse of a Castle Street balcony during a music concert on 4 March 2016, which resulted in injury to several students, has found the primary cause was overloading, Building and Housing Minister Dr Nick Smith said today in releasing the report.

“The simple reason this balcony collapsed was that nearly twice the number of people it was designed to support were on the balcony, and many of those people were grouped at one end of it. The investigation has found the balcony was properly designed as per the Building Code of that time, was properly consented, was built to standard, and received a Code Compliance Certificate. Inspection and testing of the joists that failed has not identified any concerns about the standard of timber used in the construction,” Dr Smith says.

“The most valuable lesson for this accident is for people not to use residential balconies as grandstands. They are designed for a loading of two kilopascals (kPa), or about two people per square metre, and crowding more than this poses risks for the people on them and others. A further lesson is for people to co-operate with Police and other officials responsible for public safety during events like concerts because crowds can pose additional risks that may not be obvious to people having a good time.”

Dr Smith also noted there were two technical areas where he had asked officials to undertake additional work to ensure buildings were constructed as safely as possible.

“I have asked officials to review the buildings loading standard (NZS1170) in respect of residential balconies that have a risk of being crowded because of their context and surrounds. The code currently provides for 1.5kPa on decks less than a metre off the ground, and 2kPa for standard residential decks, but 4kPa for balconies used for community activities and 5kPa for sports stadiums. There are environments, such as on streets commonly used for street parades or in close proximity to concert venues, where it may be justifiable to require the higher loadings.

“The second technical area I wish to have further investigated is the building practice of notching structural timber. The joists supported the balcony were reduced from a 200 x 50 millimetre depth to 150 x 50 millimetre depth at the interface with the building. This was quite within the Code, but is a building technique some timber engineers are concerned may create stress weaknesses. The Ministry is to undertake further technical investigations.

“I also welcome the proposal by the Council and University of Otago for a review of the event that led to the overcrowding to see how this sort of accident could be prevented in future, now we know the building met standard. Dunedin has a great reputation as a university town, and safety of students is paramount. The Council and University have done good work historically with the Students’ Association in coordinating how events can be enjoyable as well as safe. This proposed review will also provide an opportunity for the students at the event, and those injured, to have input into how these events could in future be better managed.

“Structural failures of buildings in New Zealand are thankfully rare but when failings occur we do need to heed every lesson possible. This investigation may result in some technical revisions to the Code but the most powerful lesson is that buildings should not be used for purposes they were not designed.”