Misdirected energy: Hong Kong City University roof collapse highlights danger of adding vegetation to existing roofs
Adding greenery may be too much for a roof to bear, compounded by laxity over the submission of building plans for structural changes
The giant rooftop that collapsed at a City University sports centre and left three injured has highlighted the potential threat of adding rooftop vegetation, a novel way to fight the heat-island effect, to old buildings.
The accident, which could have injured hundreds of people originally scheduled to attend a dinner event on Saturday night, also called into question the lack of government supervision of this kind of rooftop vegetation, which is promoted by the Environment Bureau.
At the City University, the vegetation was understood to have been added last year to the top of Chan Tai Ho Multi-purpose Hall, which was completed back in the 1990s.
While the roof was not designed to hold anything substantial – as indicated in the building plan submitted to the government in 1989 – vegetation that would have required a roof five times stronger was nonetheless planted last year, as part of the university’s pledge to go green.
“The figures showed that the rooftop was not supposed to hold a lot of [vegetation],” said Vincent Ho Kui-yip of the Institute of Surveyors.
Ho said the current building regulations relied heavily on owners’ own initiative in submitting a plan for approval if they altered a building’s structure. But the Buildings Department would never know if owners skipped this procedure.