Buildings Department releases final investigation report on roof structure collapse at CityU sports hall
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The investigation concluded that the collapse of the roof structure was caused by overloading, as a result of the following three factors:
(i) The screeding of the roof structure was thicker than the original design;
(ii) The laying of greenery cover on the roof; and
(iii) Localised water ponding on the greenery cover.
The findings of the investigation revealed that the main structural element of the roof structure of the sports hall was a space truss system (STS). The STS provided support for a reinforced concrete slab that served as the decking of the roof. Screeding, an insulation layer, waterproofing membrane and the greenery cover were on top of the roof slab.
The screeding, which was thicker than the original design, together with the laying of the greenery cover increased the loading imposed on the STS. As such, the gradient of the roof was reduced, which affected the rate and flow of water discharge, resulting in localised ponding on the greenery cover. Following the increase in the extent of water ponding on the greenery cover, the loading on the STS was further increased and finally exceeded the loading capacity of the STS, leading to the collapse incident.
The investigation results have been provided to the Department of Justice (DoJ) for consideration of taking legal actions under the Buildings Ordinance (BO). After thorough examination and consideration of the relevant information, evidence and circumstances of the case, the DoJ has decided that prosecution should not be instigated. Nevertheless, the BD is seeking further legal advice from the DoJ as to whether disciplinary action should be taken against the relevant persons registered under the BO.
The BD has issued a circular letter on "Roof Greening in Existing Buildings", reminding the building industry of the technical issues to be considered in designing and installing roof greening in existing buildings, such as structural issues, loading and drainage systems. To further enhance public awareness on greening in buildings, the BD has promulgated the "Introductory Guide on Greening in Buildings" on its website to provide an easy reference to the general public for safe provision of greening in buildings, and to remind the general public on the potential impact of greening on building safety, the areas of concern and the need to seek professional advice as necessary for ensuring building safety.
The final investigation report has been uploaded to the BD's website at www.bd.gov.hk for public inspection. For information which was provided to the BD on a confidential or without prejudice basis, and in order not to affect any legal actions that may be taken, relevant contents of the report have been redacted.
Ends/Wednesday, May 31, 2017
Issued at HKT 16:38
Issued at HKT 16:38
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