LCQ18: Rooftop greening

Following is a question by the Hon Joseph Lee Kok-long and a written reply by the Secretary for Development, Mrs Carrie Lam, in the Legislative Council today (October 29):


It has been reported that some contractors have recently introduced a new rooftop greening technology from Japan which uses lightweight materials underneath the growing medium in place of conventional soil.  As a result, the total weight of the greening project is only one-eighth of that for common rooftop greening projects, and roofs with smaller loading capacities can also carry out greening works.  However, the cost of such technology is relatively high.  In this connection, will the Government inform this Council:

(a) whether it has adopted the above new technology in carrying out rooftop greening works for government buildings; if it has, of the expenditure involved for such works; if not, the reasons for that;

(b) of the latest rooftop greening technologies adopted by the Government at present and its effectiveness;

(c) whether it has provided the relevant technical and funding support to the private sector to promote rooftop greening; if it has, of the details; and

(d) whether it will formulate a comprehensive long-term strategy to actively promote rooftop greening so as to alleviate the continual rise in Hong Kong's temperature?



(a) & (b) The Government has been promoting greening to improve our living environment.  This includes actively implementing rooftop greening where practicable to enhance the cityscape and mitigate the heat island effect in urban areas.

We are also continuously reviewing and have introduced new technology where necessary to achieve better results in rooftop greening.  The lightweight planting soil mentioned in the question is one of the types of technology adopted.  We have used this in individual projects on a trial basis and achieved satisfactory result.  Details are as follows.

Lightweight planting soil is usually produced from pumice, light expanded clay aggregate and other synthetic materials.  This type of new technology has become more widely adopted in green roof projects since 2007.  In that year, we began to introduce this type of technology in roof renovation and alteration projects in Government buildings.  As the weight of lightweight planting soil is only one quarter of that of normal planting soil of the same volume, it helps to cope with the loading constraints of existing buildings.  We have also introduced lightweight plastic drainage modules to replace traditional granular drainage layer to further reduce the loading imposed by green roofs on buildings.  Since 2007, we have adopted these types of technology in 21 projects at a total additional expenditure of around $4.4 million.
However, the cost of using lightweight planting soil and lightweight plastic drainage modules is higher and is about three to four times of the cost of using traditional materials (assessed on the basis of unit planting area).

(c) The Architectural Services Department (ArchSD) completed the Study on Green Roof Application in Hong Kong in 2007 which reviewed the latest concepts and design technology of green roof and recommended technical guidelines suitable for application in Hong Kong, covering various aspects including choice of plants, waterproofing layer, thermal insulating layer, drainage layer, planting soil, irrigation as well as maintenance and repair.  The report has been uploaded onto ArchSD's website for public access so as to promote awareness and understanding of rooftop greening.

Non-profit organisations (such as schools and social service organisations) may apply for funding under the Environment and Conservation Fund (ECF) administered by the Environment Bureau (ENB) to subsidise greening works, including green roof projects.  ENB has organised briefings for eligible organisations to explain the application procedures and has invited professionals with relevant experience to share their insight on early project planning and preparatory work as well as matters required attention.  The ECF has already subsidised 47 non-profit organisations to undertake greening projects.  The Government hopes to continue to promote rooftop greening in private buildings through the ECF.

(d) We strive to include rooftop greening in so far as possible in the design of public housing estates, new Government buildings and renovation of existing Government buildings.  Moreover, the Government is studying the feasibility of promoting green features in private development projects. The Buildings Department has commissioned a consultancy study on sustainable building designs to explore the feasibility of providing more green features in private development projects so as to improve the urban living environment.  The Government will consult the public and consider their views before deciding on the way forward.

Ends/Wednesday, October 29, 2008
Issued at HKT 14:36