Urban climatic mapping and objective standards for air ventilation assessments will be considered to improve natural air flow through the city fabric, Director of Planning Bosco Fung says.

The Government will adopt air ventilation assessments for its large-scale development projects, redevelopment works, as well as drafting and revision of outline zoning plans. Discussions with other departments will be held to explore ways to refine the air ventilation assessment system.

Breathing easier: To have better air ventilation, signage should be vertical to minimise wind blockage. Greenery will also help reduce urban heat.

Urban acupuncture

The department released today findings of a feasibility study for the setting up of an air ventilation assessment system.

The study, commissioned in October 2003, promotes more scientific based urban intervention - conceptually described as a form of "urban acupuncture" - for enhanced, long-term livability in the city's high-density urban context.

Chinese University Department of Architecture Edward Ng, a member of the study team, said the study focuses on how to design and plan the city fabric for better natural air ventilation. It took Mong Kok and Tseung Kwan O as typical examples of the metro area and new town in Hong Kong.

Mr Ng said taking into account the city's climatic and urban factors and high-density condition, it is considered that the more air ventilation the better, and a general breeze at pedestrian level of at least 1.5 metres per second is a useful criterion of air ventilation assessments. This will be beneficial for providing thermal relief and a comfortable outdoor urban environment.

The study has proposed a number of qualitative guidelines to help achieve better air ventilation, including:

* increasing the overall permeability of the district at ground level by proper linking of open spaces, setting up of open plazas at road junctions, maintaining low-rise structures along prevailing wind direction routes, and widening of minor roads connecting to major roads;

* avoiding obstruction of sea and land breezes;

* using vertical type of signages to minimise wind blockage;

* aligning main streets, wide main avenues and breezeways in a way to maximise the penetration of prevailing wind;

* linking up opening spaces to form breezeways or ventilation corridors, with structures along these places should be low-rise;

* providing ventilation corridors for podiums or adopting a terraced podium design;

* considering height variation for buildings and providing adequate wide gaps between building blocks; and,

* planting tall trees with wide and dense canopy to enhance pedestrian comfort and reduce urban heat island effect.

4 key stages

The study has also recommended air ventilation assessment be implemented in four key stages, namely:

* Stage A - establishment of a generic framework and methodology for air ventilation assessment to enable objective comparison between different design options and formulation of qualitative urban design guidelines;

* Stage B - identification of climatically problematic or sensitive areas (urban climatic mapping) that require particular attention or in need of planning and design inventions;

* Stage C - setting up of a set of objective assessment standards and criteria for air ventilation assessment; and

* Stage D - formulation of quantitative design guidelines to enable practitioners to grasp the basic and most important design requirements for a well-ventilated urban environment at an early design stage.

Mr Fung said the study has offered directions in the setting up of an air ventilation assessment system, adding more studies may be needed. The Government will first consider stages B and C, and will look into stage D after the implementation of stage A.

More measures

He said measures had been adopted to improve air flow before the launch of the study, such as introducing planning guidelines, revising outline zoning plans, and setting restrictions on building height.

Several public housing estates have adopted environmental and air ventilation assessments. It is expected the first one, Ngau Tau Kok Upper Estate, will be completed in 2008.

Mr Fung said relevant sections on improving air flow in the Hong Kong Planning Standards & Guidelines will be revised this year. Efforts to promote air ventilation assessments for projects by Housing Society, Urban Renewal Authority, two railway companies and private developers will continue.

Regarding concerns that air ventilation assessments may impact the scope of future developments, Mr Fung said the recommendations have gained support from the academic, real estate, construction sectors and professional groups, adding there is no plan to impose the assessment compulsorily on private developments at the moment.