Survey on the Effectiveness of Balconies in Promoting Sustainable Building Design in Hong Kong
Arthur Tong Yee Hang 唐以恒
自「聯合作業備考環保及創新的樓宇」(Joint Practice Note: Green and Innovative Buildings)於2001年頒佈以來，在住宅樓宇加設露台已成為香港一個普遍現象。這些露台據稱有利於環保，政府因此給予它們普遍的樓面面積及地盆覆蓋率優惠，即使地盆環境有異，藉以推廣。是項調查旨在評估由2010年至2015年落成的住宅樓宇，在考慮過地盤環境後，其露台作為遮陽板或隔聲板的效用。調查的結論是：只有約三分之一的露台可以能夠作為遮陽板或隔聲板，其餘三分之二的露台未能提供任何環境益處，卻加大樓宇體積，對視覺及微氣侯產生不良影響。
One of the important elements of hygienic design in buildings is good natural ventilation. The Buildings Ordinance, however, only stipulates minimum design standards for ventilation. In 2001, the Buildings Department, Lands Department and Planning Department issued the Joint Practice Note: Green and Innovative Buildings (‘2001 policy’) to encourage sustainable building design by incorporating green features in buildings. Having balconies for residential buildings was one of these green features. By fulfilling six conditions listed in the Joint Practice Note, areas of balconies in residential buildings could be exempted from the development’s gross floor area (GFA) and site coverage (SC) calculations. As a result, any extra area comprised of ‘environmental balconies,’ as such a kind of balconies are known, could be built on top of the maximum GFAs and SCs permitted on a site. In Hong Kong where property prices were (and still are) among the highest globally, this presented an attractive incentive for both developers and buyers.
The Joint Practice Note, however, did not mention how balconies could improve the natural ventilation performance of buildings. Indeed, they apparently led to adverse visual and micro-climatic impacts resulting from buildings having a larger bulk that, far outweighing the intangible environmental benefits a balcony brought. The general public was left with the impression that the policy did more harm than good to Hong Kong’s residential environment. Consequently, the Joint Practice Note was revised in 2011 with the previous exemption conditions tightened and seven new ones incorporated. The two most important changes in the new note were:
1) Not more than 50% of a balcony’s area can be exempted from GFA and SC calculations;
2) The granting of GFA concessions is subject to compliance with the pre-requisites and overall cap on GFA concessions stipulated in PNAP APP-151 on Building Design to Foster a Quality and Sustainable Built Environment.
Between them, these two conditions imposed caps on the GFA and SC concessions for individual balconies as well as the total GFA concession for balconies and other desirable green features, amenities, non-mandatory and non-essential plant rooms and services. Yet the revised policy still failed to provide a solution to the excessive development problem, merely curbing its adverse impacts. Such an evasive approach is unsatisfactory. After nearly twenty years of implementation, with thousands of buildings completed, the Government has yet to find a way of looking policies holistically that will allow it to reviewing their strengths and weaknesses, and propose areas of improvement.
This article documents the results of a survey conducted to evaluate the effectiveness of the 2001 policy in promoting sustainable building design by assessing whether environmental balconies actually achieved their intended environmental functions. The survey of residential buildings or residential parts of composite buildings was carried out from January 2010 to December 2015. Its data was obtained from the monthly digests published by the Buildings Department and record plans kept by the department.
The topic of the environmental functions of balconies was first touched upon in a green building policy proposal the Buildings Department submitted to the Legislative Council in 2000. That proposal claimed that balconies in buildings should be encouraged because they would: (1) enhance natural lighting and ventilation, (2) provide individual flat occupiers with space for greenery and recreation, (3) act as a sunshade; (4) act as a noise barrier; (5) improve the architectural appearance of a building or townscape (Buildings Department, 2000). There was no elaboration as to how the claimed benefits could be achieved. As far as environment benefits are concerned, only the first, third and fourth items are relevant due to the way balconies can enhance natural lighting and ventilation in the adjoining room by allowing larger external wall fenestrations and act as barriers against unwanted sunshine and noise.
Residential units can enjoy better natural ventilation as long as more openings are made in their external walls. However, for a balcony to be an effective sunshade, proper orientation is critical. A sunshade reduces a building’s energy consumption by blocking the entry of direct sunlight and thus heat gain into its adjoining room. A balcony can be regarded as a cantilevered sunshade that can shield against sunlight from a high angle. As Hong Kong is situated in the northern hemisphere, its sunlight shines at a high angle from the south, so only south-facing balconies can benefit from sun shading. For a balcony to be an effective noise barrier, orientation is also an important factor. Research has found that a balcony facing a noisy road can reduce noise levels in an adjoining room (Mohsen and Oldham, 1977; Tzekakis, 1983; Hammad and Gibbs, 1983). If a room does not face a source of noise such as a road, the noise problem is non-existent and the balcony attached to the room cannot have any such environmental function. In short, a balcony needs to face either south or a noise source such as a road for it to be environmentally functional.
Survey Methodology and Results
The survey aimed at finding out the number of environmental balconies which face south or noisy roads. Since a balcony rarely faces exactly south or a noisy road, this survey considers any balcony facing angles ranging from southeast and southwest as south-facing. Similarly, a balcony was taken as facing a noisy road if its facade made an angle of less than 45 degrees with the road. For the purposes of this survey, we defined noisy roads as those with two or more lanes of motor traffic. Although the degree of noise generated from a road depends on a range of factors, such as its traffic flow, vehicle types, surface condition, distance to the buildings being survey and presence of noise barriers or reflectance from neighbouring buildings, the advantage of adopting a simplified definition of ‘noisy roads’ is that it allowed the survey to include the greatest possible number of environmental balconies. This had the benefit of allowing the survey to assume the best scenario resulting from the implementation of the 2001 policy.
We found that from January 2010 to December 2015, 65,431 residential units were completed. Of this total, 60,660 (92.8%) of them had balconies. The other units, which included penthouse units and podium floor units, did not have balconies due to design constraints. These results overwhelmingly confirmed the popularity of incorporating balconies into development projects. However, of those 60,660 balconies, only 22,152 (36.5%) faced noisy roads and 19,869 (32.8%) faced south. These figures suggest that at least two-thirds of the balconies granted GFA and SC exemptions were not performing any environmental function.
A closer analysis of the survey results also revealed that the primary concerns for developers in deciding balcony orientation were their view and their noise exposure level, rather than the mitigation of environmental factors. On Hong Kong Island, only 23% (1,856 out of 8,031) of units had south-facing balconies, significantly fewer than the 34% of units in Kowloon and the New Territories. Most buildings on Hong Kong Island were designed to face the north towards Victoria Harbour for a better view. In contrast, 38% (15,050 out of 39,804) of balconies in the New Territories residential buildings, where units were generally larger, were oriented towards the central landscaped gardens of site interiors. Only 28% (11,260 out of 39,804) of balconies faced outward towards surrounding roads. Developers chose to avoid noise exposure by orienting their residential units away from traffic noise instead of using balconies as noise screens.
Only about one-third of the balconies built in developments completed from January 2010 to December 2015 served as effective sunshades or noise barriers, according to our survey. Even this number might be an over-estimation due to the characteristics of individual sites rendering balconies ineffective not being taken into account. The survey also showed that developers did not incorporate environmental considerations in the design of balconies. It is clear, therefore, that the 2001 policy failed to achieve its intention of promoting sustainable building design. Its fundamental flaw arose from the Building Authority’s questionable aim of encouraging developers to build balconies by granting them area concessions. This improved the building design’s attractiveness to buyers, but did not produce significant environmental benefits. Before the implementation of the 2001 policy, balconies were provided only in residential units with large floor areas as a luxury feature. The policy now directs developers to include balconies even in small units where it is not necessary for them to be included. It is imperative that the Government does not to interfere in the property market by inadvertently promoting the provision of such luxuries. The viability of the 2001 policy can only be justified by having balconies which function environmentally, and not by having them as luxury add-ons. It is time to revise the Green and Innovative Buildings joint practice note once again, this time to exclude environmentally non-functional balconies from concessionary consideration.
Arthur Tong is a Hong Kong registered architect and the author of Building and Development Control Legislation in Hong Kong.
唐以恒,香港註冊建築師，著有 《香港樓宇及發展管制法例》 一書。
1 Buildings Department (2000), “Green buildings – a proposal to enhance the quality of our living”, retrieved from http://www.legco.gov.hk/yr00-01/english/panels/plw/papers/a181e02.pdf.
2 Hammad, R.N.S. and Gibbs, B.M. (1983), “The acoustic performance of building facades in hot climates: Part 2- Closed balconies”, Applied Acoustics, Vol. 16, pp. 441-54.
3 Mohsen, E.A. and Oldham, D.J. (1977), “Traffic noise reduction due to the screening effect of balconies on a building on a building facade”, Applied Acoustics, Vol. 10, pp. 243-57.
4 Tzekakis, E.G. (1983), “On the noise-reducing properties of balconies”, Acustica, Vol. 52, pp. 117-21.
Percentage of Environmental Balconies
Completed in 2010-15 Facing Noisy Roads
Percentage of Environmental Balconies
Completed in 2010-15 Facing the South