The government should incorporate indoor air quality into the minimum standard requirements for living conditions in subdivided units

A joint submission from Clean Air Network and Health In Action

1. Purpose

Clean Air Network continues to place emphasis on indoor air quality, as numerous scientific studies have indicated that long-term residence in spaces with substandard air quality in subdivided units can lead to physical and mental health issues. Considering the government’s establishment of the “Task Force on Subdivided Units” and their plan to set “Minimum Standards for Subdivided Unit Living Environment” by August of this year, which will establish criteria for living space, hygiene, building, and fire safety to crack down on substandard subdivided units, our organization welcomes these measures. We also recommend that the related “standards” should encompass aspects such as indoor air quality, ventilation systems, and the provision of separate kitchen and toilet facilities to ensure a hygienic living environment. Additionally, it is crucial to include residents living in inadequate dwellings within the scope of protection to improve the living conditions of low-income families.

2. Executive summary

2.1. Residents of subdivided units face long-term exposure to indoor air pollution

According to the latest “Long-Term Housing Strategy,” a total of 127,500 households or 4.8% of households in Hong Kong were classified as living in inadequate private housing by 2022, with three-quarters of them residing in subdivided units, commonly known as “cage homes.” According to statistics, in 2021, there were 215,700 residents living in 107,400 subdivided units across Hong Kong.

Research has shown that more than half of the residents in subdivided units experience poor living conditions, including indoor overheating, excessive humidity, and air pollution exceeding WHO standards. Such inadequate environments can have detrimental effects on physical and mental health. In recent years, the frequency of extreme weather events, such as heatwaves, has further exacerbated the challenges faced by residents of subdivided units.

2.2. Impact on children, the elderly, and patients

On average, people spend 90% of their daily time in indoor spaces, which often have higher levels of air pollution compared to outdoor environments, posing greater health risks. Children are particularly vulnerable to the effects of air pollution as they have a higher breathing rate and inhale more air than adults. Additionally, their bodies are still developing and more susceptible to harm. Indoor air pollution also has a significant impact on the elderly and individuals with respiratory sensitivities.

Our organizations’ recommendations regarding the “Minimum Standards for Subdivided Unit Living Environment”:

  • Indoor air quality should be included in the minimum standards for subdivided unit living environment;
  • Provide knowledge and preparedness for residents of subdivided units to cope with extreme weather conditions;
  • Ensure protection for all residents living in inadequately housed household;
  • Revise the “Air Pollution Control Ordinance” to strengthen monitoring of indoor air quality in all settings.

3. Current situation

3.1. Indoor Air and Environmental Pollution in Subdivided Units

According to the following research reports, residents of subdivided units commonly face issues of poor indoor air quality, heat, and humidity pollution. Based on the recommendations of the World Health Organization, dwellings should be warm, dry, with temperatures between 18°C and 21°C, and relative humidity between 40% and 60%. However, the findings from two research reports indicate that these standards are exceeded. The third research report also indicates that the level of airborne bacteria transmitted within the subdivided unit environment is exceptionally high.

Data collected by the Hong Kong Red Cross in 2023 from 33 subdivided units [1] revealed that over half of the households had an average indoor temperature reaching as high as 30 degrees Celsius, and over 60% of households had an average humidity level of 70%, indicating excessive indoor humidity. All households experienced inadequate lighting. As for air quality, nearly half of the households had high levels of carbon dioxide, and fine particulate matter (PM2.5) exceeded the World Health Organization standards by four times, while inhalable particulate matter (PM10) exceeded the standards by six times. Poor environmental conditions can have detrimental effects on physical and mental health, leading to emotional distress, allergies, and headaches.

In 2023, Associate Professor WONG Pui Yun Paulina from the Science Unit at Lingnan, collected environmental data from 20 subdivided units in the Sham Shui Po district. The data showed an average temperature of 25.5 degrees Celsius, an average humidity of 62.3%, and an average concentration of fine particulate matter (PM2.5) at 60.1 micrograms per cubic meter, exceeding the World Health Organization standards by four times.

In 2016, “Air and hygiene quality in crowded housing environments – a case study of subdivided units in Hong Kong” by HKBU [2], explore the environmental quality and hygiene in crowded living environments, subdivided units in Hong Kong. Subdivided units are an emerging form of housing environment for the urban poor. It is hypothesised that subdivided unit residents have a higher risk of exposure to poor hygiene conditions, but no measurement has ever been taken to test this hypothesis. Twenty questionnaires and environmental assessments were conducted. Dominant bacterial species were identified as Micrococcus luteus and Staphylococcus spp., and the microbial counts were correlated with building, occupants and environmental parameters. Driven by the high bacterial counts and poor hygiene observation, eight subdivided units were selected for endotoxin, glucan and allergen analysis in bed and floor dust. Total airborne bacterial counts and endotoxin and glucan in dust were found at very high levels in some subdivided units.

3.2. Health Risks Associated with Extreme Weather

Facing the frequent occurrence of extreme weather events in Hong Kong in recent years, residents of subdivided units are also among the affected groups. According to records from the Hong Kong Observatory [3], the number of hot weather days [4], hot nights [5], and extremely hot weather days [6] in 2023 were 54, 56, and 4, respectively, which ranked among the highest recorded numbers. In June to August of the same year, Hong Kong experienced the hottest summer on record, with an average temperature of a record-breaking 29.7c, while the autumn season recorded record-breaking rainfall.

An inter-university research team by The Hong Kong University of Science and Technology (HKUST), The Chinese University of Hong Kong (CUHK), and the University of Hong Kong (HKU), studied the correlation between extreme weather and the built environment in Hong Kong, as well as the trends and impacts of extreme weather events [7]. The team found that extreme heatwaves and heavy rainfall are expected to become more frequent and severe, potentially evolving into a new normal. Prof. Jimmy FUNG Chi-Hung, Chair Prof. in the Department of Mathematics and the Division of Environment and Sustainability at HKUST, highlighted the destructive nature of prolonged heavy rainfall, which poses immediate threats to the safety and lives of citizens through flooding, waterlogging, and landslides. It is evident that various sectors of society need to assist residents of subdivided units in preparing for extreme weather conditions, including strengthening disaster preparedness training and having emergency supplies readily available.

Under hot weather, besides temperature rising, ozone is more likely to form under high temperatures. Ozone is one of the common air pollutants in Hong Kong, which may trigger asthma and other respiratory diseases.

3.3. Ventilation and Separation of Kitchen and Toilet

In order to comply with the requirements of the Building (Planning) Regulations for natural lighting and ventilation, subdivided units must have windows of sufficient area in their rooms, bathrooms, toilets, or kitchens. If the indoor bathroom or toilet cannot have windows of sufficient area, an artificial lighting system that can be activated when using the bathroom or toilet, as well as a mechanical ventilation system that provides a minimum of 5 air changes per hour, must be provided. This ventilation system should bring in outdoor air. However, according to a report by the Hong Kong federation of trade unions [8], some subdivided units are located in positions within residential units where it is not possible to have windows facing the outside. Even if there are windows, they often face courtyards or back alleys, resulting in poor air circulation, unpleasant odours, and hygiene issues such as pests and rodents. As a result, residents are reluctant to open the windows, and having windows becomes equivalent to not having them.

3.4. Indoor pollution has a Significant Impact on Physical and Mental Well-being

Research shows that residents of subdivided units often face issues such as poor air quality, heat, and humidity pollution. The indoor air quality in these units may contain harmful substances such as volatile organic compounds, formaldehyde, benzene, and others, which can lead to respiratory diseases, allergic reactions, and other health issues. Additionally, the high temperatures and humidity in these environments can cause discomfort, dehydration, and fatigue, negatively affecting physical health. Furthermore, studies have found that residents of subdivided units may experience higher levels of stress and mental health problems such as anxiety, depression, and emotional distress due to the harsh living conditions and poor environment. Therefore, improving indoor environmental quality is crucial for enhancing overall physical and mental well-being.

The Hong Kong Council of Social Service [9] conducted a questionnaire survey among low-income residents living in subdivided units to explore their physical and mental health status, as well as their needs for grassroots medical services. The study found that the self-rated physical and mental health of the respondents was poorer compared to the general population in Hong Kong. The worse their living environment, the lower their self-rated physical health. They were also more prone to illness, with 24% reporting discomfort in the past month, indicating the impact of living environment on their physical and mental well-being.

3.5. Minimum Housing Standards in South Korea and New Zealand

According to the research conducted by the Research and Information Division of the Legislative Council Secretariat [10], both South Korea and New Zealand have included ventilation as one of the mandatory requirements in their minimum housing standards.

South Korea enacted the “Minimum Housing Standards” in 2004, coupled with a significant increase in housing supply, which led to a notable improvement in housing quality. New Zealand, on the other hand, introduced the “Healthy Homes Standards” in 2019, which applies to privately rented properties. Both countries contribute to the understanding of the scope of “minimum housing standards.”

Based on official statistical surveys in South Korea, around 3.3 million households, or 23%, were living in substandard housing conditions in the year 2000. This was primarily due to insufficient bedroom space, which compromised privacy, followed by a lack of basic facilities such as running water, modern toilets, or proper sewage systems. In response to growing public concerns, the South Korean government shifted its focus from just the quantity of housing to the quality of housing. In 2000, they introduced the “Minimum Housing Standards” as guidelines, which emphasized the provision of basic facilities and housing safety. These included having basic independent facilities such as private kitchens, flush toilets, bathing and water supply facilities, as well as ensuring structural safety and meeting environmental standards in terms of lighting, ventilation, heating, and sound insulation.

In terms of policy effectiveness, the implementation of minimum housing standards, along with increased housing supply, has significantly improved the overall housing quality in South Korea.

The New Zealand government enacted the Healthy Homes Guarantee Act in December 2017, which sets out the statutory minimum housing standards. Regarding ventilation standards, it states that “all bedrooms, dining rooms, living rooms, lounges, and kitchens must have at least one openable door or window to the outside, with a combined area equal to at least 5% of the floor area of the room. Kitchens and bathrooms must have mechanically ventilated systems connected to the outside.”

3.6. The Universal Declaration of Human Rights Recognizes Adequate Housing as Human Right

According to Article 11 of the International Covenant on Economic, Social and Cultural Rights, which addresses the right to adequate housing, it confirms that everyone has the right to enjoy an adequate standard of living for themselves and their families, including adequate food, clothing, and housing, as well as continuous improvement of living conditions. The Committee on Economic, Social and Cultural Rights has emphasized that the right to housing should not be narrowly or restrictively interpreted, such as viewing it solely as having a roof overhead or treating housing purely as a commodity. Instead, it should be seen as the right to reside somewhere in security, peace, and dignity [11].

Regarding the “minimum standards for living conditions in subdivided units,” if only the minimum basic safety requirements are met without considering narrow living spaces, lack of independent kitchen and bathroom facilities, ventilation, lighting, and substandard air quality, it does not align with the fundamental human right to adequate housing. Authorities have a responsibility to ensure the right to adequate housing for residents living in subdivided units.

4. Recommendations

  • Include air quality in the “minimum standards for living conditions in subdivided units”
    Currently, the proposed “minimum standards for living conditions in subdivided units” include building safety, fire and sanitation requirements, and living area. We recommend that air quality should also be included, with corresponding measures such as separate toilet and kitchen compartments, requiring each household to have means to introduce fresh air and sunlight, including but not limited to windows or installation of ventilation systems, such as installing exhaust fans or circulation fans. Hoods need to be placed next to windows, etc., in order to reduce the accumulation of air pollutants;
  • Extreme weather disaster preparedness
    In the event of extreme heat weather warnings, authorities should strengthen support for residents in subdivided units by opening more shelter centers, such as extending the operating hours of community lounges as shelters. Enhanced disaster preparedness education for residents in subdivided units should also be provided;
  • Protection for all inadequately housed household
    In the long run, in addition to residents in subdivided units, other residents living in inadequately housed household such as partitioned flats, rooftop houses, tenement buildings, industrial buildings, and cage homes should also be included in the protection scope. Ensuring that grassroots individuals have the right to adequate housing and can reside in their household safely, peacefully, and with dignity;
  • Revision of the Air Pollution Control Ordinance
    Formulate strategies to strengthen the management of indoor air pollution control in the long run, consider revising the Air Pollution Control Ordinance to stipulate the different roles and their rights in managing indoor air pollution, as well as to formulate the applicable scope and exemptions.

[1]  Hong Kong Red Cross. Building climate-resilience in communities 2023. Published on MPWeekly. (Only in Chinese)
[2]  Lai KM, Lee KM, Yu W. (2016) Air and hygiene quality in crowded housing environments – a case study of subdivided units in Hong Kong. Sage Journals.
[3]  HKO. The Year’s Weather – 2023
[4]  ‘Very Hot Day’ refers to the condition with the daily maximum temperature equal to or higher than 33.0 degrees.
[5]  ‘Hot Night’ refers to the condition with the daily minimum temperature equal to or higher than 28.0 degrees.
[6]  ‘Extremely Hot Day’ refers to the condition with the daily maximum temperature equal to or higher than 35.0 degrees.
[7]  HKUST. HKUST Collaborative Research Predicts Hot Nights to Increase by 50% in 2040s And Extreme Rainfall to Increase by Over 40%.
[8]  Hong Kong federation of trade unions. (Only in Chinese)
[9]  The Hong Kong Council of Social Service. Research on the physical and mental health conditions of low-income subdivided housing residents and their needs for primary healthcare services. (Only in Chinese)
[10]  Research and Information Division of the Legislative Council Secretariat (IN05/2024) Minimum Home Standard in South Korea and New Zealand.
[11]  Committee on Economic, Social and Cultural Right, General comment (1991) E/1992/23 Chinese Page 110